Re: [PATCH v2 4/5] powerpc: Fix duplicate const clang warning in user access code
From: Nick Desaulniers <ndesaulniers@google.com>
Date: 2018-09-14 17:57:21
On Thu, Sep 13, 2018 at 9:07 PM Joel Stanley [off-list ref] wrote:
From: Anton Blanchard <redacted>
This re-applies b91c1e3e7a6f which was reverted in f2ca80905929
d466f6c5cac1 f84ed59a612d (powerpc/sparse: Constify the address pointer
...").
We see a large number of duplicate const errors in the user access
code when building with llvm/clang:
include/linux/pagemap.h:576:8: warning: duplicate 'const' declaration specifier
[-Wduplicate-decl-specifier]
ret = __get_user(c, uaddr);
The problem is we are doing const __typeof__(*(ptr)), which will hit the
warning if ptr is marked const.
Removing const does not seem to have any effect on GCC code generation.I wouldn't expect it to for a local variable with such localized usage. I myself am quite liberal in applying `const` to everything, so I will try to fix this in Clang as well, but this should silence the warning for users of older versions of Clang and results in no functional change. Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
quoted hunk ↗ jump to hunk
Signed-off-by: Anton Blanchard <redacted> Signed-off-by: Joel Stanley <joel@jms.id.au> --- If we don't want to apply this, other options are suppressing the warning, or wait for a fix to land in clang (https://github.com/ClangBuiltLinux/linux/issues/52). --- arch/powerpc/include/asm/uaccess.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h index bac225bb7f64..15bea9a0f260 100644 --- a/arch/powerpc/include/asm/uaccess.h +++ b/arch/powerpc/include/asm/uaccess.h@@ -260,7 +260,7 @@ do { \ ({ \ long __gu_err; \ __long_type(*(ptr)) __gu_val; \ - const __typeof__(*(ptr)) __user *__gu_addr = (ptr); \ + __typeof__(*(ptr)) __user *__gu_addr = (ptr); \ __chk_user_ptr(ptr); \ if (!is_kernel_addr((unsigned long)__gu_addr)) \ might_fault(); \@@ -274,7 +274,7 @@ do { \ ({ \ long __gu_err = -EFAULT; \ __long_type(*(ptr)) __gu_val = 0; \ - const __typeof__(*(ptr)) __user *__gu_addr = (ptr); \ + __typeof__(*(ptr)) __user *__gu_addr = (ptr); \ might_fault(); \ if (access_ok(VERIFY_READ, __gu_addr, (size))) { \ barrier_nospec(); \@@ -288,7 +288,7 @@ do { \ ({ \ long __gu_err; \ __long_type(*(ptr)) __gu_val; \ - const __typeof__(*(ptr)) __user *__gu_addr = (ptr); \ + __typeof__(*(ptr)) __user *__gu_addr = (ptr); \ __chk_user_ptr(ptr); \ barrier_nospec(); \ __get_user_size(__gu_val, __gu_addr, (size), __gu_err); \ --2.17.1
-- Thanks, ~Nick Desaulniers