Re: [PATCH, ARM] Fix handling of GOT and PLT access to IFUNC symbols

[Richard Sandiford <rdsandiford at googlemail dot com>]

Richard Earnshaw <rearnsha@arm.com> writes:
> On 12/04/13 17:42, Will Newton wrote:
>>
>> Hi all,
>>
>> The current ARM IFUNC code appears to have a bug when an access is made via
>> the PLT and GOT in the same object. This results in two relocs being swapped
>> out into the same slot so one R_ARM_IRELATIVE reloc goes missing.
>>
>> This patch changes the behaviour to use an incremented reloc count rather
>> than the calculated PLT index to match the behaviour of elf32_arm_add_dynreloc
>> and as a result requires the order of relocs in the ifunc tests to be
>> adjusted.
>>
>> bfd/ChangeLog:
>>
>> 2013-04-12  Will Newton  <will.newton@linaro.org>
>>
>> 	* elf32-arm.c (elf32_arm_populate_plt_entry): Increment reloc_count
>> 	when emitting R_ARM_IRELATIVE relocs.
>>
>
> Hmm, it looks somewhat suspicious to me to be changing the reloc count 
> this late on.
>
> Richard, do you know if this is safe?  If not, can you recommend a 
> better approach?

Sorry for the slow reply, been on holiday.  The patch looks good to me.
At this stage, ->reloc_count is the number of relocations that have been
filled in, whereas ->size is the number of bytes that have been allocated
in the relocation section.  .rel.plt is special in that the relocation
index has to match the PLT index, but as Will says, .rel.iplt is more
like a normal relocation section, and can have a mixture of both "PLT"
and non-PLT relocations.

In some ways it might be clearer to use elf32_arm_add_dynreloc in
the dynindx == -1 case, which would also give us the assert that
we have allocated enough relocation entries.  Both should be
correct though.

BTW, there's a typo in the testcase:

>+#------ libfunc1's .iplt entry

should be "appfunc1".

Richard