Re: [PATCH] Fix section corruption bug

[Mark Wielaard <mjw at redhat dot com>]

On Thu, 2014-06-12 at 14:30 +0200, Mark Wielaard wrote:
> On Tue, 2014-06-10 at 15:31 +0200, Thilo Schulz wrote:
> > > I was wondering whether we want to check scn->rawdata.s directly, or if
> > > we could rely on ELF_F_FILEDATA being set for scn->flags?
> > 
> > Seems reasonable though I don't know the code as well as you do I guess.
> 
> I wish I understood the code very well :) But now that I wrote the
> testcase and you pointed out the second bug, I am not sure of the fix
> anymore. It does seem to fix the first issue, but then you immediately
> hit the second.
> 
> > As a further note: A similar bug, albeit for slightly different reasons, occurs 
> > when adding relocations. Adding a relocation with elf_newdata() then 
> > elf_update() 
> > results in the old data being "forgotten" if there was no elf_getdata() call 
> > before to load that data into memory. The cause is a bit different because in 
> > this case, there was not a call to elf_rawdata() before and this still 
> > happened. I imagine, this might also be a problem for string tables.
> 
> Indeed. The attached testcase shows both issues. Calling elf_getdata()
> and then elf_newdata() works as expected. But elf_newdata drops all
> existing data when elf_rawdata is called before and elf_newdata keeps
> the size, but not the actual content bytes of existing data of a section
> if elf_getdata isn't called before.
> 
> Still scratching my head a little how to resolve both issues properly.

Sorry this took 9 months... But I believe these issues have finally been
resolved in current git elfutils. At least my testcase now works as
expected. Hope it also now works for your code.

Cheers,

Mark