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Message-ID: <ZamodtvgqscAqW8N@ghost>
Date: Thu, 18 Jan 2024 14:38:46 -0800
From: Charlie Jenkins <charlie@...osinc.com>
To: Palmer Dabbelt <palmer@...belt.com>
Cc: Conor Dooley <conor@...nel.org>,
Paul Walmsley <paul.walmsley@...ive.com>, aou@...s.berkeley.edu,
linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] riscv: lib: Support csum on GCC <11
On Thu, Jan 18, 2024 at 02:20:42PM -0800, Palmer Dabbelt wrote:
> On Thu, 18 Jan 2024 14:05:44 PST (-0800), Conor Dooley wrote:
> > On Thu, Jan 18, 2024 at 01:53:59PM -0800, Charlie Jenkins wrote:
> > > The OutputOperands field for asm goto statements is only supported
> > > starting from GCC 11. Split the asm goto to remove the use of this
> > > feature.
> > >
> > > Signed-off-by: Charlie Jenkins <charlie@...osinc.com>
> > > Fixes: a04c192eabfb ("riscv: Add checksum library")
> > > ---
> > > The OutputOperands field for asm goto statements is only supported
> > > starting from GCC 11. Split the asm goto to remove the use of this
> > > feature.
> >
> > Maybe this is a super naive question, but is it possible to just not
> > use the custom csum code for gcc older than 11?
>
> Charlie and I were talking, these old GCC versions also don't support ZBB.
> So I think we can get away with something like
I sent an updated version that uses CC_HAS_ASM_GOTO_TIED_OUTPUT since
there may exist a compiler that supports ZBB but doesn't support output
in asm goto.
- Charlie
>
> diff --git a/arch/riscv/lib/csum.c b/arch/riscv/lib/csum.c
> index 06ce8e7250d9..17f883b612c9 100644
> --- a/arch/riscv/lib/csum.c
> +++ b/arch/riscv/lib/csum.c
> @@ -158,10 +158,16 @@ do_csum_with_alignment(const unsigned char *buff, int len)
>
> /*
> * Zbb support saves 6 instructions, so not worth checking without
> - * alternatives if supported
> + * alternatives if supported.
> + *
> + * Note that we pull the check for ZBB into the preprocessor proper
> + * here, as otherwise GCC will attempt to compile the code inside the
> + * "if (IS_ENABLED(ZBB)" block which fails because GCC10 doesn't
> + * support ASM goto output operands. GCC 10 also doesn't support ZBB,
> + * so we're safe with that check here.
> */
> - if (IS_ENABLED(CONFIG_RISCV_ISA_ZBB) &&
> - IS_ENABLED(CONFIG_RISCV_ALTERNATIVE)) {
> +#if defined(CONFIG_RISCV_ISA_ZBB)
> + if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE)) {
> unsigned long fold_temp;
>
> /*
> @@ -213,6 +219,7 @@ do_csum_with_alignment(const unsigned char *buff, int len)
> end:
> return csum >> 16;
> }
> +#endif /*CONFIG_RISCV_ISA_ZBB*/
> no_zbb:
> #ifndef CONFIG_32BIT
> csum += ror64(csum, 32);
> @@ -244,10 +251,11 @@ do_csum_no_alignment(const unsigned char *buff, int len)
>
> /*
> * Zbb support saves 6 instructions, so not worth checking without
> - * alternatives if supported
> + * alternatives if supported. See above for the ZBB preprocessor
> + * check.
> */
> - if (IS_ENABLED(CONFIG_RISCV_ISA_ZBB) &&
> - IS_ENABLED(CONFIG_RISCV_ALTERNATIVE)) {
> +#if defined(CONFIG_RISCV_ISA_ZBB)
> + if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE)) {
> unsigned long fold_temp;
>
> /*
> @@ -287,6 +295,7 @@ do_csum_no_alignment(const unsigned char *buff, int len)
> #endif /* !CONFIG_32BIT */
> return csum >> 16;
> }
> +#endif /*CONFIG_RISCV_ISA_ZBB*/
> no_zbb:
> #ifndef CONFIG_32BIT
> csum += ror64(csum, 32);
>
> which is building for me on GCC-10/defconfig.
