perf probe: Add --range option to show a variable's location range
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 the scope of the probe point
are showed with a byte offset range, and can be added according to this
range information.
For example, there are some variables in the 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 fail 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 the source code do not match the assembly, so a variable
may not be available in the source code line where it appears.
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 the 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 clear for us to add a 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)
Signed-off-by: He Kuang <hekuang@huawei.com>
Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/1431336304-16863-2-git-send-email-hekuang@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
He Kuang
Arnaldo Carvalho de Melo
parent
fb9596d173
commit
349e8d2611
5 changed files with 170 additions and 13 deletions
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@ -372,6 +372,8 @@ __cmd_probe(int argc, const char **argv, const char *prefix __maybe_unused)
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"Show accessible variables on PROBEDEF", opt_show_vars),
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OPT_BOOLEAN('\0', "externs", &probe_conf.show_ext_vars,
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"Show external variables too (with --vars only)"),
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OPT_BOOLEAN('\0', "range", &probe_conf.show_location_range,
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"Show variables location range in scope (with --vars only)"),
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OPT_STRING('k', "vmlinux", &symbol_conf.vmlinux_name,
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"file", "vmlinux pathname"),
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OPT_STRING('s', "source", &symbol_conf.source_prefix,
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@ -913,3 +913,124 @@ int die_get_varname(Dwarf_Die *vr_die, struct strbuf *buf)
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return 0;
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}
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/**
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* die_get_var_innermost_scope - Get innermost scope range of given variable DIE
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* @sp_die: a subprogram DIE
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* @vr_die: a variable DIE
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* @buf: a strbuf for variable byte offset range
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*
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* Get the innermost scope range of @vr_die and stores it in @buf as
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* "@<function_name+[NN-NN,NN-NN]>".
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*/
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static int die_get_var_innermost_scope(Dwarf_Die *sp_die, Dwarf_Die *vr_die,
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struct strbuf *buf)
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{
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Dwarf_Die *scopes;
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int count;
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size_t offset = 0;
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Dwarf_Addr base;
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Dwarf_Addr start, end;
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Dwarf_Addr entry;
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int ret;
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bool first = true;
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const char *name;
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ret = dwarf_entrypc(sp_die, &entry);
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if (ret)
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return ret;
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name = dwarf_diename(sp_die);
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if (!name)
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return -ENOENT;
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count = dwarf_getscopes_die(vr_die, &scopes);
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/* (*SCOPES)[1] is the DIE for the scope containing that scope */
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if (count <= 1) {
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ret = -EINVAL;
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goto out;
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}
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while ((offset = dwarf_ranges(&scopes[1], offset, &base,
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&start, &end)) > 0) {
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start -= entry;
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end -= entry;
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if (first) {
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strbuf_addf(buf, "@<%s+[%lu-%lu",
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name, start, end);
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first = false;
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} else {
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strbuf_addf(buf, ",%lu-%lu",
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start, end);
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}
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}
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if (!first)
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strbuf_addf(buf, "]>");
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out:
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free(scopes);
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return ret;
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}
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/**
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* die_get_var_range - Get byte offset range of given variable DIE
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* @sp_die: a subprogram DIE
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* @vr_die: a variable DIE
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* @buf: a strbuf for type and variable name and byte offset range
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*
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* Get the byte offset range of @vr_die and stores it in @buf as
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* "@<function_name+[NN-NN,NN-NN]>".
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*/
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int die_get_var_range(Dwarf_Die *sp_die, Dwarf_Die *vr_die, struct strbuf *buf)
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{
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int ret = 0;
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Dwarf_Addr base;
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Dwarf_Addr start, end;
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Dwarf_Addr entry;
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Dwarf_Op *op;
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size_t nops;
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size_t offset = 0;
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Dwarf_Attribute attr;
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bool first = true;
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const char *name;
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ret = dwarf_entrypc(sp_die, &entry);
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if (ret)
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return ret;
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name = dwarf_diename(sp_die);
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if (!name)
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return -ENOENT;
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if (dwarf_attr(vr_die, DW_AT_location, &attr) == NULL)
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return -EINVAL;
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while ((offset = dwarf_getlocations(
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&attr, offset, &base,
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&start, &end, &op, &nops)) > 0) {
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if (start == 0) {
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/* Single Location Descriptions */
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ret = die_get_var_innermost_scope(sp_die, vr_die, buf);
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return ret;
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}
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/* Location Lists */
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start -= entry;
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end -= entry;
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if (first) {
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strbuf_addf(buf, "@<%s+[%lu-%lu",
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name, start, end);
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first = false;
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} else {
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strbuf_addf(buf, ",%lu-%lu",
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start, end);
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}
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}
