[PATCH v3] Generate NT_PROCSTAT_{AUXV,VMMAP,PS_STRINGS} in FreeBSD coredumps

[Simon Ser <contact at emersion dot fr>]

gcore generates NT_AUXV and NT_FILE notes for Linux targets. On
FreeBSD auxv is stored in a NT_PROCSTAT_AUXV section, file mappings
are stored in a NT_PROCSTAT_VMMAP and both are prefixed with the
struct size.

2018-08-21  Simon Ser  <contact@emersion.fr>
        * target.h (enum target_object): add FreeBSD-specific
        TARGET_OBJECT_FREEBSD_VMMAP and TARGET_OBJECT_FREEBSD_PS_STRINGS
        * fbsd-nat.c (fbsd_nat_target::xfer_partial): add support for
        TARGET_OBJECT_FREEBSD_VMMAP and TARGET_OBJECT_FREEBSD_PS_STRINGS
        * fbsd-tdep.c (fbsd_make_corefile_notes): write NT_PROCSTAT_AUXV,
        NT_PROCSTAT_VMMAP and NT_PROCSTAT_PS_STRINGS notes
---

Changes from v2 to v3:
- Remove constants, prepend struct size for FreeBSD-specific objects
- Use gdbarch_ptr_bit instead of gdbarch_addr_bit
- Fixed typo

This addresses all of John's comments except the VMMAP packed one.

John, you said coredumps use the unpacked format, but looking at the
`gcore` utility source code (in usr.bin/gcore/elfcore.c) I believe it
uses the packed format for coredumps. It also makes more sense to me
to use the packed format for coredumps because it allows us not to
store PATH_MAX zeros for each entry. I may be wrong though, let me know
what you think.

 gdb/fbsd-nat.c  | 50 ++++++++++++++++++++++++++++++++++++++++++
 gdb/fbsd-tdep.c | 58 +++++++++++++++++++++++++++++++++++++++++++++++++
 gdb/target.h    |  4 ++++
 3 files changed, 112 insertions(+)

diff --git a/gdb/fbsd-nat.c b/gdb/fbsd-nat.c
index 115deac0..7cd325e4 100644
--- a/gdb/fbsd-nat.c
+++ b/gdb/fbsd-nat.c
@@ -751,6 +751,56 @@ fbsd_nat_target::xfer_partial (enum target_object object,
 	  }
 	return TARGET_XFER_E_IO;
       }
+    case TARGET_OBJECT_FREEBSD_VMMAP:
+    case TARGET_OBJECT_FREEBSD_PS_STRINGS:
+      {
+	gdb::byte_vector buf_storage;
+	gdb_byte *buf;
+	size_t buflen;
+	int mib[4];
+
+        int proc_target;
+        uint32_t struct_size;
+        switch (object) {
+        case TARGET_OBJECT_FREEBSD_VMMAP:
+          proc_target = KERN_PROC_VMMAP;
+          struct_size = sizeof (struct kinfo_vmentry);
+          break;
+        case TARGET_OBJECT_FREEBSD_PS_STRINGS:
+          proc_target = KERN_PROC_PS_STRINGS;
+          struct_size = sizeof (void *);
+          break;
+        }
+
+	if (writebuf != NULL)
+	  return TARGET_XFER_E_IO;
+
+	mib[0] = CTL_KERN;
+	mib[1] = KERN_PROC;
+	mib[2] = proc_target;
+	mib[3] = pid;
+
+	buflen = sizeof (struct_size) + offset + len;
+	buf_storage.resize (buflen);
+	buf = buf_storage.data ();
+
+	memcpy (buf, &struct_size, sizeof (struct_size));
+
+	if (sysctl (mib, 4, buf + sizeof (struct_size), &buflen, NULL, 0) == 0)
+	  {
+	    buflen += sizeof (struct_size);
+	    if (buflen > offset)
+	      {
+		buflen -= offset;
+		memcpy (readbuf, buf + offset, buflen);
+	      }
+	    else
+	      buflen = 0;
+	    *xfered_len = buflen;
+	    return (buflen == 0) ? TARGET_XFER_EOF : TARGET_XFER_OK;
+	  }
+	return TARGET_XFER_E_IO;
+      }
     default:
       return inf_ptrace_target::xfer_partial (object, annex,
 					      readbuf, writebuf, offset,
diff --git a/gdb/fbsd-tdep.c b/gdb/fbsd-tdep.c
index 9cea0098..659e64b6 100644
--- a/gdb/fbsd-tdep.c
+++ b/gdb/fbsd-tdep.c
@@ -25,6 +25,9 @@
 #include "regset.h"
 #include "gdbthread.h"
 #include "xml-syscall.h"
+#include <sys/user.h>
+#include <sys/sysctl.h>
+#include <sys/types.h>
 
