Re: [PATCH V2] modpost: Amend ppc64 save/restfpr symnames for -Os build

["René Rebe" <rene@exactco.de>]

Hi,

On 3. Feb 2026, at 07:48, Nathan Chancellor <nathan@kernel.org> wrote:
> 
> On Sun, Nov 23, 2025 at 04:25:51PM +0100, René Rebe wrote:
>> Hey,
>> 
>> On Sun, 23 Nov 2025 16:09:41 +0100 (CET), René Rebe <rene@exactco.de> wrote:
>> 
>>> On Sun, 23 Nov 2025 15:57:24 +0100, "Christophe Leroy (CS GROUP)" <chleroy@kernel.org> wrote:
>>> 
>>>> Le 23/11/2025 à 13:13, René Rebe a écrit :
>>>>> Building a size optimized ppc64 kernel (-Os), gcc emits more FP
>>>>> save/restore symbols, that the linker generates on demand into the
>>>>> .sfpr section. Explicitly allow-list those in scripts/mod/modpost.c,
>>>>> too. They are needed for the amdgpu in-kernel floating point support.
>>>> 
>>>> Would have been interested to know with which version of GCC the
>>>> problem started.
>>> 
>>> idk, maybe forever, or at least a decade fo GCC? Most devs probably
>>> don't build size optimized, and addtionally we only use in kernel
>>> floating point for amdgpu since recently? Should I add Fixes: for the
>>> in-kernel FP hash?
>>> 
>>>> By the way you seem to fix the problem for modules, but does it also
>>>> work when amdgpu is in kernel ? I would have expected a need to add
>>>> functions in arch/powerpc/lib/crtsavres.S as well, just like following
>>>> commits:
>>>> 
>>>> 8fe9c93e7453 ("powerpc: Add vr save/restore functions")
>>>> 7fca5dc8aa7a ("powerpc: Fix module building for gcc 4.5 and 64 bit")
>>>> da3de6df33f5 ("[POWERPC] Fix -Os kernel builds with newer gcc
>>>> versions")
>>> 
>>> idk, I avoid linking that big stuff directly into the kernel and would
>>> need to specically test that, too. I guess I go do that now, too, ...
>> 
>> It appears built-in amdgpu FP somehow magically works for me:
>> 
>> debug-linux:[linux-6.17]# grep DRM.*AMD .config
>> CONFIG_DRM_AMDGPU=y
>> CONFIG_DRM_AMDGPU_SI=y
>> CONFIG_DRM_AMDGPU_CIK=y
>> CONFIG_DRM_AMDGPU_USERPTR=y
>> CONFIG_DRM_AMD_ACP=y
>> CONFIG_DRM_AMD_DC=y
>> CONFIG_DRM_AMD_DC_FP=y
>> CONFIG_DRM_AMD_DC_SI=y
>> ...
>>  CC      drivers/gpu/drm/amd/amdgpu/../display/modules/hdcp/hdcp_ddc.o
>>  CC      drivers/gpu/drm/amd/amdgpu/../display/modules/hdcp/hdcp_log.o
>>  CC      drivers/gpu/drm/amd/amdgpu/../display/modules/hdcp/hdcp_psp.o
>>  CC      drivers/gpu/drm/amd/amdgpu/../display/modules/hdcp/hdcp.o
>>  CC      drivers/gpu/drm/amd/amdgpu/../display/modules/hdcp/hdcp1_execution.o
>>  CC      drivers/gpu/drm/amd/amdgpu/../display/modules/hdcp/hdcp1_transition.o
>>  CC      drivers/gpu/drm/amd/amdgpu/../display/modules/hdcp/hdcp2_execution.o
>>  CC      drivers/gpu/drm/amd/amdgpu/../display/modules/hdcp/hdcp2_transition.o
>>  AR      drivers/gpu/drm/amd/amdgpu/built-in.a
>>  AR      drivers/gpu/drm/built-in.a
>>  AR      drivers/gpu/built-in.a
>>  AR      drivers/built-in.a
>>  AR      built-in.a
>>  AR      vmlinux.a
>>  LD      vmlinux.o
>>  GEN     modules.builtin.modinfo
>>  GEN     modules.builtin
>>  MODPOST vmlinux.symvers
>>  CC      .vmlinux.export.o
>>  UPD     include/generated/utsversion.h
>>  CC      init/version-timestamp.o
>>  KSYMS   .tmp_vmlinux0.kallsyms.S
>>  AS      .tmp_vmlinux0.kallsyms.o
>>  LD      .tmp_vmlinux1
>>  NM      .tmp_vmlinux1.syms
>>  KSYMS   .tmp_vmlinux1.kallsyms.S
>>  AS      .tmp_vmlinux1.kallsyms.o
>>  LD      .tmp_vmlinux2
>>  NM      .tmp_vmlinux2.syms
>>  KSYMS   .tmp_vmlinux2.kallsyms.S
>>  AS      .tmp_vmlinux2.kallsyms.o
>>  LD      vmlinux.unstripped
>>  NM      System.map
>>  SORTTAB vmlinux.unstripped
>> make[3]: Nothing to be done for 'vmlinux.unstripped'.
>>  OBJCOPY vmlinux
>> 
>> So I guess the patch is good to go after clarifying which kind of
>> Fixes: to use?
> 
> Was this ever picked up or addressed elswhere?

