diff mbox

[1/2] perf symbols: Ignore mapping symbols on aarch64

Message ID CAA3XUr2ej57VxAF1D3tbhjcVFtgyvHWKQxMiTBJ9RcmYCUHekQ@mail.gmail.com
State New
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Commit Message

vkamensky Jan. 15, 2015, 2:51 a.m. UTC 
On 14 January 2015 at 16:03, Russell King - ARM Linux
<linux@arm.linux.org.uk> wrote:
> On Wed, Jan 14, 2015 at 10:38:38AM -0800, Victor Kamensky wrote:
>> >From fed6caab410ddcaf487ff23a3908eca129e50b89 Mon Sep 17 00:00:00 2001
>> From: Victor Kamensky <victor.kamensky@linaro.org>
>> Date: Wed, 14 Jan 2015 07:42:41 -0800
>> Subject: [PATCH 3/3] perf symbols: improve abi compliance in arm mapping
>>  symbols handling
>>
>> Both Arm and Aarch64 ELF ABI allow mapping symbols be in from
>> either "$d" or "$d.<any>". But current code that handles mapping
>> symbols only deals with the first, dollar character and a single
>> letter, case.
>>
>> The patch adds handling of the second case with period
>> followed by any characters.
>>
>> Suggested-by: Will Deacon <will.deacon@arm.com>
>> Signed-off-by: Victor Kamensky <victor.kamensky@linaro.org>
>
> I wonder if it would make more sense to re-use the "is_arm_mapping_symbol"
> thing which we have in kernel/module.c and scripts/kallsyms.c - it
> seems silly to re-invent code which we already have to detect these
> symbols.

Thanks for pointing this out. I did not know about
"is_arm_mapping_symbol" function.

Do you suggest we copy one of those functions into tools/perf?
Since tools/perf is separate user-land utility I don't see easy way
how can we reuse those directly.

Also those functions check for mapping symbols
seems to be more efficient that one I come with, for example
one from scripts/kallsyms.c

static inline int is_arm_mapping_symbol(const char *str)
{
    return str[0] == '$' && strchr("axtd", str[1])
           && (str[2] == '\0' || str[2] == '.');
}

But it seems that they are somewhat accurate: because they bundle
EM_ARM and EM_AARCH64 into one case. According to ABIs
for EM_ARM we have $a, $t, $d, $a.<any>, $t.<any>, $d.<any>;
and for EM_AARCH64 we have $x, $d, $x.<any>, $d.<any>.

How about the following two variants of the patch. It follows the same
mapping handling logic as in other 3 copies of is_arm_mapping_symbol
function in kernel, but it still separate copy in tools/perf code. Personally I
prefer variant 1, but I am fine with variant 2 too, because practically it
will be OK.

Variant 1 (as addition to this patch, as above):

From e08d348bd72d406d8939993d266729d805577c4b Mon Sep 17 00:00:00 2001
From: Victor Kamensky <victor.kamensky@linaro.org>
Date: Wed, 14 Jan 2015 07:42:41 -0800
Subject: [PATCH 3/3] perf symbols: improve abi compliance in arm mapping
 symbols handling

Both Arm and Aarch64 ELF ABI allow mapping symbols be in from
either "$d" or "$d.<any>". But current code that handles mapping
symbols only deals with the first, dollar character and a single
letter, case.

The patch adds handling of the second case with period
followed by any characters.

Suggested-by: Russell King <linux@arm.linux.org.uk>
Suggested-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Victor Kamensky <victor.kamensky@linaro.org>
---
 tools/perf/util/symbol-elf.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)
diff mbox

Patch

diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index 1e188dd..a038c98 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -857,17 +857,16 @@  int dso__load_sym(struct dso *dso, struct map *map,
          * don't identify functions, so will confuse the profile
          * output: */
         if (ehdr.e_machine == EM_ARM) {
-            if (!strcmp(elf_name, "$a") ||
-                !strcmp(elf_name, "$d") ||
-                !strcmp(elf_name, "$t"))
+                        if (elf_name[0] == '$' && strchr("adt", elf_name[1])
+                        && (elf_name[2] == '\0' || elf_name[2] == '.'))
                 continue;
         }
         /* Reject Aarch64 ELF "mapping symbols": these aren't unique and
          * don't identify functions, so will confuse the profile
          * output: */
         if (ehdr.e_machine == EM_AARCH64) {
-            if (!strcmp(elf_name, "$x") ||
-                !strcmp(elf_name, "$d"))
+                        if (elf_name[0] == '$' && strchr("dx", elf_name[1])
+                        && (elf_name[2] == '\0' || elf_name[2] == '.'))
                 continue;
         }

-- 
1.9.3

Variant 2 instead of patch posted with current subject:

 From c8d08ebddc61203daf21b17c891c26c1d08e14f1 Mon Sep 17 00:00:00 2001
From: Victor Kamensky <victor.kamensky@linaro.org>
Date: Mon, 12 Jan 2015 14:13:36 -0800
Subject: [PATCH 1/2] perf symbols: Ignore mapping symbols on aarch64

Aarch64 ELF files use mapping symbols with special names $x, $d
to identify regions of Aarch64 code (see Aarch64 ELF ABI - "ARM
IHI 0056B", section "4.5.4 Mapping symbols").

The patch filters out these symbols at load time, similar to
"696b97a perf symbols: Ignore mapping symbols on ARM" changes
done for ARM before V8.

Also added handling of mapping symbols that has format
"$d.<any>" and similar for both cases.

Note we are not making difference between EM_ARM and
EM_AARCH64 mapping symbols instead code handles superset
of both.

Signed-off-by: Victor Kamensky <victor.kamensky@linaro.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Avi Kivity <avi@cloudius-systems.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Anton Blanchard <anton@samba.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Dave Martin <Dave.Martin@arm.com>
---
 tools/perf/util/symbol-elf.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index 06fcd1b..b2eb0f9 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -856,10 +856,9 @@  int dso__load_sym(struct dso *dso, struct map *map,
         /* Reject ARM ELF "mapping symbols": these aren't unique and
          * don't identify functions, so will confuse the profile
          * output: */
-        if (ehdr.e_machine == EM_ARM) {
-            if (!strcmp(elf_name, "$a") ||
-                !strcmp(elf_name, "$d") ||
-                !strcmp(elf_name, "$t"))
+        if (ehdr.e_machine == EM_ARM || ehdr.e_machine == EM_AARCH64) {
+                        if (elf_name[0] == '$' && strchr("adtx", elf_name[1])
+                        && (elf_name[2] == '\0' || elf_name[2] == '.'))
                 continue;
         }