diff options
| -rw-r--r-- | src/client/linux/minidump_writer/linux_dumper.cc | 172 |
1 files changed, 172 insertions, 0 deletions
diff --git a/src/client/linux/minidump_writer/linux_dumper.cc b/src/client/linux/minidump_writer/linux_dumper.cc index 64b967b7..a95ec7ec 100644 --- a/src/client/linux/minidump_writer/linux_dumper.cc +++ b/src/client/linux/minidump_writer/linux_dumper.cc @@ -84,6 +84,173 @@ inline static bool IsMappedFileOpenUnsafe( namespace google_breakpad { +#if defined(__CHROMEOS__) + +namespace { + +// Recover memory mappings before writing dump on ChromeOS +// +// On Linux, breakpad relies on /proc/[pid]/maps to associate symbols from +// addresses. ChromeOS' hugepage implementation replaces some segments with +// anonymous private pages, which is a restriction of current implementation +// in Linux kernel at the time of writing. Thus, breakpad can no longer +// symbolize addresses from those text segments replaced with hugepages. +// +// This postprocess tries to recover the mappings. Because hugepages are always +// inserted in between some .text sections, it tries to infer the names and +// offsets of the segments, by looking at segments immediately precede and +// succeed them. +// +// For example, a text segment before hugepage optimization +// 02001000-03002000 r-xp /opt/google/chrome/chrome +// +// can be broken into +// 02001000-02200000 r-xp /opt/google/chrome/chrome +// 02200000-03000000 r-xp +// 03000000-03002000 r-xp /opt/google/chrome/chrome +// +// For more details, see: +// crbug.com/628040 ChromeOS' use of hugepages confuses crash symbolization + +// Copied from CrOS' hugepage implementation, which is unlikely to change. +// The hugepage size is 2M. +const unsigned int kHpageShift = 21; +const size_t kHpageSize = (1 << kHpageShift); +const size_t kHpageMask = (~(kHpageSize - 1)); + +// Find and merge anonymous r-xp segments with surrounding named segments. +// There are two cases: + +// Case 1: curr, next +// curr is anonymous +// curr is r-xp +// curr.size >= 2M +// curr.size is a multiple of 2M. +// next is backed by some file. +// curr and next are contiguous. +// offset(next) == sizeof(curr) +void TryRecoverMappings(MappingInfo *curr, MappingInfo *next) { + // Merged segments are marked with size = 0. + if (curr->size == 0 || next->size == 0) + return; + + if (curr->size >= kHpageSize && + curr->exec && + (curr->size & kHpageMask) == curr->size && + (curr->start_addr & kHpageMask) == curr->start_addr && + curr->name[0] == '\0' && + next->name[0] != '\0' && + curr->start_addr + curr->size == next->start_addr && + curr->size == next->offset) { + + // matched + my_strlcpy(curr->name, next->name, NAME_MAX); + if (next->exec) { + // (curr, next) + curr->size += next->size; + next->size = 0; + } + } +} + +// Case 2: prev, curr, next +// curr is anonymous +// curr is r-xp +// curr.size >= 2M +// curr.size is a multiple of 2M. +// next and prev are backed by the same file. +// prev, curr and next are contiguous. +// offset(next) == offset(prev) + sizeof(prev) + sizeof(curr) +void TryRecoverMappings(MappingInfo *prev, MappingInfo *curr, + MappingInfo *next) { + // Merged segments are marked with size = 0. + if (prev->size == 0 || curr->size == 0 || next->size == 0) + return; + + if (curr->size >= kHpageSize && + curr->exec && + (curr->size & kHpageMask) == curr->size && + (curr->start_addr & kHpageMask) == curr->start_addr && + curr->name[0] == '\0' && + next->name[0] != '\0' && + curr->start_addr + curr->size == next->start_addr && + prev->start_addr + prev->size == curr->start_addr && + my_strncmp(prev->name, next->name, NAME_MAX) == 0 && + next->offset == prev->offset + prev->size + curr->size) { + + // matched + my_strlcpy(curr->name, prev->name, NAME_MAX); + if (prev->exec) { + curr->offset = prev->offset; + curr->start_addr = prev->start_addr; + if (next->exec) { + // (prev, curr, next) + curr->size += prev->size + next->size; + prev->size = 0; + next->size = 0; + } else { + // (prev, curr), next + curr->size += prev->size; + prev->size = 0; + } + } else { + curr->offset = prev->offset + prev->size; + if (next->exec) { + // prev, (curr, next) + curr->size += next->size; + next->size = 0; + } else { + // prev, curr, next + } + } + } +} + +// mappings_ is sorted excepted for the first entry. +// This function tries to merge segemnts into the first entry, +// then check for other sorted entries. +// See LinuxDumper::EnumerateMappings(). +void CrOSPostProcessMappings(wasteful_vector<MappingInfo*>& mappings) { + // Find the candidate "next" to first segment, which is the only one that + // could be out-of-order. + size_t l = 1; + size_t r = mappings.size(); + size_t next = mappings.size(); + while (l < r) { + int m = (l + r) / 2; + if (mappings[m]->start_addr > mappings[0]->start_addr) + r = next = m; + else + l = m + 1; + } + + // Try to merge segments into the first. + if (next < mappings.size()) { + TryRecoverMappings(mappings[0], mappings[next]); + if (next - 1 > 0) + TryRecoverMappings(mappings[next - 1], mappings[0], mappings[next]); + } + + // Iterate through normal, sorted cases. + // Normal case 1. + for (size_t i = 1; i < mappings.size() - 1; i++) + TryRecoverMappings(mappings[i], mappings[i + 1]); + + // Normal case 2. + for (size_t i = 1; i < mappings.size() - 2; i++) + TryRecoverMappings(mappings[i], mappings[i + 1], mappings[i + 2]); + + // Collect merged (size == 0) segments. + size_t f, e; + for (f = e = 0; e < mappings.size(); e++) + if (mappings[e]->size > 0) + mappings[f++] = mappings[e]; + mappings.resize(f); +} + +} // namespace +#endif // __CHROMEOS__ + // All interesting auvx entry types are below AT_SYSINFO_EHDR #define AT_MAX AT_SYSINFO_EHDR @@ -113,6 +280,11 @@ bool LinuxDumper::LateInit() { #if defined(__ANDROID__) LatePostprocessMappings(); #endif + +#if defined(__CHROMEOS__) + CrOSPostProcessMappings(mappings_); +#endif + return true; } |