From: Peter Zijlstra <peterz@infradead.org>
To: "Jürgen Groß" <jgross@suse.com>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org,
llvm@lists.linux.dev, xin@zytor.com,
"H. Peter Anvin" <hpa@zytor.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
Nathan Chancellor <nathan@kernel.org>,
Nick Desaulniers <nick.desaulniers+lkml@gmail.com>,
Bill Wendling <morbo@google.com>,
Justin Stitt <justinstitt@google.com>
Subject: Re: [PATCH v2 09/12] x86/msr: Use the alternatives mechanism for WRMSR
Date: Wed, 1 Oct 2025 08:43:39 +0200 [thread overview]
Message-ID: <20251001064339.GL4067720@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <2ad137cb-ed38-42f6-ac0a-a81569051779@suse.com>
On Tue, Sep 30, 2025 at 05:42:13PM +0200, Jürgen Groß wrote:
> Could it be that the labels should be local ones?
I already tried 's/#pfx/".L" #pfx/g' and that made no difference.
> What does the failure look like?
Its complaining about label re-definitions.
$ make O=defconfig-build/ arch/x86/kernel/alternative.o
../arch/x86/include/asm/cpufeature.h: Assembler messages:
../arch/x86/include/asm/cpufeature.h:102: Error: symbol `.L__UNIQUE_ID_altinstr_67_begin' is already defined
../arch/x86/include/asm/cpufeature.h:104: Error: symbol `.L__UNIQUE_ID_altinstr_66_begin' is already defined
../arch/x86/include/asm/cpufeature.h:106: Error: symbol `.L__UNIQUE_ID_altinstr_66_pad' is already defined
../arch/x86/include/asm/cpufeature.h:109: Error: symbol `.L__UNIQUE_ID_altinstr_66_end' is already defined
../arch/x86/include/asm/cpufeature.h:119: Error: symbol `.L__UNIQUE_ID_altinstr_66_alt_begin' is already defined
../arch/x86/include/asm/cpufeature.h:121: Error: symbol `.L__UNIQUE_ID_altinstr_66_alt_end' is already defined
../arch/x86/include/asm/cpufeature.h:124: Error: symbol `.L__UNIQUE_ID_altinstr_67_pad' is already defined
../arch/x86/include/asm/cpufeature.h:127: Error: symbol `.L__UNIQUE_ID_altinstr_67_end' is already defined
../arch/x86/include/asm/cpufeature.h:137: Error: symbol `.L__UNIQUE_ID_altinstr_67_alt_begin' is already defined
../arch/x86/include/asm/cpufeature.h:139: Error: symbol `.L__UNIQUE_ID_altinstr_67_alt_end' is already defined
../arch/x86/include/asm/cpufeature.h:102: Error: symbol `.L__UNIQUE_ID_altinstr_67_begin' is already defined
../arch/x86/include/asm/cpufeature.h:104: Error: symbol `.L__UNIQUE_ID_altinstr_66_begin' is already defined
../arch/x86/include/asm/cpufeature.h:106: Error: symbol `.L__UNIQUE_ID_altinstr_66_pad' is already defined
../arch/x86/include/asm/cpufeature.h:109: Error: symbol `.L__UNIQUE_ID_altinstr_66_end' is already defined
../arch/x86/include/asm/cpufeature.h:119: Error: symbol `.L__UNIQUE_ID_altinstr_66_alt_begin' is already defined
../arch/x86/include/asm/cpufeature.h:121: Error: symbol `.L__UNIQUE_ID_altinstr_66_alt_end' is already defined
../arch/x86/include/asm/cpufeature.h:124: Error: symbol `.L__UNIQUE_ID_altinstr_67_pad' is already defined
../arch/x86/include/asm/cpufeature.h:127: Error: symbol `.L__UNIQUE_ID_altinstr_67_end' is already defined
../arch/x86/include/asm/cpufeature.h:137: Error: symbol `.L__UNIQUE_ID_altinstr_67_alt_begin' is already defined
../arch/x86/include/asm/cpufeature.h:139: Error: symbol `.L__UNIQUE_ID_altinstr_67_alt_end' is already defined
../arch/x86/include/asm/cpufeature.h:102: Error: symbol `.L__UNIQUE_ID_altinstr_67_begin' is already defined
../arch/x86/include/asm/cpufeature.h:104: Error: symbol `.L__UNIQUE_ID_altinstr_66_begin' is already defined
../arch/x86/include/asm/cpufeature.h:106: Error: symbol `.L__UNIQUE_ID_altinstr_66_pad' is already defined
../arch/x86/include/asm/cpufeature.h:109: Error: symbol `.L__UNIQUE_ID_altinstr_66_end' is already defined
../arch/x86/include/asm/cpufeature.h:119: Error: symbol `.L__UNIQUE_ID_altinstr_66_alt_begin' is already defined
../arch/x86/include/asm/cpufeature.h:121: Error: symbol `.L__UNIQUE_ID_altinstr_66_alt_end' is already defined
../arch/x86/include/asm/cpufeature.h:124: Error: symbol `.L__UNIQUE_ID_altinstr_67_pad' is already defined
../arch/x86/include/asm/cpufeature.h:127: Error: symbol `.L__UNIQUE_ID_altinstr_67_end' is already defined
...
