signal handlers that return should not modify errno

Signed-off-by: Mattias Andrée <maandree@operamail.com>

9 files changed, 61 insertions, 0 deletions

diff --git a/doc/info/mds.texinfo b/doc/info/mds.texinfo
index 03b2a1a..b2f1192 100644
--- a/doc/info/mds.texinfo
+++ b/doc/info/mds.texinfo
@@ -6460,6 +6460,28 @@ if no error occurs@footnote{@code{glibc} will not clear
 will be defined.}, and creates the alias
 @code{CLOCK_MONOTONIC_RAW} for @code{CLOCK_MONOTONIC}
 unless @code{CLOCK_MONOTONIC_RAW} is already defined.
+The header file also ensure that all aliases for socket
+protocol families and address families, for all definied
+protocol families and address families.
+
+The header file @file{<libmdsserver/macros.h>}, also
+provides to macros to help write signal handlers.
+@table @code
+@item SIGHANDLER_START
+Normal signal handlers should place this macro
+at the top of the function. It will save the value
+of @code{errno}.
+@item SIGHANDLER_END
+Normal signal handlers should place this macro
+at the bottom of the function, or just before
+any @code{return}. It will restore the value of
+@code{errno} saved by @code{SIGHANDLER_START}.
+@end table
+These macros should be used, because signal handlers
+should not modify @code{errno}. The one occasion where
+exiting a signal handler with a modified @code{errno}
+is acceptable, is when the signal handler exits the
+program without returning.
 
 
 
diff --git a/src/libmdsserver/macros.h b/src/libmdsserver/macros.h
index 89db22f..f17da94 100644
--- a/src/libmdsserver/macros.h
+++ b/src/libmdsserver/macros.h
@@ -752,5 +752,22 @@
 #endif
 
 
+/**
+ * Normal signal handlers should place this macro
+ * at the top of the function
+ */
+#define SIGHANDLER_START  \
+  int sighandler_saved_errno = errno
+
+
+/**
+ * Normal signal handlers should place this macro
+ * at the bottom of the function, or just before
+ * any `return`
+ */
+#define SIGHANDLER_END  \
+  (errno = sighandler_saved_errno)
+
+
 #endif
 
diff --git a/src/mds-base.c b/src/mds-base.c
index 2220003..e9c7c8b 100644
--- a/src/mds-base.c
+++ b/src/mds-base.c
@@ -334,6 +334,7 @@ static void __attribute__((const)) received_noop(int signo)
  */
 void __attribute__((weak)) received_reexec(int signo)
 {
+  SIGHANDLER_START;
   (void) signo;
   if (reexecing == 0)
     {
@@ -341,6 +342,7 @@ void __attribute__((weak)) received_reexec(int signo)
       eprint("re-exec signal received.");
       signal_all(signo);
     }
+  SIGHANDLER_END;
 }
 
 
@@ -354,6 +356,7 @@ void __attribute__((weak)) received_reexec(int signo)
  */
 void __attribute__((weak)) received_terminate(int signo)
 {
+  SIGHANDLER_START;
   (void) signo;
   if (terminating == 0)
     {
@@ -361,6 +364,7 @@ void __attribute__((weak)) received_terminate(int signo)
       eprint("terminate signal received.");
       signal_all(signo);
     }
+  SIGHANDLER_END;
 }
 
 
@@ -375,12 +379,14 @@ void __attribute__((weak)) received_terminate(int signo)
  */
 void __attribute__((weak)) received_danger(int signo)
 {
+  SIGHANDLER_START;
   (void) signo;
   if (danger == 0)
     {
       danger = 1;
       eprint("danger signal received.");
     }
+  SIGHANDLER_END;
 }
 
 
diff --git a/src/mds-clipboard.c b/src/mds-clipboard.c
index cbfed79..6c0a2ed 100644
--- a/src/mds-clipboard.c
+++ b/src/mds-clipboard.c
@@ -899,6 +899,7 @@ int clipboard_get_size(int level, const char* recv_client_id, const char* recv_m
  */
 void received_info(int signo)
 {
+  SIGHANDLER_START;
   clipitem_t clipitem;
   size_t i, j, n;
   struct timespec now;
@@ -937,5 +938,6 @@ void received_info(int signo)
 		  clipitem.content);
 	}
     }
+  SIGHANDLER_END;
 }
 
