Re: [PATCH 3/3] rseq/selftests: Add support for arm64

Mathieu Desnoyers
2018-06-25T18:10:16Z

----- On Jun 25, 2018, at 1:54 PM, Will Deacon will.deacon@arm.com wrote:

[...]

> +#define __RSEQ_ASM_DEFINE_TABLE(label, version, flags, start_ip, \
> + post_commit_offset, abort_ip) \
> + " .pushsection __rseq_table, \"aw\"\n" \
> + " .balign 32\n" \
> + __rseq_str(label) ":\n" \
> + " .long " __rseq_str(version) ", " __rseq_str(flags) "\n" \
> + " .quad " __rseq_str(start_ip) ", " \
> + __rseq_str(post_commit_offset) ", " \
> + __rseq_str(abort_ip) "\n" \
> + " .popsection\n"
> +
> +#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)
> +
> +#define RSEQ_ASM_STORE_RSEQ_CS(label, cs_label, rseq_cs) \
> + RSEQ_INJECT_ASM(1) \
> + " adrp " RSEQ_ASM_TMP_REG ", " __rseq_str(cs_label) "\n" \
> + " add " RSEQ_ASM_TMP_REG ", " RSEQ_ASM_TMP_REG \
> + ", :lo12:" __rseq_str(cs_label) "\n" \
> + " str " RSEQ_ASM_TMP_REG ", %[" __rseq_str(rseq_cs) "]\n" \
> + __rseq_str(label) ":\n"
> +
> +#define RSEQ_ASM_DEFINE_ABORT(label, abort_label) \
> + " .pushsection __rseq_failure, \"ax\"\n" \
> + " .long " __rseq_str(RSEQ_SIG) "\n" \
> + __rseq_str(label) ":\n" \
> + " b %l[" __rseq_str(abort_label) "]\n" \
> + " .popsection\n"

Thanks Will for porting rseq to arm64 !

I notice you are using the instructions

adrp
add
str

to implement RSEQ_ASM_STORE_RSEQ_CS(). Did you compare
performance-wise with an approach using a literal pool
near the instruction pointer like I did on arm32 ?

With that approach, this ends up being simply

adr
str

which provides significantly better performance on my test
platform over loading a pointer targeting a separate data
section.

Thanks,

Mathieu

--
Mathieu Desnoyers
EfficiOS Inc.