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Re: [Patch, avr] Fix PR 20221 - adjust syms and relocs only if relax shrunk section
- From: Senthil Kumar Selvaraj <senthil_kumar dot selvaraj at atmel dot com>
- To: Denis Chertykov <chertykov at gmail dot com>
- Cc: "binutils at sourceware dot org" <binutils at sourceware dot org>, Andrew Burgess <andrew dot burgess at embecosm dot com>, Nick Clifton <nickc at redhat dot com>
- Date: Fri, 10 Jun 2016 14:55:49 +0530
- Subject: Re: [Patch, avr] Fix PR 20221 - adjust syms and relocs only if relax shrunk section
- Authentication-results: sourceware.org; auth=none
- References: <8760tkawob dot fsf at atmel dot com> <CADOs=zYtb4c7Cryc6QHrz5xOPoZ7oh5-ewp3Gams0fS7LHwTDQ at mail dot gmail dot com>
Denis Chertykov writes:
> 2016-06-08 11:53 GMT+03:00 Senthil Kumar Selvaraj
> <senthil_kumar.selvaraj@atmel.com>:
>> Hi,
>>
>> This patch fixes an edge case in linker relaxation that causes symbol
>> values to be computed incorrectly in the presence of align directives
>> in input source code.
>>
>> As the below testcase demonstrates, for code like
>>
>> _start:
>> CALL dest
>> .align 1
>> dest:
>> NOP
>>
>> where the bytes to be deleted (CALL to RCALL, 2 bytes) are adjacent to an
>> alignment boundary, no deletion happens - the prop record handling
>> merely overwrites the to-be-deleted-bytes with NOPs. AFAICT, this is
>> ok - eventually, relaxation sees that the padding is unnecessary and
>> strips the NOPs away.
>>
>> However, the rest of elf32_avr_relax_delete_bytes runs with the assumption
>> that the bytes have been deleted, and this causes symbol values and/or
>> reloc offsets to be decremented even if nothing has moved. dest, in the
>> above testcase, gets decremented by 2 even when the gap got alignment
>> padded, and then again when the padding was removed - it ends up
>> getting adjusted down twice.
>>
>> The patch fixes this by recording whether shrinking actually occurred,
>> and then skipping the reloc offset/sym value adjutment if it did
>> not. There's also a testcase that fails with master (and 2.26) that
>> passes with this patch.
>>
>> Ok for master? Can I backport to 2.26 branch if ok?
>>
>> Regards
>> Senthil
>>
>>
>> bfd/ChangeLog
>>
>> 2016-06-08 Senthil Kumar Selvaraj <senthil_kumar.selvaraj@atmel.com>
>>
>> PR ld/20221
>> * elf32-avr.c (elf32_avr_relax_delete_bytes): Adjust syms
>> and relocs only if shrinking occurred.
>>
>> ld/ChangeLog
>>
>> 2016-06-08 Senthil Kumar Selvaraj <senthil_kumar.selvaraj@atmel.com>
>>
>> PR ld/20221
>> * testsuite/ld-avr/avr-prop-5.d: New.
>> * testsuite/ld-avr/avr-prop-5.s: New.
>>
>>
>
> Committed.
Is this ok for binutils-2_26-branch?
Regards
Senthil