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[Qemu-devel] [PATCH v2 15/19] linux-user: Use safe_syscall for kill, tki

From: Peter Maydell
Subject: [Qemu-devel] [PATCH v2 15/19] linux-user: Use safe_syscall for kill, tkill and tgkill syscalls
Date: Fri, 27 May 2016 15:51:57 +0100

Use the safe_syscall wrapper for the kill, tkill and tgkill syscalls.
Without this, if a thread sent a SIGKILL to itself it could kill the
thread before we had a chance to process a signal that arrived just
before the SIGKILL, and that signal would get lost.

We drop all the ifdeffery for tkill and tgkill, because every guest
architecture we support implements them, and they've been in Linux
since 2003 so we can assume the host headers define the __NR_tkill
and __NR_tgkill constants.

Signed-off-by: Peter Maydell <address@hidden>
Timothy's patchset used block_signals() for this, but I
think safe_syscall is nicer when it can be used, since
it's lower overhead and less intrusive. Also extended to
cover all the thread-killing syscalls rather than just kill.
 linux-user/syscall.c | 23 +++++++----------------
 1 file changed, 7 insertions(+), 16 deletions(-)

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index cb5d519..549f571 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -186,8 +186,6 @@ static type name (type1 arg1,type2 arg2,type3 arg3,type4 
arg4,type5 arg5,   \
 #define __NR_sys_getpriority __NR_getpriority
 #define __NR_sys_rt_sigqueueinfo __NR_rt_sigqueueinfo
 #define __NR_sys_syslog __NR_syslog
-#define __NR_sys_tgkill __NR_tgkill
-#define __NR_sys_tkill __NR_tkill
 #define __NR_sys_futex __NR_futex
 #define __NR_sys_inotify_init __NR_inotify_init
 #define __NR_sys_inotify_add_watch __NR_inotify_add_watch
@@ -225,12 +223,6 @@ _syscall5(int, _llseek,  uint,  fd, ulong, hi, ulong, lo,
 _syscall3(int,sys_rt_sigqueueinfo,int,pid,int,sig,siginfo_t *,uinfo)
-#if defined(TARGET_NR_tgkill) && defined(__NR_tgkill)
-#if defined(TARGET_NR_tkill) && defined(__NR_tkill)
 #ifdef __NR_exit_group
@@ -704,6 +696,9 @@ safe_syscall6(int, pselect6, int, nfds, fd_set *, readfds, 
fd_set *, writefds, \
 safe_syscall6(int,futex,int *,uaddr,int,op,int,val, \
               const struct timespec *,timeout,int *,uaddr2,int,val3)
 safe_syscall2(int, rt_sigsuspend, sigset_t *, newset, size_t, sigsetsize)
+safe_syscall2(int, kill, pid_t, pid, int, sig)
+safe_syscall2(int, tkill, int, tid, int, sig)
+safe_syscall3(int, tgkill, int, tgid, int, pid, int, sig)
 static inline int host_to_target_sock_type(int host_type)
@@ -6528,7 +6523,7 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
         ret = 0;
     case TARGET_NR_kill:
-        ret = get_errno(kill(arg1, target_to_host_signal(arg2)));
+        ret = get_errno(safe_kill(arg1, target_to_host_signal(arg2)));
 #ifdef TARGET_NR_rename
     case TARGET_NR_rename:
@@ -9764,18 +9759,14 @@ abi_long do_syscall(void *cpu_env, int num, abi_long 
-#if defined(TARGET_NR_tkill) && defined(__NR_tkill)
     case TARGET_NR_tkill:
-        ret = get_errno(sys_tkill((int)arg1, target_to_host_signal(arg2)));
+        ret = get_errno(safe_tkill((int)arg1, target_to_host_signal(arg2)));
-#if defined(TARGET_NR_tgkill) && defined(__NR_tgkill)
     case TARGET_NR_tgkill:
-       ret = get_errno(sys_tgkill((int)arg1, (int)arg2,
+        ret = get_errno(safe_tgkill((int)arg1, (int)arg2,
-       break;
+        break;
 #ifdef TARGET_NR_set_robust_list
     case TARGET_NR_set_robust_list:

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