Discussion:
[PATCH][Binutils][AArch64] Fix regression in Cortex A53 erratum when PIE. (PR ld/23904)
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Tamar Christina
2018-11-23 17:19:54 UTC
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Hi All,

The fix for PR ld/22263 causes TLS relocations using ADRP to be relaxed
into MOVZ, however this causes issues for the erratum code.

The erratum code scans the input sections looking for ADRP instructions
and notes their location in the stream.

It then later tries to find them again in order to generate the linker
stubs. Due to the relaxation it instead finds a MOVZ and hard aborts.

Since this relaxation is a valid one, and in which case the erratum no
longer applies, it shouldn't abort but instead just continue.

This changes the TLS relaxation code such that when it finds an ADRP and
it relaxes it, it removes the erratum entry from the work list by changing
the stub type into none so the stub is ignored.

The entry is not actually removed as removal is a more expensive operation
and we have already allocated the memory anyway.

The clearing is done for IE->LE and GD->LE relaxations, and a testcase is
added for the IE case. The GD case I believe to be impossible to get together
with the erratum sequence due to the required BL which would break the sequence.
However to cover all basis I have added the guard there as well.

build on native hardware and regtested on
aarch64-none-elf, aarch64-none-elf (32 bit host),
aarch64-none-linux-gnu, aarch64-none-linux-gnu (32 bit host)

Cross-compiled and regtested on
aarch64-none-linux-gnu, aarch64_be-none-linux-gnu

Testcase in PR23940 tested and works as expected now and benchmarks ran on A53
showing no regressions.

and no issues.

Ok for master? and for backport to binutils-2.31?

Thanks,
Tamar

bfd/ChangeLog:

2018-11-23 Tamar Christina <***@arm.com>

PR ld/23904
* elfnn-aarch64.c (_bfd_aarch64_adrp_p): Use existing constants.
(_bfd_aarch64_erratum_843419_branch_to_stub): Use _bfd_aarch64_adrp_p.
(struct erratum_835769_branch_to_stub_clear_data): New.
(_bfd_aarch64_erratum_843419_clear_stub): New.
(clear_erratum_843419_entry): New.
(elfNN_aarch64_tls_relax): Use it.
(elfNN_aarch64_relocate_section): Pass input_section.
(aarch64_map_one_stub): Handle branch type none as valid.

ld/ChangeLog:

2018-11-23 Tamar Christina <***@arm.com>

PR ld/23904
* testsuite/ld-aarch64/aarch64-elf.exp: Add erratum843419_tls_ie.
* testsuite/ld-aarch64/erratum843419_tls_ie.d: New test.
* testsuite/ld-aarch64/erratum843419_tls_ie.s: New test.

--
Nick Clifton
2018-11-27 12:08:39 UTC
Permalink
Hi Tamar,
Post by Tamar Christina
Ok for master? and for backport to binutils-2.31?
PR ld/23904
* elfnn-aarch64.c (_bfd_aarch64_adrp_p): Use existing constants.
(_bfd_aarch64_erratum_843419_branch_to_stub): Use _bfd_aarch64_adrp_p.
(struct erratum_835769_branch_to_stub_clear_data): New.
(_bfd_aarch64_erratum_843419_clear_stub): New.
(clear_erratum_843419_entry): New.
(elfNN_aarch64_tls_relax): Use it.
(elfNN_aarch64_relocate_section): Pass input_section.
(aarch64_map_one_stub): Handle branch type none as valid.
PR ld/23904
* testsuite/ld-aarch64/aarch64-elf.exp: Add erratum843419_tls_ie.
* testsuite/ld-aarch64/erratum843419_tls_ie.d: New test.
* testsuite/ld-aarch64/erratum843419_tls_ie.s: New test.
Approved for the mainline and for backporting. Please apply.

Cheers
Nick

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