[PATCH v2] perf probe: Fix failure to probe events on arm

From: He Kuang
Date: Wed Jun 17 2015 - 22:49:39 EST

Fix failure to probe events on arm, problem is introduced by commit
5a51fcd1f30c ("perf probe: Skip kernel symbols which is out of
.text"). For some architectures, label '_etext' is not in the .text
section(in .notes section for arm/arm64). Label out of .text section is
not loaded as symbols and we got a zero value when look up its address,
which causes all events be wrongly skiped.

This patch skip checking text address range when failed to get the
address of '_etext' and fixes the problem.

Problem can be reproduced on arm as following:

# perf probe --add='generic_perform_write'
generic_perform_write+0 is out of .text, skip it.
Probe point 'generic_perform_write' not found.
Error: Failed to add events.

After this patch:

# perf probe --add='generic_perform_write'
Added new event:
probe:generic_perform_write (on generic_perform_write)

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

perf record -e probe:generic_perform_write -aR sleep 1

Signed-off-by: He Kuang <hekuang@xxxxxxxxxx>
tools/perf/util/probe-event.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index 076527b..381f23a 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -249,8 +249,12 @@ 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;
/* Get the address of _etext for checking non-probable text symbol */
- if (kernel_get_symbol_address_by_name("_etext", false) < address)
+ etext_addr = kernel_get_symbol_address_by_name("_etext", false);
+ if (etext_addr != 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);

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/