linux-kernel - Re: [PATCH v8 04/14] linkage: add macros for putting ASM functions into own sections

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Message-ID: <Yanj8qvo3Wj4ePyV@hirez.programming.kicks-ass.net>
Date:   Fri, 3 Dec 2021 10:31:30 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alexander Lobakin <alexandr.lobakin@...el.com>
Cc:     linux-hardening@...r.kernel.org, x86@...nel.org,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Kristen Carlson Accardi <kristen@...ux.intel.com>,
        Kees Cook <keescook@...omium.org>,
        Miklos Szeredi <miklos@...redi.hu>,
        Ard Biesheuvel <ardb@...nel.org>,
        Tony Luck <tony.luck@...el.com>,
        Bruce Schlobohm <bruce.schlobohm@...el.com>,
        Jessica Yu <jeyu@...nel.org>,
        kernel test robot <lkp@...el.com>,
        Miroslav Benes <mbenes@...e.cz>,
        Evgenii Shatokhin <eshatokhin@...tuozzo.com>,
        Jonathan Corbet <corbet@....net>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Marios Pomonis <pomonis@...gle.com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org,
        linux-arch@...r.kernel.org, live-patching@...r.kernel.org,
        llvm@...ts.linux.dev
Subject: Re: [PATCH v8 04/14] linkage: add macros for putting ASM functions
 into own sections

On Thu, Dec 02, 2021 at 11:32:04PM +0100, Alexander Lobakin wrote:

> diff --git a/include/linux/linkage.h b/include/linux/linkage.h
> index dbf8506decca..baaab7dece08 100644
> --- a/include/linux/linkage.h
> +++ b/include/linux/linkage.h
> @@ -355,4 +355,86 @@
>  
>  #endif /* __ASSEMBLY__ */
>  
> +/*
> + * Allow ASM symbols to have their own unique sections if they are being
> + * generated by the compiler for C functions (DCE, FG-KASLR, LTO).
> + */
> +#if (defined(CONFIG_LD_DEAD_CODE_DATA_ELIMINATION) && !defined(MODULE)) || \
> +    (defined(CONFIG_FG_KASLR) && !defined(MODULE)) || \
> +    (defined(CONFIG_MODULE_FG_KASLR) && defined(MODULE)) || \
> +    (defined(CONFIG_LTO_CLANG))
> +
> +#define SYM_TEXT_SECTION(name)				\
> +	.pushsection .text.##name, "ax"
> +
> +#define ASM_TEXT_SECTION(name)				\
> +	".text." #name
> +
> +#define ASM_PUSH_SECTION(name)				\
> +	".pushsection .text." #name ", \"ax\""
> +
> +#else /* just .text */
> +
> +#define SYM_TEXT_SECTION(name)				\
> +	.pushsection .text, "ax"
> +
> +#define ASM_TEXT_SECTION(name)				\
> +	".text"
> +
> +#define ASM_PUSH_SECTION(name)				\
> +	".pushsection .text, \"ax\""
> +
> +#endif /* just .text */

That's terribly inconsistent, SYM_TEXT_SECTION is in fact
PUSH_TEXT_SECTION, ASM_PUSH_SECTION is in fact ASM_PUSH_TEXT_SECTION and
should be stringify(PUSH_TEXT_SECTION()) or something, and they're all
repeating that ASM_TEXT_SECTION thing :/


> +
> +#ifdef __ASSEMBLY__
> +
> +#define SYM_TEXT_END_SECTION				\
> +	.popsection
> +
> +#define SYM_FUNC_START_LOCAL_ALIAS_SECTION(name)	\
> +	SYM_TEXT_SECTION(name) ASM_NL			\
> +	SYM_FUNC_START_LOCAL_ALIAS(name)
> +
> +#define SYM_FUNC_START_LOCAL_SECTION(name)		\
> +	SYM_TEXT_SECTION(name) ASM_NL			\
> +	SYM_FUNC_START_LOCAL(name)
> +
> +#define SYM_FUNC_START_NOALIGN_SECTION(name)		\
> +	SYM_TEXT_SECTION(name) ASM_NL			\
> +	SYM_FUNC_START_NOALIGN(name)
> +
> +#define SYM_FUNC_START_WEAK_SECTION(name)		\
> +	SYM_TEXT_SECTION(name) ASM_NL			\
> +	SYM_FUNC_START_WEAK(name)
> +
> +#define SYM_FUNC_START_SECTION(name)			\
> +	SYM_TEXT_SECTION(name) ASM_NL			\
> +	SYM_FUNC_START(name)
> +
> +#define SYM_CODE_START_LOCAL_NOALIGN_SECTION(name)	\
> +	SYM_TEXT_SECTION(name) ASM_NL			\
> +	SYM_CODE_START_LOCAL_NOALIGN(name)
> +
> +#define SYM_CODE_START_NOALIGN_SECTION(name)		\
> +	SYM_TEXT_SECTION(name) ASM_NL			\
> +	SYM_CODE_START_NOALIGN(name)
> +
> +#define SYM_CODE_START_SECTION(name)			\
> +	SYM_TEXT_SECTION(name) ASM_NL			\
> +	SYM_CODE_START(name)
> +
> +#define SYM_FUNC_END_ALIAS_SECTION(name)		\
> +	SYM_FUNC_END_ALIAS(name) ASM_NL			\
> +	SYM_TEXT_END_SECTION
> +
> +#define SYM_FUNC_END_SECTION(name)			\
> +	SYM_FUNC_END(name) ASM_NL			\
> +	SYM_TEXT_END_SECTION
> +
> +#define SYM_CODE_END_SECTION(name)			\
> +	SYM_CODE_END(name) ASM_NL			\
> +	SYM_TEXT_END_SECTION
> +
> +#endif /* __ASSEMBLY__ */

*URGH* why do we have to have new macros for this? SYM_FUNC_START*()
already takes the name as argument.