linux-kernel - Re: [PATCH v8 2/3] rseq/selftests: add rseq_offset_deref

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Message-ID: <1143241390.67886.1600954399326.JavaMail.zimbra@efficios.com>
Date:   Thu, 24 Sep 2020 09:33:19 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Peter Oskolkov <posk@...gle.com>
Cc:     paulmck <paulmck@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Boqun Feng <boqun.feng@...il.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Paul Turner <pjt@...gle.com>,
        Chris Kennelly <ckennelly@...gle.com>,
        Peter Oskolkov <posk@...k.io>, shuah <shuah@...nel.org>,
        linux-kselftest <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH v8 2/3] rseq/selftests: add rseq_offset_deref_addv

----- On Sep 23, 2020, at 7:36 PM, Peter Oskolkov posk@...gle.com wrote:

The patch title should state that it only adds rseq_offset_deref_addv
to x86-64. Considering that other architecture maintainers will look
at it as inspiration for other architectures, we should also state in
the commit message that architectures implementing it should define
"RSEQ_ARCH_HAS_OFFSET_DEREF_ADDV".

Thanks,

Mathieu

> This patch adds rseq_offset_deref_addv function to
> tools/testing/selftests/rseq/rseq-x86.h, to be used
> in a selftest in the next patch in the patchset.
> 
> v7->v8: this patch split out of the v7 selftest patch.
> 
> Signed-off-by: Peter Oskolkov <posk@...gle.com>
> ---
> tools/testing/selftests/rseq/rseq-x86.h | 57 +++++++++++++++++++++++++
> 1 file changed, 57 insertions(+)
> 
> diff --git a/tools/testing/selftests/rseq/rseq-x86.h
> b/tools/testing/selftests/rseq/rseq-x86.h
> index b2da6004fe30..640411518e46 100644
> --- a/tools/testing/selftests/rseq/rseq-x86.h
> +++ b/tools/testing/selftests/rseq/rseq-x86.h
> @@ -279,6 +279,63 @@ int rseq_addv(intptr_t *v, intptr_t count, int cpu)
> #endif
> }
> 
> +#define RSEQ_ARCH_HAS_OFFSET_DEREF_ADDV
> +
> +/*
> + *   pval = *(ptr+off)
> + *  *pval += inc;
> + */
> +static inline __attribute__((always_inline))
> +int rseq_offset_deref_addv(intptr_t *ptr, off_t off, intptr_t inc, int cpu)
> +{
> +	RSEQ_INJECT_C(9)
> +
> +	__asm__ __volatile__ goto (
> +		RSEQ_ASM_DEFINE_TABLE(3, 1f, 2f, 4f) /* start, commit, abort */
> +#ifdef RSEQ_COMPARE_TWICE
> +		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
> +#endif
> +		/* Start rseq by storing table entry pointer into rseq_cs. */
> +		RSEQ_ASM_STORE_RSEQ_CS(1, 3b, RSEQ_CS_OFFSET(%[rseq_abi]))
> +		RSEQ_ASM_CMP_CPU_ID(cpu_id, RSEQ_CPU_ID_OFFSET(%[rseq_abi]), 4f)
> +		RSEQ_INJECT_ASM(3)
> +#ifdef RSEQ_COMPARE_TWICE
> +		RSEQ_ASM_CMP_CPU_ID(cpu_id, RSEQ_CPU_ID_OFFSET(%[rseq_abi]), %l[error1])
> +#endif
> +		/* get p+v */
> +		"movq %[ptr], %%rbx\n\t"
> +		"addq %[off], %%rbx\n\t"
> +		/* get pv */
> +		"movq (%%rbx), %%rcx\n\t"
> +		/* *pv += inc */
> +		"addq %[inc], (%%rcx)\n\t"
> +		"2:\n\t"
> +		RSEQ_INJECT_ASM(4)
> +		RSEQ_ASM_DEFINE_ABORT(4, "", abort)
> +		: /* gcc asm goto does not allow outputs */
> +		: [cpu_id]		"r" (cpu),
> +		  [rseq_abi]		"r" (&__rseq_abi),
> +		  /* final store input */
> +		  [ptr]			"m" (*ptr),
> +		  [off]			"er" (off),
> +		  [inc]			"er" (inc)
> +		: "memory", "cc", "rax", "rbx", "rcx"
> +		  RSEQ_INJECT_CLOBBER
> +		: abort
> +#ifdef RSEQ_COMPARE_TWICE
> +		  , error1
> +#endif
> +	);
> +	return 0;
> +abort:
> +	RSEQ_INJECT_FAILED
> +	return -1;
> +#ifdef RSEQ_COMPARE_TWICE
> +error1:
> +	rseq_bug("cpu_id comparison failed");
> +#endif
> +}
> +
> static inline __attribute__((always_inline))
> int rseq_cmpeqv_trystorev_storev(intptr_t *v, intptr_t expect,
> 				 intptr_t *v2, intptr_t newv2,
> --
> 2.28.0.709.gb0816b6eb0-goog

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com