Re: [AArch64] Disable pcrelative_literal_loads with fix-cortex-a53-843419

[Christophe Lyon <christophe dot lyon at linaro dot org>]

On 10 March 2016 at 12:43, James Greenhalgh <james.greenhalgh@arm.com> wrote:
> On Tue, Jan 26, 2016 at 03:43:36PM +0100, Christophe Lyon wrote:
>> With the attachment....
>>
>>
>> On 26 January 2016 at 15:42, Christophe Lyon <christophe.lyon@linaro.org> wrote:
>> > Hi,
>> >
>> > This is a followup to PR63304.
>> >
>> > As discussed in bugzilla, this patch disables pcrelative_literal_loads
>> > when -mfix-cortex-a53-843419 (or its default configure option) is
>> > used.
>> >
>> > I copied the behavior of -mfix-cortex-a53-835769 (e.g. in
>> > aarch64_can_inline_p), and I have tested by building the Linux kernel
>> > using -mfix-cortex-a53-843419 and checked that
>> > R_AARCH64_ADR_PREL_PG_HI21 relocations are not emitted anymore (under
>> > CONFIG_ARM64_ERRATUM_843419).
>> >
>> > For reference, this is motivated by:
>> > https://bugs.linaro.org/show_bug.cgi?id=1994
>> > and further details on Launchpad:
>> > https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1533009
>> >
>> > OK for trunk?
>
> Thanks, this looks like a clear regression from GCC 5 (we can no longer
> build the kernel, so this workaround is fine to go in now). Please remember
> to add the link to the relevant PR in the ChangeLog.
>
> I'd also really appreciate a nice big comment over this code:
>
>> +  /* If it is not set on the command line, we default to no pc
>> +     relative literal loads, unless the workaround for Cortex-A53
>> +     erratum 843419 is in effect.  */
>> +  if (opts->x_nopcrelative_literal_loads == 2
>> +      && !TARGET_FIX_ERR_A53_843419)
>
> Explaining why this is important (i.e. some summary of the discussion
> in PR63304 regarding the kernel module loader).
>
> Can you repost with that comment added? I don't have any other objections
> to the patch.
>

OK, here is an updated version.


> Thanks,
> James
>
>

Attachment: pr70113.log.txt
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Attachment: pr70113.patch.txt
Description: Text document