Re: [PATCH v4] perf record: Add support for arch_sdt_arg_parse_op() on s390

[Ian Rogers]

On Wed, Mar 18, 2026 at 4:34 AM Thomas Richter <tmricht@xxxxxxxxxxxxx> wrote:
>
> V4: Add comments from Ian and Sashiko:
>     Reset variable initialized to zero on error
>     Rework regular expression and reduce to one case.
> V3: Add comments from Ian
>     Print register expression without leading 'r' (wrong).
> V2: Add comments from Sumanth Koirkkar

nit: these need to be placed after a line of "---" so that git mailbox
won't include it in the commit message.

> commit e5e66adfe45a6 ("perf regs: Remove __weak attributive arch_sdt_arg_parse_op() function")
> removes arch_sdt_arg_parse_op() functions and reveals missing s390 support.
> The following warning is printed:
>
>   Unknown ELF machine 22, standard arguments parse will be skipped.
>
> ELF machine 22 is the EM_S390 host. This happens with command
>   # ./perf record -v -- stress-ng -t 1s --matrix 0
> on a z/VM system when the event is not specified.
>
> Add s390 specific __perf_sdt_arg_parse_op_s390() function to support
> -architecture calls to arch_sdt_arg_parse_op() for s390.
> The warning disappears.
>
> Signed-off-by: Thomas Richter <tmricht@xxxxxxxxxxxxx>
> Cc: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>
> Cc: Ian Rogers <irogers@xxxxxxxxxx>
> Tested-by: Jan Polensky <japo@xxxxxxxxxxxxx>

Reviewed-by: Ian Rogers <irogers@xxxxxxxxxx>

> ---
>  .../perf/util/perf-regs-arch/perf_regs_s390.c | 77 +++++++++++++++++++
>  tools/perf/util/perf_regs.c                   |  3 +
>  tools/perf/util/perf_regs.h                   |  1 +
>  3 files changed, 81 insertions(+)
>
> diff --git a/tools/perf/util/perf-regs-arch/perf_regs_s390.c b/tools/perf/util/perf-regs-arch/perf_regs_s390.c
> index c61df24edf0f..9d34549be477 100644
> --- a/tools/perf/util/perf-regs-arch/perf_regs_s390.c
> +++ b/tools/perf/util/perf-regs-arch/perf_regs_s390.c
> @@ -1,7 +1,13 @@
>  // SPDX-License-Identifier: GPL-2.0
>
> +#include <errno.h>
> +#include <regex.h>
>  #include "../perf_regs.h"
>  #include "../../arch/s390/include/perf_regs.h"
> +#include "debug.h"
> +
> +#include <linux/zalloc.h>
> +#include <linux/kernel.h>
>
>  uint64_t __perf_reg_mask_s390(bool intr __maybe_unused)
>  {
> @@ -95,3 +101,74 @@ uint64_t __perf_reg_sp_s390(void)
>  {
>         return PERF_REG_S390_R15;
>  }
> +
> +/* %rXX */
> +#define SDT_OP_REGEX1  "^(%r([0-9]|1[0-5]))$"
> +/* +-###(%rXX) */
> +#define SDT_OP_REGEX2  "^([+-]?[0-9]+\\(%r([0-9]|1[0-5])\\))$"
> +static regex_t sdt_op_regex1, sdt_op_regex2;
> +
> +static int sdt_init_op_regex(void)
> +{
> +       static int initialized;
> +       int ret = 0;
> +
> +       if (initialized)
> +               return 0;
> +
> +       ret = regcomp(&sdt_op_regex1, SDT_OP_REGEX1, REG_EXTENDED);
> +       if (ret)
> +               goto error;
> +       initialized = 1;
> +
> +       ret = regcomp(&sdt_op_regex2, SDT_OP_REGEX2, REG_EXTENDED);
> +       if (ret)
> +               goto free_regex1;
> +       initialized = 2;
> +
> +       return 0;
> +
> +free_regex1:
> +       regfree(&sdt_op_regex1);
> +error:
> +       pr_debug4("Regex compilation error, initialized %d\n", initialized);
> +       initialized = 0;
> +       return ret;
> +}
> +
> +/*
> + * Parse OP and convert it into uprobe format, which is, +/-NUM(%gprREG).
> + * Possible variants of OP are:
> + *     Format          Example
> + *     -------------------------
> + *     NUM(%rREG)      48(%r1)
> + *     -NUM(%rREG)     -48(%r1)
> + *     %rREG           %r1
> + */

