The old value passed to cmpxchg() is semantically read-only: it is only loaded into a register as a comparand and is never written back. However, the macro currently assigns it implicitly to a local variable of type __typeof__(*(ptr)), which triggers -Werror=discarded-qualifiers when old is a const-qualified pointer and ptr points to a non-const type.
To avoid this, let's add an explicit cast to __typeof__(*(ptr)) for the old local variable in the cmpxchg macros. This explicit cast suppresses the -Wdiscarded-qualifiers diagnostic. The new value is intentionally left without a cast: new will be stored into *ptr, so silently accepting a const-qualified new would allow callers to store a pointer-to-const into a non-const location without any compiler warning. Suggested-by: Jakub Kicinski <[email protected]> Signed-off-by: Hangbin Liu <[email protected]> --- This is my first time posting a patch with multi-architecture specific changes, so I'm not sure which target repository I should use. Please correct me if I made any mistakes. --- arch/alpha/include/asm/cmpxchg.h | 4 ++-- arch/arc/include/asm/cmpxchg.h | 4 ++-- arch/hexagon/include/asm/cmpxchg.h | 2 +- arch/parisc/include/asm/cmpxchg.h | 2 +- arch/powerpc/include/asm/cmpxchg.h | 8 ++++---- arch/riscv/include/asm/cmpxchg.h | 4 ++-- arch/sh/include/asm/cmpxchg.h | 2 +- arch/sparc/include/asm/cmpxchg_32.h | 2 +- arch/sparc/include/asm/cmpxchg_64.h | 2 +- arch/x86/include/asm/cmpxchg.h | 2 +- arch/xtensa/include/asm/cmpxchg.h | 2 +- tools/arch/x86/include/asm/cmpxchg.h | 2 +- 12 files changed, 18 insertions(+), 18 deletions(-) diff --git a/arch/alpha/include/asm/cmpxchg.h b/arch/alpha/include/asm/cmpxchg.h index ae1b96479d0c..b4b8dac759c4 100644 --- a/arch/alpha/include/asm/cmpxchg.h +++ b/arch/alpha/include/asm/cmpxchg.h @@ -234,7 +234,7 @@ ____cmpxchg(volatile void *ptr, unsigned long old, unsigned long new, #define arch_cmpxchg_local(ptr, o, n) \ ({ \ - __typeof__(*(ptr)) _o_ = (o); \ + __typeof__(*(ptr)) _o_ = (__typeof__(*(ptr)))(o); \ __typeof__(*(ptr)) _n_ = (n); \ (__typeof__(*(ptr))) ____cmpxchg((ptr), (unsigned long)_o_, \ (unsigned long)_n_, \ @@ -265,7 +265,7 @@ ____cmpxchg(volatile void *ptr, unsigned long old, unsigned long new, #define arch_cmpxchg(ptr, o, n) \ ({ \ __typeof__(*(ptr)) __ret; \ - __typeof__(*(ptr)) _o_ = (o); \ + __typeof__(*(ptr)) _o_ = (__typeof__(*(ptr)))(o); \ __typeof__(*(ptr)) _n_ = (n); \ smp_mb(); \ __ret = (__typeof__(*(ptr))) ____cmpxchg((ptr), \ diff --git a/arch/arc/include/asm/cmpxchg.h b/arch/arc/include/asm/cmpxchg.h index 76f43db0890f..9637e2cdb5b1 100644 --- a/arch/arc/include/asm/cmpxchg.h +++ b/arch/arc/include/asm/cmpxchg.h @@ -42,7 +42,7 @@ #define arch_cmpxchg_relaxed(ptr, old, new) \ ({ \ __typeof__(ptr) _p_ = (ptr); \ - __typeof__(*(ptr)) _o_ = (old); \ + __typeof__(*(ptr)) _o_ = (__typeof__(*(ptr)))(old); \ __typeof__(*(ptr)) _n_ = (new); \ __typeof__(*(ptr)) _prev_; \ \ @@ -64,7 +64,7 @@ #define arch_cmpxchg(ptr, old, new) \ ({ \ volatile __typeof__(ptr) _p_ = (ptr); \ - __typeof__(*(ptr)) _o_ = (old); \ + __typeof__(*(ptr)) _o_ = (__typeof__(*(ptr)))(old); \ __typeof__(*(ptr)) _n_ = (new); \ __typeof__(*(ptr)) _prev_; \ unsigned long __flags; \ diff --git a/arch/hexagon/include/asm/cmpxchg.h b/arch/hexagon/include/asm/cmpxchg.h index 9c58fb81f7fd..7e117964cb6b 100644 --- a/arch/hexagon/include/asm/cmpxchg.h +++ b/arch/hexagon/include/asm/cmpxchg.h @@ -54,7 +54,7 @@ __arch_xchg(unsigned long x, volatile void *ptr, int size) #define arch_cmpxchg(ptr, old, new) \ ({ \ __typeof__(ptr) __ptr = (ptr); \ - __typeof__(*(ptr)) __old = (old); \ + __typeof__(*(ptr)) __old = (__typeof__(*(ptr)))(old); \ __typeof__(*(ptr)) __new = (new); \ __typeof__(*(ptr)) __oldval = (__typeof__(*(ptr))) 0; \ \ diff --git a/arch/parisc/include/asm/cmpxchg.h b/arch/parisc/include/asm/cmpxchg.h index bf0a0f1189eb..2a87942227f8 100644 --- a/arch/parisc/include/asm/cmpxchg.h +++ b/arch/parisc/include/asm/cmpxchg.h @@ -78,7 +78,7 @@ __cmpxchg(volatile void *ptr, unsigned long old, unsigned long new_, int size) #define arch_cmpxchg(ptr, o, n) \ ({ \ - __typeof__(*(ptr)) _o_ = (o); \ + __typeof__(*(ptr)) _o_ = (__typeof__(*(ptr)))(o); \ __typeof__(*(ptr)) _n_ = (n); \ (__typeof__(*(ptr))) __cmpxchg((ptr), (unsigned long)_o_, \ (unsigned long)_n_, sizeof(*(ptr))); \ diff --git a/arch/powerpc/include/asm/cmpxchg.h b/arch/powerpc/include/asm/cmpxchg.h index dbb50c06f0bf..36d113b13623 100644 --- a/arch/powerpc/include/asm/cmpxchg.h +++ b/arch/powerpc/include/asm/cmpxchg.h @@ -698,7 +698,7 @@ __cmpxchg_acquire(void *ptr, unsigned long old, unsigned long new, } #define arch_cmpxchg(ptr, o, n) \ ({ \ - __typeof__(*(ptr)) _o_ = (o); \ + __typeof__(*(ptr)) _o_ = (__typeof__(*(ptr)))(o); \ __typeof__(*(ptr)) _n_ = (n); \ (__typeof__(*(ptr))) __cmpxchg((ptr), (unsigned long)_o_, \ (unsigned long)_n_, sizeof(*(ptr))); \ @@ -707,7 +707,7 @@ __cmpxchg_acquire(void *ptr, unsigned long old, unsigned long new, #define arch_cmpxchg_local(ptr, o, n) \ ({ \ - __typeof__(*(ptr)) _o_ = (o); \ + __typeof__(*(ptr)) _o_ = (__typeof__(*(ptr)))(o); \ __typeof__(*(ptr)) _n_ = (n); \ (__typeof__(*(ptr))) __cmpxchg_local((ptr), (unsigned long)_o_, \ (unsigned long)_n_, sizeof(*(ptr))); \ @@ -715,7 +715,7 @@ __cmpxchg_acquire(void *ptr, unsigned long old, unsigned long new, #define arch_cmpxchg_relaxed(ptr, o, n) \ ({ \ - __typeof__(*(ptr)) _o_ = (o); \ + __typeof__(*(ptr)) _o_ = (__typeof__(*(ptr)))(o); \ __typeof__(*(ptr)) _n_ = (n); \ (__typeof__(*(ptr))) __cmpxchg_relaxed((ptr), \ (unsigned long)_o_, (unsigned long)_n_, \ @@ -724,7 +724,7 @@ __cmpxchg_acquire(void *ptr, unsigned long old, unsigned long new, #define arch_cmpxchg_acquire(ptr, o, n) \ ({ \ - __typeof__(*(ptr)) _o_ = (o); \ + __typeof__(*(ptr)) _o_ = (__typeof__(*(ptr)))(o); \ __typeof__(*(ptr)) _n_ = (n); \ (__typeof__(*(ptr))) __cmpxchg_acquire((ptr), \ (unsigned long)_o_, (unsigned long)_n_, \ diff --git a/arch/riscv/include/asm/cmpxchg.h b/arch/riscv/include/asm/cmpxchg.h index 8712cf9c69dc..3026a9ff43c4 100644 --- a/arch/riscv/include/asm/cmpxchg.h +++ b/arch/riscv/include/asm/cmpxchg.h @@ -215,7 +215,7 @@ cas_prepend, cas_append) \ ({ \ __typeof__(ptr) __ptr = (ptr); \ - __typeof__(*(__ptr)) __old = (old); \ + __typeof__(*(__ptr)) __old = (__typeof__(*(__ptr)))(old); \ __typeof__(*(__ptr)) __new = (new); \ __typeof__(*(__ptr)) __ret; \ \ @@ -331,7 +331,7 @@ union __u128_halves { #define __arch_cmpxchg128(p, o, n, cas_sfx) \ ({ \ - __typeof__(*(p)) __o = (o); \ + __typeof__(*(p)) __o = (__typeof__(*(p)))(o); \ union __u128_halves __hn = { .full = (n) }; \ union __u128_halves __ho = { .full = (__o) }; \ register unsigned long t1 asm ("t1") = __hn.low; \ diff --git a/arch/sh/include/asm/cmpxchg.h