RE: [PATCH 6/6] x86/gsseg: use the LKGS instruction if available for load_gs_index()

[H. Peter Anvin]

On October 7, 2022 11:07:34 AM PDT, "Li, Xin3" <xin3.li@xxxxxxxxx> wrote:
>> >> +	alternative_io("1: call asm_load_gs_index\n"
>> >> +		       ".pushsection \".fixup\",\"ax\"\n"
>> >> +		       "2:	xorl %k[sel], %k[sel]\n"
>> >> +		       "	jmp 1b\n"
>> >> +		       ".popsection\n"
>> >> +		       _ASM_EXTABLE(1b, 2b),
>> >> +		       _ASM_BYTES(0x3e) LKGS_DI,
>> >> +		       X86_FEATURE_LKGS,
>> >> +		       ASM_OUTPUT2([sel] "+D" (sel), ASM_CALL_CONSTRAINT),
>> >> +		       ASM_NO_INPUT_CLOBBER(_ASM_AX));
>> >>  }
>> >
>> >I'm very sure none of this was tested... the .fixup section hasn't
>> >existed for almost a year now.
>> >
>> >  e5eefda5aa51 ("x86: Remove .fixup section")
>> 
>> Xin, what did you use as the forward-porting baseline?
>
>6.0 release, and my kernel dump shows me a fixup section is there, and a fixup section is created anyway if we do "pushsection "\.fixup\"".
>
>
>

Yeah. .fixup is really Just Another Text Section ™, so it is probably not surprising if it has crept back in.