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SubjectRe: [PATCH 7/8] perf probe: Support SDT markers having reference counter (semaphore)
Hi Ravi,

This code logic looks good. I just have several small comments for style.

On Tue, 13 Mar 2018 18:26:02 +0530
Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com> wrote:

> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> index e1dbc98..2cbe68a 100644
> --- a/tools/perf/util/probe-event.c
> +++ b/tools/perf/util/probe-event.c
> @@ -1832,6 +1832,12 @@ int parse_probe_trace_command(const char *cmd, struct probe_trace_event *tev)
> tp->offset = strtoul(fmt2_str, NULL, 10);
> }
>
> + if (tev->uprobes) {
> + fmt2_str = strchr(p, '(');
> + if (fmt2_str)
> + tp->ref_ctr_offset = strtoul(fmt2_str + 1, NULL, 0);
> + }
> +
> tev->nargs = argc - 2;
> tev->args = zalloc(sizeof(struct probe_trace_arg) * tev->nargs);
> if (tev->args == NULL) {
> @@ -2054,15 +2060,22 @@ char *synthesize_probe_trace_command(struct probe_trace_event *tev)
> }
>
> /* Use the tp->address for uprobes */
> - if (tev->uprobes)
> - err = strbuf_addf(&buf, "%s:0x%lx", tp->module, tp->address);
> - else if (!strncmp(tp->symbol, "0x", 2))
> + if (tev->uprobes) {
> + if (tp->ref_ctr_offset)
> + err = strbuf_addf(&buf, "%s:0x%lx(0x%lx)", tp->module,
> + tp->address, tp->ref_ctr_offset);
> + else
> + err = strbuf_addf(&buf, "%s:0x%lx", tp->module,
> + tp->address);
> + } else if (!strncmp(tp->symbol, "0x", 2)) {
> /* Absolute address. See try_to_find_absolute_address() */
> err = strbuf_addf(&buf, "%s%s0x%lx", tp->module ?: "",
> tp->module ? ":" : "", tp->address);
> - else
> + } else {
> err = strbuf_addf(&buf, "%s%s%s+%lu", tp->module ?: "",
> tp->module ? ":" : "", tp->symbol, tp->offset);
> + }

What the purpose of this {}?

> +
> if (err)
> goto error;
>
> diff --git a/tools/perf/util/probe-event.h b/tools/perf/util/probe-event.h
> index 45b14f0..15a98c3 100644
> --- a/tools/perf/util/probe-event.h
> +++ b/tools/perf/util/probe-event.h
> @@ -27,6 +27,7 @@ struct probe_trace_point {
> char *symbol; /* Base symbol */
> char *module; /* Module name */
> unsigned long offset; /* Offset from symbol */
> + unsigned long ref_ctr_offset; /* SDT reference counter offset */
> unsigned long address; /* Actual address of the trace point */
> bool retprobe; /* Return probe flag */
> };
> diff --git a/tools/perf/util/probe-file.c b/tools/perf/util/probe-file.c
> index 4ae1123..08ba3a6 100644
> --- a/tools/perf/util/probe-file.c
> +++ b/tools/perf/util/probe-file.c
> @@ -701,6 +701,12 @@ static unsigned long long sdt_note__get_addr(struct sdt_note *note)
> : (unsigned long long)note->addr.a64[0];
> }
>
> +static unsigned long long sdt_note__get_ref_ctr_offset(struct sdt_note *note)
> +{
> + return note->bit32 ? (unsigned long long)note->addr.a32[2]
> + : (unsigned long long)note->addr.a64[2];
> +}

Could you please introduce an enum for specifying the index by name?

e.g.
enum {
SDT_NOTE_IDX_ADDR = 0,
SDT_NOTE_IDX_REFCTR = 2,
};

> +
> static const char * const type_to_suffix[] = {
> ":s64", "", "", "", ":s32", "", ":s16", ":s8",
> "", ":u8", ":u16", "", ":u32", "", "", "", ":u64"
> @@ -776,14 +782,24 @@ static char *synthesize_sdt_probe_command(struct sdt_note *note,
> {
> struct strbuf buf;
> char *ret = NULL, **args;
> - int i, args_count;
> + int i, args_count, err;
> + unsigned long long ref_ctr_offset;
>
> if (strbuf_init(&buf, 32) < 0)
> return NULL;
>
> - if (strbuf_addf(&buf, "p:%s/%s %s:0x%llx",
> + ref_ctr_offset = sdt_note__get_ref_ctr_offset(note);
> +
> + if (ref_ctr_offset)
> + err = strbuf_addf(&buf, "p:%s/%s %s:0x%llx(0x%llx)",
> sdtgrp, note->name, pathname,
> - sdt_note__get_addr(note)) < 0)
> + sdt_note__get_addr(note), ref_ctr_offset);
> + else
> + err = strbuf_addf(&buf, "p:%s/%s %s:0x%llx",
> + sdtgrp, note->name, pathname,
> + sdt_note__get_addr(note));

This can be minimized (and avoid repeating) by using 2 strbuf_addf()s, like

err = strbuf_addf(&buf, "p:%s/%s %s:0x%llx",
sdtgrp, note->name, pathname,
sdt_note__get_addr(note));
if (ref_ctr_offset && !err < 0)
err = strbuf_addf("(0x%llx)", ref_ctr_offset);


> +
> + if (err < 0)
> goto error;
>
> if (!note->args)
> diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
> index 2de7705..76c7b54 100644
> --- a/tools/perf/util/symbol-elf.c
> +++ b/tools/perf/util/symbol-elf.c
> @@ -1928,6 +1928,16 @@ static int populate_sdt_note(Elf **elf, const char *data, size_t len,
> }
> }
>
> + /* Adjust reference counter offset */
> + if (elf_section_by_name(*elf, &ehdr, &shdr, SDT_PROBES_SCN, NULL)) {
> + if (shdr.sh_offset) {
> + if (tmp->bit32)
> + tmp->addr.a32[2] -= (shdr.sh_addr - shdr.sh_offset);
> + else
> + tmp->addr.a64[2] -= (shdr.sh_addr - shdr.sh_offset);

Here we should use enum above too.

Thank you,

> + }
> + }
> +
> list_add_tail(&tmp->note_list, sdt_notes);
> return 0;
>
> diff --git a/tools/perf/util/symbol.h b/tools/perf/util/symbol.h
> index 70c16741..ad0c4f2 100644
> --- a/tools/perf/util/symbol.h
> +++ b/tools/perf/util/symbol.h
> @@ -384,6 +384,7 @@ struct sdt_note {
> int cleanup_sdt_note_list(struct list_head *sdt_notes);
> int sdt_notes__get_count(struct list_head *start);
>
> +#define SDT_PROBES_SCN ".probes"
> #define SDT_BASE_SCN ".stapsdt.base"
> #define SDT_NOTE_SCN ".note.stapsdt"
> #define SDT_NOTE_TYPE 3
> --
> 1.8.3.1
>


--
Masami Hiramatsu <mhiramat@kernel.org>

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