Re: [PATCH v8 6/6] x86/vdso: Enable sframe generation in VDSO

["H. Peter Anvin" <hpa@zytor.com>]

On 2026-02-06 11:36, Jens Remus wrote:
> From: Josh Poimboeuf <jpoimboe@kernel.org>
> 
> Enable sframe generation in the VDSO library so kernel and user space
> can unwind through it.
> 
> SFrame isn't supported for x32 or x86-32.  Discard .sframe sections for
> those VDSOs.
> 
> [ Jens Remus: Add support for SFrame V3.  Prevent GNU_SFRAME program
> table entry to empty .sframe section. ]
> 

This will not break the x86-32 build if the assembler encounters .sframe?

> Notes (jremus):
>     Changes in v8:
>     - Discard .sframe for x32 and x86-32 VDSOs. (Josh/Indu)
>       Note that the use of KEEP_SFRAME enables to define it for x86-64
>       VDSO only.  Unlike CONFIG_AS_SFRAME, which may also be defined
>       for x32 and x86-32 VDSO.  In x32 VDSO it would result in superfluous
>       .sframe (copied from the x86-64 build - could be removed in X32
>       build step).  In x86-32 VDSO it would cause a bogus GNU_SFRAME
>       program table entry.

For x32, this would be a "valid" sframe, right, even if the tools currently
don't know how to consume it (and potentially never will)? If so, is there
really any reason to explicitly remove it?

>  	/*
>  	 * Text is well-separated from actual data: there's plenty of
>  	 * stuff that isn't used at runtime in between.
> @@ -80,6 +87,10 @@ SECTIONS
>  		*(.discard)
>  		*(.discard.*)
>  		*(__bug_table)
> +#ifndef KEEP_SFRAME
> +		*(.sframe)
> +		*(.sframe.*)
> +#endif

This #ifndef is actually not necessary: if we have already "consumed" the
.sframe* sections they will not be encountered here.

I would prefer to have KEEP_SFRAME always defined (as true or false, and using
#if) instead of using #ifdef. I believe that also means you can do:

#define KEEP_SFRAME IS_ENABLED(CONFIG_AS_SFRAME)

... instead of #ifdef.

	-hpa