From: Tony Garnock-Jones <tony.garnock-jo...@glasgow.ac.uk> Bring linux-user write(2) handling into line with linux for the case of a 0-byte write with a NULL buffer. Based on a patch originally written by Zhuowei Zhang.
Addresses https://bugs.launchpad.net/qemu/+bug/1716292. >From Zhuowei Zhang's patch >(https://lists.gnu.org/archive/html/qemu-devel/2017-09/msg08073.html): Linux returns success for the special case of calling write with a zero-length NULL buffer: compiling and running int main() { ssize_t ret = write(STDOUT_FILENO, NULL, 0); fprintf(stderr, "write returned %ld\n", ret); return 0; } gives "write returned 0" when run directly, but "write returned -1" in QEMU. This commit checks for this situation and returns success if found. Subsequent discussion raised the following questions (and my answers): - Q. Should TARGET_NR_read pass through to safe_read in this situation too? A. I'm wary of changing unrelated code to the specific problem I'm addressing. TARGET_NR_read is already consistent with Linux for this case. - Q. Do pread64/pwrite64 need to be changed similarly? A. Experiment suggests not: both linux and linux-user yield -1 for NULL 0-length reads/writes. Signed-off-by: Tony Garnock-Jones <tonygarnockjo...@gmail.com> Reviewed-by: Philippe Mathieu-Daudé <f4...@amsat.org> Reviewed-by: Laurent Vivier <laur...@vivier.eu> Message-Id: <20180908182205.gb...@mornington.dcs.gla.ac.uk> Signed-off-by: Laurent Vivier <laur...@vivier.eu> (cherry picked from commit 58cfa6c2e6eb51b23cc98f81d16136b3ca929b31) Signed-off-by: Michael Roth <mdr...@linux.vnet.ibm.com> --- linux-user/syscall.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/linux-user/syscall.c b/linux-user/syscall.c index 5a4af76c03..1477509cf2 100644 --- a/linux-user/syscall.c +++ b/linux-user/syscall.c @@ -8077,6 +8077,9 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1, } break; case TARGET_NR_write: + if (arg2 == 0 && arg3 == 0) { + return get_errno(safe_write(arg1, 0, 0)); + } if (!(p = lock_user(VERIFY_READ, arg2, arg3, 1))) goto efault; if (fd_trans_target_to_host_data(arg1)) { -- 2.17.1
