linux-kernel - RE: [PATCH 1/2] x86/fred: Fix build with clang

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Message-ID: <SA1PR11MB673408407EE572F5043C1C2EA87F2@SA1PR11MB6734.namprd11.prod.outlook.com>
Date: Sun, 28 Jan 2024 20:27:49 +0000
From: "Li, Xin3" <xin3.li@...el.com>
To: "H. Peter Anvin" <hpa@...or.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
CC: "tglx@...utronix.de" <tglx@...utronix.de>, "mingo@...hat.com"
	<mingo@...hat.com>, "bp@...en8.de" <bp@...en8.de>,
	"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>, "x86@...nel.org"
	<x86@...nel.org>, "luto@...nel.org" <luto@...nel.org>, "Shankar, Ravi V"
	<ravi.v.shankar@...el.com>, "andrew.cooper3@...rix.com"
	<andrew.cooper3@...rix.com>
Subject: RE: [PATCH 1/2] x86/fred: Fix build with clang

> >>> @@ -43,13 +43,12 @@ SYM_INNER_LABEL(asm_fred_exit_user,
> >> SYM_L_GLOBAL)
> >>> 	_ASM_EXTABLE_TYPE(1b, asm_fred_entrypoint_user, EX_TYPE_ERETU)
> >>> SYM_CODE_END(asm_fred_entrypoint_user)
> >>>
> >>> -.fill asm_fred_entrypoint_kernel - ., 1, 0xcc
> >>> -
> >>> /*
> >>>   * The new RIP value that FRED event delivery establishes is
> >>>   * (IA32_FRED_CONFIG & ~FFFH) + 256 for events that occur in
> >>>   * ring 0, i.e., asm_fred_entrypoint_user + 256.
> >>>   */
> >>> +	.fill asm_fred_entrypoint_user + 256 - ., 1, 0xcc
> >>> 	.org asm_fred_entrypoint_user + 256
> >>> SYM_CODE_START_NOALIGN(asm_fred_entrypoint_kernel)
> >>> 	FRED_ENTER
> >>
> >> .fill and .org here are redundant; in fact, there two directives mean
> >> exactly the same thing except that .org implicitly subtracts the current offset.
> >
> > Ah, right, .fill already does the job!
> >
> > I will remove .org.
> >
> 
> Incidentally, was there a problem with .org ..., 0xcc?

Oh, it's just that I didn't know .org can be used to fill.

 
> Not a criticism, I just want to know to better understand current binutils
> limitations.
> 
> 	-hpa