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Subject[PATCH perf/core v2 1/4] perf-probe: Fix to show correct locations for events on modules
Date
Fix to show correct locations for events on modules by relocating
given address instead of retrying after failure.

This happens when the module text size is enough big, bigger than
sh_addr, because original code retries withgiven address + sh_addr
if it failed to find CU DIE at the given address. Any address
smaller than sh_addr always fails and it retries with correct
address, but the address which bigger than sh_addr will get a CU
DIE which is on given address (not adjusted by sh_addr).

In my environment(x86-64), the sh_addr of ".text" section is
0x10030. Since i915 is a huge kernel module, we can see this
issue as below.

$ grep "[Tt] .*\[i915\]" /proc/kallsyms | sort | head -n1
ffffffffc0270000 t i915_switcheroo_can_switch [i915]

ffffffffc0270000 + 0x10030 = ffffffffc0280030, so we'll check
symbols cross this boundary.

$ grep "[Tt] .*\[i915\]" /proc/kallsyms | grep -B1 ^ffffffffc028\
| head -n 2
ffffffffc027ff80 t haswell_init_clock_gating [i915]
ffffffffc0280110 t valleyview_init_clock_gating [i915]

So setup probes on both function and see what happen.

$ sudo ./perf probe -m i915 -a haswell_init_clock_gating \
-a valleyview_init_clock_gating
Added new events:
probe:haswell_init_clock_gating (on haswell_init_clock_gating in i915)
probe:valleyview_init_clock_gating (on valleyview_init_clock_gating in i915)

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

perf record -e probe:valleyview_init_clock_gating -aR sleep 1

$ sudo ./perf probe -l
probe:haswell_init_clock_gating (on haswell_init_clock_gating@gpu/drm/i915/intel_pm.c in i915)
probe:valleyview_init_clock_gating (on i915_vga_set_decode:4@gpu/drm/i915/i915_drv.c in i915)

As you can see, haswell_init_clock_gating is correctly shown,
but valleyview_init_clock_gating is not.

With this patch, both events are shown correctly.

$ sudo ./perf probe -l
probe:haswell_init_clock_gating (on haswell_init_clock_gating@gpu/drm/i915/intel_pm.c in i915)
probe:valleyview_init_clock_gating (on valleyview_init_clock_gating@gpu/drm/i915/intel_pm.c in i915)

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
---
Changes in v2:
- Rewrite patch description with precise instructions.
---
tools/perf/util/probe-finder.c | 10 +++-------
1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
index df4debe..0278fe1 100644
--- a/tools/perf/util/probe-finder.c
+++ b/tools/perf/util/probe-finder.c
@@ -1543,16 +1543,12 @@ 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:
+ /* We always need to relocate the address for aranges */
+ if (debuginfo__get_text_offset(dbg, &baseaddr) == 0)
+ addr += baseaddr;
/* 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;
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