Messages in this thread | | | Date | Thu, 22 Sep 2022 14:25:15 +0100 | From | Conor Dooley <> | Subject | Re: [PATCH] riscv: Fix build with CONFIG_CC_OPTIMIZE_FOR_SIZE=y |
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On Thu, Sep 22, 2022 at 01:09:58AM -0500, Samuel Holland wrote: > commit 8eb060e10185 ("arch/riscv: add Zihintpause support") broke > building with CONFIG_CC_OPTIMIZE_FOR_SIZE enabled (gcc 11.1.0):
clang-15 chucks a fit too.. Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
> > 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 > > > _______________________________________________ > linux-riscv mailing list > linux-riscv@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-riscv
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