diff --git a/src/mds-colour.c b/src/mds-colour.c
index c5151dc..b4b166d 100644
--- a/src/mds-colour.c
+++ b/src/mds-colour.c
@@ -477,6 +477,7 @@ int handle_set_colour(const char* recv_name, const char* recv_remove, const char
  */
 void received_info(int signo)
 {
+  SIGHANDLER_START;
   size_t i;
   colour_list_entry_t* entry;
   (void) signo;
@@ -489,6 +490,7 @@ void received_info(int signo)
 	    entry->value.bytes, entry->value.red, entry->value.green,
 	    entry->value.blue, entry->key_hash, entry->key);
   iprint("END DEFINED COLOURS");
+  SIGHANDLER_END;
 }
 
 
diff --git a/src/mds-echo.c b/src/mds-echo.c
index a531812..c434656 100644
--- a/src/mds-echo.c
+++ b/src/mds-echo.c
@@ -351,9 +351,11 @@ int echo_message(void)
  */
 void received_info(int signo)
 {
+  SIGHANDLER_START;
   (void) signo;
   iprintf("next message ID: %" PRIu32, message_id);
   iprintf("connected: %s", connected ? "yes" : "no");
   iprintf("echo buffer size: %zu bytes", echo_buffer_size);
+  SIGHANDLER_END;
 }
 
diff --git a/src/mds-kkbd.c b/src/mds-kkbd.c
index 284c56b..1088385 100644
--- a/src/mds-kkbd.c
+++ b/src/mds-kkbd.c
@@ -1730,6 +1730,7 @@ void shrink_map(void)
  */
 void received_info(int signo)
 {
+  SIGHANDLER_START;
   size_t i;
   (void) signo;
   iprintf("next message ID: %" PRIu32, message_id);
@@ -1746,5 +1747,6 @@ void received_info(int signo)
   for (i = 0; i < mapping_size; i++)
     if ((int)i != mapping[i])
       iprintf("  %zu -> %i", i, mapping[i]);
+  SIGHANDLER_END;
 }
 
diff --git a/src/mds-respawn.c b/src/mds-respawn.c
index 785eb67..0b68d08 100644
--- a/src/mds-respawn.c
+++ b/src/mds-respawn.c
@@ -225,9 +225,11 @@ static void spawn_server(size_t index)
  */
 static void received_revive(int signo)
 {
+  SIGHANDLER_START;
   (void) signo;
   reviving = 1;
   eprint("revive signal received.");
+  SIGHANDLER_END;
 }
 
 
@@ -545,6 +547,7 @@ int master_loop(void)
  */
 void received_info(int signo)
 {
+  SIGHANDLER_START;
   server_state_t state;
   size_t i, n = servers;
   char** cmdline;
@@ -577,5 +580,6 @@ void received_info(int signo)
       while (*cmdline)
 	iprintf("  %z", *cmdline++);
     }
+  SIGHANDLER_END;
 }
 
diff --git a/src/mds-vt.c b/src/mds-vt.c
index 2449aba..0264904 100644
--- a/src/mds-vt.c
+++ b/src/mds-vt.c
@@ -716,8 +716,10 @@ void signal_all(int signo)
  */
 void received_switch_vt(int signo)
 {
+  SIGHANDLER_START;
   int leaving = signo == (SIGRTMIN + 2);
   switching_vt = leaving ? 1 : -1;
+  SIGHANDLER_END;
 }
 
 
@@ -881,6 +883,7 @@ void vt_construct_mode(int vt_switch_control, int vt_leave_signal,
  */
 void received_info(int signo)
 {
+  SIGHANDLER_START;
   (void) signo;
   iprintf("next message ID: %" PRIu32, message_id);
   iprintf("connected: %s", connected ? "yes" : "no");
@@ -896,5 +899,6 @@ void received_info(int signo)
   iprintf("secondary thread started: %s", secondary_thread_started ? "yes" : "no");
   iprintf("secondary thread failed: %s", secondary_thread_failed ? "yes" : "no");
   iprintf("non-exclusive counter: %zi", nonexclusive_counter);
+  SIGHANDLER_END;
 }