From: Nick Desaulniers <ndesaulniers@google.com>
To: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>
Cc: Jesse Brandeburg <jesse.brandeburg@intel.com>,
Sedat Dilek <sedat.dilek@gmail.com>,
"kernelci . org bot" <bot@kernelci.org>,
Andy Shevchenko <andriy.shevchenko@intel.com>,
Brian Gerst <brgerst@gmail.com>,
"H . Peter Anvin" <hpa@zytor.com>,
Ilie Halip <ilie.halip@gmail.com>,
"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
<x86@kernel.org>, Marco Elver <elver@google.com>,
"Paul E. McKenney" <paulmck@kernel.org>,
Andrey Ryabinin <aryabinin@virtuozzo.com>,
Andrew Morton <akpm@linux-foundation.org>,
Masahiro Yamada <yamada.masahiro@socionext.com>,
Daniel Axtens <dja@axtens.net>,
Luc Van Oostenryck <luc.vanoostenryck@gmail.com>,
"Peter Zijlstra (Intel)" <peterz@infradead.org>,
LKML <linux-kernel@vger.kernel.org>,
clang-built-linux <clang-built-linux@googlegroups.com>
Subject: Re: [PATCH v3] x86: bitops: fix build regression
Date: Fri, 8 May 2020 11:08:46 -0700 [thread overview]
Message-ID: <CAKwvOdm=AskJo4h=_P9oSXr_eV7DXu+q_sbYhU7pNQByRwHLBw@mail.gmail.com> (raw)
In-Reply-To: <20200508180549.212957-1-ndesaulniers@google.com>
On Fri, May 8, 2020 at 11:06 AM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> This is easily reproducible via CC=clang+CONFIG_STAGING=y+CONFIG_VT6656=m.
>
> It turns out that if your config tickles __builtin_constant_p via
> differences in choices to inline or not, these statements produce
> invalid assembly:
>
> $ cat foo.c
> long a(long b, long c) {
> asm("orb\t%1, %0" : "+q"(c): "r"(b));
> return c;
> }
> $ gcc foo.c
> foo.c: Assembler messages:
> foo.c:2: Error: `%rax' not allowed with `orb'
>
> Use the `%b` "x86 Operand Modifier" to instead force register allocation
> to select a lower-8-bit GPR operand.
>
> The "q" constraint only has meaning on -m32 otherwise is treated as
> "r". Not all GPRs have low-8-bit aliases for -m32.
>
> Cc: Jesse Brandeburg <jesse.brandeburg@intel.com>
> Link: https://github.com/ClangBuiltLinux/linux/issues/961
> Link: https://lore.kernel.org/lkml/20200504193524.GA221287@google.com/
> Link: https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html#x86Operandmodifiers
> Fixes: 1651e700664b4 ("x86: Fix bitops.h warning with a moved cast")
> Reported-by: Sedat Dilek <sedat.dilek@gmail.com>
> Reported-by: kernelci.org bot <bot@kernelci.org>
> Suggested-by: Andy Shevchenko <andriy.shevchenko@intel.com>
> Suggested-by: Brian Gerst <brgerst@gmail.com>
> Suggested-by: H. Peter Anvin <hpa@zytor.com>
> Suggested-by: Ilie Halip <ilie.halip@gmail.com>
> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
> ---
> Changes V2 -> V3:
> * use `%b` "x86 Operand Modifier" instead of bitwise op then cast.
> * reword commit message.
> * add Brian and HPA suggested by tags
> * drop Nathan & Sedat Tested by/reviewed by tags (new patch is different
> enough).
Oh, and I took over authorship for this version.
>
> Changes V1 -> V2:
> * change authorship/signed-off-by to Ilie
> * add Nathan's Tested by/reviewed by
> * update commit message slightly with info sent to HPA.