b/arch/sh/include/asm/cmpxchg.h index 1e5dc5ccf7bf..7fb9214d246f 100644 --- a/arch/sh/include/asm/cmpxchg.h +++ b/arch/sh/include/asm/cmpxchg.h @@ -68,7 +68,7 @@ static inline unsigned long __cmpxchg(volatile void * ptr, unsigned long old, #define arch_cmpxchg(ptr,o,n) \ ({ \ - __typeof__(*(ptr)) _o_ = (o); \ + __typeof__(*(ptr)) _o_ = (__typeof__(*(ptr)))(o); \ __typeof__(*(ptr)) _n_ = (n); \ (__typeof__(*(ptr))) __cmpxchg((ptr), (unsigned long)_o_, \ (unsigned long)_n_, sizeof(*(ptr))); \ diff --git a/arch/sparc/include/asm/cmpxchg_32.h b/arch/sparc/include/asm/cmpxchg_32.h index 8c1a3ca34eeb..f733bd5b5d3b 100644 --- a/arch/sparc/include/asm/cmpxchg_32.h +++ b/arch/sparc/include/asm/cmpxchg_32.h @@ -55,7 +55,7 @@ __cmpxchg(volatile void *ptr, unsigned long old, unsigned long new_, int size) #define arch_cmpxchg(ptr, o, n) \ ({ \ - __typeof__(*(ptr)) _o_ = (o); \ + __typeof__(*(ptr)) _o_ = (__typeof__(*(ptr)))(o); \ __typeof__(*(ptr)) _n_ = (n); \ (__typeof__(*(ptr))) __cmpxchg((ptr), (unsigned long)_o_, \ (unsigned long)_n_, sizeof(*(ptr))); \ diff --git a/arch/sparc/include/asm/cmpxchg_64.h b/arch/sparc/include/asm/cmpxchg_64.h index 3de25262c411..4a9ccf80487a 100644 --- a/arch/sparc/include/asm/cmpxchg_64.h +++ b/arch/sparc/include/asm/cmpxchg_64.h @@ -170,7 +170,7 @@ __cmpxchg(volatile void *ptr, unsigned long old, unsigned long new, int size) #define arch_cmpxchg(ptr,o,n) \ ({ \ - __typeof__(*(ptr)) _o_ = (o); \ + __typeof__(*(ptr)) _o_ = (__typeof__(*(ptr)))(o); \ __typeof__(*(ptr)) _n_ = (n); \ (__typeof__(*(ptr))) __cmpxchg((ptr), (unsigned long)_o_, \ (unsigned long)_n_, sizeof(*(ptr))); \ diff --git a/arch/x86/include/asm/cmpxchg.h b/arch/x86/include/asm/cmpxchg.h index a88b06f1c35e..a7984842c58a 100644 --- a/arch/x86/include/asm/cmpxchg.h +++ b/arch/x86/include/asm/cmpxchg.h @@ -85,7 +85,7 @@ extern void __add_wrong_size(void) #define __raw_cmpxchg(ptr, old, new, size, lock) \ ({ \ __typeof__(*(ptr)) __ret; \ - __typeof__(*(ptr)) __old = (old); \ + __typeof__(*(ptr)) __old = (__typeof__(*(ptr)))(old); \ __typeof__(*(ptr)) __new = (new); \ switch (size) { \ case __X86_CASE_B: \ diff --git a/arch/xtensa/include/asm/cmpxchg.h b/arch/xtensa/include/asm/cmpxchg.h index b6db4838b175..0f68eddb6d2d 100644 --- a/arch/xtensa/include/asm/cmpxchg.h +++ b/arch/xtensa/include/asm/cmpxchg.h @@ -83,7 +83,7 @@ __cmpxchg(volatile void *ptr, unsigned long old, unsigned long new, int size) } #define arch_cmpxchg(ptr,o,n) \ - ({ __typeof__(*(ptr)) _o_ = (o); \ + ({ __typeof__(*(ptr)) _o_ = (__typeof__(*(ptr)))(o); \ __typeof__(*(ptr)) _n_ = (n); \ (__typeof__(*(ptr))) __cmpxchg((ptr), (unsigned long)_o_, \ (unsigned long)_n_, sizeof (*(ptr))); \ diff --git a/tools/arch/x86/include/asm/cmpxchg.h b/tools/arch/x86/include/asm/cmpxchg.h index 0ed9ca2766ad..b71938db9422 100644 --- a/tools/arch/x86/include/asm/cmpxchg.h +++ b/tools/arch/x86/include/asm/cmpxchg.h @@ -35,7 +35,7 @@ extern void __cmpxchg_wrong_size(void) #define __raw_cmpxchg(ptr, old, new, size, lock) \ ({ \ __typeof__(*(ptr)) __ret; \ - __typeof__(*(ptr)) __old = (old); \ + __typeof__(*(ptr)) __old = (__typeof__(*(ptr)))(old); \ __typeof__(*(ptr)) __new = (new); \ switch (size) { \ case __X86_CASE_B: \ --- base-commit: 48b3cd69265f346f64b93064723492da46206e9b change-id: 20260402-cmpxchg-2fd307f44a41 Best regards, -- Hangbin Liu <[email protected]>
