Comment 0 for bug 1716292

QEMU version: latest master (fcea73709b966a7ded9efa7b106ea50c7fe9025c)
OS version: Ubuntu 14.04.3
Configured with: ../configure --target-list=x86_64-linux-user

QEMU Linux usermode emulation does not handle write() syscalls with zero length and a null pointer correctly: on Linux this returns 0, but in emulation this returns -1.

I ran into this while using an aarch64 abuild-tar from Alpine Linux in user-mode emulation; here's the minimized reproduction test case:

zhuowei@zhuowei-tablet:/tmp$ cat writezerobytes.c
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>

int main() {
 ssize_t ret = write(STDOUT_FILENO, NULL, 0);
 fprintf(stderr, "write returned %ld\n", ret);
 return 0;
}
zhuowei@zhuowei-tablet:/tmp$ gcc -o writezerobytes writezerobytes.c
zhuowei@zhuowei-tablet:/tmp$ uname -a
Linux zhuowei-tablet 3.13.0-129-generic #178-Ubuntu SMP Fri Aug 11 12:48:20 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux
zhuowei@zhuowei-tablet:/tmp$ ./writezerobytes
write returned 0
zhuowei@zhuowei-tablet:/tmp$ /media/zhuowei/redhd/docs/repos/qemu/build4/x86_64-linux-user/qemu-x86_64 ./writezerobytes
write returned -1
zhuowei@zhuowei-tablet:/tmp$ /media/zhuowei/redhd/docs/repos/qemu/build4/x86_64-linux-user/qemu-x86_64 --version
qemu-x86_64 version 2.10.50 (v2.10.0-471-gfcea737-dirty)
Copyright (c) 2003-2017 Fabrice Bellard and the QEMU Project developers