risc-v 64-bit stubs build successfully in developer environment

This is the "bottom half" to add support for riscv64 to UPX.
Need update to stubtools for: gcc objcopy objdump ld
   Now using local cross tools /usr/bin/riscv64-linux-gnu-* on Ubuntu 24.04.
Need fix for riscv64-linux.elf-fold.h being 224 KB.
TODO: extend p_lx_elf.cpp  linker.cpp
TODO: implement nrv2d_d.S nrv2e_d.S lzma_d.S
TODO: testing  (using qemu-riscv64 and gdb-multiarch on Ubuntu 24.04)

        https://github.com/upx/upx/discussions/793

	modified:   src/stub/Makefile
	modified:   src/stub/scripts/xstrip.py
	modified:   src/stub/src/amd64-linux.elf-main2.c
	modified:   src/stub/src/arch/amd64/macros.S
	new file:   src/stub/src/arch/riscv/64/Makefile
	new file:   src/stub/src/arch/riscv/64/Makefile.extra
	new file:   src/stub/src/arch/riscv/64/macros.S
	new file:   src/stub/src/arch/riscv/64/nrv2b_d.S
	new file:   src/stub/src/arch/riscv/64/regs.h
	new file:   src/stub/src/riscv64-expand.S
	new file:   src/stub/src/riscv64-linux.elf-entry.S
	new file:   src/stub/src/riscv64-linux.elf-fold.S
	new file:   src/stub/src/riscv64-linux.elf-fold.lds
	new file:   src/stub/src/riscv64-linux.elf-help_umf.S
	new file:   src/stub/src/riscv64-linux.elf-main2.c
	modified:   src/stub/src/upxfd_linux.c

src/stub/Makefile

@@ -42,6 +42,8 @@ endif
 # ************************************************************************/
 
 ifndef STUBS
+STUBS += riscv64-linux.elf-entry.h
+STUBS += riscv64-linux.elf-fold.h
 STUBS += amd64-darwin.dylib-entry.h
 STUBS += amd64-darwin.macho-entry.h
 STUBS += amd64-darwin.macho-fold.h
@@ -320,7 +322,7 @@ define tc.default.f-embed_objinfo_without_xstrip_keep_dot_text
 	chmod a-x $1
 	$(call tc,objcopy)          -R .data -R .bss $1
 	$(call tc,objcopy) -R .comment -R .note -R .note.GNU-stack -R .reginfo $1
-	$(call tc,objcopy) --strip-unneeded --keep-symbol=_start --keep-symbol=upx_so_main $1
+	$(call tc,objcopy) --strip-unneeded --keep-symbol=_start --keep-symbol=upx_so_main --keep-symbol=str_upx $1
 #
 # Disassemble for human readability
 # objdump
@@ -2182,6 +2184,72 @@ powerpc64-linux.kernel.vmlinux-head.h : $(srcdir)/src/$$T.S
 	$(call tc,objcopy) --output-target binary --only-section .text tmp/$T.o tmp/$T.bin
 	$(call tc,bin2h) tmp/$T.bin $@
 
+# =====
+# /***********************************************************************
+# // riscv64-linux.elf
+# ************************************************************************/
+
+riscv64-linux.elf%.h : tc_list = riscv64-linux.elf default
+riscv64-linux.elf%.h : tc_bfdname = elf64-littleriscv64
+
+tc.riscv64-linux.elf.gcc  = /usr/bin/riscv64-linux-gnu-gcc -nostdinc -MMD -MT $@
+tc.riscv64-linux.elf.gcc += -fno-exceptions -fno-asynchronous-unwind-tables   # -fno-stack-protector
+tc.riscv64-linux.elf.gcc += -Wall -W -Wcast-align -Wcast-qual -Wstrict-prototypes -Wwrite-strings -Werror
+
+tc.riscv64-linux.elf.objcopy = /usr/bin/riscv64-linux-gnu-objcopy
+# Override of objcopy is needed because:
+#   multiarch-objcopy-2.17 -F elf64-littleriscv64 --strip-unneeded --keep-symbol=_start --keep-symbol=upx_so_main tmp/riscv64-linux.elf-entry.bin
+#   multiarch-objcopy-2.17: tmp/riscv64-linux.elf-entry.bin: Invalid bfd target
+
+tc.riscv64-linux.elf.objdump = /usr/bin/riscv64-linux-gnu-objdump
+# Override of objdump is needed because:
+#   multiarch-objdump-2.17 -b elf64-littleriscv64  -Dr  tmp/riscv64-linux.elf-entry.bin | sed -e 's/[ 	]*$//' > tmp/riscv64-linux.elf-entry.bin.disasm
+#   multiarch-objdump-2.17: tmp/riscv64-linux.elf-entry.bin: Invalid bfd target
+#   multiarch-objdump-2.17 -b elf64-littleriscv64  -htr -w tmp/riscv64-linux.elf-entry.bin | sed -e 's/[ 	]*$//' | cat --squeeze-blank | sed -e '1{/^$/d}' -e '${/^$/d}' | sed -e '1s/^.*: *file format/file format/' -e 's/	/ /g' -e 's/ 00*/ 0/g' -e 's/CONTENTS.*/CONTENTS/' > tmp/riscv64-linux.elf-entry.bin.dump
+#   multiarch-objdump-2.17: tmp/riscv64-linux.elf-entry.bin: Invalid bfd target
+
+
+tc.riscv64-linux.elf.ld =      /usr/bin/riscv64-linux-gnu-ld
+# Override of ld is needed because:
+#   multiarch-objcopy-2.17 -F elf64-littleriscv64 --strip-unneeded --keep-symbol=_start --keep-symbol=upx_so_main tmp/riscv64-linux.elf-entry.bin
+#   multiarch-objcopy-2.17: tmp/riscv64-linux.elf-entry.bin: Invalid bfd target
+
+riscv64-linux.elf-entry.h : $(srcdir)/src/$$T.S
+	$(call tc,gcc) -c $< -o tmp/$T.bin
+	$(call tc,f-embed_objinfo,tmp/$T.bin)
+	$(call tc,bin2h) tmp/$T.bin $@
+
+riscv64-linux.elf-fold.h : $(srcdir)/src/$$T.lds \
+	    tmp/$$T.o \
+	    tmp/riscv64-linux.elf-help_umf.o \
+	    tmp/riscv64-linux.elf-upxfd_linux.o \
+	    tmp/riscv64-expand.o \
+	    tmp/riscv64-linux.elf-main2.o
+	$(call tc,ld) -r                    -Map tmp/$T.map $(filter %.o,$^) -o tmp/$T.bin
+	$(call tc,f-embed_objinfo_without_xstrip_keep_dot_text,tmp/$T.bin)
+	$(call tc,bin2h) tmp/$T.bin $@
+
+tmp/riscv64-linux.elf-fold.o : $(srcdir)/src/$$T.S
+	$(call tc,gcc) -c $< -o $@
+	$(call tc,f-objstrip,$@)
+
+tmp/riscv64-linux.elf-main2.o : $(srcdir)/src/$$T.c $(srcdir)/src/i386-linux.elf-main2.c
+	$(call tc,gcc) -c $< -o $@
+	$(call tc,f-objstrip,$@)
+
+tmp/riscv64-linux.elf-help_umf.o: $(srcdir)/src/$$T.S
+	$(call tc,gcc) -c $< -o $@
+
+tmp/riscv64-linux.elf-upxfd_linux.o : $(srcdir)/src/upxfd_linux.c
+	$(call tc,gcc) -c -O $< -o $@
+	$(call tc,objcopy) --strip-unneeded --rename-section .text=UMF_LINUX \
+	    -R .riscv.attributes -R .data -R .bss -R .note.GNU-stack $@
+	$(call tc,objdump) -Dr $(tc_objdump_disasm_options) $@ | $(RTRIM) > $@.disasm
+
+tmp/riscv64-expand.o: $(srcdir)/src/$$T.S
+	$(call tc,gcc) -c $< -o $@
+
+# =====
 