nit: Sashiko notes this comment may be stale:
https://sashiko.dev/#/patchset/20260318113416.2287472-1-tmricht%40linux.ibm.com

This isn't a bug, but the comment mentions converting the OP into the
+/-NUM(%gprREG) format. Is this a leftover copy-paste from the PowerPC
implementation?

The actual s390 implementation correctly parses and outputs the %rREG format
as shown in the examples.

Thanks,
Ian

> +int __perf_sdt_arg_parse_op_s390(char *old_op, char **new_op)
> +{
> +       int ret, new_len;
> +       regmatch_t rm[6];
> +
> +       *new_op = NULL;
> +       ret = sdt_init_op_regex();
> +       if (ret)
> +               return -EINVAL;
> +
> +       if (!regexec(&sdt_op_regex1, old_op, ARRAY_SIZE(rm), rm, 0) ||
> +           !regexec(&sdt_op_regex2, old_op, ARRAY_SIZE(rm), rm, 0)) {
> +               new_len = 1;    /* NULL byte */
> +               new_len += (int)(rm[1].rm_eo - rm[1].rm_so);
> +               *new_op = zalloc(new_len);
> +               if (!*new_op)
> +                       return -ENOMEM;
> +
> +               scnprintf(*new_op, new_len, "%.*s",
> +                         (int)(rm[1].rm_eo - rm[1].rm_so), old_op + rm[1].rm_so);
> +       } else {
> +               pr_debug4("Skipping unsupported SDT argument: %s\n", old_op);
> +               return SDT_ARG_SKIP;
> +       }
> +
> +       return SDT_ARG_VALID;
> +}
> diff --git a/tools/perf/util/perf_regs.c b/tools/perf/util/perf_regs.c
> index 5b8f34beb24e..f52b0e1f7fc7 100644
> --- a/tools/perf/util/perf_regs.c
> +++ b/tools/perf/util/perf_regs.c
> @@ -23,6 +23,9 @@ int perf_sdt_arg_parse_op(uint16_t e_machine, char *old_op, char **new_op)
>         case EM_X86_64:
>                 ret = __perf_sdt_arg_parse_op_x86(old_op, new_op);
>                 break;
> +       case EM_S390:
> +               ret = __perf_sdt_arg_parse_op_s390(old_op, new_op);
> +               break;
>         default:
>                 pr_debug("Unknown ELF machine %d, standard arguments parse will be skipped.\n",
>                          e_machine);
> diff --git a/tools/perf/util/perf_regs.h b/tools/perf/util/perf_regs.h
> index 7c04700bf837..573f0d1dfe04 100644
> --- a/tools/perf/util/perf_regs.h
> +++ b/tools/perf/util/perf_regs.h
> @@ -62,6 +62,7 @@ uint64_t __perf_reg_mask_s390(bool intr);
>  const char *__perf_reg_name_s390(int id);
>  uint64_t __perf_reg_ip_s390(void);
>  uint64_t __perf_reg_sp_s390(void);
> +int __perf_sdt_arg_parse_op_s390(char *old_op, char **new_op);
>
>  int __perf_sdt_arg_parse_op_x86(char *old_op, char **new_op);
>  uint64_t __perf_reg_mask_x86(bool intr);
> --
> 2.53.0
>