FYI, I applied this patch to the qemu build that zig uses to run non-native tests ( https://github.com/ziglang/qemu-static/blob/master/patch/mremap-underflow.diff )
After applying it, my new code that calls mremap now passes, whereas before the fix I was getting a segfault. On Sat, May 2, 2020 at 10:12 AM Jonathan Marler <johnnymar...@gmail.com> wrote: > Fixes: https://bugs.launchpad.net/bugs/1876373 > > This code path in mmap occurs when a page size is decreased with mremap. > When a section of pages is shrunk, qemu calls mmap_reserve on the pages > that were released. However, it has the diff operation reversed, > subtracting the larger old_size from the smaller new_size. Instead, it > should be subtracting the smaller new_size from the larger old_size. You > can also see in the previous line of the change that this mmap_reserve call > only occurs when old_size > new_size. > > Signed-off-by: Jonathan Marler <johnnymar...@gmail.com> > --- > linux-user/mmap.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/linux-user/mmap.c b/linux-user/mmap.c > index e378033797..caab62909e 100644 > --- a/linux-user/mmap.c > +++ b/linux-user/mmap.c > @@ -708,7 +708,7 @@ abi_long target_mremap(abi_ulong old_addr, abi_ulong > old_size, > if (prot == 0) { > host_addr = mremap(g2h(old_addr), old_size, new_size, flags); > if (host_addr != MAP_FAILED && reserved_va && old_size > > new_size) { > - mmap_reserve(old_addr + old_size, new_size - old_size); > + mmap_reserve(old_addr + old_size, old_size - new_size); > } > } else { > errno = ENOMEM; > -- > 2.23.1 > >
