[Qemu-devel] [PULL 6/9] linux-user: don't short-circuit read with zero length

[Laurent Vivier <laurent@vivier.eu>]

From: Andreas Schwab <schwab@suse.de>

A zero-length read still needs to do the usual checks, thus it may return
errors like EBADF.  This makes the read syscall emulation consistent with
the pread64 syscall emulation.

Signed-off-by: Andreas Schwab <schwab@suse.de>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <mvm5zsxz2we.fsf@suse.de>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
---
 linux-user/syscall.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 5f72209debc9..9f7eb7d7a896 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -7009,8 +7009,8 @@ static abi_long do_syscall1(void *cpu_env, int num, abi_long arg1,
         _exit(arg1);
         return 0; /* avoid warning */
     case TARGET_NR_read:
-        if (arg3 == 0) {
-            return 0;
+        if (arg2 == 0 && arg3 == 0) {
+            return get_errno(safe_read(arg1, 0, 0));
         } else {
             if (!(p = lock_user(VERIFY_WRITE, arg2, arg3, 0)))
                 return -TARGET_EFAULT;
-- 
2.20.1