 # /***********************************************************************
 # // dependencies

src/stub/scripts/xstrip.py

@@ -157,7 +157,7 @@ def do_file(fn):
         # ELF64 LE
         eh, idata = idata[:64], idata[64:]
         e_shnum, e_shstrndx = struct.unpack("<HH", eh[60:64])
-        assert e_shstrndx + 3 == e_shnum
+        assert e_shstrndx + 3 >= e_shnum
     elif idata[4:7] == "\x02\x02\x01":
         # ELF64 BE
         eh, idata = idata[:64], idata[64:]
@@ -178,6 +178,8 @@ def do_file(fn):
             assert pos >= len(odata), ("unexpected strip_with_dump", pos, len(odata))
         elif re.search(r"^arm64-", os.path.basename(fn)):
             assert pos >= len(odata), ("unexpected strip_with_dump", pos, len(odata))
+        elif re.search(r"^riscv", os.path.basename(fn)):
+            assert pos >= len(odata), ("unexpected strip_with_dump", pos, len(odata))
         else:
             assert pos == len(odata), ("unexpected strip_with_dump", pos, len(odata))
     else:

src/stub/src/amd64-linux.elf-main2.c

@@ -77,6 +77,16 @@ extern void my_bkpt(void *, ...);
 /*und*/ : "x30"); \
     str; \
 })
+#elif defined(__riscv) //}{
+#define ANDROID_FRIEND 0
+#define addr_string(string) ({ \
+    char const *str; \
+    asm("jal 0f; .string \"" string "\"; .balign 4; 0: mv %0,ra" \
+/*out*/ : "=r"(str) \
+/* in*/ : \
+/*und*/ : "x30"); \
+    str; \
+})
 #else  //}{
 #error;
 #endif  //}
@@ -279,6 +289,36 @@ make_hatch(
     DPRINTF("hatch=%%p\\n", hatch);
     return hatch;
 }
+#elif defined(__riscv)  //{
+static void *
+make_hatch(
+    ElfW(Phdr) const *const phdr,
+    char *next_unc,
+    unsigned const frag_mask
+)
+{
+    unsigned long a = (unsigned long)next_unc;
+    int *hatch = (int *)((3u & -a) + a);
+    int code[3] =  {
+        0,0,0  //NYI illegal instruction
+    };
+    DPRINTF("make_hatch %%p %%p %%x\\n", phdr, next_unc, frag_mask);
+    if (phdr->p_type==PT_LOAD && phdr->p_flags & PF_X) {
+        if (sizeof(code) <= (unsigned)(frag_mask & -(long)hatch)) {
+            hatch[0] = code[0];
+            hatch[1] = code[1];
+            hatch[2] = code[2];
+        }
+        else { // Does not fit at hi end of .text, so must use a new page "permanently"
+            int mfd = upxfd_create(addr_string("upx"), MFD_EXEC);  // the directory entry
+            write(mfd, &code, sizeof(code));
+            hatch = mmap(0, sizeof(code), PROT_READ|PROT_EXEC, MAP_SHARED, mfd, 0);
+            close(mfd);
+        }
+    }
+    DPRINTF("hatch=%%p\\n", hatch);
+    return hatch;
+}
 #elif defined(__powerpc64__)  //}{
 static void *
 make_hatch(
@@ -660,7 +700,7 @@ upx_main2(  // returns entry address
 /*arg4*/    ElfW(auxv_t) *const av
 #if defined(__x86_64)  //{
 /*arg5*/    , ElfW(Addr) elfaddr  // In: &ElfW(Ehdr) for stub
-#elif defined(__aarch64__) //}{
+#elif defined(__aarch64__) || defined(__riscv) //}{
 /*arg5*/    , ElfW(Addr) elfaddr
 #elif defined(__powerpc64__)  //}{
 /*arg5*/    , ElfW(Addr) *p_reloc  // In: &ElfW(Ehdr) for stub; Out: 'slide' for PT_INTERP
@@ -681,7 +721,7 @@ upx_main2(  // returns entry address
     // ehdr = Uncompress Ehdr and Phdrs
     unpackExtent(&xi2, &xo);  // never filtered?
 
-#if defined(__x86_64) || defined(__aarch64__)  //{
+#if defined(__x86_64) || defined(__aarch64__) || defined(__riscv)  //{
     ElfW(Addr) *const p_reloc = &elfaddr;
 #endif  //}
     ElfW(Addr) page_mask = get_page_mask(); (void)page_mask;

src/stub/src/arch/amd64/macros.S

@@ -34,7 +34,6 @@
 #undef x86_64
 
                 //.altmacro       // not supported by x86_64-linux-as-2.15
-                .code64
 
 .macro          section name
                 .section \name

src/stub/src/arch/riscv/64/Makefile

@@ -0,0 +1,3 @@
+# convenience Makefile
+default %:
+	$(MAKE) -C ../../.. $@

src/stub/src/arch/riscv/64/Makefile.extra

@@ -0,0 +1,55 @@
+MAKEFLAGS += -rR
+.SUFFIXES:
+.SECONDEXPANSION:
+
+ifndef top_srcdir
+__dir_list   = . .. ../.. ../../.. ../../../.. ../../../../..
+__dir_list  += ../../../../../.. ../../../../../../.. ../../../../../../../..
+__dir_search = $(firstword $(foreach v,$1,$(if $(wildcard $v/$2),$v)) $3)
+top_srcdir := $(call __dir_search,$(__dir_list),src/bele.h,NOT_FOUND)
+endif
+include $(wildcard $(top_srcdir)/Makevars-global.mk ./Makevars-local.mk)
+vpath %.c $(top_srcdir)/src/stub/src/c
+
+STUBS =
+include $(top_srcdir)/src/stub/src/c/Makevars-lzma.mk
+ifneq ($(UPX_LZMA_VERSION),)
+STUBS += lzma_d_cf.S lzma_d_cs.S lzma_d_cn.S
+endif
+
+default.targets = all
+ifeq ($(strip $(STUBS)),)
+STUBS = NO_STUBS
+all.targets =
+endif
+include $(top_srcdir)/src/stub/Makefile
+
+
+# /***********************************************************************
+# // method-lzma
+# ************************************************************************/
+
+lzma_d_c%.S : tc_list = method-lzma riscv64-linux.elf default
+lzma_d_c%.S : tc_bfdname = elf64-riscv64
+
+c := tc.method-lzma.gcc
+$c  = $(tc.riscv64-linux.elf.gcc)
+$c += -Os -fomit-frame-pointer
+$c += -fno-unit-at-a-time
+$c += -ffunction-sections
+$c += -fwrapv
+$c += -DWITH_LZMA=$(UPX_LZMA_VERSION)
+$c += -I$(UPX_LZMADIR)
+$c += -I$(top_srcdir)/src
+
+lzma_d_c%.S : lzma_d_c.c
+	$(call tc,gcc) $(PP_FLAGS) -c $< -o tmp/$T.o
+	$(call tc,f-objstrip,tmp/$T.o)
+	$(call tc,objcopy) -O binary --only-section .text.LzmaDecode tmp/$T.o tmp/$T.bin
+	head -c-1 tmp/$T.bin > tmp/$T.out
+	$(call tc,objdump) -b binary -m i386:x86-64 -D tmp/$T.out | $(RTRIM) > tmp/$T.out.disasm
+	$(call tc,bin2h) --mode=gas tmp/$T.out $@
+
+lzma_d_cf.% : PP_FLAGS = -DFAST
+lzma_d_cs.% : PP_FLAGS = -DSMALL
+lzma_d_cn.% : PP_FLAGS = -DFAST -mno-red-zone

