From e557b674a9470dae99916be6105e6780b3a072ca Mon Sep 17 00:00:00 2001 From: Chris Phlipot Date: Tue, 19 Apr 2016 19:32:11 -0700 Subject: [PATCH] perf script: Fix segfault when printing callchains This fixes a bug caused by an unitialized callchain cursor. The crash frist appeared in: 6f736735e30f ("perf evsel: Require that callchains be resolved before calling fprintf_{sym,callchain}") The callchain cursor is a struct that contains pointers, that when uninitialized will cause unpredictable behavior (usually a crash) when trying to append to the callchain. The existing implementation has the following issues: 1. The callchain cursor used is not initialized, resulting in unpredictable behavior when used. 2. The cursor is declared on the stack. Even if it is properly initalized, the implmentation will leak memory when the function returns, since all the references to the callchain_nodes allocated by callchain_cursor_append will be lost when the cursor goes out of scope. 3. Storing the cursor on the stack is inefficient. Even if memory is properly freed when it goes out of scope, a performance penalty will be incurred due to reallocation of callchain nodes. callchain_cursor_append is designed to avoid these reallocations when an existing cursor is reused. This patch fixes the crash by replacing cursor_callchain with a reference to the global callchain_cursor which also resolves all 3 issues mentioned above. How to reproduce the crash: $ perf record --call-graph=dwarf stress -t 1 -c 1 $ perf script > /dev/null Segfault Signed-off-by: Chris Phlipot Tested-by: Arnaldo Carvalho de Melo Cc: Peter Zijlstra Fixes: 6f736735e30f ("perf evsel: Require that callchains be resolved before calling fprintf_{sym,callchain}") Link: http://lkml.kernel.org/r/1461119531-2529-1-git-send-email-cphlipot0@gmail.com Signed-off-by: Arnaldo Carvalho de Melo --- tools/perf/builtin-script.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/tools/perf/builtin-script.c b/tools/perf/builtin-script.c index 5099740aa50b..f43b0c6f88f4 100644 --- a/tools/perf/builtin-script.c +++ b/tools/perf/builtin-script.c @@ -570,12 +570,12 @@ static void print_sample_bts(struct perf_sample *sample, /* print branch_from information */ if (PRINT_FIELD(IP)) { unsigned int print_opts = output[attr->type].print_ip_opts; - struct callchain_cursor *cursor = NULL, cursor_callchain; + struct callchain_cursor *cursor = NULL; if (symbol_conf.use_callchain && sample->callchain && - thread__resolve_callchain(al->thread, &cursor_callchain, evsel, + thread__resolve_callchain(al->thread, &callchain_cursor, evsel, sample, NULL, NULL, scripting_max_stack) == 0) - cursor = &cursor_callchain; + cursor = &callchain_cursor; if (cursor == NULL) { putchar(' '); @@ -789,12 +789,12 @@ static void process_event(struct perf_script *script, printf("%16" PRIu64, sample->weight); if (PRINT_FIELD(IP)) { - struct callchain_cursor *cursor = NULL, cursor_callchain; + struct callchain_cursor *cursor = NULL; if (symbol_conf.use_callchain && sample->callchain && - thread__resolve_callchain(al->thread, &cursor_callchain, evsel, + thread__resolve_callchain(al->thread, &callchain_cursor, evsel, sample, NULL, NULL, scripting_max_stack) == 0) - cursor = &cursor_callchain; + cursor = &callchain_cursor; putchar(cursor ? '\n' : ' '); sample__fprintf_sym(sample, al, 0, output[attr->type].print_ip_opts, cursor, stdout);