Nope, still needs to be applied AFAICS ;-)

Thanks!

	René

>>>>> MODPOST Module.symvers
>>>>> ERROR: modpost: "_restfpr_20" [drivers/gpu/drm/amd/amdgpu/amdgpu.ko]
>>>>> undefined!
>>>>> ERROR: modpost: "_restfpr_26" [drivers/gpu/drm/amd/amdgpu/amdgpu.ko]
>>>>> undefined!
>>>>> ERROR: modpost: "_restfpr_22" [drivers/gpu/drm/amd/amdgpu/amdgpu.ko]
>>>>> undefined!
>>>>> ERROR: modpost: "_savegpr1_27" [drivers/gpu/drm/amd/amdgpu/amdgpu.ko]
>>>>> undefined!
>>>>> ERROR: modpost: "_savegpr1_25" [drivers/gpu/drm/amd/amdgpu/amdgpu.ko]
>>>>> undefined!
>>>>> ERROR: modpost: "_restfpr_28" [drivers/gpu/drm/amd/amdgpu/amdgpu.ko]
>>>>> undefined!
>>>>> ERROR: modpost: "_savegpr1_29" [drivers/gpu/drm/amd/amdgpu/amdgpu.ko]
>>>>> undefined!
>>>>> ERROR: modpost: "_savefpr_20" [drivers/gpu/drm/amd/amdgpu/amdgpu.ko]
>>>>> undefined!
>>>>> ERROR: modpost: "_savefpr_22" [drivers/gpu/drm/amd/amdgpu/amdgpu.ko]
>>>>> undefined!
>>>>> ERROR: modpost: "_restfpr_15" [drivers/gpu/drm/amd/amdgpu/amdgpu.ko]
>>>>> undefined!
>>>>> WARNING: modpost: suppressed 56 unresolved symbol warnings because
>>>>> there were too many)
>>>>> Signed-off-by: René Rebe <rene@exactco.de>
>>>>> ---
>>>>> V2: description
>>>>> Theoretically for -stable, but no previous commit that broke it.
>>>> 
>>>> In that case you have to add Cc: stable@vger.kernel.org
>>>> Add indeed it is likely a gcc upgrade that broke it, not a previous
>>>> commit.
>>> 
>>> Should I then simply use enabling amdgpu dc_fp and in-kernel FP as the
>>> breaking commit for Fixes:?
>>> 
>>> Thanks!
>>> 
>>> René
>>> 
>>>>> ---
>>>>>  scripts/mod/modpost.c | 4 ++++
>>>>>  1 file changed, 4 insertions(+)
>>>>> diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
>>>>> index 47c8aa2a6939..133dfa16308a 100644
>>>>> --- a/scripts/mod/modpost.c
>>>>> +++ b/scripts/mod/modpost.c
>>>>> @@ -602,6 +602,10 @@ static int ignore_undef_symbol(struct elf_info
>>>>> *info, const char *symname)
>>>>>   /* Special register function linked on all modules during final link of
>>>>>   .ko */
>>>>>   if (strstarts(symname, "_restgpr0_") ||
>>>>>      strstarts(symname, "_savegpr0_") ||
>>>>> +    strstarts(symname, "_restgpr1_") ||
>>>>> +    strstarts(symname, "_savegpr1_") ||
>>>>> +    strstarts(symname, "_restfpr_") ||
>>>>> +    strstarts(symname, "_savefpr_") ||
>>>>>      strstarts(symname, "_restvr_") ||
>>>>>      strstarts(symname, "_savevr_") ||
>>>>>      strcmp(symname, ".TOC.") == 0)
>>>> 
>>> 
>>> -- 
>>> René Rebe, ExactCODE GmbH, Berlin, Germany
>>> https://exactco.de • https://t2linux.com • https://patreon.com/renerebe
>> 
>> -- 
>> René Rebe, ExactCODE GmbH, Berlin, Germany
>> https://exactco.de • https://t2linux.com • https://patreon.com/renerebe

-- 
https://exactco.de • https://t2linux.com • https://patreon.com/renerebe