Read signal information from FreeBSD core dumps.

FreeBSD recently added a new ELF core note which dumps the entire LWP
info structure (the same structure returned by the ptrace PT_LWPINFO
operation) for each thread.  The plan is for this note to eventually
supplant the older "thrmisc" ELF core note as it contains more
information and it permits new information to be exported via both
ptrace() and core dumps using the same structure.

For signal information, the implementation is similar to the native
implementation for FreeBSD processes.  The PL_FLAG_SI flag must be
checked to determine if the embedded siginfo_t structure is valid, and
if so it is transferred into the caller's buffer.

gdb/ChangeLog:

	* fbsd-tdep.c (LWPINFO_OFFSET, LWPINFO_PL_FLAGS)
	(LWPINFO64_PL_SIGINFO, LWPINFO32_PL_SIGINFO, PL_FLAG_SI)
	(SIZE64_SIGINFO_T, SIZE32_SIGINFO_T, fbsd_core_xfer_siginfo): New.
	(fbsd_init_abi): Install gdbarch "core_xfer_siginfo" method.

2 files changed, 75 insertions, 0 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 02397df..42fdda6 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,12 @@
 2017-07-07  John Baldwin  <jhb@FreeBSD.org>
 
+	* fbsd-tdep.c (LWPINFO_OFFSET, LWPINFO_PL_FLAGS)
+	(LWPINFO64_PL_SIGINFO, LWPINFO32_PL_SIGINFO, PL_FLAG_SI)
+	(SIZE64_SIGINFO_T, SIZE32_SIGINFO_T, fbsd_core_xfer_siginfo): New.
+	(fbsd_init_abi): Install gdbarch "core_xfer_siginfo" method.
+
+2017-07-07  John Baldwin  <jhb@FreeBSD.org>
+
 	* fbsd-tdep.c (fbsd_core_thread_name): Use thread_section_name.
 
 2017-07-07  John Baldwin  <jhb@FreeBSD.org>
diff --git a/gdb/fbsd-tdep.c b/gdb/fbsd-tdep.c
index 32df104..6f30197 100644
--- a/gdb/fbsd-tdep.c
+++ b/gdb/fbsd-tdep.c
@@ -30,6 +30,28 @@
 #include "fbsd-tdep.h"
 
 
+/* FreeBSD kernels 12.0 and later include a copy of the
+   'ptrace_lwpinfo' structure returned by the PT_LWPINFO ptrace
+   operation in an ELF core note (NT_FREEBSD_PTLWPINFO) for each LWP.
+   The constants below define the offset of field members and flags in
+   this structure used by methods in this file.  Note that the
+   'ptrace_lwpinfo' struct in the note is preceded by a 4 byte integer
+   containing the size of the structure.  */
+
+#define	LWPINFO_OFFSET		0x4
+
+/* Offsets in ptrace_lwpinfo.  */
+#define	LWPINFO_PL_FLAGS	0x8
+#define	LWPINFO64_PL_SIGINFO	0x30
+#define	LWPINFO32_PL_SIGINFO	0x2c
+
+/* Flags in pl_flags.  */
+#define	PL_FLAG_SI	0x20	/* siginfo is valid */
+
+/* Sizes of siginfo_t.	*/
+#define	SIZE64_SIGINFO_T	80
+#define	SIZE32_SIGINFO_T	64
+
 static struct gdbarch_data *fbsd_gdbarch_data_handle;
 
 struct fbsd_gdbarch_data
@@ -113,6 +135,51 @@ fbsd_core_thread_name (struct gdbarch *gdbarch, struct thread_info *thr)
   return NULL;
 }
 
+/* Implement the "core_xfer_siginfo" gdbarch method.  */
+
+static LONGEST
+fbsd_core_xfer_siginfo (struct gdbarch *gdbarch, gdb_byte *readbuf,
+			ULONGEST offset, ULONGEST len)
+{
+  size_t siginfo_size;
+
+  if (gdbarch_bfd_arch_info (gdbarch)->bits_per_word == 32)
+    siginfo_size = SIZE32_SIGINFO_T;
+  else
+    siginfo_size = SIZE64_SIGINFO_T;
+  if (offset > siginfo_size)
+    return -1;
+
+  thread_section_name section_name (".note.freebsdcore.lwpinfo", inferior_ptid);
+  asection *section = bfd_get_section_by_name (core_bfd, section_name.c_str ());
+  if (section == NULL)
+    return -1;
+
+  gdb_byte buf[4];
+  if (!bfd_get_section_contents (core_bfd, section, buf,
+				 LWPINFO_OFFSET + LWPINFO_PL_FLAGS, 4))
+    return -1;
+
+  int pl_flags = extract_signed_integer (buf, 4, gdbarch_byte_order (gdbarch));
+  if (!(pl_flags & PL_FLAG_SI))
+    return -1;
+
+  if (offset + len > siginfo_size)
+    len = siginfo_size - offset;
+
+  ULONGEST siginfo_offset;
+  if (gdbarch_bfd_arch_info (gdbarch)->bits_per_word == 32)
+    siginfo_offset = LWPINFO_OFFSET + LWPINFO32_PL_SIGINFO;
+  else
+    siginfo_offset = LWPINFO_OFFSET + LWPINFO64_PL_SIGINFO;
+
+  if (!bfd_get_section_contents (core_bfd, section, readbuf,
+				 siginfo_offset + offset, len))
+    return -1;
+
+  return len;
+}
+
 static int
 find_signalled_thread (struct thread_info *info, void *data)
 {
@@ -447,6 +514,7 @@ fbsd_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
 {
   set_gdbarch_core_pid_to_str (gdbarch, fbsd_core_pid_to_str);
   set_gdbarch_core_thread_name (gdbarch, fbsd_core_thread_name);
+  set_gdbarch_core_xfer_siginfo (gdbarch, fbsd_core_xfer_siginfo);
   set_gdbarch_make_corefile_notes (gdbarch, fbsd_make_corefile_notes);
   set_gdbarch_print_auxv_entry (gdbarch, fbsd_print_auxv_entry);
   set_gdbarch_get_siginfo_type (gdbarch, fbsd_get_siginfo_type);