Re: Linux 2.2. ELF loader mystery

[John Reiser <jreiser@BitWagon.com>]

Udo A. Steinberg wrote:
> Linux 2.2 refuses to allocate certain .bss ELF sections in memory if there
> are PT_LOAD sections following them. Is there any convention saying that
> .bss must always be the last section and must not be followed by PT_LOAD
> sections? OTOH both Linux 2.4 and 2.6 have no trouble getting this right
> and load the binary just fine.

Please give the complete kernel version number: 2.2.19, 2.4.23, 2.6.0, etc.
binfmt_elf has had bugs that were introduced/fixed/re-introduced/re-fixed
within the 2.4 series, for example.

Yes, there was an interpretation of ELF that p_filesz < p_memsz implied .bss
only for the last PT_LOAD in the array of Elf32_Phdr.  Later this was changed
so that .bss applied only on the PT_LOAD with the highest p_vaddr, regardless
of position in Elf32_Phdr.  [In your example this accounts for the missing
.bss from 0x000a6468 to 0x000b8818, because the p_paddr is 0x00001000 but
the other p_vaddr is 0x000ba000 which is greater.]  The best interpretation
is that p_filesz < p_memsz implies ".bss" [kernel-supplied, zeroed bytes
and/or pages] separately for _each_ PT_LOAD.

[Note that binfmt_elf ignores Sections.  binfmt_elf pays attention only to
PT_LOAD.  Aggregating from Elf32_Shdr into ELf32_Phdr is the job of /bin/ld.]

-- 
John Reiser, jreiser@BitWagon.com