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Date: Mon, 11 May 2015 10:22:53 +0800
From: He Kuang <hekuang@...wei.com>
To: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
<a.p.zijlstra@...llo.nl>, <acme@...nel.org>, <jolsa@...nel.org>,
<mingo@...hat.com>
CC: <wangnan0@...wei.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/3] perf probe: Add --range option to show variable
location range
Hi, Masami
On 2015/5/10 11:21, Masami Hiramatsu wrote:
> On 2015/05/09 18:55, 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@...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]>
>>
> Thanks, this looks easier to understand :)
>
> [...]
>> diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
>> index dcca551..30a1a1b 100644
>> --- a/tools/perf/util/probe-finder.c
>> +++ b/tools/perf/util/probe-finder.c
>> @@ -43,6 +43,9 @@
>> /* Kprobe tracer basic type is up to u64 */
>> #define MAX_BASIC_TYPE_BITS 64
>>
>> +/* Variable location invalid at addr but valid in scope */
>> +#define VARIABLE_LOCATION_INVALID_AT_ADDR -10000
> Hmm, could you use -ERANGE instead of this?
> Other part is OK for me.
>
> Thank you!
I've checked libdw, it never returns -ERANGE, but there is an
errno conflict in the function convert_variable_location itself:
268 regs = get_arch_regstr(regn);
269 if (!regs) {
270 /* This should be a bug in DWARF or this tool */
271 pr_warning("Mapping for the register number %u "
272 "missing on this architecture.\n", regn);
273 return -ERANGE;
274 }
So shell we change the above errno to -ENOENT or choose another
errno for current 'VARIABLE_LOCATION_INVALID_AT_ADDR', what's
your opinion?
Thanks!
>
>
>> +
>> /* Dwarf FL wrappers */
>> static char *debuginfo_path; /* Currently dummy */
>>
>> @@ -177,7 +180,7 @@ 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 +190,19 @@ 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 = VARIABLE_LOCATION_INVALID_AT_ADDR;
>> + } 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 +223,7 @@ 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 +233,7 @@ 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 */
>> @@ -250,7 +263,7 @@ static_var:
>> }
>>
>> if (!tvar)
>> - return 0;
>> + return ret2;
>>
>> regs = get_arch_regstr(regn);
>> if (!regs) {
>> @@ -269,7 +282,7 @@ 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 +1281,34 @@ 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 == VARIABLE_LOCATION_INVALID_AT_ADDR) {
>> + 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));
>> }
>>
>
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