src/stub/src/arch/riscv/64/macros.S

@@ -0,0 +1,96 @@
+/*
+;  macros.S --
+;
+;  This file is part of the UPX executable compressor.
+;
+;  Copyright (C) 1996-2025 Markus Franz Xaver Johannes Oberhumer
+;  Copyright (C) 1996-2025 Laszlo Molnar
+;  All Rights Reserved.
+;
+;  UPX and the UCL library are free software; you can redistribute them
+;  and/or modify them under the terms of the GNU General Public License as
+;  published by the Free Software Foundation; either version 2 of
+;  the License, or (at your option) any later version.
+;
+;  This program is distributed in the hope that it will be useful,
+;  but WITHOUT ANY WARRANTY; without even the implied warranty of
+;  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;  GNU General Public License for more details.
+;
+;  You should have received a copy of the GNU General Public License
+;  along with this program; see the file COPYING.
+;  If not, write to the Free Software Foundation, Inc.,
+;  59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+;
+;  Markus F.X.J. Oberhumer              Laszlo Molnar
+;  <markus@oberhumer.com>               <ezerotven+github@gmail.com>
+;
+*/
+
+.macro          section name
+                .section \name
+.endm
+
+.macro syscall num
+	li a7,\num; ecall
+.endm
+
+NBPW= 8
+
+.macro  PUSH4 a,b,c,d
+	addi sp,sp,-4*NBPW
+	sd \a,0*NBPW(sp)
+	sd \b,1*NBPW(sp)
+	sd \c,2*NBPW(sp)
+	sd \d,3*NBPW(sp)
+.endm
+
+.macro POP4 a,b,c,d
+	ld \a,0*NBPW(sp)
+	ld \b,1*NBPW(sp)
+	ld \c,2*NBPW(sp)
+	ld \d,3*NBPW(sp)
+	addi sp,sp,4*NBPW
+.endm
+
+.macro  PUSH3 a,b,c
+	addi sp,sp,-4*NBPW
+	sd \a,0*NBPW(sp)
+	sd \b,1*NBPW(sp)
+	sd \c,2*NBPW(sp)
+.endm
+
+.macro POP3 a,b,c
+	ld \a,0*NBPW(sp)
+	ld \b,1*NBPW(sp)
+	ld \c,2*NBPW(sp)
+	addi sp,sp,4*NBPW
+.endm
+
+.macro  PUSH2 a,b
+	addi sp,sp,-2*NBPW
+	sd \a,0*NBPW(sp)
+	sd \b,1*NBPW(sp)
+.endm
+
+.macro POP2 a,b,c
+	ld \a,0*NBPW(sp)
+	ld \b,1*NBPW(sp)
+	addi sp,sp,2*NBPW
+.endm
+
+.macro  PUSH1 a
+	addi sp,sp,-2*NBPW
+	sd \a,0*NBPW(sp)
+.endm
+
+.macro POP1 a
+	ld \a,0*NBPW(sp)
+	addi sp,sp,2*NBPW
+.endm
+
+.macro SUB2 dst,src
+	sub \dst,\dst,\src
+.endm
+
+// vi:ts=8:et:nowrap

src/stub/src/arch/riscv/64/nrv2b_d.S

@@ -0,0 +1,85 @@
+/* riscv64 nrv2b_d.S -- RISCV64 decompressor for NRV2B
+
+   This file is part of the UPX executable compressor.
+
+   Copyright (C) 1996-2025 Markus Franz Xaver Johannes Oberhumer
+   Copyright (C) 1996-2025 Laszlo Molnar
+   Copyright (C) 2000-2025 John F. Reiser
+   All Rights Reserved.
+
+   UPX and the UCL library are free software; you can redistribute them
+   and/or modify them under the terms of the GNU General Public License as
+   published by the Free Software Foundation; either version 2 of
+   the License, or (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; see the file COPYING.
+   If not, write to the Free Software Foundation, Inc.,
+   59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+
+   Markus F.X.J. Oberhumer              Laszlo Molnar
+   <markus@oberhumer.com>               <ezerotven+github@gmail.com>
+
+   John F. Reiser
+   <jreiser@users.sourceforge.net>
+*/
+
+	.text
+#ifndef NO_METHOD_CHECK
+        cmpb $ M_NRV2B_LE32,methb; jne not_n2b
+#endif
+        li bits,1<<31  // empty; force refill
+        li len,0
+	li disp,-1  // initial displacement
+        j top_n2b
+
+#undef EOF
+#define EOF eof_n2b
+
+lit_n2b:
+        addi src,src,1; sb bytpre,(dst)
+        addi dst,dst,1
+top_n2b:
+        lbu bytpre,(src)  # prefetch: literal, or bottom 8 bits of offset
+        jnextb1yp lit_n2b
+        li off,1
+offmore_n2b:
+        getnextbp(off)
+        jnextb0np offmore_n2b
+
+        addi off,off,-3; blt off,zero,len_n2b  # use previous offset
+        slli off,off,8
+        or   off,off,bytpre; addi src,src,1
+        xori disp,off,~0; beq disp,zero,EOF
+len_n2b:
+        li off,1
+        getnextb(len); getnextb(len)  # two bits; cc set on result
+        bne len,zero,gotlen_n2b  # raw 1,2,3 ==> 2,3,4
+        mv len,off  # len= 1, the msb
+        addi off,off,3-1  # raw 2.. ==> 5..
+lenmore_n2b:
+        getnextb(len)
+        jnextb0n lenmore_n2b
+gotlen_n2b:
+	li t0,0x300; lui t0,0xfffff  # -0xd00
+        sltu retbit,t0,disp
+        add len,len,off; add len,len,retbit  # len += off + (disp < -0xd00)
+        //NYI call copy@plt; .extern copy
+bot_n2b:  # In: 0==len
+        j top_n2b
+
+#ifndef NO_METHOD_CHECK  //{
+not_n2b:
+        push %rdi; pop %rsi  # src = arg1
+#endif  //}
+
+        # fall into daisy chain
+/*
+vi:ts=8:et:nowrap
+*/
+

