unpackExtent() segregates rewrite() from write()

Fix the reported output file size when un-compressing.
Part of https://github.com/upx/upx/issues/60
	modified:   p_lx_elf.cpp
	modified:   p_unix.cpp
	modified:   p_unix.h

src/p_lx_elf.cpp

@@ -3388,6 +3388,12 @@ void PackLinuxElf64::unpack(OutputFile *fo)
 
     // The gaps between PT_LOAD and after last PT_LOAD
     phdr = (Elf64_Phdr *) (u.buf + sizeof(*ehdr));
+    upx_uint64_t hi_offset(0);
+    for (unsigned j = 0; j < u_phnum; ++j) {
+        if (PT_LOAD64==phdr[j].p_type
+        &&  hi_offset < phdr[j].p_offset)
+            hi_offset = phdr[j].p_offset;
+    }
     for (unsigned j = 0; j < u_phnum; ++j) {
         unsigned const size = find_LOAD_gap(phdr, j, u_phnum);
         if (size) {
@@ -3396,7 +3402,8 @@ void PackLinuxElf64::unpack(OutputFile *fo)
             if (fo)
                 fo->seek(where, SEEK_SET);
             unpackExtent(size, fo, total_in, total_out,
-                c_adler, u_adler, false, szb_info);
+                c_adler, u_adler, false, szb_info,
+                (phdr[j].p_offset != hi_offset));
         }
     }
 
@@ -3959,6 +3966,12 @@ void PackLinuxElf32::unpack(OutputFile *fo)
 
     // The gaps between PT_LOAD and after last PT_LOAD
     phdr = (Elf32_Phdr *) (u.buf + sizeof(*ehdr));
+    unsigned hi_offset(0);
+    for (unsigned j = 0; j < u_phnum; ++j) {
+        if (PT_LOAD32==phdr[j].p_type
+        &&  hi_offset < phdr[j].p_offset)
+            hi_offset = phdr[j].p_offset;
+    }
     for (unsigned j = 0; j < u_phnum; ++j) {
         unsigned const size = find_LOAD_gap(phdr, j, u_phnum);
         if (size) {
@@ -3967,7 +3980,8 @@ void PackLinuxElf32::unpack(OutputFile *fo)
             if (fo)
                 fo->seek(where, SEEK_SET);
             unpackExtent(size, fo, total_in, total_out,
-                c_adler, u_adler, false, szb_info);
+                c_adler, u_adler, false, szb_info,
+                (phdr[j].p_offset != hi_offset));
         }
     }
 

src/p_unix.cpp

@@ -448,7 +448,7 @@ void PackUnix::packExtent(
 void PackUnix::unpackExtent(unsigned wanted, OutputFile *fo,
     unsigned &total_in, unsigned &total_out,
     unsigned &c_adler, unsigned &u_adler,
-    bool first_PF_X, unsigned szb_info
+    bool first_PF_X, unsigned szb_info, bool is_rewrite
 )
 {
     b_info hdr; memset(&hdr, 0, sizeof(hdr));
@@ -501,8 +501,14 @@ void PackUnix::unpackExtent(unsigned wanted, OutputFile *fo,
         total_in  += sz_cpr;
         total_out += sz_unc;
         // write block
-        if (fo)
+        if (fo) {
-            fo->write(ibuf + j, sz_unc);
+            if (is_rewrite) {
+                fo->rewrite(ibuf + j, sz_unc);
+            }
+            else {
+                fo->write(ibuf + j, sz_unc);
+            }
+        }
         if (wanted < (unsigned)sz_unc)
             throwCantUnpack("corrupt b_info");
         wanted -= sz_unc;

src/p_unix.h

@@ -77,7 +77,7 @@ protected:
     virtual void unpackExtent(unsigned wanted, OutputFile *fo,
         unsigned &total_in, unsigned &total_out,
         unsigned &c_adler, unsigned &u_adler,
-        bool first_PF_X, unsigned szb_info );
+        bool first_PF_X, unsigned szb_info, bool is_rewrite = false);
 
     int exetype;
     unsigned blocksize;