overhaul pthread cancellation

this patch improves the correctness, simplicity, and size of
cancellation-related code. modulo any small errors, it should now be
completely conformant, safe, and resource-leak free.

the notion of entering and exiting cancellation-point context has been
completely eliminated and replaced with alternative syscall assembly
code for cancellable syscalls. the assembly is responsible for setting
up execution context information (stack pointer and address of the
syscall instruction) which the cancellation signal handler can use to
determine whether the interrupted code was in a cancellable state.

these changes eliminate race conditions in the previous generation of
cancellation handling code (whereby a cancellation request received
just prior to the syscall would not be processed, leaving the syscall
to block, potentially indefinitely), and remedy an issue where
non-cancellable syscalls made from signal handlers became cancellable
if the signal handler interrupted a cancellation point.

x86_64 asm is untested and may need a second try to get it right.

5 files changed, 12 insertions, 9 deletions

diff --git a/arch/i386/bits/pthread.h b/arch/i386/bits/pthread.h
index 7690ea39..c119dc8a 100644
--- a/arch/i386/bits/pthread.h
+++ b/arch/i386/bits/pthread.h
@@ -7,17 +7,17 @@ struct __ptcb {
 
 static inline void __pthread_register_cancel_2(struct __ptcb *__cb)
 {
-	__asm__ __volatile__( "call __pthread_register_cancel" : : "a"(__cb) );
+	__asm__ __volatile__( "call __pthread_register_cancel" : : "a"(__cb) : "ecx", "edx", "memory" );
 }
 
 static inline void __pthread_unregister_cancel_2(struct __ptcb *__cb)
 {
-	__asm__ __volatile__( "call __pthread_unregister_cancel" : : "a"(__cb) );
+	__asm__ __volatile__( "call __pthread_unregister_cancel" : : "a"(__cb) : "ecx", "edx", "memory" );
 }
 
 static inline void __pthread_unwind_next_2(struct __ptcb *__cb)
 {
-	__asm__ __volatile__( "call __pthread_unwind_next" : : "a"(__cb) );
+	__asm__ __volatile__( "call __pthread_unwind_next" : : "a"(__cb) : "ecx", "edx", "memory" );
 }
 
 #define __pthread_register_cancel __pthread_register_cancel_2
diff --git a/arch/i386/bits/syscall.h b/arch/i386/bits/syscall.h
index 519e2dcd..274f205c 100644
--- a/arch/i386/bits/syscall.h
+++ b/arch/i386/bits/syscall.h
@@ -122,7 +122,9 @@ static inline long __syscall6(long __n, long __a1, long __a2, long __a3, long __
 #define __SC_sendmsg     16
 #define __SC_recvmsg     17
 
-#define __socketcall(nm, a, b, c, d, e, f) syscall(SYS_socketcall, __SC_##nm, \
+#define __socketcall(nm,a,b,c,d,e,f) syscall(SYS_socketcall, __SC_##nm, \
+    ((long [6]){ (long)a, (long)b, (long)c, (long)d, (long)e, (long)f }))
+#define __socketcall_cp(nm,a,b,c,d,e,f) syscall_cp(SYS_socketcall, __SC_##nm, \
     ((long [6]){ (long)a, (long)b, (long)c, (long)d, (long)e, (long)f }))
 
 #define __NR_restart_syscall      0
diff --git a/arch/i386/pthread_arch.h b/arch/i386/pthread_arch.h
index 64d75cbc..b17dc87a 100644
--- a/arch/i386/pthread_arch.h
+++ b/arch/i386/pthread_arch.h
@@ -5,5 +5,5 @@ static inline struct pthread *__pthread_self()
 	return self;
 }
 
-#define PC_AT_SYS(c) \
-	(*(uint16_t *)(((ucontext_t *)(c))->uc_mcontext.__gregs[14])==0x80cd)
+#define CANCEL_REG_SP 7
+#define CANCEL_REG_IP 14
diff --git a/arch/x86_64/bits/syscall.h b/arch/x86_64/bits/syscall.h
index d18edece..21d4c23a 100644
--- a/arch/x86_64/bits/syscall.h
+++ b/arch/x86_64/bits/syscall.h
@@ -60,7 +60,8 @@ static inline long __syscall6(long __n, long __a1, long __a2, long __a3, long __
 	return __ret;
 }
 
-#define __socketcall(nm, a, b, c, d, e, f) syscall(__NR_##nm, a, b, c, d, e, f)
+#define __socketcall(nm,a,b,c,d,e,f) syscall(__NR_##nm, a, b, c, d, e, f)
+#define __socketcall_cp(nm,a,b,c,d,e,f) syscall_cp(__NR_##nm, a, b, c, d, e, f)
 
 #define __NR_read				0
 #define __NR_write				1
diff --git a/arch/x86_64/pthread_arch.h b/arch/x86_64/pthread_arch.h
index af7ae86e..c424493a 100644
--- a/arch/x86_64/pthread_arch.h
+++ b/arch/x86_64/pthread_arch.h
@@ -5,5 +5,5 @@ static inline struct pthread *__pthread_self()
 	return self;
 }
 
-#define PC_AT_SYS(c) \
-	(*(uint16_t *)(((ucontext_t *)(c))->uc_mcontext.__gregs[16])==0x050f)
+#define CANCEL_REG_SP 15
+#define CANCEL_REG_IP 16