src/stub/src/arch/riscv/64/regs.h

@@ -0,0 +1,22 @@
+#if 0  //{ pre-defined
+#define ra  x1  /* return address */
+#define sp  x2  /* stack ptr */
+#define gp  x3  /* global ptr */
+#define tp  x4  /* thread ptr */
+#endif  //}
+#define t0  x5
+#define t1  x6
+#define t2  x7
+
+#define s0  x8
+#define s1  x9
+
+#define rv  a0  /* return value */
+
+/* NOTE: THE FIRST ARGUMENT IS arg1, NOT arg0. */
+#define arg1  x10  /* same as rv */
+#define arg2  x11
+#define arg3  x12
+#define arg4  x13
+#define arg5  x14
+#define arg6  x15

src/stub/src/riscv64-expand.S

@@ -0,0 +1,211 @@
+/*
+;  riscv64-expand.S -- decompressors for riscv64
+;
+;  This file is part of the UPX executable compressor.
+;
+;  Copyright (C) 1996-2021 Markus Franz Xaver Johannes Oberhumer
+;  Copyright (C) 1996-2021 Laszlo Molnar
+;  Copyright (C) 2000-2021 John F. Reiser
+;  All Rights Reserved.
+;
+;  UPX and the UCL library are free software; you can redistribute them
+;  and/or modify them under the terms of the GNU General Public License as
+;  published by the Free Software Foundation; either version 2 of
+;  the License, or (at your option) any later version.
+;
+;  This program is distributed in the hope that it will be useful,
+;  but WITHOUT ANY WARRANTY; without even the implied warranty of
+;  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;  GNU General Public License for more details.
+;
+;  You should have received a copy of the GNU General Public License
+;  along with this program; see the file COPYING.
+;  If not, write to the Free Software Foundation, Inc.,
+;  59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+;
+;  Markus F.X.J. Oberhumer              Laszlo Molnar
+;  <markus@oberhumer.com>               <ezerotven+github@gmail.com>
+;
+;  John F. Reiser
+;  <jreiser@users.sourceforge.net>
+;
+*/
+
+NBPW = 8
+#include "arch/riscv/64/macros.S"
+.macro call subr; jal \subr; .endm
+
+  section EXP_HEAD
+
+sz_unc= 0
+sz_cpr= 4
+b_method= 8
+b_ftid=   9
+b_cto8=  10
+b_extra= 11
+sz_binfo= 12
+
+f_expand: .globl f_expand // f_expand(b_info *, dst, &dstlen)
+// Supervisor for de-compression, un-filter, and sync_cache
+// Input to supervisor:
+#define fx_src a0
+#define fx_dst a1
+#define fx_dstlen a2
+    PUSH4 fx_src,fx_dst,fx_dstlen,ra  // MATCH_95 params to unfilter and sync_cache
+
+// Input to de-compressor:
+#define xsrc    a0
+#define xsrclen a1
+#define xdst    a2
+#define xdstlen a3
+#define meth    a4
+    lbu meth,b_method(fx_src)
+    mv xdstlen,fx_dstlen  // arg4
+    mv xdst,fx_dst  // arg3
+    lw xsrclen,sz_cpr(xsrc)  // arg2
+    addi xsrc,fx_src,sz_binfo // arg1
+    call decompress
+    mv a3,a0  // save retval
+
+    POP4 fx_src,fx_dst,fx_dstlen,ra  // MATCH_95  fx_src,fx_dst,fx_dstlen,ra
+    lw fx_dst,(fx_dst)  // actual length used by decompressor
+    PUSH3 fx_src,fx_dst,a2   // MATCH_96  params for sync_cache
+    lbu a3,b_ftid(sp)
+    lbu a2,b_cto8(sp)
+    beqz a3,no_unf
+//NYI #include "arch/arm64/v8/bxx.S"  // unfilter code; args in registers, fall-through return
+no_unf:
+
+    POP2 a0,a1   // MATCH_96  dst, len
+    add a1,a1,a0  // lo, hi
+    //NYI sync_cache  // in macros.S
+    POP1 a0   // MATCH_96  retval from decompress
+    ret
+#undef fx_src
+#undef fx_dst
+#undef fx_dstlen
+#undef xsrc
+#undef xsrclen
+#undef xdst
+#undef xdstlen
+
+decompress:  // (src *, cpr_len, dst *, &dstlen);
+//  sections NRV2B, etc, inserted here by addLoader() from ::buildLinuxLoader()
+
+  section EXP_TAIL
+// Fall through: daisy chain had no matching method
+        li a0,-1
+        mv a1,meth
+        ebreak  // EXP_TAIL daisy chain fail
+
+#define src  a0
+#define bits a1
+#define dst  a2
+#define off  a3
+#define len  a4
+#define disp a5
+#define retbit t0
+#define bytpre t1
+
+
+  .globl eof
+
+// sync_cache is done in tail of f_expand, after possible unfilter
+// NYI: eof_n2b, eof_n2d, eof_n2e should be unified.
+eof_n2b: // .globl eof_n2b .type eof_n2b,%function
+eof:  // MATCH_90  end of a compressed extent; need sync_cache after unfilter
+        ld a2,0*NBPW(sp)  // &input_eof
+        sub a0,src,a3  // src -= eof;  // return 0: good; else: bad
+        ld a1,1*NBPW(sp)  // original dst
+        sub dst,dst,a1  // dst -= original dst; actual length of output
+        ld a1,2*NBPW(sp)  // &dstlen
+        sw dst,(a1)  // actual length used at dst  XXX: 4GB
+        ld ra,3*NBPW(sp)
+        addi sp,sp,4*NBPW
+        ret
+
+
+// WINDOWS_BACK compatibility seems to be broken
+// if POP3 replaces POP2+POP1 (MATCH_92, MATCH_91)
+#define srclim  a7
+eof_n2d: // .globl eof_n2d
+eof_n2e: // .globl eof_n2e
+        POP2 a3,a4   // MATCH_92  r3= orig_dst; r4= plen_dst
+        SUB2 src,srclim   // 0 if actual src length equals expected length
+        SUB2 dst,a3   // actual dst length
+        sw dst,(a4)
+        POP1 ra  // MATCH_91
+        ret
+
+eof_lzma: .globl eof_lzma
+        POP4 x2,x3, fp,ra   // MATCH_94  x2= orig_dst; x3= plen_dst
+        ret
+
+upx_mmap_and_fd: .globl upx_mmap_and_fd
+    // UMF_LINUX goes here
+
+#define M_NRV2B_LE32    2
+#define M_NRV2B_8    3
+#define M_NRV2D_LE32    5
+#define M_NRV2D_8    6
+#define M_NRV2E_LE32    8
+#define M_NRV2E_8    9
+#define M_CL1B_LE32     11
+#define M_LZMA          14
+
+#define NO_METHOD_CHECK 1  /* subsumed here by daisy chain */
+
+getbit:
+	srli retbit,bits,63  # hi bit of 64
+	slli bits,bits,1; beq bits,zero,refill
+	ret
+/* On refill: prefetch next byte, for latency reduction on literals and offsets. */
+refill:
+        lw bits,(src); addi src,src,4
+	srli retbit,bits,31  # hi bit of 4 bytes fetched
+	slli bits,bits,1; lbu bytpre,(src)  # prefetch
+	ori  bits,bits,1  # the flag bit
+	slli bits,bits,32  # hi 32 bits in 64-bit register
+	ret
+
+/* jump on next bit {0,1} with prediction {y==>likely, n==>unlikely} */
+/* Prediction omitted for now. */
+
+#define jnextb0np jnextb0yp
+#define jnextb0yp GETBITp; beq retbit,zero,
+#define jnextb1np jnextb1yp
+#define jnextb1yp GETBITp; bne retbit,zero,
+#define GETBITp \
+	call getbit
+
+/* Same, but without prefetch (not useful for length of match.) */
+#define jnextb0n jnextb0y
+#define jnextb0y GETBIT; beq retbit,zero,
+#define jnextb1n jnextb1y
+#define jnextb1y GETBIT; bne retbit,zero,
+#define GETBIT \
+	call getbit
+
+/* rotate next bit into bottom bit of reg */
+#define getnextbp(reg) GETBITp; slli reg,reg,1;  or reg,reg,retbit
+#define getnextb(reg)  getnextbp(reg)
+
+  section NRV2E
+    li t0,M_NRV2E_LE32; bne meth,t0,not_nrv2e
+//NYI #include "arch/arm64/v8/nrv2e_d.S"
+not_nrv2e:
+
+  section NRV2D
+    li t0,M_NRV2D_LE32; bne meth,t0,not_nrv2d
+//NYI #include "arch/arm64/v8/nrv2d_d.S"
+not_nrv2d:
+
+  section NRV2B
+    li t0,M_NRV2B_LE32; bne meth,t0,not_nrv2b
+#include "arch/riscv/64/nrv2b_d.S"
+not_nrv2b:
+
+  section LZMA_DAISY
+    li t0,M_LZMA; bne meth,t0,not_lzma
+//NYI #include "arch/arm64/v8/lzma_d.S"
+not_lzma:

