Messages in this thread Patch in this message | | | From | Arnaldo Carvalho de Melo <> | Date | Fri, 22 Feb 2019 16:42:44 -0300 | Subject | Re: [PATCH 6/6] perf thread-stack: Hide x86 retpolines |
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Em Wed, Jan 09, 2019 at 11:18:35AM +0200, Adrian Hunter escreveu: > x86 retpoline functions pollute the call graph by showing up everywhere > there is an indirect branch, but they do not really mean anything. Make > changes so that the default retpoline functions will no longer appear in > the call graph. Note this only affects the call graph, since all the > original branches are left unchanged. > > This does not handle function return thunks, nor is there any improvement > for the handling of inline thunks or extern thunks. > > Example: > > $ cat simple-retpoline.c > __attribute__((noinline)) int bar(void) > { > return -1; > } > > int foo(void) > { > return bar() + 1; > } > > __attribute__((indirect_branch("thunk"))) int main() > { > int (*volatile fn)(void) = foo; > > fn(); > return fn(); > } > $ gcc -ggdb3 -Wall -Wextra -O2 -o simple-retpoline simple-retpoline.c > $ objdump -d simple-retpoline > <SNIP> > 0000000000001040 <main>: > 1040: 48 83 ec 18 sub $0x18,%rsp > 1044: 48 8d 05 25 01 00 00 lea 0x125(%rip),%rax # 1170 <foo> > 104b: 48 89 44 24 08 mov %rax,0x8(%rsp) > 1050: 48 8b 44 24 08 mov 0x8(%rsp),%rax > 1055: e8 1f 01 00 00 callq 1179 <__x86_indirect_thunk_rax> > 105a: 48 8b 44 24 08 mov 0x8(%rsp),%rax > 105f: 48 83 c4 18 add $0x18,%rsp > 1063: e9 11 01 00 00 jmpq 1179 <__x86_indirect_thunk_rax> > <SNIP> > 0000000000001160 <bar>: > 1160: b8 ff ff ff ff mov $0xffffffff,%eax > 1165: c3 retq > <SNIP> > 0000000000001170 <foo>: > 1170: e8 eb ff ff ff callq 1160 <bar> > 1175: 83 c0 01 add $0x1,%eax > 1178: c3 retq > 0000000000001179 <__x86_indirect_thunk_rax>: > 1179: e8 07 00 00 00 callq 1185 <__x86_indirect_thunk_rax+0xc> > 117e: f3 90 pause > 1180: 0f ae e8 lfence > 1183: eb f9 jmp 117e <__x86_indirect_thunk_rax+0x5> > 1185: 48 89 04 24 mov %rax,(%rsp) > 1189: c3 retq > <SNIP> > $ perf record -o simple-retpoline.perf.data -e intel_pt/cyc/u ./simple-retpoline > [ perf record: Woken up 1 times to write data ] > [ perf record: Captured and wrote 0,017 MB simple-retpoline.perf.data ] > $ perf script -i simple-retpoline.perf.data --itrace=be -s ~/libexec/perf-core/scripts/python/export-to-sqlite.py simple-retpoline.db branches calls > 2019-01-08 14:03:37.851655 Creating database... > 2019-01-08 14:03:37.863256 Writing records... > 2019-01-08 14:03:38.069750 Adding indexes > 2019-01-08 14:03:38.078799 Done > $ ~/libexec/perf-core/scripts/python/exported-sql-viewer.py simple-retpoline.db > > Before: > > main > -> __x86_indirect_thunk_rax > -> __x86_indirect_thunk_rax > -> foo > -> bar > > After: > > main > -> foo > -> bar > > Signed-off-by: Adrian Hunter <adrian.hunter@intel.com> > --- > tools/perf/util/thread-stack.c | 112 ++++++++++++++++++++++++++++++++- > 1 file changed, 109 insertions(+), 3 deletions(-) > > diff --git a/tools/perf/util/thread-stack.c b/tools/perf/util/thread-stack.c > index 632c07a125ab..805e30836460 100644 > --- a/tools/perf/util/thread-stack.c > +++ b/tools/perf/util/thread-stack.c > @@ -20,6 +20,7 @@ > #include "thread.h" > #include "event.h" > #include "machine.h" > +#include "env.h" > #include "util.h" > #include "debug.h" > #include "symbol.h" > @@ -29,6 +30,19 @@ > > #define STACK_GROWTH 2048 > > +/* > + * State of retpoline detection. > + * > + * RETPOLINE_NONE: