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authorMark Rutland <mark.rutland@arm.com>2017-05-03 16:09:38 +0100
committerCatalin Marinas <catalin.marinas@arm.com>2017-05-09 17:47:27 +0100
commitd135b8b5060ea91dd751ff172d179eb4eab1e966 (patch)
tree99a6f23f30c563f1759339bb273314889c6591d6 /arch/arm64/include/asm/uaccess.h
parentarm64: atomic_lse: match asm register sizes (diff)
downloadlinux-dev-d135b8b5060ea91dd751ff172d179eb4eab1e966.tar.xz
linux-dev-d135b8b5060ea91dd751ff172d179eb4eab1e966.zip
arm64: uaccess: suppress spurious clang warning
Clang tries to warn when there's a mismatch between an operand's size, and the size of the register it is held in, as this may indicate a bug. Specifically, clang warns when the operand's type is less than 64 bits wide, and the register is used unqualified (i.e. %N rather than %xN or %wN). Unfortunately clang can generate these warnings for unreachable code. For example, for code like: do { \ typeof(*(ptr)) __v = (v); \ switch(sizeof(*(ptr))) { \ case 1: \ // assume __v is 1 byte wide \ asm ("{op}b %w0" : : "r" (v)); \ break; \ case 8: \ // assume __v is 8 bytes wide \ asm ("{op} %0" : : "r" (v)); \ break; \ } while (0) ... if op() were passed a char value and pointer to char, clang may produce a warning for the unreachable case where sizeof(*(ptr)) is 8. For the same reasons, clang produces warnings when __put_user_err() is used for types that are less than 64 bits wide. We could avoid this with a cast to a fixed-width type in each of the cases. However, GCC will then warn that pointer types are being cast to mismatched integer sizes (in unreachable paths). Another option would be to use the same union trickery as we do for __smp_store_release() and __smp_load_acquire(), but this is fairly invasive. Instead, this patch suppresses the clang warning by using an x modifier in the assembly for the 8 byte case of __put_user_err(). No additional work is necessary as the value has been cast to typeof(*(ptr)), so the compiler will have performed any necessary extension for the reachable case. For consistency, __get_user_err() is also updated to use the x modifier for its 8 byte case. Acked-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Mark Rutland <mark.rutland@arm.com> Reported-by: Matthias Kaehlcke <mka@chromium.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Diffstat (limited to '')
-rw-r--r--arch/arm64/include/asm/uaccess.h4
1 files changed, 2 insertions, 2 deletions
diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index e6540471dcda..90b5755c5003 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -257,7 +257,7 @@ do { \
(err), ARM64_HAS_UAO); \
break; \
case 8: \
- __get_user_asm("ldr", "ldtr", "%", __gu_val, (ptr), \
+ __get_user_asm("ldr", "ldtr", "%x", __gu_val, (ptr), \
(err), ARM64_HAS_UAO); \
break; \
default: \
@@ -324,7 +324,7 @@ do { \
(err), ARM64_HAS_UAO); \
break; \
case 8: \
- __put_user_asm("str", "sttr", "%", __pu_val, (ptr), \
+ __put_user_asm("str", "sttr", "%x", __pu_val, (ptr), \
(err), ARM64_HAS_UAO); \
break; \
default: \