Re: [PATCH v3 dwarves 0/5] Improve BTF concrete function accuracy

On 10/02/2026 19:57, Alan Maguire wrote:
> On 27/01/2026 17:20, Alan Maguire wrote:
>> This series brings together a few solutions to issues we have
>> with accuracy of BTF function representation at the binary level.
>>
>> The first patch detects mismatches between concrete (binary)
>> and abstract (source-level) function signatures as a means
>> of either excluding them or providing a "true" function signature.
>>
>> Patch 2 adds GCC true function signature support for optimized
>> functions; with that support, we use binary-level signatures
>> for .isra.0, .constprop.0 functions and represent them with
>> their "." suffixes as BTF_KIND_FUNC names.
>>
>> This allows for fentry attach to such functions, and
>> the "." suffix is an indicator of signature modification.
>> The feature is guarded by a default-off BTF feature because
>> older kernels did not support a "." in a function name.
>>
>> Patch 3 uses Yonghong's example program as a test; compiling
>> with -O2 we expect a parameter to "foo" to be optimized
>> out and the true function signature should reflect that.
>>
>> Patch 4 documents the non-default "true_signature" feature.
>>
>> Patch 5 is Matt's patch to favour the strong function
>> over the associated weak declaration.  The other patches
>> are important prerequisites for this as the patch selects
>> the binary-level function (with a lowpc value), and in
>> the case of optimized functions we were often selecting
>> the .isra function with optimized-out parameters.  Because
>> pahole did not previously detect this correctly we ended
>> up with functions with signatures having reordered parameters.
>>
>> Patches 1-2 help avoid this by better detecting optimized-out
>> function parameters.
>>
>> With these patches in place, ~20 functions are omitted from
>> vmlinux BTF; all these are "."-suffixed functions which
>> we were not noticing had optimized-out parameters.
>>
>> Experimenting with adding true_signature to BTF features
>> we end up adding approximately 500 .isra and .constprop
>> functions to vmlinux BTF.
>>
>> The true function signature support here will also hopefully
>> help pave the way for Yonghong's work on the LLVM side.
>>
> 
> I'm planning on landing this series shortly, so if anyone has
> any additional feedback/objections do let me know. Thanks!
>

series applied. Thanks.

Alan