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[Qemu-stable] [PATCH 79/97] linux-user: write(fd, NULL, 0) parity with l
From: |
Michael Roth |
Subject: |
[Qemu-stable] [PATCH 79/97] linux-user: write(fd, NULL, 0) parity with linux's treatment of same |
Date: |
Mon, 1 Apr 2019 15:59:53 -0500 |
From: Tony Garnock-Jones <address@hidden>
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>
Reviewed-by: Philippe Mathieu-Daudé <address@hidden>
Reviewed-by: Laurent Vivier <address@hidden>
Message-Id: <address@hidden>
Signed-off-by: Laurent Vivier <address@hidden>
(cherry picked from commit 58cfa6c2e6eb51b23cc98f81d16136b3ca929b31)
Signed-off-by: Michael Roth <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 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
- [Qemu-stable] [PATCH 04/97] target/arm: Fix typo in helper_sve_movz_d, (continued)
- [Qemu-stable] [PATCH 04/97] target/arm: Fix typo in helper_sve_movz_d, Michael Roth, 2019/04/01
- [Qemu-stable] [PATCH 64/97] qemu-img: Fix leak, Michael Roth, 2019/04/01
- [Qemu-stable] [PATCH 66/97] vfio-helpers: Fix qemu_vfio_open_pci() crash, Michael Roth, 2019/04/01
- [Qemu-stable] [PATCH 69/97] nbd/server: Advertise all contexts in response to bare LIST, Michael Roth, 2019/04/01
- [Qemu-stable] [PATCH 70/97] nbd/client: Make x-dirty-bitmap more reliable, Michael Roth, 2019/04/01
- [Qemu-stable] [PATCH 71/97] nbd/client: Send NBD_CMD_DISC if open fails after connect, Michael Roth, 2019/04/01
- [Qemu-stable] [PATCH 73/97] iotests: simple mirror test with kvm on 1G image, Michael Roth, 2019/04/01
- [Qemu-stable] [PATCH 68/97] i2c: Add a length check to the SMBus write handling, Michael Roth, 2019/04/01
- [Qemu-stable] [PATCH 76/97] pcie: set link state inactive/active after hot unplug/plug, Michael Roth, 2019/04/01
- [Qemu-stable] [PATCH 75/97] Changes requirement for "vsubsbs" instruction, Michael Roth, 2019/04/01
- [Qemu-stable] [PATCH 79/97] linux-user: write(fd, NULL, 0) parity with linux's treatment of same,
Michael Roth <=
- [Qemu-stable] [PATCH 80/97] linux-user: make pwrite64/pread64(fd, NULL, 0, offset) return 0, Michael Roth, 2019/04/01
- [Qemu-stable] [PATCH 82/97] exec.c: Don't reallocate IOMMUNotifiers that are in use, Michael Roth, 2019/04/01
- [Qemu-stable] [PATCH 86/97] tpm: Make sure the locality received from backend is valid, Michael Roth, 2019/04/01
- [Qemu-stable] [PATCH 07/97] target/arm: Fix offset for LD1R instructions, Michael Roth, 2019/04/01
- [Qemu-stable] [PATCH 85/97] tpm: Make sure new locality passed to tpm_tis_prep_abort() is valid, Michael Roth, 2019/04/01
- [Qemu-stable] [PATCH 77/97] pc:piix4: Update smbus I/O space after a migration, Michael Roth, 2019/04/01
- [Qemu-stable] [PATCH 96/97] usb-mtp: outlaw slashes in filenames, Michael Roth, 2019/04/01
- [Qemu-stable] [PATCH 95/97] 9p: fix QEMU crash when renaming files, Michael Roth, 2019/04/01
- [Qemu-stable] [PATCH 94/97] nvme: fix out-of-bounds access to the CMB, Michael Roth, 2019/04/01
- [Qemu-stable] [PATCH 32/97] vhost: fix invalid downcast, Michael Roth, 2019/04/01