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SubjectRe: [PATCH] x86: Discard .note.gnu.property sections in vDSO
On Thu, Mar 26, 2020 at 10:43:14AM -0700, H.J. Lu wrote:
> With the command-line option, -mx86-used-note=yes, the x86 assembler

I see:

-mx86-used-note=no
-mx86-used-note=yes
These options control whether the assembler should generate
GNU_PROPERTY_X86_ISA_1_USED and GNU_PROPERTY_X86_FEATURE_2_USED GNU property
notes. The default can be controlled by the --enable-x86-used-note
configure option.

Is there a plan to use this build option in the kernel in the future or
all binutils will have it enabled or what's the story here?

Because I don't see -mx86-used-note used anywhere in the kernel...

> in binutils 2.32 and above generates a program property note in a note
> section, .note.gnu.property, to encode used x86 ISAs and features. But
> x86 kernel vDSO linker script only contains a single NOTE segment:
>
> PHDRS
> {
> text PT_LOAD FLAGS(5) FILEHDR PHDRS; /* PF_R|PF_X */
> dynamic PT_DYNAMIC FLAGS(4); /* PF_R */
> note PT_NOTE FLAGS(4); /* PF_R */
> eh_frame_hdr 0x6474e550;
> }
>
> The NOTE segment generated by vDSO linker script is aligned to 4 bytes.
> But .note.gnu.property section must be aligned to 8 bytes on x86-64 and
> we get
>
> [hjl@gnu-skx-1 vdso]$ readelf -n vdso64.so
>
> Displaying notes found in: .note
> Owner Data size Description
> Linux 0x00000004 Unknown note type: (0x00000000)
> description data: 06 00 00 00
> readelf: Warning: note with invalid namesz and/or descsz found at offset 0x20
> readelf: Warning: type: 0x78, namesize: 0x00000100, descsize: 0x756e694c, alignment: 8
> [hjl@gnu-skx-1 vdso]$
>
> Since note.gnu.property section in vDSO is not checked by dynamic linker,
> this patch discards .note.gnu.property sections in vDSO by adding

Avoid having "This patch" or "This commit" in the commit message. It is
tautologically useless.

Also, do

$ git grep 'This patch' Documentation/process

for more details.

--
Regards/Gruss,
Boris.

https://people.kernel.org/tglx/notes-about-netiquette

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