Messages in this thread | | | Date | Thu, 24 Nov 2022 12:18:29 +0100 | Subject | Re: [PATCH] x86/paravirt: Use relative reference for original instruction | From | Juergen Gross <> |
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On 24.11.22 12:06, Hou Wenlong wrote: > On Thu, Nov 24, 2022 at 11:18:52AM +0100, Juergen Gross wrote: >> On 24.11.22 09:51, Hou Wenlong wrote: >>> Similar to the alternative patching, use relative reference for original >>> instruction rather than absolute one, which saves 8 bytes for one entry >>> on x86_64. And it could generate R_X86_64_PC32 relocation instead of >> >> 8 bytes saved? I think those are 4 bytes only. >> > The corresponding C structure paravirt_patch_site is not packed, Before this, > its size is 16 bytes in x86_64,due to the alignment of 8 bytes. Now the alignment > is 4 bytes, so the size is 8 bytes.
Oh, I've looked at Linus' tree. You seem to have based your reasoning on the tip/paravirt branch, which is fine.
> >>> R_X86_64_64 relocation, which also reduces relocation metadata on >>> relocatable builds. >>> >>> Signed-off-by: Hou Wenlong <houwenlong.hwl@antgroup.com> >>> --- >>> arch/x86/include/asm/paravirt.h | 6 +++--- >>> arch/x86/include/asm/paravirt_types.h | 4 ++-- >>> arch/x86/kernel/alternative.c | 8 +++++--- >>> 3 files changed, 10 insertions(+), 8 deletions(-) >>> >>> diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h >>> index 2851bc2339d5..2cbe9b64e103 100644 >>> --- a/arch/x86/include/asm/paravirt.h >>> +++ b/arch/x86/include/asm/paravirt.h >>> @@ -735,13 +735,13 @@ extern void default_banner(void); >>> #else /* __ASSEMBLY__ */ >>> -#define _PVSITE(ptype, ops, word, algn) \ >>> +#define _PVSITE(ptype, ops, algn) \ >> >> Would you please drop the algn parameter, too? It isn't needed anymore >> as the alignment can be hard coded to be 4 now. This would need to be >> adjusted in the _paravirt_alt() macro, too. >> > OK, since the aligment is 4 bytes now, it seems that _ASM_ALIGN could > be dropped too?
That's what I meant with the adjustment of _paravirt_alt().
I wouldn't drop _ASM_ALIGN, but replace it with ".align 4".
Juergen [unhandled content-type:application/pgp-keys][unhandled content-type:application/pgp-signature] | |