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SubjectRE: [PATCH 23/31] perf tools: Introduce regs_query_register_offset() for x86
Date
> From: Wang Nan [mailto:wangnan0@huawei.com]
>
> regs_query_register_offset() is a helper function which converts
> register name like "%rax" to offset of a register in 'struct pt_regs',
> which is required by BPF prologue generator. Since the function is
> identical, try to reuse the code in arch/x86/kernel/ptrace.c.
>
> Comment inside dwarf-regs.c list the differences between this
> implementation and kernel code.

Hmm, this also introduce a duplication of the code...
It might be a good time to move them into arch/x86/lib/ and
reuse it directly from perf code.

Thank you,

>
> get_arch_regstr() switches to regoffset_table and the old string table
> is dropped.
>
> Signed-off-by: Wang Nan <wangnan0@huawei.com>
> Signed-off-by: He Kuang <hekuang@huawei.com>
> Cc: Alexei Starovoitov <ast@plumgrid.com>
> Cc: Brendan Gregg <brendan.d.gregg@gmail.com>
> Cc: Daniel Borkmann <daniel@iogearbox.net>
> Cc: David Ahern <dsahern@gmail.com>
> Cc: He Kuang <hekuang@huawei.com>
> Cc: Jiri Olsa <jolsa@kernel.org>
> Cc: Kaixu Xia <xiakaixu@huawei.com>
> Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
> Cc: Namhyung Kim <namhyung@kernel.org>
> Cc: Paul Mackerras <paulus@samba.org>
> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Cc: Zefan Li <lizefan@huawei.com>
> Cc: pi3orama@163.com
> Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> ---
> tools/perf/arch/x86/Makefile | 1 +
> tools/perf/arch/x86/util/Build | 1 +
> tools/perf/arch/x86/util/dwarf-regs.c | 122 ++++++++++++++++++++++++----------
> 3 files changed, 90 insertions(+), 34 deletions(-)
>
> diff --git a/tools/perf/arch/x86/Makefile b/tools/perf/arch/x86/Makefile
> index 21322e0..09ba923 100644
> --- a/tools/perf/arch/x86/Makefile
> +++ b/tools/perf/arch/x86/Makefile
> @@ -2,3 +2,4 @@ ifndef NO_DWARF
> PERF_HAVE_DWARF_REGS := 1
> endif
> HAVE_KVM_STAT_SUPPORT := 1
> +PERF_HAVE_ARCH_REGS_QUERY_REGISTER_OFFSET := 1
> diff --git a/tools/perf/arch/x86/util/Build b/tools/perf/arch/x86/util/Build
> index 2c55e1b..d4d1f23 100644
> --- a/tools/perf/arch/x86/util/Build
> +++ b/tools/perf/arch/x86/util/Build
> @@ -4,6 +4,7 @@ libperf-y += pmu.o
> libperf-y += kvm-stat.o
>
> libperf-$(CONFIG_DWARF) += dwarf-regs.o
> +libperf-$(CONFIG_BPF_PROLOGUE) += dwarf-regs.o
>
> libperf-$(CONFIG_LIBUNWIND) += unwind-libunwind.o
> libperf-$(CONFIG_LIBDW_DWARF_UNWIND) += unwind-libdw.o
> diff --git a/tools/perf/arch/x86/util/dwarf-regs.c b/tools/perf/arch/x86/util/dwarf-regs.c
> index a08de0a..de5b936 100644
> --- a/tools/perf/arch/x86/util/dwarf-regs.c
> +++ b/tools/perf/arch/x86/util/dwarf-regs.c
> @@ -21,55 +21,109 @@
> */
>
> #include <stddef.h>
> +#include <errno.h> /* for EINVAL */
> +#include <string.h> /* for strcmp */
> +#include <linux/ptrace.h> /* for struct pt_regs */
> +#include <linux/kernel.h> /* for offsetof */
> #include <dwarf-regs.h>
>
> /*
> - * Generic dwarf analysis helpers
> + * See arch/x86/kernel/ptrace.c.
> + * Different from it:
> + *
> + * - Since struct pt_regs is defined differently for user and kernel,
> + * but we want to use 'ax, bx' instead of 'rax, rbx' (which is struct
> + * field name of user's pt_regs), we make REG_OFFSET_NAME to accept
> + * both string name and reg field name.
> + *
> + * - Since accessing x86_32's pt_regs from x86_64 building is difficult
> + * and vise versa, we simply fill offset with -1, so
> + * get_arch_regstr() still works but regs_query_register_offset()
> + * returns error.
> + * The only inconvenience caused by it now is that we are not allowed
