From: Ingo Molnar <mingo@kernel.org>
To: Nathan Chancellor <nathan@kernel.org>,
Borislav Petkov <bp@alien8.de>,
Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
"David S. Miller" <davem@davemloft.net>,
Ard Biesheuvel <ardb@kernel.org>,
Josh Poimboeuf <jpoimboe@redhat.com>,
Jonathan Corbet <corbet@lwn.net>,
Al Viro <viro@zeniv.linux.org.uk>,
llvm@lists.linux.dev
Subject: [PATCH] x86/bitops: Remove unused __sw_hweight64() assembly implementation
Date: Sat, 8 Jan 2022 12:38:14 +0100 [thread overview]
Message-ID: <Ydl3pk94T+V7E7cz@gmail.com> (raw)
In-Reply-To: <YdYQu9YxNw0CxJRn@archlinux-ax161>
* Nathan Chancellor <nathan@kernel.org> wrote:
> 4. modpost warning around __sw_hweight64
>
> With the first issue resolved:
>
> $ make -skj"$(nproc)" ARCH=i386 allmodconfig
> WARNING: modpost: EXPORT symbol "__sw_hweight64" [vmlinux] version ...
> Is "__sw_hweight64" prototyped in <asm/asm-prototypes.h>?
So I was hoping that this commit made explicit all the random indirect
header dependencies x86's <asm/asm-prototypes.h> imports on mainline:
headers/prep: x86/kbuild: Add symbol prototype header dependencies for modversions
... but a i386 case slipped through.
But, this actually highlights a real x86 symbol export bug IMO.
__arch_hweight64() on x86-32 is defined in the
arch/x86/include/asm/arch_hweight.h header as an inline, using
__arch_hweight32():
#ifdef CONFIG_X86_32
static inline unsigned long __arch_hweight64(__u64 w)
{
return __arch_hweight32((u32)w) +
__arch_hweight32((u32)(w >> 32));
}
*But* there's also a __sw_hweight64() assembly implementation:
arch/x86/lib/hweight.S
SYM_FUNC_START(__sw_hweight64)
#ifdef CONFIG_X86_64
...
#else /* CONFIG_X86_32 */
/* We're getting an u64 arg in (%eax,%edx): unsigned long hweight64(__u64 w) */
pushl %ecx
call __sw_hweight32
movl %eax, %ecx # stash away result
movl %edx, %eax # second part of input
call __sw_hweight32
addl %ecx, %eax # result
popl %ecx
ret
#endif
But this __sw_hweight64 assembly implementation is unused - and it's
essentially doing the same thing that the inline wrapper does. Then we
export this unused helper with no prototype.
This went unnoticed in mainline, because mainline defines the prototype for
the unused prototype.
So I think the real solution to resolve this is by removing the unused
32-bit variant - see the patch below.
Thanks,
Ingo
======================>
From: Ingo Molnar <mingo@kernel.org>
Date: Sat, 8 Jan 2022 12:33:58 +0100
Subject: [PATCH] x86/bitops: Remove unused __sw_hweight64() assembly implementation
Header cleanups in the fast-headers tree highlighted that we have an
unused assembly implementation for __sw_hweight64():
WARNING: modpost: EXPORT symbol "__sw_hweight64" [vmlinux] version ...
__arch_hweight64() on x86-32 is defined in the
arch/x86/include/asm/arch_hweight.h header as an inline, using
__arch_hweight32():
#ifdef CONFIG_X86_32
static inline unsigned long __arch_hweight64(__u64 w)
{
return __arch_hweight32((u32)w) +
__arch_hweight32((u32)(w >> 32));
}
*But* there's also a __sw_hweight64() assembly implementation:
arch/x86/lib/hweight.S
SYM_FUNC_START(__sw_hweight64)
#ifdef CONFIG_X86_64
...
