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Merge exec and non-exec segments while merging executable bit.

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The bfd and gold linkers create segments like this: r/x, r/w where
the r/x segment covers the start of the ELF file.

lld's segments look like this: r, r/x, r/w where the r segment covers
the start of the ELF file.

So we cannot rely on the location of the r/x to tell where the start
of the ELF is. But we can still rely on the r and r/x mappings being
adjacent. So what we do is when we see an r segment followed by an r/x,
merge the r into the r/x and claim that it is executable. This way,
the minidump writer will continue to see a single executable segment
covering the entire executable.

Testing: "make check" passes when breakpad is compiled with
lld compiled from trunk (requires bug fix from LLVM r303689).

Also patched change into chromium and tested these builds:

$ cat args.gn
is_chrome_branded = true
is_debug = false
is_official_build = true
use_lld = true
allow_posix_link_time_opt = false
is_cfi = false

$ cat args.gn
target_os = "android"
target_cpu = "arm"
is_debug = false
is_official_build = true
is_chrome_branded = true

With both builds breakpad_unittests passes and
chrome/chrome_modern_public_apk create good minidumps after navigating
to chrome://inducebrowsercrashforrealz (checked that minidump contains
stack trace entry for content::HandleDebugURL).

Bug: chromium:716484
Change-Id: Ib6ed3a8420b83acf4a5962843930fb006734cb95
Reviewed-on: https://chromium-review.googlesource.com/513610
Reviewed-by: Primiano Tucci <primiano@chromium.org>
This commit is contained in:
Peter Collingbourne 2017-05-26 09:32:08 -07:00 committed by Primiano Tucci
parent 08bea455d4
commit 94b6309aec
1 changed files with 8 additions and 3 deletions
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11
src/client/linux/minidump_writer/linux_dumper.cc
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@ -520,15 +520,20 @@ bool LinuxDumper::EnumerateMappings() {
name = kLinuxGateLibraryName;
offset = 0;
}
// Merge adjacent mappings with the same name into one module,
// assuming they're a single library mapped by the dynamic linker
// Merge adjacent mappings into one module, assuming they're a single
// library mapped by the dynamic linker. Do this only if their name
// matches and either they have the same +x protection flag, or if the
// previous mapping is not executable and the new one is, to handle
// lld's output (see crbug.com/716484).
if (name && !mappings_.empty()) {
MappingInfo* module = mappings_.back();
if ((start_addr == module->start_addr + module->size) &&
(my_strlen(name) == my_strlen(module->name)) &&
(my_strncmp(name, module->name, my_strlen(name)) == 0) &&
(exec == module->exec)) {
((exec == module->exec) || (!module->exec && exec))) {
module->system_mapping_info.end_addr = end_addr;
module->size = end_addr - module->start_addr;
module->exec |= exec;
line_reader->PopLine(line_len);
continue;
}