linux-kernel - Re: [PATCH v8 05/14] x86: conditionally place regular ASM functions into separate sections

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Message-ID: <28856p61-r54s-791n-q6s1-27575s62r2q9@syhkavp.arg>
Date:   Fri, 3 Dec 2021 14:46:39 -0500 (EST)
From:   Nicolas Pitre <nico@...xnic.net>
To:     Peter Zijlstra <peterz@...radead.org>
cc:     Alexander Lobakin <alexandr.lobakin@...el.com>,
        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>,
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        Arnd Bergmann <arnd@...db.de>,
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        Masami Hiramatsu <mhiramat@...nel.org>,
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        linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org,
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        llvm@...ts.linux.dev, hjl.tools@...il.com
Subject: Re: [PATCH v8 05/14] x86: conditionally place regular ASM functions
 into separate sections

On Fri, 3 Dec 2021, Peter Zijlstra wrote:

> On Fri, Dec 03, 2021 at 03:10:51PM +0100, Alexander Lobakin wrote:
> > From: Peter Zijlstra <peterz@...radead.org>
> > Date: Fri, 3 Dec 2021 10:44:10 +0100
> > 
> > > On Thu, Dec 02, 2021 at 11:32:05PM +0100, Alexander Lobakin wrote:
> > > > Use the newly introduces macros to create unique separate sections
> > > > for (almost) every "regular" ASM function (i.e. for those which
> > > > aren't explicitly put into a specific one).
> > > > There should be no leftovers as input .text will be size-asserted
> > > > in the LD script generated for FG-KASLR.
> > > 
> > > *groan*...
> > > 
> > > Please, can't we do something like:
> > > 
> > > #define SYM_PUSH_SECTION(name)	\
> > > .if section == .text		\
> > > .push_section .text.##name	\
> > > .else				\
> > > .push_section .text		\
> > > .endif
> > > 
> > > #define SYM_POP_SECTION()	\
> > > .pop_section
> > > 
> > > and wrap that inside the existing SYM_FUNC_START*() SYM_FUNC_END()
> > > macros.
> > 
> > Ah I see. I asked about this in my previous mail and you replied
> > already (: Cool stuff, I'll use it, it simplifies things a lot.
> 
> Note, I've no idea if it works. GAS and me aren't really on speaking
> terms. It would be my luck for that to be totally impossible, hjl?

Surely this would do it:

http://sourceware.org/git/?p=binutils-gdb.git;a=commitdiff;h=451133cefa839104


Nicolas