no retpoline detection > + * X86_RETPOLINE_POSSIBLE: x86 retpoline possible > + * X86_RETPOLINE_DETECTED: x86 retpoline detected > + */ > +enum retpoline_state_t { > + RETPOLINE_NONE, > + X86_RETPOLINE_POSSIBLE, > + X86_RETPOLINE_DETECTED, > +}; > + > /** > * struct thread_stack_entry - thread stack entry. > * @ret_addr: return address > @@ -64,6 +78,7 @@ struct thread_stack_entry { > * @crp: call/return processor > * @comm: current comm > * @arr_sz: size of array if this is the first element of an array > + * @rstate: used to detect retpolines > */ > struct thread_stack { > struct thread_stack_entry *stack; > @@ -76,6 +91,7 @@ struct thread_stack { > struct call_return_processor *crp; > struct comm *comm; > unsigned int arr_sz; > + enum retpoline_state_t rstate; > }; > > /* > @@ -115,10 +131,16 @@ static int thread_stack__init(struct thread_stack *ts, struct thread *thread, > if (err) > return err; > > - if (thread->mg && thread->mg->machine) > - ts->kernel_start = machine__kernel_start(thread->mg->machine); > - else > + if (thread->mg && thread->mg->machine) { > + struct machine *machine = thread->mg->machine; > + const char *arch = perf_env__arch(machine->env); > + > + ts->kernel_start = machine__kernel_start(machine); > + if (!strcmp(arch, "x86")) > + ts->rstate = X86_RETPOLINE_POSSIBLE; > + } else { > ts->kernel_start = 1ULL << 63; > + } > ts->crp = crp; > > return 0; > @@ -733,6 +755,70 @@ static int thread_stack__trace_end(struct thread_stack *ts, > false, true); > } > > +static bool is_x86_retpoline(const char *name) > +{ > + const char *p = strstr(name, "__x86_indirect_thunk_"); > + > + return p == name || !strcmp(name, "__indirect_thunk_start"); > +} > + > +/* > + * x86 retpoline functions pollute the call graph. This function removes them. > + * This does not handle function return thunks, nor is there any improvement > + * for the handling of inline thunks or extern thunks. > + */ > +static int thread_stack__x86_retpoline(struct thread_stack *ts, > + struct perf_sample *sample, > + struct addr_location *to_al) > +{ > + struct thread_stack_entry *tse = &ts->stack[ts->cnt - 1]; > + struct call_path_root *cpr = ts->crp->cpr; > + struct symbol *sym = tse->cp->sym; > + struct symbol *tsym = to_al->sym; > + struct call_path *cp; > + > + if (sym && sym->name && is_x86_retpoline(sym->name)) {
CC /tmp/build/perf/util/scripting-engines/trace-event-perl.o CC /tmp/build/perf/util/intel-pt.o CC /tmp/build/perf/util/intel-pt-decoder/intel-pt-log.o util/thread-stack.c:780:18: error: address of array 'sym->name' will always evaluate to 'true' [-Werror,-Wpointer-bool-conversion] if (sym && sym->name && is_x86_retpoline(sym->name)) { ~~ ~~~~~^~~~ 1 error generated. mv: cannot stat '/tmp/build/perf/util/.thread-stack.o.tmp': No such file or directory make[4]: *** [/git/linux/tools/build/Makefile.build:96: /tmp/build/perf/util/thread-stack.o] Error 1
[acme@quaco perf]$ pahole -C symbol ~/bin/perf struct symbol { struct rb_node rb_node; /* 0 24 */ u64 start; /* 24 8 */ u64 end; /* 32 8 */ u16 namelen; /* 40 2 */ u8 type:4; /* 42: 4 1 */ u8 binding:4; /* 42: 0 1 */ u8 idle:1; /* 43: 7 1 */ u8 ignore:1; /* 43: 6 1 */ u8 inlined:1; /* 43: 5 1 */
/* XXX 5 bits hole, try to pack */
u8 arch_sym; /* 44 1 */ _Bool annotate2; /* 45 1 */ char name[0]; /* 46 0 */
/* size: 48, cachelines: 1, members: 12 */ /* bit holes: 1, sum bit holes: 5 bits */ /* padding: 2 */ /* last cacheline: 48 bytes */ }; [acme@quaco perf]$
I'm removing that sym->name test.
