Re: [PATCH v3 2/3] perf probe: Add --range option to show variable location range

Masami Hiramatsu
2015-05-11T12:04:45Z

On 2015/05/11 18:25, He Kuang wrote:
> It is not easy for users to get the accurate byte offset or the line
> number where a local variable can be probed. With '--range' option,
> local variables in scope of the probe point are showed with byte offset
> range, and can be added according to this range information.
>
> For example, there are some variables in function
> generic_perform_write():
>
> <generic_perform_write@mm/filemap.c:0>
> 0 ssize_t generic_perform_write(struct file *file,
> 1 struct iov_iter *i, loff_t pos)
> 2 {
> 3 struct address_space *mapping = file->f_mapping;
> 4 const struct address_space_operations *a_ops = mapping->a_ops;
> ...
> 42 status = a_ops->write_begin(file, mapping, pos, bytes, flags,
> &page, &fsdata);
> 44 if (unlikely(status < 0))
>
> But we got failed when we try to probe the variable 'a_ops' at line 42
> or 44.
>
> $ perf probe --add 'generic_perform_write:42 a_ops'
> Failed to find the location of a_ops at this address.
> Perhaps, it has been optimized out.
>
> This is because source code do not match assembly, so a variable may not
> be available in the sourcecode line where it presents. After this patch,
> we can lookup the accurate byte offset range of a variable, 'INV'
> indicates that this variable is not valid at the given point, but
> available in scope:
>
> $ perf probe --vars 'generic_perform_write:42' --range
> Available variables at generic_perform_write:42
> @<generic_perform_write+141>
> [INV] ssize_t written @<generic_perform_write+[324-331]>
> [INV] struct address_space_operations* a_ops @<generic_perform_write+[55-61,170-176,223-246]>
> [VAL] (unknown_type) fsdata @<generic_perform_write+[70-307,346-411]>
> [VAL] loff_t pos @<generic_perform_write+[0-286,286-336,346-411]>
> [VAL] long int status @<generic_perform_write+[83-342,346-411]>
> [VAL] long unsigned int bytes @<generic_perform_write+[122-311,320-338,346-403,403-411]>
> [VAL] struct address_space* mapping @<generic_perform_write+[35-344,346-411]>
> [VAL] struct iov_iter* i @<generic_perform_write+[0-340,346-411]>
> [VAL] struct page* page @<generic_perform_write+[70-307,346-411]>
>
> Then it is more clearly for us to do the probe with this variable:
>
> $ perf probe --add 'generic_perform_write+170 a_ops'
> Added new event:
> probe:generic_perform_write (on generic_perform_write+170 with a_ops)

Looks good to me:)

Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>

Thank you!

