From: Dan Carpenter <dan.carpenter@oracle.com>
To: Miguel Ojeda <ojeda@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>,
Kees Cook <keescook@chromium.org>,
Peter Zijlstra <peterz@infradead.org>,
linux-kernel@vger.kernel.org, llvm@lists.linux.dev
Subject: Re: [PATCH] compiler_types: mark __compiletime_assert failure as __noreturn
Date: Thu, 2 Dec 2021 09:12:18 +0300 [thread overview]
Message-ID: <20211202061218.GA30793@kili> (raw)
In-Reply-To: <20211014132331.GA4811@kernel.org>
On Thu, Oct 14, 2021 at 03:23:31PM +0200, Miguel Ojeda wrote:
> `__compiletime_assert` declares a fake `extern` function
> which appears (to the compiler) to be called when the test fails.
>
> Therefore, compilers may emit possibly-uninitialized warnings
> in some cases, even if it will be an error anyway (for compilers
> supporting the `error` attribute, e.g. GCC and Clang >= 14)
> or a link failure (for those that do not, e.g. Clang < 14).
>
> Annotating the fake function as `__noreturn` gives them
> the information they need to avoid the warning,
> e.g. see https://godbolt.org/z/x1v69jjYY.
>
> Link: https://lore.kernel.org/llvm/202110100514.3h9CI4s0-lkp@intel.com/
> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
This patch is kind of a headache for Smatch.
The patch basically turns BUILD_BUG() into BUG(). That's fine.
But it also turn BUILD_BUG_ON(!__builtin_constant_p(foo) into a BUG_ON().
A lot of places call BUILD_BUG_ON() to ensure that functions are inlined
and the build breaks if not. For example, the FIELD_GET() macro will
trigger a build bug if "mask" is not a compile time constant.
295 static __always_inline u32 cal_read_field(struct cal_dev *cal, u32 offset, u32 mask)
296 {
297 return FIELD_GET(mask, cal_read(cal, offset));
298 }
Unfortunately, Smatch doesn't respect the __always_inline annotation so
now it thinks cal_read_field calls BUG() and records it as a noreturn
function. And all the callers get marked as noreturn functions as well.
Could we make it so that BUILD_BUG() is a noreturn function and
BUILD_BUG_ON() is left as it was?
regards,
dan carpenter
next prev parent reply other threads:[~2021-12-02 6:12 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-14 13:23 [PATCH] compiler_types: mark __compiletime_assert failure as __noreturn Miguel Ojeda
2021-10-14 15:01 ` Peter Zijlstra
2021-10-14 17:48 ` Nick Desaulniers
2021-10-14 18:33 ` Miguel Ojeda
2021-10-14 18:41 ` Miguel Ojeda
2021-10-14 18:55 ` Nick Desaulniers
2021-10-14 19:33 ` Miguel Ojeda
2021-10-15 7:55 ` Rasmus Villemoes
2021-10-15 8:11 ` Rasmus Villemoes
2021-10-15 12:36 ` Miguel Ojeda
2021-10-14 17:26 ` Nathan Chancellor
2021-10-14 17:36 ` Nick Desaulniers
2021-10-21 23:20 ` Miguel Ojeda
2021-12-02 6:12 ` Dan Carpenter [this message]
2021-12-02 6:24 ` Dan Carpenter
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