Bugfix for eu-readelf --exception elf32-binary

[Karel Klic]

Hello,

the attached tiny patch fixes the output of `eu-readelf --exception /path/to/binary` for
32-bit stripped binaries. Both elfutils-0.152 and recent git are affected, AFAICT.


Reproducer:
$ eu-readelf --exception zyGrib-3.9.9-3.fc16.i686/usr/bin/zyGrib
...
Call frame information section [17] '.eh_frame' at offset 0x109440:

 [     0] CIE length=20
...
 [    18] FDE length=16 cie=[     0]
...
 [    2c] CIE length=28
   CIE_id:                   0
   version:                  1
   augmentation:             "zPLR"
   code_alignment_factor:    1
   data_alignment_factor:    -4
   return_address_register:  8
   Augmentation data:        0 eu-readelf: invalid encoding
<end of output>


What happens (all functions are in readelf.c):
1. In function print_debug, the 'dwfl_module_getdwarf (dwflmod, &dwbias)' call
returns NULL as the binary is stripped, so 'dummy_dbg' from the same function is
assigned to 'dbg' variable.

Dwarf dummy_dbg = { .other_byte_order = MY_ELFDATA != ehdr->e_ident[EI_DATA] };
dbg = &dummy_dbg;

2. Later, when reading the .eh_frame contents in function print_debug_frame_section,
read_encoded is called.
3. The parameter encoding of read_encoded represents DW_EH_PE_absptr.
4. read_encoded: gelf_getclass (dbg->elf) is called.
5. read_encoded: dbg->elf is NULL, because elf member is not being assigned for
'dummy_dbg'.
6. read_encoded: So gelf_getclass (NULL) returns ELFCLASSNONE
7. read_encoded: "encoding = gelf_getclass (dbg->elf) == ELFCLASS32 ?
DW_EH_PE_udata4 : DW_EH_PE_udata8" is evaluated to DW_EH_PE_udata8.
8. read_encoded: Reading of udata8 fails, because this is 32-bit ELF, so there is only
udata4 in the binary.


Karel

[Roland McGrath]

Your fix looks fine modulo coding style, lack of ChangeLog, etc.
I've put it in with those cleanups.

It would be nice to have a regression test for this change too.
But I'll leave that to you, Mark, and Petr.


Thanks,
Roland