src/stub/src/riscv64-linux.elf-entry.S

@@ -0,0 +1,287 @@
+/*  riscv64-linux.elf-entry.S -- Linux program entry point & decompressor (Elf binary)
+*
+*  This file is part of the UPX executable compressor.
+*
+*  Copyright (C) 1996-2025 Markus Franz Xaver Johannes Oberhumer
+*  Copyright (C) 1996-2025 Laszlo Molnar
+*  Copyright (C) 2000-2025 John F. Reiser
+*  All Rights Reserved.
+*
+*  UPX and the UCL library are free software; you can redistribute them
+*  and/or modify them under the terms of the GNU General Public License as
+*  published by the Free Software Foundation; either version 2 of
+*  the License, or (at your option) any later version.
+*
+*  This program is distributed in the hope that it will be useful,
+*  but WITHOUT ANY WARRANTY; without even the implied warranty of
+*  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+*  GNU General Public License for more details.
+*
+*  You should have received a copy of the GNU General Public License
+*  along with this program; see the file COPYING.
+*  If not, write to the Free Software Foundation, Inc.,
+*  59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+*
+*  Markus F.X.J. Oberhumer              Laszlo Molnar
+*  <markus@oberhumer.com>               <ezerotven+github@gmail.com>
+*
+*  John F. Reiser
+*  <jreiser@users.sourceforge.net>
+*/
+
+#include "arch/riscv/64/macros.S"
+#include "arch/riscv/64/regs.h"
+NBPW= 8
+
+/* These from /usr/include/unistd_64.h */
+__NR_close=     57
+__NR_exit=      93
+__NR_ftruncate= 64
+__NR_memfd_create= 279
+__NR_mmap=     222
+__NR_mprotect= 226
+__NR_msync=    227
+__NR_openat=    56
+__NR_write=     64
+
+sz_Ehdr= 64
+e_phnum= 56
+sz_Phdr= 56
+
+sz_l_info= 12
+  l_lsize= 8
+
+sz_p_info= 12
+
+sz_b_info= 12
+  sz_unc= 0
+  sz_cpr= 4
+  b_method= 8
+
+AT_PAGESZ= 6
+
+PROT_READ=  1
+PROT_WRITE= 2
+PROT_EXEC=  4
+
+MAP_SHARED=  1
+MAP_PRIVATE= 2
+MAP_FIXED=     0x10
+MAP_ANONYMOUS= 0x20
+
+MFD_EXEC= 0x0010
+
+SYS_mmap= 9  // 64-bit mode only!
+
+FD_stderr= 2
+
+M_NRV2B_LE32=2  // ../conf.h
+M_NRV2D_LE32=5
+M_NRV2E_LE32=8
+
+
+// https://www.uclibc.org/docs/psABI-x86_64.pdf
+  section ELFMAINX
+sz_pack2= .-4
+_start: .globl _start
+////    nop; int3  # uncomment for debugging
+
+        ld s0,0(sp)  // argc
+	addi s1,sp,NBPW  // argv
+        //NYI lea cancel_dummy(%rip),%r15
+
+  section ELFMAINX2
+
+// same as in riscv64-linux.elf-fold.S
+F_FRAME= 8*NBPW
+F_EOF=  7*NBPW
+F_ENTR= 6*NBPW; F_PMASK= F_ENTR
+F_RDX=  5*NBPW
+F_LENU= 4*NBPW
+F_ADRU= 3*NBPW
+F_ELFA= 2*NBPW
+F_LENX= 1*NBPW
+F_ADRX= 0*NBPW
+
+D_FOLD=  2*NBPW  // .data space at start of unfold
+D_PMASK= 0*NBPW
+D_XSIGSEGV= 1*NBPW
+
+// find auxv
+	slli t0,s0,3  // NBPW * argc
+	add t0,t0,a1  // end argv
+0: // find end of env
+	addi t0,t0,NBPW  // &env[k]
+	ld t1,(t0); bnez t1,0b
+
+// find AT_PAGESZ in auxv
+	addi t0,t0,NBPW  // &auxv
+	li a7,AT_PAGESZ  // desired key
+0:
+	ld t1,(t0); ld t2,NBPW(t0); addi t0,t0,2*NBPW
+	beq t1,a7,1f  // found it
+	bne t1,zero,0b  // keep searching
+	li t2,0x1000  // default PAGE_SIZE
+1:
+	sub a7,zero,t2  // PAGE_MASK
+2:
+// Create anonymous temporary file on mfd; like upxfd_create
+	jal arg1,0f
+str_upx:
+	.asciz "upx"
+0:
+//	lla arg1,str_upx
+	li arg2,MFD_EXEC  // flags
+        syscall __NR_memfd_create
+        bne a0,zero,ok_memfd  // success
+no_memfd:  // so try /dev/shm
+
+O_RDWR= 2
+O_DIRECTORY= 0200000  // 0x010000
+O_TMPFILE= 020000000  // 0x400000
+#	lla arg1,str_devmem
+	jal arg1,0f
+str_devmem:
+	.asciz "/dev/mem"
+	.balign 4
+0:
+        li arg2,0700  // mode
+	li arg3,O_RDWR | O_TMPFILE | O_DIRECTORY
+	syscall __NR_openat
+ok_memfd:
+#define mfd s2
+        mv mfd,rv
+
+	lla t0,sz_pack2
+#define elfa s3
+	lw t1,(t0); sub elfa,t0,t1
+#define binf s4
+	lla binf,4+o_binfo
+#define lenu s5
+	lw lenu,sz_unc(binf)
+#define szp2 s6
+#define lenx s7
+	sub lenx,szp2,binf
+#define adrx s8
+	add adrx,elfa,binf
+
+#define old_sp s9
+	mv old_sp,sp
+// alloca()
+	sub sp,sp,lenu; andi sp,sp,-2*NBPW
+
+// Decompress the rest of this loader, and jump to it.
+
+#define dst  a2
+#define src  a0
+#define lsrc a1
+	mv dst,sp
+	lw lsrc,sz_cpr(binf)
+	lbu t0,b_method(binf); li t1,M_NRV2B_LE32|(0<<8); beq t0,t1,0f; ebreak
+0:
+	add t0,lsrc,src; sw t0,F_EOF(old_sp)
+	
+//%rsp:
+//  MATCH_10  old_sp
+//  MATCH_11  &input_eof
+
+//%rbp  === old_sp:  array of F_FRAME
+
+#define src  a0
+#define bits a1
+#define dst  a2
+#define off  a3
+#define len  a4
+#define disp a5
+#define retbit t0
+#define bytpre t1
+
+/* jump on next bit {0,1} with prediction {y==>likely, n==>unlikely} */
+/* Prediction omitted for now. */
+
+#define jnextb0np jnextb0yp
+#define jnextb0yp GETBITp; beq retbit,zero,
+#define jnextb1np jnextb1yp
+#define jnextb1yp GETBITp; bne retbit,zero,
+#define GETBITp \
+	call getbit
+
+/* Same, but without prefetch (not useful for length of match.) */
+#define jnextb0n jnextb0y
+#define jnextb0y GETBIT; beq retbit,zero,
+#define jnextb1n jnextb1y
+#define jnextb1y GETBIT; bne retbit,zero,
+#define GETBIT \
+	call getbit
+
+/* rotate next bit into bottom bit of reg */
+#define getnextbp(reg) GETBITp; slli reg,reg,1;  or reg,reg,retbit
+#define getnextb(reg)  getnextbp(reg)
+
+// We already checked the method and no filter.
+#define NO_METHOD_CHECK 1
+#include "arch/riscv/64/nrv2b_d.S"
+
+getbit:
+	srli retbit,bits,63  # hi bit of 64
+	slli bits,bits,1; beq bits,zero,refill
+	ret
+/* On refill: prefetch next byte, for latency reduction on literals and offsets. */
+refill:
+        lw bits,(src); addi src,src,4
+	srli retbit,bits,31  # hi bit of 4 bytes fetched
+	slli bits,bits,1; lbu bytpre,(src)  # prefetch
+	ori  bits,bits,1  # the flag bit
+	slli bits,bits,32  # hi 32 bits in 64-bit register
+	ret
+
+n2b_EOFbad:
+	ebreak
+eof_n2b:
+	lw t0,F_EOF(old_sp)
+        bne t0,src,n2b_EOFbad
+
+// Write de-compressed 'fold' to file
+	lw t0,F_PMASK(old_sp); sw t0,D_PMASK(sp)  // propagate PAGE_MASK
+        lwu arg3,F_LENU(old_sp)
+	mv arg2,sp
+	mv arg1,mfd
+        mv s2,arg3  // LENU
+0:  // /dev/shm might be restricted to 8KiB at a time!
+	syscall __NR_write
+        add arg2,arg2,rv  // ptr += count
+        sub  arg3,arg3,rv  // decrement count
+	bnez arg3,0b  // not finished
+// de-alloca()
+        mv sp,old_sp
+
+// Map unfolded code the SELinux way
+        li arg6,0  // offset
+        mv arg5,mfd
+	li arg4,MAP_SHARED
+        li arg3,PROT_READ|PROT_EXEC  // FIXME: add PROT_WRITE for DEBUG only
+	mv arg2,s2  // LENU
+        li arg1,0  // (%arg1)dst = 0;  // kernel chooses addr
+	syscall __NR_mmap
+        sw rv,F_ADRU(old_sp)
+
+	mv arg1,mfd
+        syscall __NR_close
+
+// Use the copy.
+        ld a0,F_ADRU(sp)  //
+        addi a0,a0,D_FOLD  // beyond .data
+        jr a0  // goto unfolded stub
+
+        // IDENTSTR goes here
+
+  section ELFMAINZ
+        .balign 4
+o_binfo:
+        .long O_BINFO  // offset of b_info for .text | is_ptinerp | unmap_all_pages
+FOLD:
+        // { b_info={sz_unc, sz_cpr, {4 char}}, folded_loader...}
+
+/*__XTHEENDX__*/
+
+/* vim:set ts=8 sw=8 et: */

