linux-kernel - Re: arch/x86/include/asm/current.h:49:9: error: call to undeclared function '__typeof_unqual__'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]

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Message-ID: <CAFULd4Yw2RWVmQQ5tMy_DfY+9aPoEYBsGDBMXdP3HDcGH6dgsA@mail.gmail.com>
Date: Wed, 18 Dec 2024 17:33:24 +0100
From: Uros Bizjak <ubizjak@...il.com>
To: Naresh Kamboju <naresh.kamboju@...aro.org>
Cc: rust-for-linux@...r.kernel.org, 
	"open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@...r.kernel.org>, open list <linux-kernel@...r.kernel.org>, 
	lkft-triage@...ts.linaro.org, Anders Roxell <anders.roxell@...aro.org>, 
	Dan Carpenter <dan.carpenter@...aro.org>, Arnd Bergmann <arnd@...db.de>
Subject: Re: arch/x86/include/asm/current.h:49:9: error: call to undeclared
 function '__typeof_unqual__'; ISO C99 and later do not support implicit
 function declarations [-Wimplicit-function-declaration]

On Wed, Dec 18, 2024 at 5:08 PM Naresh Kamboju
<naresh.kamboju@...aro.org> wrote:
>
> The Rust gcc builds failed due to following build warnings / errors on the
> x86_64 and arm64 architectures with selftests/rust/config on the Linux
> next-20241216...next-20241218.
>
> First seen on the next-20241216 tag.
> Good: next-20241213
> Bad: next-20241216
>
> Reported-by: Linux Kernel Functional Testing <lkft@...aro.org>
>
> Anders bisected this regressions and found,
> # first bad commit:
>   [20b3c3eccd9361c9976af640be280526bef72248]
>   percpu: use TYPEOF_UNQUAL() in variable declarations
>
> Build log:
> -------
> arch/x86/include/asm/current.h:49:9: error: call to undeclared
> function '__typeof_unqual__'; ISO C99 and later do not support
> implicit function declarations [-Wimplicit-function-declaration]
> arch/x86/include/asm/current.h:49:9: error: expected ';' after expression
> arch/x86/include/asm/current.h:49:9: error: use of undeclared
> identifier 'pscr_ret__'

__typeof_unqual__ is a keyword in c23 (and an extension in gcc-14+ and
clang-19+).

https://en.cppreference.com/w/c/language/typeof
https://learn.microsoft.com/en-us/cpp/c-language/typeof-unqual-c?view=msvc-170

The compiler support is detected in init/Kconfig:

config CC_HAS_TYPEOF_UNQUAL
    def_bool $(success,echo 'int foo (int a) { __typeof_unqual__(a) b
= a; return b; }' | $(CC) -x c - -S -o /dev/null)

so, if your compiler doesn't support this keyword,
CC_HAS_TYPEOF_UNQUAL should not be enabled and
include/linux/compiler.h should disable usage of __typeof_unqual__:

#if defined(CONFIG_CC_HAS_TYPEOF_UNQUAL) && !defined(__CHECKER__)
# define TYPEOF_UNQUAL(exp) __typeof_unqual__(exp)
#else
# define TYPEOF_UNQUAL(exp) __typeof__(exp)
#endif

Can you please investigate what happens here for your build?

Thanks,
Uros.