From: Sandipan Das sandipan@linux.ibm.com
[ Upstream commit 9068533e4f470daf2b0f29c71d865990acd8826e ]
For powerpc64, perf will filter out the second entry in the callchain, i.e. the LR value, if the return address of the function corresponding to the probed location has already been saved on its caller's stack.
The state of the return address is determined using debug information. At any point within a function, if the return address is already saved somewhere, a DWARF expression can tell us about its location. If the return address in still in LR only, no DWARF expression would exist.
Typically, the instructions in a function's prologue first copy the LR value to R0 and then pushes R0 on to the stack. If LR has already been copied to R0 but R0 is yet to be pushed to the stack, we can still get a DWARF expression that says that the return address is in R0. This is indicating that getting a DWARF expression for the return address does not guarantee the fact that it has already been saved on the stack.
This can be observed on a powerpc64le system running Fedora 27 as shown below.
# objdump -d /usr/lib64/libc-2.26.so | less ... 000000000015af20 <inet_pton>: 15af20: 0b 00 4c 3c addis r2,r12,11 15af24: e0 c1 42 38 addi r2,r2,-15904 15af28: a6 02 08 7c mflr r0 15af2c: f0 ff c1 fb std r30,-16(r1) 15af30: f8 ff e1 fb std r31,-8(r1) 15af34: 78 1b 7f 7c mr r31,r3 15af38: 78 23 83 7c mr r3,r4 15af3c: 78 2b be 7c mr r30,r5 15af40: 10 00 01 f8 std r0,16(r1) 15af44: c1 ff 21 f8 stdu r1,-64(r1) 15af48: 28 00 81 f8 std r4,40(r1) ...
# readelf --debug-dump=frames-interp /usr/lib64/libc-2.26.so | less ... 00027024 0000000000000024 00027028 FDE cie=00000000 pc=000000000015af20..000000000015af88 LOC CFA r30 r31 ra 000000000015af20 r1+0 u u u 000000000015af34 r1+0 c-16 c-8 r0 000000000015af48 r1+64 c-16 c-8 c+16 000000000015af5c r1+0 c-16 c-8 c+16 000000000015af78 r1+0 u u ...
# perf probe -x /usr/lib64/libc-2.26.so -a inet_pton+0x18 # perf record -e probe_libc:inet_pton -g ping -6 -c 1 ::1 # perf script
Before:
ping 2829 [005] 512917.460174: probe_libc:inet_pton: (7fff7e2baf38) 7fff7e2baf38 __GI___inet_pton+0x18 (/usr/lib64/libc-2.26.so) 7fff7e2705b4 getaddrinfo+0x164 (/usr/lib64/libc-2.26.so) 12f152d70 _init+0xbfc (/usr/bin/ping) 7fff7e1836a0 generic_start_main.isra.0+0x140 (/usr/lib64/libc-2.26.so) 7fff7e183898 __libc_start_main+0xb8 (/usr/lib64/libc-2.26.so) 0 [unknown] ([unknown])
After:
ping 2829 [005] 512917.460174: probe_libc:inet_pton: (7fff7e2baf38) 7fff7e2baf38 __GI___inet_pton+0x18 (/usr/lib64/libc-2.26.so) 7fff7e26fa54 gaih_inet.constprop.7+0xf44 (/usr/lib64/libc-2.26.so) 7fff7e2705b4 getaddrinfo+0x164 (/usr/lib64/libc-2.26.so) 12f152d70 _init+0xbfc (/usr/bin/ping) 7fff7e1836a0 generic_start_main.isra.0+0x140 (/usr/lib64/libc-2.26.so) 7fff7e183898 __libc_start_main+0xb8 (/usr/lib64/libc-2.26.so) 0 [unknown] ([unknown])
Reported-by: Ravi Bangoria ravi.bangoria@linux.ibm.com Signed-off-by: Sandipan Das sandipan@linux.ibm.com Cc: Jiri Olsa jolsa@redhat.com Cc: Maynard Johnson maynard@us.ibm.com Cc: Naveen N. Rao naveen.n.rao@linux.vnet.ibm.com Cc: Ravi Bangoria ravi.bangoria@linux.vnet.ibm.com Cc: Sukadev Bhattiprolu sukadev@linux.vnet.ibm.com Link: http://lkml.kernel.org/r/66e848a7bdf2d43b39210a705ff6d828a0865661.1530724939... Signed-off-by: Arnaldo Carvalho de Melo acme@redhat.com Signed-off-by: Sasha Levin alexander.levin@microsoft.com --- tools/perf/arch/powerpc/util/skip-callchain-idx.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/tools/perf/arch/powerpc/util/skip-callchain-idx.c b/tools/perf/arch/powerpc/util/skip-callchain-idx.c index bd630c222e65..9d1f6e976a5a 100644 --- a/tools/perf/arch/powerpc/util/skip-callchain-idx.c +++ b/tools/perf/arch/powerpc/util/skip-callchain-idx.c @@ -58,9 +58,13 @@ static int check_return_reg(int ra_regno, Dwarf_Frame *frame) }
/* - * Check if return address is on the stack. + * Check if return address is on the stack. If return address + * is in a register (typically R0), it is yet to be saved on + * the stack. */ - if (nops != 0 || ops != NULL) + if ((nops != 0 || ops != NULL) && + !(nops == 1 && ops[0].atom == DW_OP_regx && + ops[0].number2 == 0 && ops[0].offset == 0)) return 0;
/*