diff options
| author | Corinna Vinschen <corinna@vinschen.de> | 2017-12-10 16:11:03 +0300 |
|---|---|---|
| committer | Corinna Vinschen <corinna@vinschen.de> | 2017-12-10 16:14:24 +0300 |
| commit | 67a657cb1d41e6ae90e9fdeba9e69fff09a2ea06 (patch) | |
| tree | 1a89c4af79fa80ef2717f94607383a4663527b86 | |
| parent | c6f14b3c81f5a40317452625ef8d56c2612fe776 (diff) | |
cygwin: mmap: fix a fork failure with private, anonymous mappings
Rounddown incoming addr on a page boundary. Without this, we may end
up with a fork error for private, anonymous maps. The reason is, we
use VirtualAlloc in this case which will potentially overcommit if
addr is not on a page boundary. This isn't taken into account in
bookkeeping, but fixup_mmaps_after_fork will eventually stumble over
this when trying to reproduce the copy-on-write pages: VirtualQuery
returns a region reaching beyond the supposedly allocated address
range and from there it goes downhill.
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
| -rw-r--r-- | winsup/cygwin/mmap.cc | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/winsup/cygwin/mmap.cc b/winsup/cygwin/mmap.cc index 4218466f0..d4eddfcb4 100644 --- a/winsup/cygwin/mmap.cc +++ b/winsup/cygwin/mmap.cc @@ -917,6 +917,13 @@ mmap64 (void *addr, size_t len, int prot, int flags, int fd, off_t off) goto out; } + /* POSIX: When MAP_FIXED is not set, the implementation uses addr in an + implementation-defined manner to arrive at pa [the return address]. + Given that we refuse addr if it's not exactly at a page boundary, we + can just make sure addr does so indiscriminately. Just round down + to the next lower page boundary. */ + addr = (void *) rounddown ((uintptr_t) addr, pagesize); + if (!anonymous (flags) && fd != -1) { /* Ensure that fd is open */ |