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Subject[PATCH 12/16] perf probe: Show correct source lines of probes on kmodules
Date
From: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>

Perf probe always failed to find appropriate line numbers because of
failing to find .text start address offset from debuginfo.

e.g.
----
# ./perf probe -m pcspkr pcspkr_event:5
Added new events:
probe:pcspkr_event (on pcspkr_event:5 in pcspkr)
probe:pcspkr_event_1 (on pcspkr_event:5 in pcspkr)

You can now use it in all perf tools, such as:

perf record -e probe:pcspkr_event_1 -aR sleep 1

# ./perf probe -l
Failed to find debug information for address ffffffffa031f006
Failed to find debug information for address ffffffffa031f016
probe:pcspkr_event (on pcspkr_event+6 in pcspkr)
probe:pcspkr_event_1 (on pcspkr_event+22 in pcspkr)
----

This fixes the above issue as below.
1. Get the relative address of the symbol in .text by using
map->start.
2. Adjust the address by adding the offset of .text section
in the kernel module binary.

With this fix, perf probe -l shows lines correctly.
----
# ./perf probe -l
probe:pcspkr_event (on pcspkr_event:5@drivers/input/misc/pcspkr.c in pcspkr)
probe:pcspkr_event_1 (on pcspkr_event:5@drivers/input/misc/pcspkr.c in pcspkr)
----

Reported-by: Arnaldo Carvalho de Melo <acme@kernel.org>
Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/20150930164132.3733.24643.stgit@localhost.localdomain
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
tools/perf/util/probe-event.c | 35 +++++++++++++++++++++++------------
tools/perf/util/probe-finder.c | 42 ++++++++++++++++++++++++++++++++++++++++++
2 files changed, 65 insertions(+), 12 deletions(-)

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index 5d68f68797a9..65be284823d5 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -137,7 +137,8 @@ static struct ref_reloc_sym *kernel_get_ref_reloc_sym(void)
return kmap->ref_reloc_sym;
}

-static u64 kernel_get_symbol_address_by_name(const char *name, bool reloc)
+static int kernel_get_symbol_address_by_name(const char *name, u64 *addr,
+ bool reloc, bool reladdr)
{
struct ref_reloc_sym *reloc_sym;
struct symbol *sym;
@@ -146,12 +147,14 @@ static u64 kernel_get_symbol_address_by_name(const char *name, bool reloc)
/* ref_reloc_sym is just a label. Need a special fix*/
reloc_sym = kernel_get_ref_reloc_sym();
if (reloc_sym && strcmp(name, reloc_sym->name) == 0)
- return (reloc) ? reloc_sym->addr : reloc_sym->unrelocated_addr;
+ *addr = (reloc) ? reloc_sym->addr : reloc_sym->unrelocated_addr;
else {
sym = __find_kernel_function_by_name(name, &map);
- if (sym)
- return map->unmap_ip(map, sym->start) -
- ((reloc) ? 0 : map->reloc);
+ if (!sym)
+ return -ENOENT;
+ *addr = map->unmap_ip(map, sym->start) -
+ ((reloc) ? 0 : map->reloc) -
+ ((reladdr) ? map->start : 0);
}
return 0;
}
@@ -245,12 +248,14 @@ static void clear_probe_trace_events(struct probe_trace_event *tevs, int ntevs)
static bool kprobe_blacklist__listed(unsigned long address);
static bool kprobe_warn_out_range(const char *symbol, unsigned long address)
{
- u64 etext_addr;
+ u64 etext_addr = 0;
+ int ret;

/* Get the address of _etext for checking non-probable text symbol */
- etext_addr = kernel_get_symbol_address_by_name("_etext", false);
+ ret = kernel_get_symbol_address_by_name("_etext", &etext_addr,
+ false, false);

- if (etext_addr != 0 && etext_addr < address)
+ if (ret == 0 && etext_addr < address)
pr_warning("%s is out of .text, skip it.\n", symbol);
else if (kprobe_blacklist__listed(address))
pr_warning("%s is blacklisted function, skip it.\n", symbol);
@@ -517,8 +522,10 @@ static int find_perf_probe_point_from_dwarf(struct probe_trace_point *tp,
goto error;
addr += stext;
} else if (tp->symbol) {
- addr = kernel_get_symbol_address_by_name(tp->symbol, false);
- if (addr == 0)
+ /* If the module is given, this returns relative address */
+ ret = kernel_get_symbol_address_by_name(tp->symbol, &addr,
+ false, !!tp->module);
+ if (ret != 0)
goto error;
addr += tp->offset;
}
@@ -1884,8 +1891,12 @@ static int find_perf_probe_point_from_map(struct probe_trace_point *tp,
goto out;
sym = map__find_symbol(map, addr, NULL);
} else {
- if (tp->symbol)
- addr = kernel_get_symbol_address_by_name(tp->symbol, true);
+ if (tp->symbol && !addr) {
+ ret = kernel_get_symbol_address_by_name(tp->symbol,
+ &addr, true, false);
+ if (ret < 0)
+ goto out;
+ }
if (addr) {
addr += tp->offset;
sym = __find_kernel_function(addr, &map);
diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
index 35f905f4f34c..f0708ffd5e07 100644
--- a/tools/perf/util/probe-finder.c
+++ b/tools/perf/util/probe-finder.c
@@ -1402,6 +1402,41 @@ int debuginfo__find_available_vars_at(struct debuginfo *dbg,
return (ret < 0) ? ret : af.nvls;
}

+/* For the kernel module, we need a special code to get a DIE */
+static int debuginfo__get_text_offset(struct debuginfo *dbg, Dwarf_Addr *offs)
+{
+ int n, i;
+ Elf32_Word shndx;
+ Elf_Scn *scn;
+ Elf *elf;
+ GElf_Shdr mem, *shdr;
+ const char *p;
+
+ elf = dwfl_module_getelf(dbg->mod, &dbg->bias);
+ if (!elf)
+ return -EINVAL;
+
+ /* Get the number of relocations */
+ n = dwfl_module_relocations(dbg->mod);
+ if (n < 0)
+ return -ENOENT;
+ /* Search the relocation related .text section */
+ for (i = 0; i < n; i++) {
+ p = dwfl_module_relocation_info(dbg->mod, i, &shndx);
+ if (strcmp(p, ".text") == 0) {
+ /* OK, get the section header */
+ scn = elf_getscn(elf, shndx);
+ if (!scn)
+ return -ENOENT;
+ shdr = gelf_getshdr(scn, &mem);
+ if (!shdr)
+ return -ENOENT;
+ *offs = shdr->sh_addr;
+ }
+ }
+ return 0;
+}
+
/* Reverse search */
int debuginfo__find_probe_point(struct debuginfo *dbg, unsigned long addr,
struct perf_probe_point *ppt)
@@ -1410,9 +1445,16 @@ int debuginfo__find_probe_point(struct debuginfo *dbg, unsigned long addr,
Dwarf_Addr _addr = 0, baseaddr = 0;
const char *fname = NULL, *func = NULL, *basefunc = NULL, *tmp;
int baseline = 0, lineno = 0, ret = 0;
+ bool reloc = false;

+retry:
/* Find cu die */
if (!dwarf_addrdie(dbg->dbg, (Dwarf_Addr)addr, &cudie)) {
+ if (!reloc && debuginfo__get_text_offset(dbg, &baseaddr) == 0) {
+ addr += baseaddr;
+ reloc = true;
+ goto retry;
+ }
pr_warning("Failed to find debug information for address %lx\n",
addr);
ret = -EINVAL;
--
2.1.0


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