 #include "elf-bfd.h"
 #include "fbsd-tdep.h"
@@ -512,6 +515,23 @@ fbsd_corefile_thread (struct thread_info *info,
      args->note_size, args->stop_signal);
 }
 
+static gdb::optional<gdb::byte_vector>
+fbsd_make_note_desc (enum target_object object, uint32_t structsize)
+{
+  gdb::optional<gdb::byte_vector> buf =
+    target_read_alloc (current_top_target (), object, NULL);
+  if (!buf || buf->empty ())
+    return {};
+
+  if (structsize == 0)
+    return buf;
+
+  gdb::byte_vector desc (sizeof (structsize) + buf->size ());
+  memcpy (desc.data (), &structsize, sizeof (structsize));
+  memcpy (desc.data () + sizeof (structsize), buf->data (), buf->size ());
+  return desc;
+}
+
 /* Create appropriate note sections for a corefile, returning them in
    allocated memory.  */
 
@@ -586,6 +606,44 @@ fbsd_make_corefile_notes (struct gdbarch *gdbarch, bfd *obfd, int *note_size)
 
   note_data = thread_args.note_data;
 
+  pid_t pid = inferior_ptid.pid ();
+
+  /* Auxiliary vector.  */
+  uint32_t structsize = gdbarch_ptr_bit (gdbarch) / 4; /* Elf_Auxinfo  */
+  gdb::optional<gdb::byte_vector> note_desc =
+    fbsd_make_note_desc (TARGET_OBJECT_AUXV, structsize);
+  if (note_desc && !note_desc->empty ())
+    {
+      note_data = elfcore_write_note (obfd, note_data, note_size,
+                                      "FreeBSD", NT_FREEBSD_PROCSTAT_AUXV,
+                                      note_desc->data (), note_desc->size ());
+      if (!note_data)
+        return NULL;
+    }
+  
+  /* File mappings  */
+  note_desc = fbsd_make_note_desc (TARGET_OBJECT_FREEBSD_VMMAP, 0);
+  if (note_desc && !note_desc->empty ())
+    {
+      note_data = elfcore_write_note (obfd, note_data, note_size,
+                                      "FreeBSD", NT_FREEBSD_PROCSTAT_VMMAP,
+                                      note_desc->data (), note_desc->size ());
+      if (!note_data)
+        return NULL;
+    }
+
+  note_desc =
+    fbsd_make_note_desc (TARGET_OBJECT_FREEBSD_PS_STRINGS, 0);
+  if (note_desc && !note_desc->empty ())
+    {
+      note_data = elfcore_write_note (obfd, note_data, note_size,
+                                      "FreeBSD",
+                                      NT_FREEBSD_PROCSTAT_PSSTRINGS,
+                                      note_desc->data (), note_desc->size ());
+      if (!note_data)
+        return NULL;
+    }
+
   return note_data;
 }
 
diff --git a/gdb/target.h b/gdb/target.h
index 18c4a84c..83f1172c 100644
--- a/gdb/target.h
+++ b/gdb/target.h
@@ -203,6 +203,10 @@ enum target_object
      of the process ID of the process in question, in hexadecimal
      format.  */
   TARGET_OBJECT_EXEC_FILE,
+  /* FreeBSD file mappings  */
+  TARGET_OBJECT_FREEBSD_VMMAP,
+  /* FreeBSD process strings  */
+  TARGET_OBJECT_FREEBSD_PS_STRINGS,
   /* Possible future objects: TARGET_OBJECT_FILE, ...  */
 };
 
-- 
2.18.0