[PATCH v2] gas: sframe: Represent .cfi_undefined RA as SFrame FDE without FREs

[Jens Remus]

On 23.07.2025 07:09, Indu Bhagat via Binutils wrote:
> On 7/22/25 8:05 PM, Indu Bhagat wrote:
>> On 7/22/25 9:08 AM, Jens Remus wrote:
>>> On 22.07.2025 16:31, Jens Remus wrote:

>>>> As replied in the other thread on libc-aplha there is no such indication
>>>> on s390x (s390 64-bit).  I'll post a V3 of this patch, which introduces
>>>> a SFrame FDE infor word flag "ra_undefined".
>>>
>>> An attempt to build Glibc with my Binutils patch applied fails due to
>>> one or more relocation(s) out or range during link.  I guess the .sframe
>>> merge logic chokes on a FDE without any FREs.
>>>
>>> Please let me know if you gave any guess, where I should start.  I will
>>> continue tomorrow.

> A possible reason (not confirmed by debugging): In
> sframe_encoder_write_sframe, we do not emit SFrame section if there
> are no FREs:
> 
>   if (fr_info == NULL)
>     return sframe_set_errno (&err, SFRAME_ERR_FRE_INVAL);
> 
> This would cause us to emit no SFrame section, when now we want to
> emit an SFrame section with possibly zero FREs.  In the link you run
> into problems with, there was likely only one object with its .sframe
> section having one SFrame FDE with no FREs among all the inputs.

Thanks a lot!  That was indeed the culprit.  Using that I managed to
get Binutils and Glibc backtrace working.

This did not cause any warnings/errors to be reported, as all callers
of sframe_encoder_write ignore the return code.  Not sure whether we
should do something about that?

Regards,
Jens
-- 
Jens Remus
Linux on Z Development (D3303)
+49-7031-16-1128 Office
jremus@de.ibm.com

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