>
> Signed-off-by: He Kuang <hekuang@huawei.com>
> ---
> tools/perf/builtin-probe.c | 2 +
> tools/perf/util/dwarf-aux.c | 121 +++++++++++++++++++++++++++++++++++++++++
> tools/perf/util/dwarf-aux.h | 2 +
> tools/perf/util/probe-event.h | 1 +
> tools/perf/util/probe-finder.c | 57 ++++++++++++++-----
> 5 files changed, 170 insertions(+), 13 deletions(-)
>
> diff --git a/tools/perf/builtin-probe.c b/tools/perf/builtin-probe.c
> index 7fa2c7a..1272559 100644
> --- a/tools/perf/builtin-probe.c
> +++ b/tools/perf/builtin-probe.c
> @@ -372,6 +372,8 @@ __cmd_probe(int argc, const char **argv, const char *prefix __maybe_unused)
> "Show accessible variables on PROBEDEF", opt_show_vars),
> OPT_BOOLEAN('\0', "externs", &probe_conf.show_ext_vars,
> "Show external variables too (with --vars only)"),
> + OPT_BOOLEAN('\0', "range", &probe_conf.show_location_range,
> + "Show variables location range in scope (with --vars only)"),
> OPT_STRING('k', "vmlinux", &symbol_conf.vmlinux_name,
> "file", "vmlinux pathname"),
> OPT_STRING('s', "source", &symbol_conf.source_prefix,
> diff --git a/tools/perf/util/dwarf-aux.c b/tools/perf/util/dwarf-aux.c
> index 737c9db..afa0971 100644
> --- a/tools/perf/util/dwarf-aux.c
> +++ b/tools/perf/util/dwarf-aux.c
> @@ -913,3 +913,124 @@ int die_get_varname(Dwarf_Die *vr_die, struct strbuf *buf)
> return 0;
> }
>
> +/**
> + * die_get_var_innermost_scope - Get innermost scope range of given variable DIE
> + * @sp_die: a subprogram DIE
> + * @vr_die: a variable DIE
> + * @buf: a strbuf for variable byte offset range
> + *
> + * Get the innermost scope range of @vr_die and stores it in @buf as
> + * "@<function_name+[NN-NN,NN-NN]>".
> + */
> +static int die_get_var_innermost_scope(Dwarf_Die *sp_die, Dwarf_Die *vr_die,
> + struct strbuf *buf)
> +{
> + Dwarf_Die *scopes;
> + int count;
> + size_t offset = 0;
> + Dwarf_Addr base;
> + Dwarf_Addr start, end;
> + Dwarf_Addr entry;
> + int ret;
> + bool first = true;
> + const char *name;
> +
> + ret = dwarf_entrypc(sp_die, &entry);
> + if (ret)
> + return ret;
> +
> + name = dwarf_diename(sp_die);
> + if (!name)
> + return -ENOENT;
> +
> + count = dwarf_getscopes_die(vr_die, &scopes);
> +
> + /* (*SCOPES)[1] is the DIE for the scope containing that scope */
> + if (count <= 1) {
> + ret = -EINVAL;
> + goto out;
> + }
> +
> + while ((offset = dwarf_ranges(&scopes[1], offset, &base,
> + &start, &end)) > 0) {
> + start -= entry;
> + end -= entry;
> +
> + if (first) {
> + strbuf_addf(buf, "@<%s+[%lu-%lu",
> + name, start, end);
> + first = false;
> + } else {
> + strbuf_addf(buf, ",%lu-%lu",
> + start, end);
> + }
> + }
> +
> + if (!first)
> + strbuf_addf(buf, "]>");
> +
> +out:
> + free(scopes);
> + return ret;
> +}
> +
> +/**
> + * die_get_var_range - Get byte offset range of given variable DIE
> + * @sp_die: a subprogram DIE
> + * @vr_die: a variable DIE
> + * @buf: a strbuf for type and variable name and byte offset range
> + *
> + * Get the byte offset range of @vr_die and stores it in @buf as
> + * "@<function_name+[NN-NN,NN-NN]>".
> + */
> +int die_get_var_range(Dwarf_Die *sp_die, Dwarf_Die *vr_die, struct strbuf *buf)
> +{
> + int ret = 0;
> + Dwarf_Addr base;
> + Dwarf_Addr start, end;
> + Dwarf_Addr entry;
> + Dwarf_Op *op;
> + size_t nops;
> + size_t offset = 0;
> + Dwarf_Attribute attr;
> + bool first = true;
> + const char *name;
> +
> + ret = dwarf_entrypc(sp_die, &entry);
> + if (ret)
> + return ret;
> +
> + name = dwarf_diename(sp_die);
> + if (!name)
> + return -ENOENT;
> +
> + if (dwarf_attr(vr_die, DW_AT_location, &attr) == NULL)
> + return -EINVAL;
> +
> + while ((offset = dwarf_getlocations(
> + &attr, offset, &base,
> + &start, &end, &op, &nops)) > 0) {
> + if (start == 0) {
> + /* Single Location Descriptions */
> + ret = die_get_var_innermost_scope(sp_die, vr_die, buf);
> + return ret;
> + }
> +
> + /* Location Lists */
> + start -= entry;
> + end -= entry;
> + if (first) {
> + strbuf_addf(buf, "@<%s+[%lu-%lu",
> + name, start, end);
> + first = false;
> + } else {
> + strbuf_addf(buf, ",%lu-%lu",
> + start, end);
> + }
> + }
> +
> + if (!first)
> + strbuf_addf(buf, "]>");
> +
> + return ret;
> +}
> diff --git a/tools/perf/util/dwarf-aux.h b/tools/perf/util/dwarf-aux.h
