proposed siginfo changes

proposed siginfo changes

[Rich Felker]

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I've realized that our siginfo_t structure (and also the kernel and
glibc versions of it) have a bug: due to the way the union is laid
out, it's illegal to initialize both si_pid and si_value. This is
because __sigchld and __rt are both members of the same union and at
most one member of a union can be initialized.

The attached patch is a proposal for fixing this, with a more complex
setup of unions and structs. I'm going to hold off on applying it
immediately in case anyone has better ideas for how to do this. One
possible improvement would be to set things up so we could #define
away all of the __-prefixed names on GNUC or C11 compilers and thereby
use anonymous structs and unions instead of the hideous preprocessor
mess to access members.

Rich

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diff --git a/include/signal.h b/include/signal.h
index 3fb21b2..b6e1e98 100644
--- a/include/signal.h
+++ b/include/signal.h
@@ -89,19 +89,24 @@ typedef struct {
 	union {
 		char __pad[128 - 2*sizeof(int) - sizeof(long)];
 		struct {
-			pid_t si_pid;
-			uid_t si_uid;
-			union sigval si_sigval;
-		} __rt;
-		struct {
-			unsigned int si_timer1, si_timer2;
-		} __timer;
-		struct {
-			pid_t si_pid;
-			uid_t si_uid;
-			int si_status;
-			clock_t si_utime, si_stime;
-		} __sigchld;
+			union {
+				struct {
+					pid_t si_pid;
+					uid_t si_uid;
+				} __piduid;
+				struct {
+					int si_tid;
+					int si_overrun;
+				} __timer;
+			} __first;
+			union {
+				union sigval si_sigval;
+				struct {
+					int si_status;
+					clock_t si_utime, si_stime;
+				} __sigchld;
+			} __second;
+		} __si_common;
 		struct {
 			void *si_addr;
 			short si_addr_lsb;
@@ -117,20 +122,20 @@ typedef struct {
 		} __sigsys;
 	} __si_fields;
 } siginfo_t;
-#define si_pid     __si_fields.__sigchld.si_pid
-#define si_uid     __si_fields.__sigchld.si_uid
-#define si_status  __si_fields.__sigchld.si_status
-#define si_utime   __si_fields.__sigchld.si_utime
-#define si_stime   __si_fields.__sigchld.si_stime
-#define si_value   __si_fields.__rt.si_sigval
+#define si_pid     __si_fields.__si_common.__first.__piduid.si_pid
+#define si_uid     __si_fields.__si_common.__first.__piduid.si_uid
+#define si_status  __si_fields.__si_commin.__second.__sigchld.si_status
+#define si_utime   __si_fields.__si_commin.__second.__sigchld.si_utime
+#define si_stime   __si_fields.__si_commin.__second.__sigchld.si_stime
+#define si_value   __si_fields.__si_commin.__second.si_sigval
 #define si_addr    __si_fields.__sigfault.si_addr
 #define si_addr_lsb __si_fields.__sigfault.si_addr_lsb
 #define si_band    __si_fields.__sigpoll.si_band
 #define si_fd      __si_fields.__sigpoll.si_fd
-#define si_timer1  __si_fields.__timer.si_timer1
-#define si_timer2  __si_fields.__timer.si_timer2
-#define si_ptr     __si_fields.__rt.si_sigval.sival_ptr
-#define si_int     __si_fields.__rt.si_sigval.sival_int
+#define si_tid     __si_fields.__si_common.__first.__timer.si_tid
+#define si_overrun __si_fields.__si_common.__first.__timer.si_overrun
+#define si_ptr     __si_fields.__si_commin.__second.si_sigval.sival_ptr
+#define si_int     __si_fields.__si_commin.__second.si_sigval.sival_int
 #define si_call_addr __si_fields.__sigsys.si_call_addr
 #define si_syscall __si_fields.__sigsys.si_syscall
 #define si_arch    __si_fields.__sigsys.si_arch