Chrome (and therefore mini_chromium) has always built with
_FILE_OFFSET_BITS=64, which is intended to enable a 64-bit off_t even
for 32-bit programs. However, support was never present in Android with
NDK traditional headers.
The new NDK unified headers do recognize _FILE_OFFSET_BITS=64 and enable
a 64-bit off_t, along with corresponding functions and system call
wrappers. However, no mmap() wrapper supporting a 64-bit off_t for
32-bit programs was available prior to API 21 (Android 5.0 “Lollipop”),
so when targeting older API levels, NDK headers do not proivde an mmap()
declaration. This avoids silently truncating 64-bit off_t values to 32
bits. NDK r15b did make such an mmap() wrapper available
(https://android.googlesource.com/platform/bionic/+/785b249df024), and
it did silently truncate, but this was removed for r15c
(https://android.googlesource.com/platform/bionic/+/00fedf587917).
How should this work if _FILE_OFFSET_BITS is set to 64 and recent
unified headers are in use?
The strategy employed here is to provide an mmap() declaration in
compat, with a 64-bit off_t. That mmap() will call to Bionic’s mmap64()
wrapper if available (it’s available since Android 5.0 “Lollipop”). If
unavailable, it implements the same logic that mmap64() does directly,
which predominantly involves calling the __mmap2() system call. Bionic
has always provided wrappers for __mmap2().
Additional reading:
https://android.googlesource.com/platform/bionic/+/0bfcbaf4d069/docs/32-bit-abi.md#is-32_bit-1https://github.com/android-ndk/ndk/issues/442
Bug: crashpad:30
Change-Id: I98c10e2eda773cb6f3d9eb8db9b8bfde43c885e7
Reviewed-on: https://chromium-review.googlesource.com/705674
Reviewed-by: Joshua Peraza <jperaza@chromium.org>
ProcessReader is responsible for collecting information needed to build
a snapshot of the target process, independent of the Snapshot
interface. This CL includes implementation and tests for collecting
thread information, but does not yet collect module information.
Bug: crashpad:30
Change-Id: I911f155c953129a5fa8c031e923c0de2bd740ce0
Reviewed-on: https://chromium-review.googlesource.com/488162
Reviewed-by: Mark Mentovai <mark@chromium.org>