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if (!first)
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strbuf_addf(buf, "]>");
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return ret;
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}
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@ -121,4 +121,6 @@ extern int die_get_typename(Dwarf_Die *vr_die, struct strbuf *buf);
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/* Get the name and type of given variable DIE, stored as "type\tname" */
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extern int die_get_varname(Dwarf_Die *vr_die, struct strbuf *buf);
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extern int die_get_var_range(Dwarf_Die *sp_die, Dwarf_Die *vr_die,
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struct strbuf *buf);
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#endif
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@ -9,6 +9,7 @@
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/* Probe related configurations */
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struct probe_conf {
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bool show_ext_vars;
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bool show_location_range;
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bool force_add;
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bool no_inlines;
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int max_probes;
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@ -177,7 +177,7 @@ static int convert_variable_location(Dwarf_Die *vr_die, Dwarf_Addr addr,
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Dwarf_Word offs = 0;
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bool ref = false;
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const char *regs;
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int ret;
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int ret, ret2 = 0;
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if (dwarf_attr(vr_die, DW_AT_external, &attr) != NULL)
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goto static_var;
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@ -187,9 +187,19 @@ static int convert_variable_location(Dwarf_Die *vr_die, Dwarf_Addr addr,
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return -EINVAL; /* Broken DIE ? */
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if (dwarf_getlocation_addr(&attr, addr, &op, &nops, 1) <= 0) {
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ret = dwarf_entrypc(sp_die, &tmp);
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if (ret || addr != tmp ||
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dwarf_tag(vr_die) != DW_TAG_formal_parameter ||
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dwarf_highpc(sp_die, &tmp))
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if (ret)
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return -ENOENT;
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if (probe_conf.show_location_range &&
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(dwarf_tag(vr_die) == DW_TAG_variable)) {
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ret2 = -ERANGE;
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} else if (addr != tmp ||
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dwarf_tag(vr_die) != DW_TAG_formal_parameter) {
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return -ENOENT;
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}
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ret = dwarf_highpc(sp_die, &tmp);
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if (ret)
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return -ENOENT;
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/*
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* This is fuzzed by fentry mcount. We try to find the
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@ -210,7 +220,7 @@ static int convert_variable_location(Dwarf_Die *vr_die, Dwarf_Addr addr,
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if (op->atom == DW_OP_addr) {
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static_var:
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if (!tvar)
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return 0;
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return ret2;
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/* Static variables on memory (not stack), make @varname */
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ret = strlen(dwarf_diename(vr_die));
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tvar->value = zalloc(ret + 2);
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@ -220,7 +230,7 @@ static int convert_variable_location(Dwarf_Die *vr_die, Dwarf_Addr addr,
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tvar->ref = alloc_trace_arg_ref((long)offs);
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if (tvar->ref == NULL)
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return -ENOMEM;
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return 0;
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return ret2;
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}
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/* If this is based on frame buffer, set the offset */
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@ -250,14 +260,14 @@ static int convert_variable_location(Dwarf_Die *vr_die, Dwarf_Addr addr,
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}
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if (!tvar)
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return 0;
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return ret2;
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regs = get_arch_regstr(regn);
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if (!regs) {
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/* This should be a bug in DWARF or this tool */
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pr_warning("Mapping for the register number %u "
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"missing on this architecture.\n", regn);
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return -ERANGE;
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return -ENOTSUP;
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}
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tvar->value = strdup(regs);
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@ -269,7 +279,7 @@ static int convert_variable_location(Dwarf_Die *vr_die, Dwarf_Addr addr,
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if (tvar->ref == NULL)
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return -ENOMEM;
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}
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return 0;
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return ret2;
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}
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#define BYTES_TO_BITS(nb) ((nb) * BITS_PER_LONG / sizeof(long))
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@ -1270,13 +1280,34 @@ static int collect_variables_cb(Dwarf_Die *die_mem, void *data)
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ret = convert_variable_location(die_mem, af->pf.addr,
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af->pf.fb_ops, &af->pf.sp_die,
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NULL);
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if (ret == 0) {
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if (ret == 0 || ret == -ERANGE) {
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int ret2;
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bool externs = !af->child;
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struct strbuf buf;
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strbuf_init(&buf, 64);
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ret = die_get_varname(die_mem, &buf);
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pr_debug2("Add new var: %s\n", buf.buf);
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if (ret == 0) {
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if (probe_conf.show_location_range) {
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if (!externs) {
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if (ret)
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strbuf_addf(&buf, "[INV]\t");
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else
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strbuf_addf(&buf, "[VAL]\t");
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} else
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strbuf_addf(&buf, "[EXT]\t");
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}
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ret2 = die_get_varname(die_mem, &buf);
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if (!ret2 && probe_conf.show_location_range &&
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!externs) {
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strbuf_addf(&buf, "\t");
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ret2 = die_get_var_range(&af->pf.sp_die,
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die_mem, &buf);
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}
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pr_debug("Add new var: %s\n", buf.buf);
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if (ret2 == 0) {
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strlist__add(vl->vars,
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strbuf_detach(&buf, NULL));
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}
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