From 34df0d6ef1b91d9a6125de4e29c855bd3c92b749 Mon Sep 17 00:00:00 2001
From: John Reiser <jreiser@BitWagon.com>
Date: Sat, 12 Mar 2022 14:21:51 -0800
Subject: [PATCH] More empty HASH and/or GNU_HASH when Rust-musl

https://github.com/upx/upx/issues/568
	modified:   p_lx_elf.cpp
---
 src/p_lx_elf.cpp | 148 ++++++++++++++++++++++++-----------------------
 1 file changed, 75 insertions(+), 73 deletions(-)

diff --git a/src/p_lx_elf.cpp b/src/p_lx_elf.cpp
index 5d4c5018..6050153d 100644
--- a/src/p_lx_elf.cpp
+++ b/src/p_lx_elf.cpp
@@ -5732,19 +5732,20 @@ Elf32_Sym const *PackLinuxElf32::elf_lookup(char const *name) const
         unsigned const nbucket = get_te32(&hashtab[0]);
         unsigned const *const buckets = &hashtab[2];
         unsigned const *const chains = &buckets[nbucket];
-        if (!nbucket
-        ||  (unsigned)(file_size - ((char const *)buckets - (char const *)(void const *)file_image))
+        if ((unsigned)(file_size - ((char const *)buckets - (char const *)(void const *)file_image))
                 <= sizeof(unsigned)*nbucket ) {
             char msg[80]; snprintf(msg, sizeof(msg),
                 "bad nbucket %#x\n", nbucket);
             throwCantPack(msg);
         }
-        unsigned const m = elf_hash(name) % nbucket;
-        unsigned si;
-        for (si= get_te32(&buckets[m]); 0!=si; si= get_te32(&chains[si])) {
-            char const *const p= get_dynsym_name(si, (unsigned)-1);
-            if (0==strcmp(name, p)) {
-                return &dynsym[si];
+        if (nbucket) {
+            unsigned const m = elf_hash(name) % nbucket;
+            unsigned si;
+            for (si= get_te32(&buckets[m]); 0!=si; si= get_te32(&chains[si])) {
+                char const *const p= get_dynsym_name(si, (unsigned)-1);
+                if (0==strcmp(name, p)) {
+                    return &dynsym[si];
+                }
             }
         }
     }
@@ -5756,8 +5757,7 @@ Elf32_Sym const *PackLinuxElf32::elf_lookup(char const *name) const
         unsigned const *const bitmask = &gashtab[4];
         unsigned const *const buckets = &bitmask[n_bitmask];
         unsigned const *const hasharr = &buckets[n_bucket];
-        if (!n_bucket
-        || (void const *)&file_image[file_size] <= (void const *)hasharr) {
+        if ((void const *)&file_image[file_size] <= (void const *)hasharr) {
             char msg[80]; snprintf(msg, sizeof(msg),
                 "bad n_bucket %#x\n", n_bucket);
             throwCantPack(msg);
@@ -5769,33 +5769,33 @@ Elf32_Sym const *PackLinuxElf32::elf_lookup(char const *name) const
                 "bad n_bitmask %#x\n", n_bitmask);
             throwCantPack(msg);
         }
+        if (n_bucket) {
+            unsigned const h = gnu_hash(name);
+            unsigned const hbit1 = 037& h;
+            unsigned const hbit2 = 037& (h>>gnu_shift);
+            unsigned const w = get_te32(&bitmask[(n_bitmask -1) & (h>>5)]);
 
