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Date:   Fri, 7 Oct 2022 21:24:13 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     "Li, Xin3" <xin3.li@intel.com>
Cc:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "x86@kernel.org" <x86@kernel.org>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "mingo@redhat.com" <mingo@redhat.com>,
        "bp@alien8.de" <bp@alien8.de>,
        "dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
        "hpa@zytor.com" <hpa@zytor.com>
Subject: Re: [PATCH 6/6] x86/gsseg: use the LKGS instruction if available for
 load_gs_index()
Message-ID: <Y0B83cSSwJnRtGAn@hirez.programming.kicks-ass.net>
References: <20221006154041.13001-1-xin3.li@intel.com>
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 <BN6PR1101MB21611798953AADA4DFD71719A85F9@BN6PR1101MB2161.namprd11.prod.outlook.com>
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On Fri, Oct 07, 2022 at 06:01:06PM +0000, Li, Xin3 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.
> 
> Weird, did you ever check a kernel dump?

$ readelf -WS defconfig-build/vmlinux | grep fixup
[ 5] .pci_fixup        PROGBITS        ffffffff826a5350 18a5350 003570 00   A  0   0 16
[ 6] .rela.pci_fixup   RELA            0000000000000000 360c388 005028 18   I 60   5  8

In fact, when I add one I get:

ld: warning: orphan section `.fixup' from `arch/x86/kernel/traps.o' being placed in section `.fixup'