#else /* CONFIG_X86_32 */
/* We're getting an u64 arg in (%eax,%edx): unsigned long hweight64(__u64 w) */
pushl %ecx
call __sw_hweight32
movl %eax, %ecx # stash away result
movl %edx, %eax # second part of input
call __sw_hweight32
addl %ecx, %eax # result
popl %ecx
ret
#endif
But this __sw_hweight64 assembly implementation is unused - and it's
essentially doing the same thing that the inline wrapper does.
Remove the assembly version and add a comment about it.
Reported-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
arch/x86/lib/hweight.S | 20 ++++++--------------
1 file changed, 6 insertions(+), 14 deletions(-)
diff --git a/arch/x86/lib/hweight.S b/arch/x86/lib/hweight.S
index dbf8cc97b7f5..585e2f1372d0 100644
--- a/arch/x86/lib/hweight.S
+++ b/arch/x86/lib/hweight.S
@@ -36,8 +36,12 @@ SYM_FUNC_START(__sw_hweight32)
SYM_FUNC_END(__sw_hweight32)
EXPORT_SYMBOL(__sw_hweight32)
-SYM_FUNC_START(__sw_hweight64)
+/*
+ * No 32-bit variant, because it's implemented as an inline wrapper
+ * on top of __arch_hweight32():
+ */
#ifdef CONFIG_X86_64
+SYM_FUNC_START(__sw_hweight64)
pushq %rdi
pushq %rdx
@@ -66,18 +70,6 @@ SYM_FUNC_START(__sw_hweight64)
popq %rdx
popq %rdi
ret
-#else /* CONFIG_X86_32 */
- /* We're getting an u64 arg in (%eax,%edx): unsigned long hweight64(__u64 w) */
- pushl %ecx
-
- call __sw_hweight32
- movl %eax, %ecx # stash away result
- movl %edx, %eax # second part of input
- call __sw_hweight32
- addl %ecx, %eax # result
-
- popl %ecx
- ret
-#endif
SYM_FUNC_END(__sw_hweight64)
EXPORT_SYMBOL(__sw_hweight64)
+#endif
next prev parent reply other threads:[~2022-01-08 11:38 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-02 21:57 [PATCH 0000/2297] [ANNOUNCE, RFC] "Fast Kernel Headers" Tree -v1: Eliminate the Linux kernel's "Dependency Hell" Ingo Molnar
2022-01-03 10:11 ` Greg Kroah-Hartman
2022-01-03 11:12 ` Ingo Molnar
2022-01-03 13:46 ` Greg Kroah-Hartman
2022-01-03 16:29 ` Ingo Molnar
2022-01-10 10:28 ` Peter Zijlstra
2022-01-04 14:10 ` [PATCH] per_task: Remove the PER_TASK_BYTES hard-coded constant Ingo Molnar
2022-01-04 15:14 ` Andy Shevchenko
2022-01-04 23:27 ` Ingo Molnar
2022-01-04 17:51 ` [PATCH 0000/2297] [ANNOUNCE, RFC] "Fast Kernel Headers" Tree -v1: Eliminate the Linux kernel's "Dependency Hell" Arnd Bergmann
2022-01-05 0:05 ` Ingo Molnar
2022-01-05 1:37 ` Arnd Bergmann
2022-01-05 9:37 ` Andy Shevchenko
2022-01-04 14:05 ` [PATCH] per_task: Implement single template to define 'struct task_struct_per_task' fields and offsets Ingo Molnar
2022-01-03 13:54 ` [PATCH 0000/2297] [ANNOUNCE, RFC] "Fast Kernel Headers" Tree -v1: Eliminate the Linux kernel's "Dependency Hell" Kirill A. Shutemov
2022-01-04 10:54 ` Ingo Molnar
2022-01-04 13:34 ` Greg Kroah-Hartman