src/stub/src/riscv64-linux.elf-fold.S

@@ -0,0 +1,340 @@
+/*  riscv64-linux.elf-fold.S -- linkage to C code to process Elf binary
+*
+*  This file is part of the UPX executable compressor.
+*
+*  Copyright (C) 2000-2025 John F. Reiser
+*  All Rights Reserved.
+*
+*  UPX and the UCL library are free software; you can redistribute them
+*  and/or modify them under the terms of the GNU General Public License as
+*  published by the Free Software Foundation; either version 2 of
+*  the License, or (at your option) any later version.
+*
+*  This program is distributed in the hope that it will be useful,
+*  but WITHOUT ANY WARRANTY; without even the implied warranty of
+*  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+*  GNU General Public License for more details.
+*
+*  You should have received a copy of the GNU General Public License
+*  along with this program; see the file COPYING.
+*  If not, write to the Free Software Foundation, Inc.,
+*  59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+*
+*  Markus F.X.J. Oberhumer              Laszlo Molnar
+*  <markus@oberhumer.com>               <ezerotven+github@gmail.com>
+*
+*  John F. Reiser
+*  <jreiser@users.sourceforge.net>
+*/
+
+NBPW= 8
+#include "arch/riscv/64/macros.S"
+#include "arch/riscv/64/regs.h"
+
+PATH_MAX= 4096  // /usr/include/linux/limits.h
+
+sz_b_info= 12
+  sz_unc= 0
+  sz_cpr= 4
+
+sz_l_info= 12
+sz_p_info= 12
+
+MAP_PRIVATE=   0x02
+MAP_FIXED=     0x10
+
+PROT_READ=     0x1
+
+O_RDONLY=       0
+FD_CWD= -100
+
+OVERHEAD=2048
+
+/* 64-bit mode only! */
+__NR_read=  0
+__NR_write= 1
+__NR_openat=  2  //NYI
+__NR_close= 3
+
+__NR_mmap=      9
+__NR_mprotect= 10
+__NR_munmap=   11
+__NR_msync=    26  // 0x1a
+  MS_SYNC= 4
+__NR_brk=      12
+__NR_memfd_create= 0x13f  // 319
+__NR_ftruncate= 0x4d  // 77
+
+__NR_exit= 60
+__NR_readlink= 89
+
+unmap_all_pages= (1<<1)
+is_ptinterp=     (1<<0)
+
+// same as in riscv64-linux.elf-entry.S
+F_FRAME= 8*NBPW
+F_EOF=  7*NBPW  // sometimes omitted from FRAME
+F_ENTR= 6*NBPW; F_PMASK= F_ENTR
+F_RDX=  5*NBPW
+F_LENU= 4*NBPW
+F_ADRU= 3*NBPW
+F_ELFA= 2*NBPW
+F_LENX= 1*NBPW
+F_ADRX= 0*NBPW
+
+D_FOLD=  2*NBPW  // .data space at start of unfold
+D_PMASK= 0*NBPW
+D_XSIGSEGV= 1*NBPW
+
+#define rsp sp  /* x2 */
+#define rax a0  /* x10 */
+#define rbx s1  /* x9 */
+#define rbp s0  /* x8 */
+#define rcx t2  /* x7 */
+#define rdx t1  /* x6 */
+#define r12 t0  /* x5 */
+
+#define rdi a5  /* x15 */
+#define rsi a4  /* x14 */
+#define r15 a3  /* x13 */
+#define r14 a2  /* x12 */
+#define r13 a1  /* x11 */
+
+#define rfd rbp  /* file descriptor for /proc/self/exe */
+
+        .balign 8
+PAGE_MASK: .quad -1<<12  // default
+cancel_sigsegv: .quad 0  // subroutine that cancels sigaction(SIGSEGV,)
+
+// IN: [ADRX,+LENX): compressed data; [ADRU,+LENU): expanded fold (w/ upx_main2)
+// %rsp= %rbp= &F_ADRX; %r13= O_BINFO | is_ptinterp | unmap_all_pages
+
+// no 'section', thus '.text'; also loaded first in riscv64-linux.elf-fold.bin.
+// Code from riscv64-linux2.elf-main.c is also .text, and is next.
+fold_begin:
+////    ebreak  # DEBUG
+// copy is_interp bit from r13 to F_ELFA(rbp)
+	ld t0,F_ELFA(rbp); andi t1,r13,is_ptinterp; or t0,t0,t1;
+	sd t0,F_ELFA(rbp)
+// if !unmap_all_pages then need space on stack for result of readlink("/proc/self/exe",...)
+        mv rsi,rsp
+	  andi t0,r13,unmap_all_pages
+	  bnez t0,5f; li t0,PATH_MAX; sub rsp,rsp,t0; 0:
+        mv rdi,rsp
+	li rcx,8
+0:  // copy down  ADRX,LDRX,ELFA,ADRU,LENU,rdx,%entry,argc
+	ld t0,(rsi); addi rsi,rsi,NBPW; addi rcx,rcx,-1
+	sd t0,(rdi); addi rdi,rdi,NBPW; bnez rcx,0b
+
+5:
+0:  // copy down argv
+	ld t0,(rsi); addi rsi,rsi,NBPW
+	sd t0,(rdi); addi rdi,rdi,NBPW
+	bnez t0,0b
+	mv r14,rdi  // remember &new_env[0]
+
+	andi t0,r13,unmap_all_pages; bnez t0,0f
+	sd zero,(rdi); addi rdi,rdi,NBPW  // space for new_env[0]
+0:  // find old Elf64_auxv
+	ld t0,(rsi); sd t0,(rdi); bnez t0,0b
+        mv t2,rdi  # &old Elf64_auxv
+
+0:  // find &strings (beyond auxv)
+	ld t0,(rsi); ld t1,NBPW(rsi); addi rsi,rsi,2*NBPW
+	sd t0,(rdi); sd t1,NBPW(rdi); addi rdi,rdi,2*NBPW
+	bnez t0,0b
+        mv r15,rdi  # beyond auxv
+        mv r13,rsi  # beginning of strings
+        sub rdi,rdi,t2  # -length of auxv
+
+	andi t0,r13,unmap_all_pages; beqz t0,env_pse
+        ori rfd,rfd,~0; mv r14,rdi;   j   no_env_pse  # no fd; beyond auxv
+env_pse:
+	li arg3,0  # O_RdONLY
+	lla arg2,proc_self_exe
+	li arg1,FD_CWD
+        call openat; mv rfd,rv  # fd
+
+        li arg3,-1+ PATH_MAX  # buflen
+	mv arg2,sp  # buffer
+	lla arg1,proc_self_exe
+	syscall __NR_readlink; bgez rv,0f
+// readlink() failed. Set the result equal to the argument.
+        lla arg2,proc_self_exe  # failure result= "/proc/self/exe"
+	li rcx,15  # sizeof "/proc/self/exe"
+0:
