On Jul 20 09:34, Ken Brown via Cygwin-patches wrote: > Commit 605bdcd410384dda6db66b9b8cd19e863702e1bb enabled mapping beyond > EOF in 64 bit environments. But the variable 'orig_len' did not get > rounded up to a multiple of 64K. This rounding was done on 32 bit > only. Fix this by rounding up orig_len on 64 bit, in the same place > where 'len' is rounded up. > > One consequence of this bug is that orig_len could be slightly smaller > than len. Since these are both unsigned values, the statement > 'orig_len -= len' would then cause orig_len to be huge, and mmap would > fail with errno EFBIG. > > I observed this failure while debugging the problem reported in > > https://sourceware.org/pipermail/cygwin/2020-July/245557.html. > > The failure can be seen by running the test case in that report under > gdb or strace. > --- > winsup/cygwin/mmap.cc | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/winsup/cygwin/mmap.cc b/winsup/cygwin/mmap.cc > index feb9e5d0e..a08d00f83 100644 > --- a/winsup/cygwin/mmap.cc > +++ b/winsup/cygwin/mmap.cc > @@ -1144,6 +1144,7 @@ go_ahead: > ends in, but there's nothing at all we can do about that. */ > #ifdef __x86_64__ > len = roundup2 (len, wincap.allocation_granularity ()); > + orig_len = roundup2 (orig_len, wincap.allocation_granularity ());
Wouldn't it be simpler to just check for - if (orig_len - len) + if (orig_len > len) in the code following this #if/#else/#endif snippet? Thanks, Corinna -- Corinna Vinschen Cygwin Maintainer