> index 60676fd..c154c0b8 100644
> --- a/tools/perf/util/dwarf-aux.h
> +++ b/tools/perf/util/dwarf-aux.h
> @@ -121,4 +121,6 @@ extern int die_get_typename(Dwarf_Die *vr_die, struct strbuf *buf);
>
> /* Get the name and type of given variable DIE, stored as "type\tname" */
> extern int die_get_varname(Dwarf_Die *vr_die, struct strbuf *buf);
> +extern int die_get_var_range(Dwarf_Die *sp_die, Dwarf_Die *vr_die,
> + struct strbuf *buf);
> #endif
> diff --git a/tools/perf/util/probe-event.h b/tools/perf/util/probe-event.h
> index 1e2faa3..537eb32 100644
> --- a/tools/perf/util/probe-event.h
> +++ b/tools/perf/util/probe-event.h
> @@ -9,6 +9,7 @@
> /* Probe related configurations */
> struct probe_conf {
> bool show_ext_vars;
> + bool show_location_range;
> bool force_add;
> bool no_inlines;
> int max_probes;
> diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
> index dcca551..f032329 100644
> --- a/tools/perf/util/probe-finder.c
> +++ b/tools/perf/util/probe-finder.c
> @@ -177,7 +177,7 @@ static int convert_variable_location(Dwarf_Die *vr_die, Dwarf_Addr addr,
> Dwarf_Word offs = 0;
> bool ref = false;
> const char *regs;
> - int ret;
> + int ret, ret2 = 0;
>
> if (dwarf_attr(vr_die, DW_AT_external, &attr) != NULL)
> goto static_var;
> @@ -187,9 +187,19 @@ static int convert_variable_location(Dwarf_Die *vr_die, Dwarf_Addr addr,
> return -EINVAL; /* Broken DIE ? */
> if (dwarf_getlocation_addr(&attr, addr, &op, &nops, 1) <= 0) {
> ret = dwarf_entrypc(sp_die, &tmp);
> - if (ret || addr != tmp ||
> - dwarf_tag(vr_die) != DW_TAG_formal_parameter ||
> - dwarf_highpc(sp_die, &tmp))
> + if (ret)
> + return -ENOENT;
> +
> + if (probe_conf.show_location_range &&
> + (dwarf_tag(vr_die) == DW_TAG_variable)) {
> + ret2 = -ERANGE;
> + } else if (addr != tmp ||
> + dwarf_tag(vr_die) != DW_TAG_formal_parameter) {
> + return -ENOENT;
> + }
> +
> + ret = dwarf_highpc(sp_die, &tmp);
> + if (ret)
> return -ENOENT;
> /*
> * This is fuzzed by fentry mcount. We try to find the
> @@ -210,7 +220,7 @@ found:
> if (op->atom == DW_OP_addr) {
> static_var:
> if (!tvar)
> - return 0;
> + return ret2;
> /* Static variables on memory (not stack), make @varname */
> ret = strlen(dwarf_diename(vr_die));
> tvar->value = zalloc(ret + 2);
> @@ -220,7 +230,7 @@ static_var:
> tvar->ref = alloc_trace_arg_ref((long)offs);
> if (tvar->ref == NULL)
> return -ENOMEM;
> - return 0;
> + return ret2;
> }
>
> /* If this is based on frame buffer, set the offset */
> @@ -250,14 +260,14 @@ static_var:
> }
>
> if (!tvar)
> - return 0;
> + return ret2;
>
> regs = get_arch_regstr(regn);
> if (!regs) {
> /* This should be a bug in DWARF or this tool */
> pr_warning("Mapping for the register number %u "
> "missing on this architecture.\n", regn);
> - return -ERANGE;
> + return -ENOTSUP;
> }
>
> tvar->value = strdup(regs);
> @@ -269,7 +279,7 @@ static_var:
> if (tvar->ref == NULL)
> return -ENOMEM;
> }
> - return 0;
> + return ret2;
> }
>
> #define BYTES_TO_BITS(nb) ((nb) * BITS_PER_LONG / sizeof(long))
> @@ -1268,13 +1278,34 @@ static int collect_variables_cb(Dwarf_Die *die_mem, void *data)
> ret = convert_variable_location(die_mem, af->pf.addr,
> af->pf.fb_ops, &af->pf.sp_die,
> NULL);
> - if (ret == 0) {
> + if (ret == 0 || ret == -ERANGE) {
> + int ret2;
> + bool externs = !af->child;
> struct strbuf buf;
>
> strbuf_init(&buf, 64);
> - ret = die_get_varname(die_mem, &buf);
> - pr_debug2("Add new var: %s\n", buf.buf);
> - if (ret == 0) {
> +
> + if (probe_conf.show_location_range) {
> + if (!externs) {
> + if (ret)
> + strbuf_addf(&buf, "[INV]\t");
> + else
> + strbuf_addf(&buf, "[VAL]\t");
> + } else
> + strbuf_addf(&buf, "[EXT]\t");
> + }
> +
> + ret2 = die_get_varname(die_mem, &buf);
> +
> + if (!ret2 && probe_conf.show_location_range &&
> + !externs) {
> + strbuf_addf(&buf, "\t");
> + ret2 = die_get_var_range(&af->pf.sp_die,
> + die_mem, &buf);
> + }
> +
> + pr_debug("Add new var: %s\n", buf.buf);
> + if (ret2 == 0) {
> strlist__add(vl->vars,
> strbuf_detach(&buf, NULL));
> }
>

--
Masami HIRAMATSU
Linux Technology Research Center, System Productivity Research Dept.
Center for Technology Innovation - Systems Engineering
Hitachi, Ltd., Research & Development Group
E-mail: masami.hiramatsu.pt@hitachi.com