perf script: Fix segfault when printing callchains
This fixes a bug caused by an unitialized callchain cursor. The crash frist appeared in: 6f736735 ("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: NChris Phlipot <cphlipot0@gmail.com> Tested-by: NArnaldo Carvalho de Melo <acme@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Fixes: 6f736735 ("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.comSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>
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