Re: [PATCH dwarves 0/4] Improve BTF concrete function accuracy

[Alan Maguire <alan.maguire@oracle.com>]

On 13/01/2026 13:13, 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 is from Yonghong's LLVM true function signature series,
> and helps for patch 3 which adds GCC true function signature
> support for optimized functions; with that support, we use
> binary-level signatures for .isra, .constprop 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 4 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 1-3 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.
>

hi folks, I'd like to land this series (patches 1, 3 and 4;
patch 2 isn't needed right now) soon so we have Matt's
fix in place; if anyone has cycles to further look at the patches 
or test it to ensure the vmlinux and module BTF generated doesn't 
cause problems, that would be great. Thanks!

Alan