> + * to generate BPF prologue for a x86_64 kernel if perf is built for
> + * x86_32. This is really a rare usecase.
> + *
> + * - Order is different from kernel's ptrace.c for get_arch_regstr(), which
> + * is defined by dwarf.
> */
>
> -#define X86_32_MAX_REGS 8
> -const char *x86_32_regs_table[X86_32_MAX_REGS] = {
> - "%ax",
> - "%cx",
> - "%dx",
> - "%bx",
> - "$stack", /* Stack address instead of %sp */
> - "%bp",
> - "%si",
> - "%di",
> +struct pt_regs_offset {
> + const char *name;
> + int offset;
> +};
> +
> +#define REG_OFFSET_END {.name = NULL, .offset = 0}
> +
> +#ifdef __x86_64__
> +# define REG_OFFSET_NAME_64(n, r) {.name = n, .offset = offsetof(struct pt_regs, r)}
> +# define REG_OFFSET_NAME_32(n, r) {.name = n, .offset = -1}
> +#else
> +# define REG_OFFSET_NAME_64(n, r) {.name = n, .offset = -1}
> +# define REG_OFFSET_NAME_32(n, r) {.name = n, .offset = offsetof(struct pt_regs, r)}
> +#endif
> +
> +static const struct pt_regs_offset x86_32_regoffset_table[] = {
> + REG_OFFSET_NAME_32("%ax", eax),
> + REG_OFFSET_NAME_32("%cx", ecx),
> + REG_OFFSET_NAME_32("%dx", edx),
> + REG_OFFSET_NAME_32("%bx", ebx),
> + REG_OFFSET_NAME_32("$stack", esp), /* Stack address instead of %sp */
> + REG_OFFSET_NAME_32("%bp", ebp),
> + REG_OFFSET_NAME_32("%si", esi),
> + REG_OFFSET_NAME_32("%di", edi),
> + REG_OFFSET_END,
> };
>
> -#define X86_64_MAX_REGS 16
> -const char *x86_64_regs_table[X86_64_MAX_REGS] = {
> - "%ax",
> - "%dx",
> - "%cx",
> - "%bx",
> - "%si",
> - "%di",
> - "%bp",
> - "%sp",
> - "%r8",
> - "%r9",
> - "%r10",
> - "%r11",
> - "%r12",
> - "%r13",
> - "%r14",
> - "%r15",
> +static const struct pt_regs_offset x86_64_regoffset_table[] = {
> + REG_OFFSET_NAME_64("%ax", rax),
> + REG_OFFSET_NAME_64("%dx", rdx),
> + REG_OFFSET_NAME_64("%cx", rcx),
> + REG_OFFSET_NAME_64("%bx", rbx),
> + REG_OFFSET_NAME_64("%si", rsi),
> + REG_OFFSET_NAME_64("%di", rdi),
> + REG_OFFSET_NAME_64("%bp", rbp),
> + REG_OFFSET_NAME_64("%sp", rsp),
> + REG_OFFSET_NAME_64("%r8", r8),
> + REG_OFFSET_NAME_64("%r9", r9),
> + REG_OFFSET_NAME_64("%r10", r10),
> + REG_OFFSET_NAME_64("%r11", r11),
> + REG_OFFSET_NAME_64("%r12", r12),
> + REG_OFFSET_NAME_64("%r13", r13),
> + REG_OFFSET_NAME_64("%r14", r14),
> + REG_OFFSET_NAME_64("%r15", r15),
> + REG_OFFSET_END,
> };
>
> /* TODO: switching by dwarf address size */
> #ifdef __x86_64__
> -#define ARCH_MAX_REGS X86_64_MAX_REGS
> -#define arch_regs_table x86_64_regs_table
> +#define regoffset_table x86_64_regoffset_table
> #else
> -#define ARCH_MAX_REGS X86_32_MAX_REGS
> -#define arch_regs_table x86_32_regs_table
> +#define regoffset_table x86_32_regoffset_table
> #endif
>
> +/* Minus 1 for the ending REG_OFFSET_END */
> +#define ARCH_MAX_REGS ((sizeof(regoffset_table) / sizeof(regoffset_table[0])) - 1)
> +
> /* Return architecture dependent register string (for kprobe-tracer) */
> const char *get_arch_regstr(unsigned int n)
> {
> - return (n < ARCH_MAX_REGS) ? arch_regs_table[n] : NULL;
> + return (n < ARCH_MAX_REGS) ? regoffset_table[n].name : NULL;
> +}
> +
> +/* Reuse code from arch/x86/kernel/ptrace.c */
> +/**
> + * regs_query_register_offset() - query register offset from its name
> + * @name: the name of a register
> + *
> + * regs_query_register_offset() returns the offset of a register in struct
> + * pt_regs from its name. If the name is invalid, this returns -EINVAL;
> + */
> +int regs_query_register_offset(const char *name)
> +{
> + const struct pt_regs_offset *roff;
> + for (roff = regoffset_table; roff->name != NULL; roff++)
> + if (!strcmp(roff->name, name))
> + return roff->offset;
> + return -EINVAL;
> }
> --
> 1.8.3.4

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