-        unsigned const h = gnu_hash(name);
-        unsigned const hbit1 = 037& h;
-        unsigned const hbit2 = 037& (h>>gnu_shift);
-        unsigned const w = get_te32(&bitmask[(n_bitmask -1) & (h>>5)]);
-
-        if (1& (w>>hbit1) & (w>>hbit2)) {
-            unsigned bucket = get_te32(&buckets[h % n_bucket]);
-            if (n_bucket <= bucket) {
-                char msg[90]; snprintf(msg, sizeof(msg),
-                        "bad DT_GNU_HASH n_bucket{%#x} <= buckets[%d]{%#x}\n",
-                        n_bucket, h % n_bucket, bucket);
-                throwCantPack(msg);
-            }
-            if (0!=bucket) {
-                Elf32_Sym const *dsp = &dynsym[bucket];
-                unsigned const *hp = &hasharr[bucket - symbias];
-
-                do if (0==((h ^ get_te32(hp))>>1)) {
-                    unsigned st_name = get_te32(&dsp->st_name);
-                    char const *const p = get_str_name(st_name, (unsigned)-1);
-                    if (0==strcmp(name, p)) {
-                        return dsp;
-                    }
-                } while (++dsp,
-                        (char const *)hp < (char const *)&file_image[file_size]
-                    &&  0==(1u& get_te32(hp++)));
+            if (1& (w>>hbit1) & (w>>hbit2)) {
+                unsigned bucket = get_te32(&buckets[h % n_bucket]);
+                if (n_bucket <= bucket) {
+                    char msg[90]; snprintf(msg, sizeof(msg),
+                            "bad DT_GNU_HASH n_bucket{%#x} <= buckets[%d]{%#x}\n",
+                            n_bucket, h % n_bucket, bucket);
+                    throwCantPack(msg);
+                }
+                if (0!=bucket) {
+                    Elf32_Sym const *dsp = &dynsym[bucket];
+                    unsigned const *hp = &hasharr[bucket - symbias];
+                    do if (0==((h ^ get_te32(hp))>>1)) {
+                        unsigned st_name = get_te32(&dsp->st_name);
+                        char const *const p = get_str_name(st_name, (unsigned)-1);
+                        if (0==strcmp(name, p)) {
+                            return dsp;
+                        }
+                    } while (++dsp,
+                            (char const *)hp < (char const *)&file_image[file_size]
+                        &&  0==(1u& get_te32(hp++)));
+                }
             }
         }
     }
@@ -5803,6 +5803,7 @@ Elf32_Sym const *PackLinuxElf32::elf_lookup(char const *name) const
     //    (1==n_bucket && 0==buckets[0] && 1==n_bitmask && 0==bitmask[0])
     // to minimize space in DT_GNU_HASH. This causes the fancy lookup to fail.
     // Is a fallback to linear seach assumed?
+    // 2022-03-12  Some Rust programs have 0==n_bucket.
     return nullptr;
 
