From: David Laight <david.laight.linux@gmail.com>
To: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Cc: Kees Cook <kees@kernel.org>,
Nathan Chancellor <nathan@kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>,
Bill Wendling <morbo@google.com>,
Justin Stitt <justinstitt@google.com>,
David Laight <david.laight@aculab.com>,
linux-hardening@vger.kernel.org, linux-kernel@vger.kernel.org,
llvm@lists.linux.dev
Subject: Re: [PATCH] fortify: turn strlen() into an inline function using __builtin_constant_p()
Date: Sat, 11 Jan 2025 16:58:44 +0000 [thread overview]
Message-ID: <20250111165844.6d95600f@pumpkin> (raw)
In-Reply-To: <CAMZ6RqJbinVpsGf6ADUtQTYPRRQN=D8Ne_n6pHtDUPXxED5ZvQ@mail.gmail.com>
On Sat, 11 Jan 2025 23:40:41 +0900
Vincent Mailhol <mailhol.vincent@wanadoo.fr> wrote:
> On Thu. 9 Jan 2025 at 16:52, Vincent Mailhol <mailhol.vincent@wanadoo.fr> wrote:
...
> Actually, I did more investigation and it is working for some strange
> reasons. Whenever the argument of a function named strlen() is a
> compile time constant, the compiler (both GCC and clang) will replace
> it with the string length on the argument, even if strlen() is
> programmed to return something else:
>
> https://godbolt.org/z/nK4b3fnM7
>
> So it is only working because the compiler uses its builtin strlen()
> instead of the function we provided.
It depends on whether -ffreestanding is set.
If not set gcc/clang assume a lot of the basic libc functions have their expected
behaviour.
David
next prev parent reply other threads:[~2025-01-11 16:58 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-01-08 14:27 [PATCH] fortify: turn strlen() into an inline function using __builtin_constant_p() Vincent Mailhol
2025-01-08 21:46 ` Kees Cook
2025-01-09 7:52 ` Vincent Mailhol
2025-01-11 14:40 ` Vincent Mailhol
2025-01-11 16:58 ` David Laight [this message]
2025-01-11 18:05 ` Vincent Mailhol
2025-01-09 14:14 ` kernel test robot
2025-01-11 2:13 ` kernel test robot
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