From: Xiangyu Chen <[email protected]>
commit 8eb060e10185 ("arch/riscv: add Zihintpause support") broke
building with CONFIG_CC_OPTIMIZE_FOR_SIZE enabled (gcc 11.1.0):
CC arch/riscv/kernel/vdso/vgettimeofday.o
In file included from <command-line>:
./arch/riscv/include/asm/jump_label.h: In function 'cpu_relax':
././include/linux/compiler_types.h:285:33: warning: 'asm' operand 0 probably
does not match constraints
285 | #define asm_volatile_goto(x...) asm goto(x)
| ^~~
./arch/riscv/include/asm/jump_label.h:41:9: note: in expansion of macro
'asm_volatile_goto'
41 | asm_volatile_goto(
| ^~~~~~~~~~~~~~~~~
././include/linux/compiler_types.h:285:33: error: impossible constraint in 'asm'
285 | #define asm_volatile_goto(x...) asm goto(x)
| ^~~
./arch/riscv/include/asm/jump_label.h:41:9: note: in expansion of macro
'asm_volatile_goto'
41 | asm_volatile_goto(
| ^~~~~~~~~~~~~~~~~
make[1]: *** [scripts/Makefile.build:249:
arch/riscv/kernel/vdso/vgettimeofday.o] Error 1
make: *** [arch/riscv/Makefile:128: vdso_prepare] Error 2
Having a static branch in cpu_relax() is problematic because that
function is widely inlined, including in some quite complex functions
like in the VDSO. A quick measurement shows this static branch is
responsible by itself for around 40% of the jump table.
Drop the static branch, which ends up being the same number of
instructions anyway. If Zihintpause is supported, we trade the nop from
the static branch for a div. If Zihintpause is unsupported, we trade the
jump from the static branch for (what gets interpreted as) a nop.
Fixes: 8eb060e10185 ("arch/riscv: add Zihintpause support")
Signed-off-by: Samuel Holland <[email protected]>
Reviewed-by: Conor Dooley <[email protected]>
Cc: [email protected]
Signed-off-by: Palmer Dabbelt <[email protected]>
Signed-off-by: Xiangyu Chen <[email protected]>
---
arch/riscv/include/asm/hwcap.h | 3 ---
arch/riscv/include/asm/vdso/processor.h | 25 ++++++++++---------------
2 files changed, 10 insertions(+), 18 deletions(-)
diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
index b22525290073..404349f49101 100644
--- a/arch/riscv/include/asm/hwcap.h
+++ b/arch/riscv/include/asm/hwcap.h
@@ -69,7 +69,6 @@ enum riscv_isa_ext_id {
*/
enum riscv_isa_ext_key {
RISCV_ISA_EXT_KEY_FPU, /* For 'F' and 'D' */
- RISCV_ISA_EXT_KEY_ZIHINTPAUSE,
RISCV_ISA_EXT_KEY_SVINVAL,
RISCV_ISA_EXT_KEY_MAX,
};
@@ -90,8 +89,6 @@ static __always_inline int riscv_isa_ext2key(int num)
return RISCV_ISA_EXT_KEY_FPU;
case RISCV_ISA_EXT_d:
return RISCV_ISA_EXT_KEY_FPU;
- case RISCV_ISA_EXT_ZIHINTPAUSE:
- return RISCV_ISA_EXT_KEY_ZIHINTPAUSE;
case RISCV_ISA_EXT_SVINVAL:
return RISCV_ISA_EXT_KEY_SVINVAL;
default:
diff --git a/arch/riscv/include/asm/vdso/processor.h
b/arch/riscv/include/asm/vdso/processor.h
index fa70cfe507aa..c25399711b07 100644
--- a/arch/riscv/include/asm/vdso/processor.h
+++ b/arch/riscv/include/asm/vdso/processor.h
@@ -4,30 +4,25 @@
#ifndef __ASSEMBLY__
-#include <linux/jump_label.h>
#include <asm/barrier.h>
-#include <asm/hwcap.h>
static inline void cpu_relax(void)
{
- if
(!static_branch_likely(&riscv_isa_ext_keys[RISCV_ISA_EXT_KEY_ZIHINTPAUSE])) {
#ifdef __riscv_muldiv
- int dummy;
- /* In lieu of a halt instruction, induce a long-latency stall.
*/
- __asm__ __volatile__ ("div %0, %0, zero" : "=r" (dummy));
+ int dummy;
+ /* In lieu of a halt instruction, induce a long-latency stall. */
+ __asm__ __volatile__ ("div %0, %0, zero" : "=r" (dummy));
#endif
- } else {
- /*
- * Reduce instruction retirement.
- * This assumes the PC changes.
- */
+ /*
+ * Reduce instruction retirement.
+ * This assumes the PC changes.
+ */
#ifdef CONFIG_TOOLCHAIN_HAS_ZIHINTPAUSE
- __asm__ __volatile__ ("pause");
+ __asm__ __volatile__ ("pause");
#else
- /* Encoding of the pause instruction */
- __asm__ __volatile__ (".4byte 0x100000F");
+ /* Encoding of the pause instruction */
+ __asm__ __volatile__ (".4byte 0x100000F");
#endif
- }
barrier();
}
--
2.35.5
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