Re: [PATCH 2/2] perf tools: Introduce regs_query_register_offset() for arm64

[Will Deacon <will.deacon@arm.com>]

On Tue, Jan 24, 2017 at 10:30:15AM +0000, He Kuang wrote:
> Since HAVE_KPROBES can be enabled in arm64, this patch introduces
> regs_query_register_offset() to convert register name to offset for
> arm64, so the BPF prologue feature is ready to use.
> 
> This patch also changes the 'dwarfnum' to 'offset' in register table,
> so the related functions are consistent with x86.
> 
> Signed-off-by: He Kuang <hekuang@huawei.com>
> ---
>  tools/perf/arch/arm64/Makefile          |   1 +
>  tools/perf/arch/arm64/util/dwarf-regs.c | 123 ++++++++++++++++++--------------
>  2 files changed, 71 insertions(+), 53 deletions(-)

It would've been nice to have been cc'd on this. In future, please at least
cc linux-arm-kernel for patches directly changing arm/arm64 code.

> diff --git a/tools/perf/arch/arm64/Makefile b/tools/perf/arch/arm64/Makefile
> index 18b1351..eebe1ec 100644
> --- a/tools/perf/arch/arm64/Makefile
> +++ b/tools/perf/arch/arm64/Makefile
> @@ -2,3 +2,4 @@ ifndef NO_DWARF
>  PERF_HAVE_DWARF_REGS := 1
>  endif
>  PERF_HAVE_JITDUMP := 1
> +PERF_HAVE_ARCH_REGS_QUERY_REGISTER_OFFSET := 1
> diff --git a/tools/perf/arch/arm64/util/dwarf-regs.c b/tools/perf/arch/arm64/util/dwarf-regs.c
> index d49efeb..6427ce0 100644
> --- a/tools/perf/arch/arm64/util/dwarf-regs.c
> +++ b/tools/perf/arch/arm64/util/dwarf-regs.c
> @@ -9,72 +9,89 @@
>   */
>  
>  #include <stddef.h>
> +#include <linux/ptrace.h> /* for struct user_pt_regs */
> +#include <errno.h> /* for EINVAL */
> +#include <string.h> /* for strcmp */
>  #include <dwarf-regs.h>
>  
> -struct pt_regs_dwarfnum {
> +struct pt_regs_offset {
>  	const char *name;
> -	unsigned int dwarfnum;
> +	int offset;
>  };
>  
> -#define STR(s) #s
> -#define REG_DWARFNUM_NAME(r, num) {.name = r, .dwarfnum = num}
> -#define GPR_DWARFNUM_NAME(num) \
> -	{.name = STR(%x##num), .dwarfnum = num}
> -#define REG_DWARFNUM_END {.name = NULL, .dwarfnum = 0}
> -
>  /*
>   * Reference:
>   * http://infocenter.arm.com/help/topic/com.arm.doc.ihi0057b/IHI0057B_aadwarf64.pdf
>   */
> -static const struct pt_regs_dwarfnum regdwarfnum_table[] = {
> -	GPR_DWARFNUM_NAME(0),
> -	GPR_DWARFNUM_NAME(1),
> -	GPR_DWARFNUM_NAME(2),
> -	GPR_DWARFNUM_NAME(3),
> -	GPR_DWARFNUM_NAME(4),
> -	GPR_DWARFNUM_NAME(5),
> -	GPR_DWARFNUM_NAME(6),
> -	GPR_DWARFNUM_NAME(7),
> -	GPR_DWARFNUM_NAME(8),
> -	GPR_DWARFNUM_NAME(9),
> -	GPR_DWARFNUM_NAME(10),
> -	GPR_DWARFNUM_NAME(11),
> -	GPR_DWARFNUM_NAME(12),
> -	GPR_DWARFNUM_NAME(13),
> -	GPR_DWARFNUM_NAME(14),
> -	GPR_DWARFNUM_NAME(15),
> -	GPR_DWARFNUM_NAME(16),
> -	GPR_DWARFNUM_NAME(17),
> -	GPR_DWARFNUM_NAME(18),
> -	GPR_DWARFNUM_NAME(19),
> -	GPR_DWARFNUM_NAME(20),
> -	GPR_DWARFNUM_NAME(21),
> -	GPR_DWARFNUM_NAME(22),
> -	GPR_DWARFNUM_NAME(23),
> -	GPR_DWARFNUM_NAME(24),
> -	GPR_DWARFNUM_NAME(25),
> -	GPR_DWARFNUM_NAME(26),
> -	GPR_DWARFNUM_NAME(27),
> -	GPR_DWARFNUM_NAME(28),
> -	GPR_DWARFNUM_NAME(29),
> -	REG_DWARFNUM_NAME("%lr", 30),
> -	REG_DWARFNUM_NAME("%sp", 31),
> -	REG_DWARFNUM_END,
> +#define REG_OFFSET_NAME(r) {.name = #r,		\
> +			.offset = offsetof(struct user_pt_regs, r)}
> +#define REG_OFFSET_END {.name = NULL, .offset = 0}
> +#define GPR_OFFSET_NAME(r) \
> +	{.name = "%x" #r, .offset = offsetof(struct user_pt_regs, regs[r])}
> +
> +static const struct pt_regs_offset regoffset_table[] = {
> +	GPR_OFFSET_NAME(0),
> +	GPR_OFFSET_NAME(1),
> +	GPR_OFFSET_NAME(2),
> +	GPR_OFFSET_NAME(3),
> +	GPR_OFFSET_NAME(4),
> +	GPR_OFFSET_NAME(5),
> +	GPR_OFFSET_NAME(6),
> +	GPR_OFFSET_NAME(7),
> +	GPR_OFFSET_NAME(8),
> +	GPR_OFFSET_NAME(9),
> +	GPR_OFFSET_NAME(10),
> +	GPR_OFFSET_NAME(11),
> +	GPR_OFFSET_NAME(12),
> +	GPR_OFFSET_NAME(13),
> +	GPR_OFFSET_NAME(14),
> +	GPR_OFFSET_NAME(15),
> +	GPR_OFFSET_NAME(16),
> +	GPR_OFFSET_NAME(17),
> +	GPR_OFFSET_NAME(18),
> +	GPR_OFFSET_NAME(19),
> +	GPR_OFFSET_NAME(20),
> +	GPR_OFFSET_NAME(21),
> +	GPR_OFFSET_NAME(22),
> +	GPR_OFFSET_NAME(23),
> +	GPR_OFFSET_NAME(24),
> +	GPR_OFFSET_NAME(25),
> +	GPR_OFFSET_NAME(26),
> +	GPR_OFFSET_NAME(27),
> +	GPR_OFFSET_NAME(28),
> +	GPR_OFFSET_NAME(29),
> +	GPR_OFFSET_NAME(30),
> +	{.name = "lr", .offset = offsetof(struct user_pt_regs, regs[30])},
> +	REG_OFFSET_NAME(sp),

Don't sp and lr need the leading '%'?

> +	REG_OFFSET_NAME(pc),
> +	REG_OFFSET_NAME(pstate),

The AArch64 DWARF spec says that DWARF register 32 is "RESERVED" and
register 33 is the ELR, so these pc/pstate entries are wrong.

However, with those changes, I think this patch can simply be ignored and
mainline is doing the right thing.

Will