Messages in this thread |  | | Date | Sat, 12 Mar 2022 22:17:40 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH 3/5] x86/alternative: record .altinstructions section entity size |
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On Fri, Mar 11, 2022 at 05:43:10PM +0300, Alexey Dobriyan wrote: > .altinstructions entry was 12 bytes in size, then it was 13 bytes, > now it is 12 again. It was 24 bytes on some distros as well. > Record this information as section sh_entsize value so that tools > which parse .altinstructions have easier time.
Which tools would that be? Because afaict you've not actually updated objtool.
> Signed-off-by: Alexey Dobriyan (CloudLinux) <adobriyan@gmail.com> > --- > arch/x86/include/asm/alternative.h | 13 ++++++++----- > 1 file changed, 8 insertions(+), 5 deletions(-) > > diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h > index 58eee6402832..cf7722a106b3 100644 > --- a/arch/x86/include/asm/alternative.h > +++ b/arch/x86/include/asm/alternative.h > @@ -9,6 +9,8 @@ > #define ALTINSTR_FLAG_INV (1 << 15) > #define ALT_NOT(feat) ((feat) | ALTINSTR_FLAG_INV) > > +#define sizeof_struct_alt_instr 12 > + > #ifndef __ASSEMBLY__ > > #include <linux/stddef.h> > @@ -66,6 +68,7 @@ struct alt_instr { > u8 instrlen; /* length of original instruction */ > u8 replacementlen; /* length of new instruction */ > } __packed; > +_Static_assert(sizeof(struct alt_instr) == sizeof_struct_alt_instr, "");
Would it not be much simpler to have this in asm-offsets.h ?
> + ".pushsection .altinstructions,\"aM\",@progbits," __stringify(sizeof_struct_alt_instr) "\n"\ > + ".pushsection .altinstructions,\"aM\",@progbits," __stringify(sizeof_struct_alt_instr) "\n"\ > + ".pushsection .altinstructions,\"aM\",@progbits," __stringify(sizeof_struct_alt_instr) "\n"\
> + .pushsection .altinstructions,"aM",@progbits,sizeof_struct_alt_instr > + .pushsection .altinstructions,"aM",@progbits,sizeof_struct_alt_instr
Aside of adding entsize, you're also adding the M(ergable) bit. Also, those lines are on the unwieldy side of things.
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