Juergen Gross
2022-Nov-24 11:18 UTC
[PATCH] x86/paravirt: Use relative reference for original instruction
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 at 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 -------------- next part -------------- A non-text attachment was scrubbed... Name: OpenPGP_0xB0DE9DD628BF132F.asc Type: application/pgp-keys Size: 3098 bytes Desc: OpenPGP public key URL: <http://lists.linuxfoundation.org/pipermail/virtualization/attachments/20221124/1e98f8e9/attachment.bin> -------------- next part -------------- A non-text attachment was scrubbed... Name: OpenPGP_signature Type: application/pgp-signature Size: 495 bytes Desc: OpenPGP digital signature URL: <http://lists.linuxfoundation.org/pipermail/virtualization/attachments/20221124/1e98f8e9/attachment.sig>