+  // std
+        addi rdi,r13,-1  # dst last byte
+	sb zero,(rdi)  # terminate
+        addi rsi,arg2,-1
+	add rsi,rsi,rcx  # src last byte
+0:  // slide up (hi end goes first)
+	lbu t0,(rsi); addi rsi,rsi,-1; addi rcx,rcx,-1
+	sb  t0,(rdi); addi rdi,rdi,-1; bnez rcx,0b
+// add new env "   =..."
+	li t0,' '; sb t0,-3(rdi); sb t0,-2(rdi); sb t0,-1(rdi); addi rdi,rdi,-3
+        sd rdi,(r14)  # new_env[0]
+        andi rdi,rdi,-NBPW  # align
+        mv rcx,r15
+        sub rsp,rsp,rcx  # byte count
+
+        addi rdi,rdi,-NBPW   # &last qword of new auxv
+	addi rsi,r15,-NBPW   # &last qword of old auxv
+
+        // end of auxv must move by even number of NBPW
+        mv t0,rdi
+        xor t0,t0,rsi
+        andi t0,t0,NBPW
+        sub rdi,rdi,t0
+        mv r14,rdi  # &last qword of new auxv
+
+	srl rcx,rcx,3
+0:
+	ld t0,(rsi); addi rsi,rsi,-NBPW; addi rcx,rcx,-1
+	sd t0,(rdi); addi rdi,rdi,-NBPW; bnez rcx,0b
+        addi rsp,rdi,NBPW
+  // cld
+
+        add arg4,r14,r12; addi arg4,arg4,NBPW  # &new Elf64_auxv  %r12 dead
+no_env_pse:
+	ld arg1,F_ADRX(rbp)
+	ld arg2,F_LENX(rbp)
+        andi arg1,arg1,~(is_ptinterp | unmap_all_pages)
+
+        ld arg5,F_ELFA(rbp)  # ELFA | is_ptinterp
+	andi t0,arg5,is_ptinterp; or arg4,arg4,t0  # transfer is_ptinterp to &new_ELF64_auxv
+        sub arg5,arg5,t0  # and clear from  ELFA
+        mv  r13,arg5  # save ELFA
+        addi rsp,rsp,-OVERHEAD
+        mv arg3,rsp  # &ELf64_Ehdr temporary space
+        call upx_main2  # Out: rv= entry
+
+// entry= upx_main2(
+// b_info *arg1,       {%rdi}
+// total_size arg2,    {%rsi}
+// Elf64_Ehdr *arg3,   {%rdx}
+// Elf32_Auxv_t *arg4, {%rcx}
+// Elf64_Addr elfaddr  {%r8}
+// )
+
+// rsp/ {OVERHEAD},ADRU,LENU,rdx,%entry,  argc,argv,0,envp,0,auxv,0,strings
+	li t0,OVERHEAD
+        add rsp,rsp,t0  # remove Elf64_Ehdr temporary space
+#define r_fd  ebx
+        ld rfd,(rbp)  //NYI
+        sd rv,3*NBPW(rsp)  # entry
+
+        //NYI call *cancel_sigsegv(%rip)
+
+sz_Ehdr= 8*NBPW
+e_type= 16
+ET_EXEC= 2
+sz_Phdr= 7*NBPW
+p_memsz= 5*NBPW
+// Discard pages of compressed data (includes [ADRX,+LENX) )
+        addi arg2,r13,p_memsz+sz_Phdr+sz_Ehdr  #   Phdr[C_TEXT= 1].p_memsz
+        //cmpw $ET_EXEC, e_type(%r13); jne 1f
+        mv arg1,r13; call brk  // also sets the brk
+1:
+        mv arg1,r13; call munmap  # discard C_TEXT compressed data
+
+// Map 1 page of /proc/self/exe so that the symlink does not disappear.
+	bltz rfd,no_pse_map
+        li arg6,0  # 0 offset
+        mv arg5,rfd
+        li arg4,MAP_PRIVATE
+        li arg3,PROT_READ
+        li arg2,1<<12
+        li arg1,0
+        call mmap
+
+        mv arg1,rfd
+        call close
+
+no_pse_map:
+	ld arg1,F_ADRU(rbp)  # ADRU: unfolded upx_main2 etc.
+        ld arg2,F_LENU(rbp)
+        li a7,__NR_munmap
+        jr r14  # goto: syscall; pop %rdx; ret
+
+get_page_mask: .globl get_page_mask
+        ld rv,PAGE_MASK
+        ret
+
+        section SYSCALLS
+my_bkpt: .globl my_bkpt
+        ebreak  // my_bkpt
+        ret
+
+proc_self_exe:
+        .asciz "/proc/self/exe"
+	.balign 4
+
+upxfd_create: .globl upxfd_create // (char *tag, unsigned flags)
+0: // try memfd_create
+        syscall __NR_memfd_create; j ok_memfd  //NYI
+O_RDWR= 2
+O_DIRECTORY= 0200000  // 0x010000
+O_TMPFILE= 020000000  // 0x400000
+	li arg4,0700  # mode
+	li arg3,O_RDWR|O_DIRECTORY|O_TMPFILE
+	la arg3,dev_shm
+	li arg1,FD_CWD
+	syscall __NR_openat
+ok_memfd:
+        ret
+
+Pmap: .globl Pmap  // page-align the lo end
+        ld t0,PAGE_MASK; xori t0,t0,~0  // frag mask
+        and arg1,arg1,t0  // frag
+        sub arg1,arg1,t0
+        add arg2,arg2,t0
+mmap: .globl mmap
+        li a7,__NR_mmap
+sysgo:
+sys_check:
+	ebreak  // sys_check
+        syscall 0 //NYI
+//NYI syscall error checking
+        ret
+
+Psync: .globl Psync
+        li a7,__NR_msync
+	j 5f
+
+Pprotect: .globl Pprotect
+	li a7,__NR_mprotect
+	j 5f
+
+Punmap: .globl Punmap  // page-align the lo end
+	li a7,__NR_munmap
+5:
+        ld t0,PAGE_MASK; xori t0,t0,~0  // frag mask
+        and t0,t0,arg1  // frag
+        sub arg1,arg1,t0
+        add arg2,arg2,t0
+	j sysgo
+
+munmap: .globl munmap
+        li a7,__NR_munmap; 5: j 5f
+exit: .globl exit
+        li a7,__NR_exit; 5: j 5f
+brk: .globl brk
+        li a7,__NR_brk; 5: j 5f
+close: .globl close
+        li a7,__NR_close; 5: j 5f
+ftruncate: .globl ftruncate
+        li a7,__NR_ftruncate; 5: j 5f
+open: .globl openat
+        li a7,__NR_openat; 5: j 5f
+mprotect: .globl mprotect
+        li a7,__NR_mprotect; 5: j 5f
+msync: .globl msync
+        li a7,__NR_msync; 5: j 5f
+Pwrite: .globl Pwrite
+write: .globl write
+        li a7,__NR_write; 5: j 5f
+read: .globl read
+        li a7,__NR_read; 5: j sysgo
+
+// vim:set ts=8 sw=8 et:

