[PATCH] support: Use unwinder in links-dso-program-c only with libgcc_s

[Frank Scheiner]

On 26.03.25 19:04, Frank Scheiner wrote:
> On 26.03.25 17:47, Florian Weimer wrote:
>> * Frank Scheiner:
>>
>>> Dear Florian,
>>>
>>> On 26.03.25 16:36, Florian Weimer wrote:
>>>> Do not build links-dso-program-c with exception (unwinding) support
>>>> if libgcc_s is not available.  In this case, the unwinder may be
>>>> part of libgcc.a or libgcc_eh.a, depending on how GCC was built.
>>>> If the unwinder is in libgcc_eh.a only, linking links-dso-program-c
>>>> failed before this change.  After this change, the exception
>>>> handling landing pad is only generated if libgcc_s available,
>>>> avoiding an undefined _Unwind_Resume (or equivalent) symbol
>>>> reference in the non-libgcc_s case.
>>>>
>>>> Fixes commit ffd36cc27407003a6f9efcb9c16370e3435c5b1d ("support: Use
>>>> unwinder in links-dso-program-c only with libgcc_s") and
>>>> commit 5dfbc3c43ecc1bcfc760a032c91bb002660051bc ("support: Link
>>>> links-dso-program-c with libgcc_s only if available").
>>>
>>> This seems to break our cross-builds for ia64 with T2 and IIUC also any
>>> cross builds in T2 for other architectures, starting with
>>> ffd36cc27407003a6f9efcb9c16370e3435c5b1d, where two extra lines were
>>> added to support/Makefile:
>>
>> What is “this”?
> 
> Sorry for the confusion. With "this" I meant all three patches. And that
> the problem started with ffd36cc27407003a6f9efcb9c16370e3435c5b1d.
> 
>> You talk about
>> ffd36cc27407003a6f9efcb9c16370e3435c5b1d, but the patch is supposed to
>> fix that.
> 
> I wrongly assumed that the `[...] -lgcc` line had to be guarded as
> well. See below.
> 
>> I've pushed this patch here (thanks Joseph for the quick review).
>> Please test again.
> 
> I already tested an equivalent change to what you just pushed some days
> ago when trying to solve our build issues. In my case I just commented
> the `[...] -fexceptions` line to inactivate it. And I thought I had
> also tested leaving:
> 
> ```
> LDLIBS-links-dso-program-c = -lgcc
> ```
> 
> ...active. But after retesting now it seems not, as the glibc build
> works with the above line left active.
> 
> I assume I have deactivated the `[...] -lgcc` line first when
> trying to fix the build some days ago, but saw that the build still
> failed, so deactivated the `[...] -fexceptions` line in addition and
> after it worked - wrongly - concluded that both lines have to be
> inactive for the build to complete (like it was before
> ffd36cc27407003a6f9efcb9c16370e3435c5b1d).
Correction: ffd36cc27407003a6f9efcb9c16370e3435c5b1d should be
3e2be87832781a29ed67f38f87c1ce3dd4c1b866 ("support: Link 
links-dso-program-c against libgcc_s") - most likely everywhere in
this thread IINM.

Cheers,
Frank