forked from luck/tmp_suning_uos_patched
f08046cb30
The compiler might optimize a call/ret combination by making it a jmp. However the thread-stack does not presently cater for that, so that such control flow is not visible in the call graph. Make it visible by recording on the stack a branch to the start of a different symbol. Note, that means when a ret pops the stack, all jmps must be popped off first. Example: $ cat jmp-to-fn.c __attribute__((noinline)) int bar(void) { return -1; } __attribute__((noinline)) int foo(void) { return bar() + 1; } int main() { return foo(); } $ gcc -ggdb3 -Wall -Wextra -O2 -o jmp-to-fn jmp-to-fn.c $ objdump -d jmp-to-fn <SNIP> 0000000000001040 <main>: 1040: 31 c0 xor %eax,%eax 1042: e9 09 01 00 00 jmpq 1150 <foo> <SNIP> 0000000000001140 <bar>: 1140: b8 ff ff ff ff mov $0xffffffff,%eax 1145: c3 retq <SNIP> 0000000000001150 <foo>: 1150: 31 c0 xor %eax,%eax 1152: e8 e9 ff ff ff callq 1140 <bar> 1157: 83 c0 01 add $0x1,%eax 115a: c3 retq <SNIP> $ perf record -o jmp-to-fn.perf.data -e intel_pt/cyc/u ./jmp-to-fn [ perf record: Woken up 1 times to write data ] [ perf record: Captured and wrote 0,017 MB jmp-to-fn.perf.data ] $ perf script -i jmp-to-fn.perf.data --itrace=be -s ~/libexec/perf-core/scripts/python/export-to-sqlite.py jmp-to-fn.db branches calls 2019-01-08 13:24:58.783069 Creating database... 2019-01-08 13:24:58.794650 Writing records... 2019-01-08 13:24:59.008050 Adding indexes 2019-01-08 13:24:59.015802 Done $ ~/libexec/perf-core/scripts/python/exported-sql-viewer.py jmp-to-fn.db Before: main -> bar After: main -> foo -> bar Committer testing: Install the python2-pyside package, then select these menu options on the GUI: "Reports" "Context sensitive callgraphs" Then go on expanding the symbols, to get, full picture when doing this on a fedora:29 with gcc version 8.2.1 20181215 (Red Hat 8.2.1-6) (GCC): jmp-to-fn PID:TID _start (ld-2.28.so) __libc_start_main main foo bar To verify that indeed, this fixes the problem. Signed-off-by: Adrian Hunter <adrian.hunter@intel.com> Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com> Acked-by: Jiri Olsa <jolsa@kernel.org> Link: http://lkml.kernel.org/r/20190109091835.5570-5-adrian.hunter@intel.com Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com> |
||
---|---|---|
.. | ||
accounting | ||
arch | ||
bpf | ||
build | ||
cgroup | ||
crypto | ||
firewire | ||
firmware | ||
gpio | ||
hv | ||
iio | ||
include | ||
kvm/kvm_stat | ||
laptop | ||
leds | ||
lib | ||
memory-model | ||
nfsd | ||
objtool | ||
pci | ||
pcmcia | ||
perf | ||
power | ||
scripts | ||
spi | ||
testing | ||
thermal/tmon | ||
time | ||
usb | ||
virtio | ||
vm | ||
wmi | ||
Makefile |