2022-01-04 13:54 ` [PATCH] headers/uninline: Uninline single-use function: kobject_has_children() Ingo Molnar
2022-01-04 15:09 ` Greg Kroah-Hartman
2022-01-04 15:14 ` Greg Kroah-Hartman
2022-01-05 0:11 ` Ingo Molnar
2022-01-05 15:23 ` Greg Kroah-Hartman
2022-01-06 11:26 ` Ingo Molnar
2022-01-03 17:54 ` [PATCH 0000/2297] [ANNOUNCE, RFC] "Fast Kernel Headers" Tree -v1: Eliminate the Linux kernel's "Dependency Hell" Nathan Chancellor
2022-01-04 10:47 ` Ingo Molnar
2022-01-04 10:56 ` [DEBUG PATCH] DO NOT MERGE: Enable SHADOW_CALL_STACK on GCC builds, for build testing Ingo Molnar
2022-01-04 11:02 ` [PATCH] headers/deps: dcache: Move the ____cacheline_aligned attribute to the head of the definition Ingo Molnar
2022-01-04 15:05 ` kernel test robot
2022-01-04 15:05 ` kernel test robot
2022-01-04 17:51 ` Nathan Chancellor
2022-01-05 0:20 ` Ingo Molnar
2022-01-05 0:26 ` [PATCH] headers/deps: Attribute placement fixes for Clang & GCC Ingo Molnar
2022-01-04 11:19 ` [TREE] "Fast Kernel Headers" Tree WIP/development branch Ingo Molnar
2022-01-04 17:25 ` [PATCH 0000/2297] [ANNOUNCE, RFC] "Fast Kernel Headers" Tree -v1: Eliminate the Linux kernel's "Dependency Hell" Nick Desaulniers
2022-01-05 0:43 ` Ingo Molnar
2022-01-04 17:50 ` Nathan Chancellor
2022-01-05 0:35 ` [PATCH] x86/kbuild: Enable CONFIG_KALLSYMS_ALL=y in the defconfigs Ingo Molnar
2022-01-08 21:57 ` [tip: x86/build] " tip-bot2 for Ingo Molnar
2022-01-05 0:40 ` [PATCH 0000/2297] [ANNOUNCE, RFC] "Fast Kernel Headers" Tree -v1: Eliminate the Linux kernel's "Dependency Hell" Ingo Molnar
2022-01-05 1:07 ` Ingo Molnar
2022-01-05 5:20 ` [PATCH 0000/2297] [ANNOUNCE, RFC] "Fast Kernel Headers" Tree -v1: Eliminate the Linux kernel'\''s "Dependency Hell Paul Zimmerman
2022-01-05 21:42 ` [PATCH 0000/2297] [ANNOUNCE, RFC] "Fast Kernel Headers" Tree -v1: Eliminate the Linux kernel's "Dependency Hell" Nathan Chancellor
2022-01-08 10:32 ` [PATCH] headers/deps: Add header dependencies to .c files: <linux/ptrace_api.h> Ingo Molnar
2022-01-08 11:08 ` [PATCH] FIX: headers/deps: uapi/headers: Create usr/include/uapi symbolic link Ingo Molnar
2022-01-08 11:18 ` [PATCH 0000/2297] [ANNOUNCE, RFC] "Fast Kernel Headers" Tree -v1: Eliminate the Linux kernel's "Dependency Hell" Ingo Molnar
2022-01-08 11:38 ` Ingo Molnar [this message]
2022-01-08 11:49 ` Ingo Molnar
2022-01-08 12:17 ` Ingo Molnar
2022-01-10 20:03 ` Nathan Chancellor
2022-01-10 20:05 ` Nathan Chancellor
2022-01-05 22:33 ` Nathan Chancellor
2022-01-08 15:16 ` Ingo Molnar
2022-01-07 0:29 ` Nathan Chancellor
2022-01-08 11:54 ` Ingo Molnar
2022-01-04 12:36 ` Willy Tarreau
2022-01-04 16:05 ` Andy Shevchenko
2022-01-04 16:18 ` Andy Shevchenko
2022-01-15 0:42 ` Paul E. McKenney
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