[v8,6/8] x86-64: Add rseq_load32_load32_relaxed

From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

Implement rseq_load32_load32_relaxed() for the x86-64 architecture. This
static inline function implements a rseq critical section to load two
32-bit integer values atomically with respect to preemption and signal
delivery.

This implementation is imported from the librseq project.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
---
 .../unix/sysv/linux/x86_64/rseq-internal.h    | 109 ++++++++++++++++++
 1 file changed, 109 insertions(+)
 create mode 100644 sysdeps/unix/sysv/linux/x86_64/rseq-internal.h

* copyright year
* docs?

Michael Jeanson <mjeanson@efficios.com> writes:
> This implementation is imported from the librseq project.

Same comment as [5/8]

> diff --git a/sysdeps/unix/sysv/linux/x86_64/rseq-internal.h b/sysdeps/unix/sysv/linux/x86_64/rseq-internal.h
> new file mode 100644
> index 0000000000..fdca1b6439
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/x86_64/rseq-internal.h
> @@ -0,0 +1,109 @@
> +/* Restartable Sequences internal API. x86_64 macros.
> +   Copyright (C) 2023 Free Software Foundation, Inc.

Year?  Or does this stay the same if it's a pure copy of somewhere else...

> +#include <sysdeps/unix/sysv/linux/rseq-internal.h>
> +
> +#define __RSEQ_ASM_DEFINE_TABLE(label, version, flags,			\
> +				start_ip, post_commit_offset, abort_ip)	\
> +		".pushsection __rseq_cs, \"aw\"\n\t"			\
> +		".balign 32\n\t"					\
> +		__rseq_str(label) ":\n\t"				\
> +		".long " __rseq_str(version) ", " __rseq_str(flags) "\n\t" \
> +		".quad " __rseq_str(start_ip) ", " __rseq_str(post_commit_offset) ", " __rseq_str(abort_ip) "\n\t" \
> +		".popsection\n\t"					\
> +		".pushsection __rseq_cs_ptr_array, \"aw\"\n\t"		\
> +		".quad " __rseq_str(label) "b\n\t"			\
> +		".popsection\n\t"

Ok, but each one of these needs some documentation on when/how/why to
use them, even if just a comment that says "only used below".

> +#define RSEQ_ASM_DEFINE_TABLE(label, start_ip, post_commit_ip, abort_ip) \
> +	__RSEQ_ASM_DEFINE_TABLE(label, 0x0, 0x0, start_ip,		\
> +				(post_commit_ip - start_ip), abort_ip)

Ok.

> +/*
> + * Exit points of a rseq critical section consist of all instructions outside
> + * of the critical section where a critical section can either branch to or
> + * reach through the normal course of its execution. The abort IP and the
> + * post-commit IP are already part of the __rseq_cs section and should not be
> + * explicitly defined as additional exit points. Knowing all exit points is
> + * useful to assist debuggers stepping over the critical section.
> + */
> +#define RSEQ_ASM_DEFINE_EXIT_POINT(start_ip, exit_ip)			\
> +		".pushsection __rseq_exit_point_array, \"aw\"\n\t"	\
> +		".quad " __rseq_str(start_ip) ", " __rseq_str(exit_ip) "\n\t" \
> +		".popsection\n\t"

Ok.

> +#define RSEQ_ASM_STORE_RSEQ_CS(label, cs_label, rseq_cs)		\
> +		"leaq " __rseq_str(cs_label) "(%%rip), %%rax\n\t"	\
> +		"movq %%rax, " __rseq_str(rseq_cs) "\n\t"		\
> +		__rseq_str(label) ":\n\t"

Ok.

> +#define RSEQ_ASM_CMP_CPU_ID(cpu_id, current_cpu_id, label)		\
> +		"cmpl %[" __rseq_str(cpu_id) "], " __rseq_str(current_cpu_id) "\n\t" \
> +		"jnz " __rseq_str(label) "\n\t"

Ok.

> +#define RSEQ_ASM_DEFINE_ABORT(label, teardown, abort_label)		\
> +		".pushsection __rseq_failure, \"ax\"\n\t"		\
> +		/* Disassembler-friendly signature: ud1 <sig>(%rip),%edi. */ \
> +		".byte 0x0f, 0xb9, 0x3d\n\t"				\
> +		".long " __rseq_str(RSEQ_SIG) "\n\t"			\
> +		__rseq_str(label) ":\n\t"				\
> +		teardown						\
> +		"jmp %l[" __rseq_str(abort_label) "]\n\t"		\
> +		".popsection\n\t"

Ok.

> +#define RSEQ_ASM_DEFINE_CMPFAIL(label, teardown, cmpfail_label)		\
> +		".pushsection __rseq_failure, \"ax\"\n\t"		\
> +		__rseq_str(label) ":\n\t"				\
> +		teardown						\
> +		"jmp %l[" __rseq_str(cmpfail_label) "]\n\t"		\
> +		".popsection\n\t"

Ok.

> +/*
> + * Load @src1 (32-bit) into @dst1 and load @src2 (32-bit) into @dst2.
> + */
> +#define RSEQ_HAS_LOAD32_LOAD32_RELAXED 1
> +static __always_inline int
> +rseq_load32_load32_relaxed(uint32_t *dst1, uint32_t *src1,
> +			       uint32_t *dst2, uint32_t *src2)
> +{
> +	__asm__ __volatile__ goto (
> +		RSEQ_ASM_DEFINE_TABLE(3, 1f, 2f, 4f) /* start, commit, abort */
> +		/* Start rseq by storing table entry pointer into rseq_cs. */
> +		RSEQ_ASM_STORE_RSEQ_CS(1, 3b, %%fs:RSEQ_CS_OFFSET(%[rseq_offset]))
> +		"movl %[src1], %%ebx\n\t"
> +		"movl %[src2], %%ecx\n\t"
> +		"movl %%ebx, %[dst1]\n\t"
> +		/* final store */
> +		"movl %%ecx, %[dst2]\n\t"
> +		"2:\n\t"
> +		RSEQ_ASM_DEFINE_ABORT(4, "", abort)
> +		: /* gcc asm goto does not allow outputs */
> +		: [rseq_offset]		"r" (__rseq_offset),
> +		  /* final store input */
> +		  [dst1]		"m" (*dst1),
> +		  [dst2]		"m" (*dst2),
> +		  [src1]		"m" (*src1),
> +		  [src2]		"m" (*src2)
> +		: "memory", "cc", "ebx", "ecx", "rax"
> +		: abort
> +	);
> +	rseq_after_asm_goto();
> +	return 0;
> +abort:
> +	rseq_after_asm_goto();
> +	return -1;
> +}

Ok.

On 2024-02-16 22:08, DJ Delorie wrote:
> 
> * copyright year
> * docs?
> 
> Michael Jeanson <mjeanson@efficios.com> writes:
>> This implementation is imported from the librseq project.
> 
> Same comment as [5/8]

Ack.

> 
>> diff --git a/sysdeps/unix/sysv/linux/x86_64/rseq-internal.h b/sysdeps/unix/sysv/linux/x86_64/rseq-internal.h
>> new file mode 100644
>> index 0000000000..fdca1b6439
>> --- /dev/null
>> +++ b/sysdeps/unix/sysv/linux/x86_64/rseq-internal.h
>> @@ -0,0 +1,109 @@
>> +/* Restartable Sequences internal API. x86_64 macros.
>> +   Copyright (C) 2023 Free Software Foundation, Inc.
> 
> Year?  Or does this stay the same if it's a pure copy of somewhere else...

Again, will clarify before next patchset.