path: root/arch/x86/include
diff options
authorJesse Brandeburg <jesse.brandeburg@intel.com>2020-03-10 15:17:46 -0700
committerBorislav Petkov <bp@suse.de>2020-03-18 12:30:19 +0100
commit1651e700664b4597ddf4f8adfe435252a0d11277 (patch)
treec7039be08bbd4b735c9af18f37c676fd5ffc3af8 /arch/x86/include
parentfb33c6510d5595144d585aa194d377cf74d31911 (diff)
x86: Fix bitops.h warning with a moved cast
Fix many sparse warnings when building with C=1. These are useless noise from the bitops.h file and getting rid of them helps developers make more use of the tools and possibly find real bugs. When the kernel is compiled with C=1, there are lots of messages like: arch/x86/include/asm/bitops.h:77:37: warning: cast truncates bits from constant value (ffffff7f becomes 7f) CONST_MASK() is using a signed integer "1" to create the mask which is later cast to (u8), in order to yield an 8-bit value for the assembly instructions to use. Simplify the expressions used to clearly indicate they are working on 8-bit values only, which still keeps sparse happy without an accidental promotion to a 32 bit integer. The warning was occurring because certain bitmasks that end with a bit set next to a natural boundary like 7, 15, 23, 31, end up with a mask like 0x7f, which then results in sign extension due to the integer type promotion rules[1]. It was really only clear_bit() that was having problems, and it was only on some bit checks that resulted in a mask like 0xffffff7f being generated after the inversion. Verify with a test module (see next patch) and assembly inspection that the fix doesn't introduce any change in generated code. [ bp: Massage. ] Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com> Signed-off-by: Borislav Petkov <bp@suse.de> Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com> Acked-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://stackoverflow.com/questions/46073295/implicit-type-promotion-rules [1] Link: https://lkml.kernel.org/r/20200310221747.2848474-1-jesse.brandeburg@intel.com
Diffstat (limited to 'arch/x86/include')
1 files changed, 2 insertions, 2 deletions
diff --git a/arch/x86/include/asm/bitops.h b/arch/x86/include/asm/bitops.h
index 062cdecb2f24..53f246e9df5a 100644
--- a/arch/x86/include/asm/bitops.h
+++ b/arch/x86/include/asm/bitops.h
@@ -54,7 +54,7 @@ arch_set_bit(long nr, volatile unsigned long *addr)
if (__builtin_constant_p(nr)) {
asm volatile(LOCK_PREFIX "orb %1,%0"
: CONST_MASK_ADDR(nr, addr)
- : "iq" ((u8)CONST_MASK(nr))
+ : "iq" (CONST_MASK(nr) & 0xff)
: "memory");
} else {
asm volatile(LOCK_PREFIX __ASM_SIZE(bts) " %1,%0"
@@ -74,7 +74,7 @@ arch_clear_bit(long nr, volatile unsigned long *addr)
if (__builtin_constant_p(nr)) {
asm volatile(LOCK_PREFIX "andb %1,%0"
: CONST_MASK_ADDR(nr, addr)
- : "iq" ((u8)~CONST_MASK(nr)));
+ : "iq" (CONST_MASK(nr) ^ 0xff));
} else {
asm volatile(LOCK_PREFIX __ASM_SIZE(btr) " %1,%0"
: : RLONG_ADDR(addr), "Ir" (nr) : "memory");

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