src/stub/src/riscv64-linux.elf-fold.lds

@@ -0,0 +1,37 @@
+/* riscv64-linux.elf-fold.lds -- static linker script to build riscv64-linux.elf-fold.bin
+
+   This file is part of the UPX executable compressor.
+
+   Copyright (C) 2000-2025 John F. Reiser
+   All Rights Reserved.
+
+   UPX and the UCL library are free software; you can redistribute them
+   and/or modify them under the terms of the GNU General Public License as
+   published by the Free Software Foundation; either version 2 of
+   the License, or (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; see the file COPYING.
+   If not, write to the Free Software Foundation, Inc.,
+   59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+
+   Markus F.X.J. Oberhumer              Laszlo Molnar
+   <markus@oberhumer.com>               <ezerotven+github@gmail.com>
+
+   John F. Reiser
+   <jreiser@users.sourceforge.net>
+ */
+
+
+OUTPUT_FORMAT("elf64-littleriscv64", "elf64-littleriscv64", "elf64-littleriscv64")
+OUTPUT_ARCH(riscv64)
+
+SECTIONS
+{
+  . = SIZEOF_HEADERS;
+}

src/stub/src/riscv64-linux.elf-help_umf.S

@@ -0,0 +1,5 @@
+  .section HUMF_A, "ax"
+    j upx_mmap_and_fd_android
+
+  .section HUMF_L, "ax"
+    j upx_mmap_and_fd_linux

src/stub/src/riscv64-linux.elf-main2.c

@@ -0,0 +1 @@
+#include "amd64-linux.elf-main2.c"

src/stub/src/upxfd_linux.c

@@ -74,6 +74,16 @@ extern void my_bkpt(void const *, ...);
 /*und*/ : "x30"); \
     str; \
 })
+#elif defined(__riscv) //}{
+#define ANDROID_FRIEND 0
+#define addr_string(string) ({ \
+    char const *str; \
+    asm("jal 0f; .string \"" string "\"; .balign 4; 0: mv %0,ra" \
+/*out*/ : "=r"(str) \
+/* in*/ : \
+/*und*/ : "x30"); \
+    str; \
+})
 #else  //}{
 #define ANDROID_FRIEND 0
 #error  addr_string