>
> arch/x86/include/asm/bitops.h | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/include/asm/bitops.h b/arch/x86/include/asm/bitops.h
> index b392571c1f1d..03e24286e4eb 100644
> --- a/arch/x86/include/asm/bitops.h
> +++ b/arch/x86/include/asm/bitops.h
> @@ -52,9 +52,9 @@ static __always_inline void
> arch_set_bit(long nr, volatile unsigned long *addr)
> {
> if (__builtin_constant_p(nr)) {
> - asm volatile(LOCK_PREFIX "orb %1,%0"
> + asm volatile(LOCK_PREFIX "orb %b1,%0"
> : CONST_MASK_ADDR(nr, addr)
> - : "iq" (CONST_MASK(nr) & 0xff)
> + : "iq" (CONST_MASK(nr))
> : "memory");
> } else {
> asm volatile(LOCK_PREFIX __ASM_SIZE(bts) " %1,%0"
> @@ -72,9 +72,9 @@ static __always_inline void
> arch_clear_bit(long nr, volatile unsigned long *addr)
> {
> if (__builtin_constant_p(nr)) {
> - asm volatile(LOCK_PREFIX "andb %1,%0"
> + asm volatile(LOCK_PREFIX "andb %b1,%0"
> : CONST_MASK_ADDR(nr, addr)
> - : "iq" (CONST_MASK(nr) ^ 0xff));
> + : "iq" (~CONST_MASK(nr)));
> } else {
> asm volatile(LOCK_PREFIX __ASM_SIZE(btr) " %1,%0"
> : : RLONG_ADDR(addr), "Ir" (nr) : "memory");
> --
> 2.26.2.645.ge9eca65c58-goog
>
--
Thanks,
~Nick Desaulniers
next prev parent reply other threads:[~2020-05-08 18:09 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-05 17:44 [PATCH] x86: bitops: fix build regression Nick Desaulniers
2020-05-05 18:07 ` hpa
2020-05-05 18:22 ` Nick Desaulniers
2020-05-07 11:34 ` Peter Zijlstra
2020-05-07 14:00 ` Brian Gerst
2020-05-07 19:19 ` Nick Desaulniers
2020-05-07 22:29 ` Nick Desaulniers
2020-05-08 1:57 ` Brian Gerst
2020-05-08 17:21 ` Nick Desaulniers
2020-05-08 17:31 ` H. Peter Anvin
2020-05-08 18:05 ` [PATCH v3] " Nick Desaulniers
2020-05-08 18:08 ` Nick Desaulniers [this message]
2020-05-08 18:22 ` Brian Gerst
2020-05-08 18:28 ` [PATCH v4] " Nick Desaulniers
2020-05-08 18:32 ` [PATCH v5] " Nick Desaulniers
2020-05-08 20:28 ` Nathan Chancellor
2020-05-08 23:47 ` Jesse Brandeburg
2020-05-09 4:44 ` Sedat Dilek
2020-05-09 12:20 ` Andy Shevchenko
2020-05-09 15:43 ` Brian Gerst
2020-05-11 17:22 ` Nick Desaulniers
2020-05-10 13:54 ` David Laight
2020-05-11 18:52 ` Brian Gerst
2020-05-14 23:47 ` Nick Desaulniers
2020-05-10 11:59 ` [PATCH] " David Laight
2020-05-10 12:33 ` hpa
2020-05-07 19:29 ` hpa
2020-05-06 4:30 ` Nathan Chancellor
2020-05-06 9:22 ` Sedat Dilek
2020-05-06 15:41 ` Nathan Chancellor
2020-05-06 16:37 ` Nick Desaulniers
2020-05-06 16:55 ` Ilie Halip
2020-05-06 17:05 ` [PATCH v2] " Nick Desaulniers
2020-05-07 6:18 ` [PATCH] " Brian Gerst
2020-05-07 7:02 ` hpa
2020-05-07 13:32 ` Brian Gerst
2020-05-07 15:09 ` David Laight
2020-05-07 19:31 ` hpa
2020-05-07 19:29 ` hpa
2020-05-07 7:44 ` David Laight
2020-05-07 7:59 ` hpa
2020-05-07 8:35 ` David Laight
2020-05-07 8:38 ` hpa
2020-05-07 9:17 ` Andy Shevchenko
2020-05-07 19:22 ` Nick Desaulniers
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