| // Copyright 2005 - 2007 Google Inc. |
| // All rights reserved. |
| // |
| // Author: Arun Sharma |
| // |
| // Produce stack trace using libunwind |
| |
| extern "C" { |
| #include <libunwind.h> |
| } |
| #include "base/stacktrace.h" |
| #include "base/raw_logging.h" |
| #include "base/spinlock.h" |
| |
| _START_GOOGLE_NAMESPACE_ |
| |
| // Sometimes, we can try to get a stack trace from within a stack |
| // trace, because libunwind can call mmap/sbrk (maybe indirectly via |
| // malloc), and that mmap gets trapped and causes a stack-trace |
| // request. If were to try to honor that recursive request, we'd end |
| // up with infinite recursion or deadlock. Luckily, it's safe to |
| // ignore those subsequent traces. In such cases, we return 0 to |
| // indicate the situation. |
| static SpinLock libunwind_lock(SpinLock::LINKER_INITIALIZED); |
| |
| // If you change this function, also change GetStackFrames below. |
| int GetStackTrace(void** result, int max_depth, int skip_count) { |
| void *ip; |
| int n = 0; |
| unw_cursor_t cursor; |
| unw_context_t uc; |
| |
| if (!libunwind_lock.TryLock()) { |
| return 0; |
| } |
| |
| unw_getcontext(&uc); |
| RAW_CHECK(unw_init_local(&cursor, &uc) >= 0, "unw_init_local failed"); |
| skip_count++; // Do not include the "GetStackTrace" frame |
| |
| while (n < max_depth) { |
| int ret = unw_get_reg(&cursor, UNW_REG_IP, (unw_word_t *) &ip); |
| if (ret < 0) |
| break; |
| if (skip_count > 0) { |
| skip_count--; |
| } else { |
| result[n++] = ip; |
| } |
| ret = unw_step(&cursor); |
| if (ret <= 0) |
| break; |
| } |
| |
| libunwind_lock.Unlock(); |
| return n; |
| } |
| |
| // If you change this function, also change GetStackTrace above: |
| // |
| // This GetStackFrames routine shares a lot of code with GetStackTrace |
| // above. This code could have been refactored into a common routine, |
| // and then both GetStackTrace/GetStackFrames could call that routine. |
| // There are two problems with that: |
| // |
| // (1) The performance of the refactored-code suffers substantially - the |
| // refactored needs to be able to record the stack trace when called |
| // from GetStackTrace, and both the stack trace and stack frame sizes, |
| // when called from GetStackFrames - this introduces enough new |
| // conditionals that GetStackTrace performance can degrade by as much |
| // as 50%. |
| // |
| // (2) Whether the refactored routine gets inlined into GetStackTrace and |
| // GetStackFrames depends on the compiler, and we can't guarantee the |
| // behavior either-way, even with "__attribute__ ((always_inline))" |
| // or "__attribute__ ((noinline))". But we need this guarantee or the |
| // frame counts may be off by one. |
| // |
| // Both (1) and (2) can be addressed without this code duplication, by |
| // clever use of template functions, and by defining GetStackTrace and |
| // GetStackFrames as macros that expand to these template functions. |
| // However, this approach comes with its own set of problems - namely, |
| // macros and preprocessor trouble - for example, if GetStackTrace |
| // and/or GetStackFrames is ever defined as a member functions in some |
| // class, we are in trouble. |
| int GetStackFrames(void** pcs, int* sizes, int max_depth, int skip_count) { |
| void *ip; |
| int n = 0; |
| unw_cursor_t cursor; |
| unw_context_t uc; |
| unw_word_t sp = 0, next_sp = 0; |
| |
| if (!libunwind_lock.TryLock()) { |
| return 0; |
| } |
| |
| unw_getcontext(&uc); |
| RAW_CHECK(unw_init_local(&cursor, &uc) >= 0, "unw_init_local failed"); |
| skip_count++; // Do not include the "GetStackFrames" frame |
| |
| while (skip_count--) { |
| if (unw_step(&cursor) <= 0 || |
| unw_get_reg(&cursor, UNW_REG_SP, &next_sp) < 0) { |
| goto out; |
| } |
| } |
| while (n < max_depth) { |
| sp = next_sp; |
| if (unw_get_reg(&cursor, UNW_REG_IP, (unw_word_t *) &ip) < 0) |
| break; |
| if (unw_step(&cursor) <= 0 || |
| unw_get_reg(&cursor, UNW_REG_SP, &next_sp)) { |
| // We couldn't step any further (possibly because we reached _start). |
| // Provide the last good PC we've got, and get out. |
| sizes[n] = 0; |
| pcs[n++] = ip; |
| break; |
| } |
| sizes[n] = next_sp - sp; |
| pcs[n++] = ip; |
| } |
| out: |
| libunwind_lock.Unlock(); |
| return n; |
| } |
| |
| _END_GOOGLE_NAMESPACE_ |