 }
@@ -5813,19 +5814,20 @@ Elf64_Sym const *PackLinuxElf64::elf_lookup(char const *name) const
         unsigned const nbucket = get_te32(&hashtab[0]);
         unsigned const *const buckets = &hashtab[2];
         unsigned const *const chains = &buckets[nbucket];
-        if (!nbucket
-        ||  (unsigned)(file_size - ((char const *)buckets - (char const *)(void const *)file_image))
+        if ((unsigned)(file_size - ((char const *)buckets - (char const *)(void const *)file_image))
                 <= sizeof(unsigned)*nbucket ) {
             char msg[80]; snprintf(msg, sizeof(msg),
                 "bad nbucket %#x\n", nbucket);
             throwCantPack(msg);
         }
-        unsigned const m = elf_hash(name) % nbucket;
-        unsigned si;
-        for (si= get_te32(&buckets[m]); 0!=si; si= get_te32(&chains[si])) {
-            char const *const p= get_dynsym_name(si, (unsigned)-1);
-            if (0==strcmp(name, p)) {
-                return &dynsym[si];
+        if (nbucket) { // -rust-musl can have "empty" hashtab
+            unsigned const m = elf_hash(name) % nbucket;
+            unsigned si;
+            for (si= get_te32(&buckets[m]); 0!=si; si= get_te32(&chains[si])) {
+                char const *const p= get_dynsym_name(si, (unsigned)-1);
+                if (0==strcmp(name, p)) {
+                    return &dynsym[si];
+                }
             }
         }
     }
@@ -5837,8 +5839,8 @@ Elf64_Sym const *PackLinuxElf64::elf_lookup(char const *name) const
         upx_uint64_t const *const bitmask = (upx_uint64_t const *)(void const *)&gashtab[4];
         unsigned     const *const buckets = (unsigned const *)&bitmask[n_bitmask];
         unsigned     const *const hasharr = &buckets[n_bucket];
-        if (!n_bucket
-        || (void const *)&file_image[file_size] <= (void const *)hasharr) {
+
+        if ((void const *)&file_image[file_size] <= (void const *)hasharr) {
             char msg[80]; snprintf(msg, sizeof(msg),
                 "bad n_bucket %#x\n", n_bucket);
             throwCantPack(msg);
@@ -5850,33 +5852,32 @@ Elf64_Sym const *PackLinuxElf64::elf_lookup(char const *name) const
                 "bad n_bitmask %#x\n", n_bitmask);
             throwCantPack(msg);
         }
-
-        unsigned const h = gnu_hash(name);
-        unsigned const hbit1 = 077& h;
-        unsigned const hbit2 = 077& (h>>gnu_shift);
-        upx_uint64_t const w = get_te64(&bitmask[(n_bitmask -1) & (h>>6)]);
-
-        if (1& (w>>hbit1) & (w>>hbit2)) {
-            unsigned bucket = get_te32(&buckets[h % n_bucket]);
-            if (n_bucket <= bucket) {
-                char msg[90]; snprintf(msg, sizeof(msg),
-                        "bad DT_GNU_HASH n_bucket{%#x} <= buckets[%d]{%#x}\n",
-                        n_bucket, h % n_bucket, bucket);
-                throwCantPack(msg);
-            }
-            if (0!=bucket) {
-                Elf64_Sym const *dsp = &dynsym[bucket];
-                unsigned const *hp = &hasharr[bucket - symbias];
-
-                do if (0==((h ^ get_te32(hp))>>1)) {
-                    unsigned st_name = get_te32(&dsp->st_name);
-                    char const *const p = get_str_name(st_name, (unsigned)-1);
-                    if (0==strcmp(name, p)) {
-                        return dsp;
-                    }
-                } while (++dsp,
-                        (char const *)hp < (char const *)&file_image[file_size]
-                    &&  0==(1u& get_te32(hp++)));
+        if (n_bucket) { // -rust-musl can have "empty" gashtab
+            unsigned const h = gnu_hash(name);
+            unsigned const hbit1 = 077& h;
+            unsigned const hbit2 = 077& (h>>gnu_shift);
+            upx_uint64_t const w = get_te64(&bitmask[(n_bitmask -1) & (h>>6)]);
+            if (1& (w>>hbit1) & (w>>hbit2)) {
+                unsigned bucket = get_te32(&buckets[h % n_bucket]);
+                if (n_bucket <= bucket) {
+                    char msg[90]; snprintf(msg, sizeof(msg),
+                            "bad DT_GNU_HASH n_bucket{%#x} <= buckets[%d]{%#x}\n",
+                            n_bucket, h % n_bucket, bucket);
+                    throwCantPack(msg);
+                }
+                if (0!=bucket) {
+                    Elf64_Sym const *dsp = &dynsym[bucket];
+                    unsigned const *hp = &hasharr[bucket - symbias];
+                    do if (0==((h ^ get_te32(hp))>>1)) {
+                        unsigned st_name = get_te32(&dsp->st_name);
+                        char const *const p = get_str_name(st_name, (unsigned)-1);
+                        if (0==strcmp(name, p)) {
+                            return dsp;
+                        }
+                    } while (++dsp,
+                            (char const *)hp < (char const *)&file_image[file_size]
+                        &&  0==(1u& get_te32(hp++)));
+                }
             }
         }
     }
@@ -5884,6 +5885,7 @@ Elf64_Sym const *PackLinuxElf64::elf_lookup(char const *name) const
     //    (1==n_bucket && 0==buckets[0] && 1==n_bitmask && 0==bitmask[0])
     // to minimize space in DT_GNU_HASH. This causes the fancy lookup to fail.
     // Is a fallback to linear seach assumed?
+    // 2022-03-12  Some Rust programs have 0==n_bucket.
     return nullptr;
 
 }