Re: [PATCH] STACK_PROTECTOR: Support symbols emitted by windows compiler

From: Daniel Kiper <dkiper@net-space.pl>
To: Vladimir 'phcoder' Serbinenko <phcoder@gmail.com>
Cc: The development of GRUB 2 <grub-devel@gnu.org>,
	Ard Biesheuvel <ardb@kernel.org>,
	Glenn Washburn <development@efficientek.com>,
	Dave Pickens <drummer@pobox.com>
Subject: Re: [PATCH] STACK_PROTECTOR: Support symbols emitted by windows compiler
Date: Fri, 5 Apr 2024 13:23:29 +0200	[thread overview]
Message-ID: <20240405112329.ffzjimcspht7fgr6@tomti.i.net-space.pl> (raw)
In-Reply-To: <CAEaD8JNWh_5ByoA0EoJiTceztmw13yvm-ES737g3wEqz3ScpFQ@mail.gmail.com>

On Fri, Apr 05, 2024 at 12:39:41AM +0300, Vladimir 'phcoder' Serbinenko wrote:
> I didn't know about using weakref for this but I'm fine with the approach. Just
> one thing: can we condition it on HAVE_ASM_USCORE test instead of platform?

Interestingly it is set to 0 for x86_64 MinGW and other Linux builds
and set to 1 for i686 MinGW. And it looks only x86_64 MinGW builds are
broken. So, the HAVE_ASM_USCORE itself would not work for us. Instead
I would do s/_WIN32/_WIN64/ in the ifdefery below to improve detection.
AFAICT the "#if defined(_WIN32) && !defined(__CYGWIN__)" is common
mechanism to detect MinGW in general.

> Le jeu. 4 avr. 2024, 23:47, Daniel Kiper <dkiper@net-space.pl> a écrit :
>      Adding Ard, Glenn and Dave...
>
>      First of all, sorry for late reply but I was busy with other stuff...
>
>      On Fri, Mar 15, 2024 at 09:43:22PM +0300, Vladimir 'phcoder'
>      Serbinenko wrote:
>      > stack protector needs symbols with just one underscore in C
>      > name unlike unix variant that needs double underscore.
>      > Supply both symbols for simplicity
>      >
>      > Signed-off-by: Vladimir Serbinenko <phcoder@gmail.com>
>
>      I do not like your solution because it adds unneeded code/symbols to
>      some EFI builds. I come up with two other solutions.
>
>      First, let's define an alias when using MinGW build environment:
>
>      diff --git a/include/grub/stack_protector.h b/include/grub/
>      stack_protector.h
>      index c88dc00b5..8d99fd50e 100644
>      --- a/include/grub/stack_protector.h
>      +++ b/include/grub/stack_protector.h
>      @@ -25,6 +25,10 @@
>       #ifdef GRUB_STACK_PROTECTOR
>       extern grub_addr_t EXPORT_VAR (__stack_chk_guard);
>       extern void __attribute__ ((noreturn)) EXPORT_FUNC (__stack_chk_fail) (void);
>      +#if defined(_WIN32) && !defined(__CYGWIN__)
>      +static grub_addr_t __attribute__ ((weakref("__stack_chk_guard"))) EXPORT_VAR (_stack_chk_guard);
>      +static void __attribute__ ((noreturn, weakref("__stack_chk_fail"))) EXPORT_FUNC (_stack_chk_fail) (void);
>      +#endif
>       #endif
>
>       #endif /* GRUB_STACK_PROTECTOR_H */

Daniel

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