From: Samuel Holland <samuel@sholland.org>
To: Palmer Dabbelt <palmer@dabbelt.com>, linux-riscv@lists.infradead.org
Cc: Samuel Holland <samuel@sholland.org>,
Albert Ou <aou@eecs.berkeley.edu>,
Anup Patel <anup@brainfault.org>,
Atish Patra <atishp@rivosinc.com>, Dao Lu <daolu@rivosinc.com>,
Guo Ren <guoren@kernel.org>, Heiko Stuebner <heiko@sntech.de>,
Jisheng Zhang <jszhang@kernel.org>,
Paul Walmsley <paul.walmsley@sifive.com>,
linux-kernel@vger.kernel.org
Subject: [PATCH] riscv: Fix build with CONFIG_CC_OPTIMIZE_FOR_SIZE=y
Date: Thu, 22 Sep 2022 01:09:58 -0500 [thread overview]
Message-ID: <20220922060958.44203-1-samuel@sholland.org> (raw)
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 <samuel@sholland.org>
---
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 6f59ec64175e..b21d46e68386 100644
--- a/arch/riscv/include/asm/hwcap.h
+++ b/arch/riscv/include/asm/hwcap.h
@@ -68,7 +68,6 @@ 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_MAX,
};
@@ -88,8 +87,6 @@ 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;
default:
return -EINVAL;
}
diff --git a/arch/riscv/include/asm/vdso/processor.h b/arch/riscv/include/asm/vdso/processor.h
index 1e4f8b4aef79..789bdb8211a2 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 __riscv_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();
}
--
2.35.1
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next reply other threads:[~2022-09-22 6:10 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-22 6:09 Samuel Holland [this message]
2022-09-22 13:25 ` [PATCH] riscv: Fix build with CONFIG_CC_OPTIMIZE_FOR_SIZE=y Conor Dooley
2022-09-22 15:45 ` Heiko Stuebner
2022-09-22 15:52 ` Jessica Clarke
2022-09-23 7:17 ` Heiko Stuebner
2022-09-23 18:01 ` Atish Patra
2022-09-24 23:15 ` Conor Dooley
2022-09-28 7:21 ` Atish Patra
2022-09-28 21:16 ` Conor Dooley
2022-09-29 3:26 ` Atish Patra
2022-10-01 20:13 ` Conor Dooley
2022-10-04 16:52 ` Atish Patra
2022-10-04 17:15 ` Conor Dooley
2022-10-04 17:24 ` Jessica Clarke
2022-10-05 0:38 ` Guo Ren
2022-10-05 1:01 ` Jessica Clarke
2022-10-05 1:40 ` Guo Ren
2022-10-05 14:25 ` Jessica Clarke
2022-10-06 6:48 ` Jisheng Zhang
2022-10-26 13:59 ` Palmer Dabbelt
2023-02-01 7:21 ` Palmer Dabbelt
2023-02-02 16:25 ` Jisheng Zhang
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