>
> >
> > > ---
> > > arch/riscv/lib/csum.c | 42 ++++++++++++++++++++++++++++++------------
> > > 1 file changed, 30 insertions(+), 12 deletions(-)
> > >
> > > diff --git a/arch/riscv/lib/csum.c b/arch/riscv/lib/csum.c
> > > index 06ce8e7250d9..23be289f52b6 100644
> > > --- a/arch/riscv/lib/csum.c
> > > +++ b/arch/riscv/lib/csum.c
> > > @@ -177,22 +177,35 @@ do_csum_with_alignment(const unsigned char *buff, int len)
> > > : no_zbb);
> > > #ifdef CONFIG_32BIT
> > > - asm_volatile_goto(".option push \n\
> > > + /*
> > > + * OutputOperands in asm goto is not supported until GCC 11, so
> > > + * this asm has to be split to be compatible.
> > > + */
> > > + asm (".option push \n\
> > > .option arch,+zbb \n\
> > > rori %[fold_temp], %[csum], 16 \n\
> > > andi %[offset], %[offset], 1 \n\
> > > add %[csum], %[fold_temp], %[csum] \n\
> > > - beq %[offset], zero, %l[end] \n\
> > > - rev8 %[csum], %[csum] \n\
> > > .option pop"
> > > : [csum] "+r" (csum), [fold_temp] "=&r" (fold_temp)
> > > - : [offset] "r" (offset)
> > > - :
> > > - : end);
> > > + : [offset] "r" (offset));
> > > +
> > > + if (offset == 0)
> > > + goto end;
> > > +
> > > + asm (".option push \n\
> > > + .option arch, +zbb \n\
> > > + rev8 %[csum], %[csum] \n\
> > > + .option pop"
> > > + : [csum] "+r" (csum));
> > > return (unsigned short)csum;
> > > #else /* !CONFIG_32BIT */
> > > - asm_volatile_goto(".option push \n\
> > > + /*
> > > + * OutputOperands in asm goto is not supported until GCC 11, so
> > > + * this asm has to be split to be compatible.
> > > + */
> > > + asm (".option push \n\
> > > .option arch,+zbb \n\
> > > rori %[fold_temp], %[csum], 32 \n\
> > > add %[csum], %[fold_temp], %[csum] \n\
> > > @@ -200,13 +213,18 @@ do_csum_with_alignment(const unsigned char *buff, int len)
> > > roriw %[fold_temp], %[csum], 16 \n\
> > > addw %[csum], %[fold_temp], %[csum] \n\
> > > andi %[offset], %[offset], 1 \n\
> > > - beq %[offset], zero, %l[end] \n\
> > > - rev8 %[csum], %[csum] \n\
> > > .option pop"
> > > : [csum] "+r" (csum), [fold_temp] "=&r" (fold_temp)
> > > - : [offset] "r" (offset)
> > > - :
> > > - : end);
> > > + : [offset] "r" (offset));
> > > +
> > > + if (offset == 0)
> > > + goto end;
> > > +
> > > + asm (".option push \n\
> > > + .option arch, +zbb \n\
> > > + rev8 %[csum], %[csum] \n\
> > > + .option pop"
> > > + : [csum] "+r" (csum));
> > > return (csum << 16) >> 48;
> > > #endif /* !CONFIG_32BIT */
> > >
> > > ---
> > > base-commit: 080c4324fa5e81ff3780206a138223abfb57a68e
> > > change-id: 20240118-csum_remove_output_operands_asm_goto-49922c141ce7
> > > --
> > > - Charlie
> > >
> > >
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