That specific one is this:
static inline __attribute__((__gnu_inline__)) __attribute__((__unused__)) __attribute__((no_instrument_function)) __attribute__((__always_inline__)) bool _static_cpu_has(u16 bit)
{
asm goto("# ALT: oldinstr\n" ".L" "__UNIQUE_ID_altinstr_67" "_begin:\n\t" "# ALT: oldinstr\n" ".L" "__UNIQUE_ID_altinstr_66" "_begin:\n\t" "jmp 6f" "\n" ".L" "__UNIQUE_ID_altinstr_66" "_pad:\n" "# ALT: padding\n" ".skip -(((" ".L" "_ _UNIQUE_ID_altinstr_66" "_alt_end - " ".L" "__UNIQUE_ID_altinstr_66" "_alt_begin" ")-(" ".L" "__UNIQUE_ID_altinstr_66" "_pad - " ".L" "__UNIQUE_ID_altinstr_66" "_begin" ")) > 0) * " "((" ".L" "__UNIQUE_ID_altinstr_66" "_alt_end - " " .L" "__UNIQUE_ID_altinstr_66" "_alt_begin" ")-(" ".L" "__UNIQUE_ID_altinstr_66" "_pad - " ".L" "__UNIQUE_ID_altinstr_66" "_begin" ")),0x90\n" ".L" "__UNIQUE_ID_altinstr_66" "_end:\n" ".pushsection .altinstructions,\"a\"\n" " .long " ".L" "__UNIQUE_ID_altinstr_66" "_begin - .\n" " .long " ".L" "__UNIQUE_ID_altinstr_66" "_alt_begin - .\n" " .4byte " "( 3*32+21)" "\n" " .byte " ".L" "__UNIQUE_ID_altinstr_66" "_end - " ".L" "__UNIQUE_ID_altinstr_66" "_begin" "\n" " .byte " ".L" "__UNIQUE_ID_altinstr_66" "_alt_end - " ".L" "__UNIQUE_ID_altinstr_66" "_alt_begin" "\n" ".popsection\n" ".pushsection .altinstr_replacement, \"ax\"\n" "# ALT: replacement\n" ".L" "__UNIQUE_ID_altinstr_66" "_alt_begin:\n \t" "jmp %l[t_no]" "\n" ".L" "__UNIQUE_ID_altinstr_66" "_alt_end:\n" ".popsection\n" "\n" ".L" "__UNIQUE_ID_altinstr_67" "_pad:\n" "# ALT: padding\n" ".skip -(((" ".L" "__UNIQUE_ID_altinstr_67" "_alt_end - " ".L" "__UNIQUE_ID_altinst r_67" "_alt_begin" ")-(" ".L" "__UNIQUE_ID_altinstr_67" "_pad - " ".L" "__UNIQUE_ID_altinstr_67" "_begin" ")) > 0) * " "((" ".L" "__UNIQUE_ID_altinstr_67" "_alt_end - " ".L" "__UNIQUE_ID_altinstr_67" "_alt_begin" ")-(" ".L" "__UNIQUE _ID_altinstr_67" "_pad - " ".L" "__UNIQUE_ID_altinstr_67" "_begin" ")),0x90\n" ".L" "__UNIQUE_ID_altinstr_67" "_end:\n" ".pushsection .altinstructions,\"a\"\n" " .long " ".L" "__UNIQUE_ID_altinstr_67" "_begin - .\n" " .long " ".L" "_ _UNIQUE_ID_altinstr_67" "_alt_begin - .\n" " .4byte " "%c[feature]" "\n" " .byte " ".L" "__UNIQUE_ID_altinstr_67" "_end - " ".L" "__UNIQUE_ID_altinstr_67" "_begin" "\n" " .byte " ".L" "__UNIQUE_ID_altinstr_67" "_alt_end - " ".L" "__U NIQUE_ID_altinstr_67" "_alt_begin" "\n" ".popsection\n" ".pushsection .altinstr_replacement, \"ax\"\n" "# ALT: replacement\n" ".L" "__UNIQUE_ID_altinstr_67" "_alt_begin:\n\t" "" "\n" ".L" "__UNIQUE_ID_altinstr_67" "_alt_end:\n" ".pop section\n"
".pushsection .altinstr_aux,\"ax\"\n"
"6:\n"
" testb %[bitnum], %a[cap_byte]\n"
" jnz %l[t_yes]\n"
" jmp %l[t_no]\n"
".popsection\n"
: : [feature] "i" (bit),
[bitnum] "i" (1 << (bit & 7)),
[cap_byte] "i" (&((const char *)boot_cpu_data.x86_capability)[bit >> 3])
: : t_yes, t_no);
t_yes:
return true;
t_no:
return false;
}
What I'm thinking is happening is that the __always_inline__ is causing
multiple exact copies of the thing.
Let me see how terrible it all ends up when using as macros
next prev parent reply other threads:[~2025-10-01 6:43 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-09-30 7:03 [PATCH v2 00/12] x86/msr: Inline rdmsr/wrmsr instructions Juergen Gross
2025-09-30 7:03 ` [PATCH v2 09/12] x86/msr: Use the alternatives mechanism for WRMSR Juergen Gross
2025-09-30 8:31 ` Peter Zijlstra
2025-09-30 8:46 ` Jürgen Groß
2025-09-30 8:50 ` Peter Zijlstra
2025-09-30 12:51 ` Peter Zijlstra
2025-09-30 15:42 ` Jürgen Groß
2025-10-01 6:43 ` Peter Zijlstra [this message]
2025-10-01 7:23 ` Peter Zijlstra
2025-10-03 14:23 ` Dave Hansen
2025-10-03 16:53 ` H. Peter Anvin
2025-10-01 8:49 ` Juergen Gross
2025-10-01 10:50 ` Peter Zijlstra
2025-10-01 11:16 ` Jürgen Groß
2025-09-30 16:00 ` Sean Christopherson
2025-10-01 9:13 ` Jürgen Groß
2025-09-30 19:19 ` [PATCH v2 00/12] x86/msr: Inline rdmsr/wrmsr instructions H. Peter Anvin
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