The patch below does not apply to the 6.1-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
Possible dependencies:
0b1d60d6dd9e ("riscv: Fix build with CONFIG_CC_OPTIMIZE_FOR_SIZE=y")
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 0b1d60d6dd9e2e867cc6e4277d73ea5a7ff2d4d0 Mon Sep 17 00:00:00 2001 From: Samuel Holland samuel@sholland.org Date: Thu, 22 Sep 2022 01:09:58 -0500 Subject: [PATCH] riscv: Fix build with CONFIG_CC_OPTIMIZE_FOR_SIZE=y
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 Reviewed-by: Conor Dooley conor.dooley@microchip.com Cc: stable@vger.kernel.org Signed-off-by: Palmer Dabbelt palmer@rivosinc.com
diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h index 3c8a5ca95c72..3bf10a8e665a 100644 --- a/arch/riscv/include/asm/hwcap.h +++ b/arch/riscv/include/asm/hwcap.h @@ -67,7 +67,6 @@ 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, };
@@ -87,8 +86,6 @@ 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(); }