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

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Message-ID: <882e400f-913b-4ed5-9611-ef87cd8b58b2@zytor.com>
Date: Sun, 28 Jan 2024 11:33:20 -0800
From: "H. Peter Anvin" <hpa@...or.com>
To: "Li, Xin3" <xin3.li@...el.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

On 1/27/24 11:46, Li, Xin3 wrote:
>>> diff --git a/arch/x86/entry/entry_64_fred.S
>>> b/arch/x86/entry/entry_64_fred.S index eedf98de7538..5427e0da190d
>>> 100644
>>> --- a/arch/x86/entry/entry_64_fred.S
>>> +++ b/arch/x86/entry/entry_64_fred.S
>>> @@ -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?

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

	-hpa