> + /* > + * This is a x86 retpoline fn. It pollutes the call graph by > + * showing up everywhere there is an indirect branch, but does > + * not itself mean anything. Here the top-of-stack is removed, > + * by decrementing the stack count, and then further down, the > + * resulting top-of-stack is replaced with the actual target. > + * The result is that the retpoline functions will no longer > + * appear in the call graph. Note this only affects the call > + * graph, since all the original branches are left unchanged. > + */ > + ts->cnt -= 1; > + sym = ts->stack[ts->cnt - 2].cp->sym; > + if (sym && sym == tsym && to_al->addr != tsym->start) { > + /* > + * Target is back to the middle of the symbol we came > + * from so assume it is an indirect jmp and forget it > + * altogether. > + */ > + ts->cnt -= 1; > + return 0; > + } > + } else if (sym && sym == tsym) { > + /* > + * Target is back to the symbol we came from so assume it is an > + * indirect jmp and forget it altogether. > + */ > + ts->cnt -= 1; > + return 0; > + } > + > + cp = call_path__findnew(cpr, ts->stack[ts->cnt - 2].cp, tsym, > + sample->addr, ts->kernel_start); > + if (!cp) > + return -ENOMEM; > + > + /* Replace the top-of-stack with the actual target */ > + ts->stack[ts->cnt - 1].cp = cp; > + > + return 0; > +} > + > int thread_stack__process(struct thread *thread, struct comm *comm, > struct perf_sample *sample, > struct addr_location *from_al, > @@ -740,6 +826,7 @@ int thread_stack__process(struct thread *thread, struct comm *comm, > struct call_return_processor *crp) > { > struct thread_stack *ts = thread__stack(thread, sample->cpu); > + enum retpoline_state_t rstate; > int err = 0; > > if (ts && !ts->crp) { > @@ -755,6 +842,10 @@ int thread_stack__process(struct thread *thread, struct comm *comm, > ts->comm = comm; > } > > + rstate = ts->rstate; > + if (rstate == X86_RETPOLINE_DETECTED) > + ts->rstate = X86_RETPOLINE_POSSIBLE; > + > /* Flush stack on exec */ > if (ts->comm != comm && thread->pid_ == thread->tid) { > err = __thread_stack__flush(thread, ts); > @@ -791,10 +882,25 @@ int thread_stack__process(struct thread *thread, struct comm *comm, > ts->kernel_start); > err = thread_stack__push_cp(ts, ret_addr, sample->time, ref, > cp, false, trace_end); > + > + /* > + * A call to the same symbol but not the start of the symbol, > + * may be the start of a x86 retpoline. > + */ > + if (!err && rstate == X86_RETPOLINE_POSSIBLE && to_al->sym && > + from_al->sym == to_al->sym && > + to_al->addr != to_al->sym->start) > + ts->rstate = X86_RETPOLINE_DETECTED; > + > } else if (sample->flags & PERF_IP_FLAG_RETURN) { > if (!sample->ip || !sample->addr) > return 0; > > + /* x86 retpoline 'return' doesn't match the stack */ > + if (rstate == X86_RETPOLINE_DETECTED && ts->cnt > 2 && > + ts->stack[ts->cnt - 1].ret_addr != sample->addr) > + return thread_stack__x86_retpoline(ts, sample, to_al); > + > err = thread_stack__pop_cp(thread, ts, sample->addr, > sample->time, ref, from_al->sym); > if (err) { > -- > 2.17.1
--
- Arnaldo
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