Use file size in file offset -> virtual offset translation

We were seeing an issue where normalization + file offset symbolization
was reporting an incorrect symbolization result for certain addresses in
a certain binary.
In short, in a binary with segments:

  > Type  Offset     VirtAddr           PhysAddr           FileSiz    MemSiz     Flg Align
  > LOAD  0x949be40  0x000000000969be40 0x000000000969be40 0x11d6c930 0x11d6c930 R E 0x200000
  > LOAD  0x1b208780 0x000000001b409780 0x000000001b409780 0x01b5e8   0x01c1f0   RW  0x1000
  > LOAD  0x1b224980 0x000000001b426980 0x000000001b426980 0x343888   0xca594c   RW  0x1000
  > LOAD  0x1b600000 0x000000001c200000 0x000000001c200000 0x4a358ac  0x4a358ac  R E 0x200000

We were normalizing absolute address 0x1c23b4d0 to file offset
0x1b63b4d0. That's based on the calculation

  > 0x1c23b4d0 - 0x1c200000 /*VirtAddr*/ + 0x1b600000 /*Offset*/ = 0x1b63b4d0

When subsequently symbolizing the file offset we were looking up the
wrong segment, because we took into account the segment's memory size:

  > 0x1b63b4d0 is in [0x1b224980 /*Offset*/, 0x1b224980 + 0xca594c /*MemSiz*/ = 0x1beca2cc]

Because this first fitting segment comes before the one we used as part
of normalization, we continued symbolizing virtual offset

  > 0x1b63b4d0 - 0x1b224980 /*Offset*/ + 0x1b426980 /*VirtAddr*/ = 0x1b83d4d0

which lead to a wrong symbolization. By matching up segments based on
the file size instead, we pick the correct segment instead:

  > 0x1b63b4d0 is *not* in [0x1b224980 /*Offset*/, 0x1b224980 + 0x343888 /*FileSiz*/ = 0x1b568208]
  > 0x1b63b4d0 is in [0x1b600000 /*Offset*/, 0x1b600000 + 0x4a358ac /*FileSiz*/ = 0x200358ac]

So we end up symbolizing virtual offset

  > 0x1b63b4d0 - 0x1b600000 /*Offset*/ + 0x1c200000 /*VirtAddr*/ = 0x1c23b4d0

which leads to the correct symbolization result.

Hence, fix the logic to work with the segment's file size instead.

Signed-off-by: Daniel Müller <deso@posteo.net>

src/elf/parser.rs

@@ -878,7 +878,7 @@ impl ElfParser {
         let phdrs = self.program_headers()?;
         let addr = phdrs.iter().find_map(|phdr| {
             if phdr.p_type == PT_LOAD {
-                if (phdr.p_offset..phdr.p_offset + phdr.p_memsz).contains(&offset) {
+                if (phdr.p_offset..phdr.p_offset + phdr.p_filesz).contains(&offset) {
                     return Some((offset - phdr.p_offset + phdr.p_vaddr) as Addr)
                 }
             }