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[Qemu-stable] [PATCH] linux-user: write(fd, NULL, 0) parity with linux's
From: |
Tony Garnock-Jones |
Subject: |
[Qemu-stable] [PATCH] linux-user: write(fd, NULL, 0) parity with linux's treatment of same |
Date: |
Sat, 8 Sep 2018 19:22:05 +0100 |
User-agent: |
Mutt/1.10.1 (2018-07-13) |
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 <address@hidden>
---
linux-user/syscall.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 850b72a0c7..8f46540534 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -8168,6 +8168,9 @@ static abi_long do_syscall1(void *cpu_env, int num,
abi_long arg1,
}
return ret;
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)))
return -TARGET_EFAULT;
if (fd_trans_target_to_host_data(arg1)) {
--
2.18.0
[University of Glasgow: The Times Scottish University of the Year 2018]
- [Qemu-stable] [PATCH] linux-user: write(fd, NULL, 0) parity with linux's treatment of same,
Tony Garnock-Jones <=