From e6cdd38e8f0fead14cd3c528e9a4b666e1871752 Mon Sep 17 00:00:00 2001
From: John Baldwin <jhb@FreeBSD.org>
Date: Sun, 12 Jun 2016 21:24:42 -0700
Subject: Add support for catching system calls to native FreeBSD targets.

All platforms on FreeBSD use a shared system call table, so use a
single XML file to describe the system calls available on each FreeBSD
platform.

Recent versions of FreeBSD include the identifier of the current
system call when reporting a system call entry or exit event in the
ptrace_lwpinfo structure obtained via PT_LWPINFO in fbsd_wait.  As
such, FreeBSD native targets do not use the gdbarch method to fetch
the system call code.  In addition, FreeBSD register sets fetched via
ptrace do not include an equivalent of 'orig_rax' (on amd64 for
example), so the system call code cannot be extracted from the
available registers during a system call exit.  However, GDB assumes
that system call catch points are not supported if the gdbarch method
is not present.  As a workaround, FreeBSD ABIs install a dummy gdbarch
method that throws an internal_error if it is ever invoked.

gdb/ChangeLog:

	* configure.ac: Check for support for system call LWP fields on
	FreeBSD.
	* config.in, configure: Rebuild.
	* data-directory/Makefile.in (SYSCALLS_FILES): Add freebsd.xml.
	* fbsd-nat.c (fbsd_wait) [HAVE_STRUCT_PTRACE_LWPINFO_PL_SYSCALL_CODE]:
	Report system call events.
	[HAVE_STRUCT_PTRACE_LWPINFO_PL_SYSCALL_CODE]
	(fbsd_set_syscall_catchpoint): New function.
	(fbsd_nat_add_target) [HAVE_STRUCT_PTRACE_LWPINFO_PL_SYSCALL_CODE]:
	Set "to_set_syscall_catchpoint" to "fbsd_set_syscall_catchpoint".
	* fbsd-tdep.c: Include xml-syscall.h
	(fbsd_get_syscall_number): New function.
	(fbsd_init_abi): Set XML system call file name.
	Add "get_syscall_number" gdbarch method.
	* syscalls/freebsd.xml: New file.
---
 gdb/fbsd-nat.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 50 insertions(+)

(limited to 'gdb/fbsd-nat.c')

diff --git a/gdb/fbsd-nat.c b/gdb/fbsd-nat.c
index dc65e29..c9548e9 100644
--- a/gdb/fbsd-nat.c
+++ b/gdb/fbsd-nat.c
@@ -779,6 +779,40 @@ fbsd_wait (struct target_ops *ops,
 	      return wptid;
 	    }
 #endif
+
+	  /* Note that PL_FLAG_SCE is set for any event reported while
+	     a thread is executing a system call in the kernel.  In
+	     particular, signals that interrupt a sleep in a system
+	     call will report this flag as part of their event.  Stops
+	     explicitly for system call entry and exit always use
+	     SIGTRAP, so only treat SIGTRAP events as system call
+	     entry/exit events.  */
+	  if (pl.pl_flags & (PL_FLAG_SCE | PL_FLAG_SCX)
+	      && ourstatus->value.sig == SIGTRAP)
+	    {
+#ifdef HAVE_STRUCT_PTRACE_LWPINFO_PL_SYSCALL_CODE
+	      if (catch_syscall_enabled ())
+		{
+		  if (catching_syscall_number (pl.pl_syscall_code))
+		    {
+		      if (pl.pl_flags & PL_FLAG_SCE)
+			ourstatus->kind = TARGET_WAITKIND_SYSCALL_ENTRY;
+		      else
+			ourstatus->kind = TARGET_WAITKIND_SYSCALL_RETURN;
+		      ourstatus->value.syscall_number = pl.pl_syscall_code;
+		      return wptid;
+		    }
+		}
+#endif
+	      /* If the core isn't interested in this event, just
+		 continue the process explicitly and wait for another
+		 event.  Note that PT_SYSCALL is "sticky" on FreeBSD
+		 and once system call stops are enabled on a process
+		 it stops for all system call entries and exits.  */
+	      if (ptrace (PT_CONTINUE, pid, (caddr_t) 1, 0) == -1)
+		perror_with_name (("ptrace"));
+	      continue;
+	    }
 	}
       return wptid;
     }
@@ -889,6 +923,19 @@ fbsd_remove_exec_catchpoint (struct target_ops *self, int pid)
   return 0;
 }
 #endif
+
+#ifdef HAVE_STRUCT_PTRACE_LWPINFO_PL_SYSCALL_CODE
+static int
+fbsd_set_syscall_catchpoint (struct target_ops *self, int pid, int needed,
+			     int any_count, int table_size, int *table)
+{
+
+  /* Ignore the arguments.  inf-ptrace.c will use PT_SYSCALL which
+     will catch all system call entries and exits.  The system calls
+     are filtered by GDB rather than the kernel.  */
+  return 0;
+}
+#endif
 #endif
 
 void
@@ -925,6 +972,9 @@ fbsd_nat_add_target (struct target_ops *t)
   t->to_insert_exec_catchpoint = fbsd_insert_exec_catchpoint;
   t->to_remove_exec_catchpoint = fbsd_remove_exec_catchpoint;
 #endif
+#ifdef HAVE_STRUCT_PTRACE_LWPINFO_PL_SYSCALL_CODE
+  t->to_set_syscall_catchpoint = fbsd_set_syscall_catchpoint;
+#endif
 #endif
   add_target (t);
 }
-- 
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