[binutils-gdb] Allow not saving the signal state in SIGSETJMP

[binutils-gdb] Allow not saving the signal state in SIGSETJMP

[Christian Biesinger]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=17bfe554b9a8c57c4d377bce930046138298fd8b

commit 17bfe554b9a8c57c4d377bce930046138298fd8b
Author: Christian Biesinger <cbiesinger@google.com>
Date:   Tue Oct 15 10:02:33 2019 -0500

    Allow not saving the signal state in SIGSETJMP
    
    Saving the signal state is very slow (this patch is a 14% speedup).  The
    reason we need this code is because signal handler will leave the
    signal blocked when we longjmp out of it.  But in this case we can
    just manually unblock the signal instead of taking the unconditional
    perf hit.
    
    gdb/ChangeLog:
    
    2019-10-16  Christian Biesinger  <cbiesinger@google.com>
    
    	* gdbsupport/gdb_setjmp.h (SIGSETJMP): Allow passing in the value to
    	pass on to sigsetjmp's second argument.
    	* cp-support.c (gdb_demangle): Unblock SIGSEGV if we caught a crash.
    
    Change-Id: Ib3010966050c64b4cc8b47d8cb45871652b0b3ea

Diff:
---
 gdb/ChangeLog               |  6 ++++++
 gdb/cp-support.c            | 19 ++++++++++++++++++-
 gdb/gdbsupport/gdb_setjmp.h |  6 ++++--
 3 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index d11dbfb..ba028ed 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,9 @@
+2019-10-16  Christian Biesinger  <cbiesinger@google.com>
+
+	* gdbsupport/gdb_setjmp.h (SIGSETJMP): Allow passing in the value to
+	pass on to sigsetjmp's second argument.
+	* cp-support.c (gdb_demangle): Unblock SIGSEGV if we caught a crash.
+
 2019-10-16  Keith Seitz  <keiths@redhat.com>
 
 	PR gdb/23567
diff --git a/gdb/cp-support.c b/gdb/cp-support.c
index cd732b6..253369b 100644
--- a/gdb/cp-support.c
+++ b/gdb/cp-support.c
@@ -1539,7 +1539,16 @@ gdb_demangle (const char *name, int options)
       ofunc = signal (SIGSEGV, gdb_demangle_signal_handler);
 #endif
 
-      crash_signal = SIGSETJMP (gdb_demangle_jmp_buf);
+      /* The signal handler may keep the signal blocked when we longjmp out
+         of it.  If we have sigprocmask, we can use it to unblock the signal
+	 afterwards and we can avoid the performance overhead of saving the
+	 signal mask just in case the signal gets triggered.  Otherwise, just
+	 tell sigsetjmp to save the mask.  */
+#ifdef HAVE_SIGPROCMASK
+      crash_signal = SIGSETJMP (gdb_demangle_jmp_buf, 0);
+#else
+      crash_signal = SIGSETJMP (gdb_demangle_jmp_buf, 1);
+#endif
     }
 #endif
 
@@ -1559,6 +1568,14 @@ gdb_demangle (const char *name, int options)
 	{
 	  static int error_reported = 0;
 
+#ifdef HAVE_SIGPROCMASK
+	  /* If we got the signal, SIGSEGV may still be blocked; restore it.  */
+	  sigset_t segv_sig_set;
+	  sigemptyset (&segv_sig_set);
+	  sigaddset (&segv_sig_set, SIGSEGV);
+	  sigprocmask (SIG_UNBLOCK, &segv_sig_set, NULL);
+#endif
+
 	  if (!error_reported)
 	    {
 	      std::string short_msg
diff --git a/gdb/gdbsupport/gdb_setjmp.h b/gdb/gdbsupport/gdb_setjmp.h
index d4ebbfa..4995970 100644
--- a/gdb/gdbsupport/gdb_setjmp.h
+++ b/gdb/gdbsupport/gdb_setjmp.h
@@ -23,11 +23,13 @@
 
 #ifdef HAVE_SIGSETJMP
 #define SIGJMP_BUF		sigjmp_buf
-#define SIGSETJMP(buf)		sigsetjmp((buf), 1)
+#define SIGSETJMP(buf,val)	sigsetjmp((buf), val)
 #define SIGLONGJMP(buf,val)	siglongjmp((buf), (val))
 #else
 #define SIGJMP_BUF		jmp_buf
-#define SIGSETJMP(buf)		setjmp(buf)
+/* We ignore val here because that's safer and avoids having to check
+   whether _setjmp exists.  */
+#define SIGSETJMP(buf,val)	setjmp(buf)
 #define SIGLONGJMP(buf,val)	longjmp((buf), (val))
 #endif