Re: [PATCH] s390: Add '-std=gnu11' to decompressor and purgatory CFLAGS

Heiko Carstens
2025-01-23T08:29:28Z

On Wed, Jan 22, 2025 at 07:54:27PM -0700, Nathan Chancellor wrote:
> GCC changed the default C standard dialect from gnu17 to gnu23,
> which should not have impacted the kernel because it explicitly requests
> the gnu11 standard in the main Makefile. However, there are certain
> places in the s390 code that use their own CFLAGS without a '-std='
> value, which break with this dialect change because of the kernel's own
> definitions of bool, false, and true conflicting with the C23 reserved
> keywords.
>
> include/linux/stddef.h:11:9: error: cannot use keyword 'false' as enumeration constant
> 11 | false = 0,
> | ^~~~~
> include/linux/stddef.h:11:9: note: 'false' is a keyword with '-std=c23' onwards
> include/linux/types.h:35:33: error: 'bool' cannot be defined via 'typedef'
> 35 | typedef _Bool bool;
> | ^~~~
> include/linux/types.h:35:33: note: 'bool' is a keyword with '-std=c23' onwards
>
> Add '-std=gnu11' to the decompressor and purgatory CFLAGS to eliminate
> these errors and make the C standard version of these areas match the
> rest of the kernel.
>
> Cc: stable@vger.kernel.org
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> ---

Thanks!
Tested-by: Heiko Carstens <hca@linux.ibm.com>

Alexander, can you pick this up, please?

> I only see one other error in various files with a recent GCC 15.0.1
> snapshot, which I can eliminate by dropping the version part of the
> condition for CONFIG_GCC_ASM_FLAG_OUTPUT_BROKEN. Is this a regression of
> the fix for the problem of GCC 14.2.0 or is something else doing on
> here?
>
> arch/s390/include/asm/bitops.h: Assembler messages:
> arch/s390/include/asm/bitops.h:60: Error: operand 1: syntax error; missing ')' after base register
> arch/s390/include/asm/bitops.h:60: Error: operand 2: syntax error; ')' not allowed here
> arch/s390/include/asm/bitops.h:60: Error: junk at end of line: `,4'

That is I bug I recently introduced.
The patch below fixes that. Thanks for reporting!

From 2f58027ec1302714bb4d728b08dc5c88498d18b1 Mon Sep 17 00:00:00 2001
From: Heiko Carstens <hca@linux.ibm.com>
Date: Thu, 23 Jan 2025 09:14:15 +0100
Subject: [PATCH] s390/bitops: Use correct constraint for arch_test_bit()
inline assembly

Use the "Q" instead of "R" constraint to correctly reflect the instruction
format of the tm instruction: the first operand is a memory reference
without index register and short displacement. The "R" constraint indicates
a memory reference with index register instead.

This may lead to compile errors like:

arch/s390/include/asm/bitops.h: Assembler messages:
arch/s390/include/asm/bitops.h:60: Error: operand 1: syntax error; missing ')' after base register
arch/s390/include/asm/bitops.h:60: Error: operand 2: syntax error; ')' not allowed here
arch/s390/include/asm/bitops.h:60: Error: junk at end of line: `,4'

Reported-by: Nathan Chancellor <nathan@kernel.org>
Closes: https://lore.kernel.org/r/20250122-s390-fix-std-for-gcc-15-v1-1-8b00cadee083@kernel.org
Fixes: b2bc1b1a77c0 ("s390/bitops: Provide optimized arch_test_bit()")
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
---
arch/s390/include/asm/bitops.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/s390/include/asm/bitops.h b/arch/s390/include/asm/bitops.h
index 15aa64e3020e..d5125296ade2 100644
--- a/arch/s390/include/asm/bitops.h
+++ b/arch/s390/include/asm/bitops.h
@@ -60,7 +60,7 @@ static __always_inline bool arch_test_bit(unsigned long nr, const volatile unsig
asm volatile(
" tm %[addr],%[mask]\n"
: "=@cc" (cc)
- : [addr] "R" (*addr), [mask] "I" (mask)
+ : [addr] "Q" (*addr), [mask] "I" (mask)
);
return cc == 3;
}
--
2.45.2