Date: Mon, 07 Oct 2002 17:09:39 +0100 From: Ian Dowse <iedowse@maths.tcd.ie> To: hackers@freebsd.org Subject: gdb support for kernel modules Message-ID: <200210071709.aa25499@salmon.maths.tcd.ie>
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This is something I have been meaning to investigate for a while:
when gdb encounters a userland executable that uses shared libraries
it automatically adds the symbols from each library, so it seemed
likely that gdb could be made do the same thing with kernel modules.
I am aware of the existence of `gdbmods' etc, but it would be nicer
to have the support built in to gdb.
Anyway, below is a proof-of-concept patch that does the basics, but
among other things, its logic for locating the kernel module files
needs a lot of work - currently it just assumes /boot/kernel/<module>,
which is almost never what you actually want. It works for debugging
vmcores and live /dev/mem access, but I don't know if it can work
for remote debugging. Does anybody know gdb internals enough to
comment on how this is done or suggest improvements?
Ian
# gdb -k kernel.debug /dev/mem
...
This GDB was configured as "i386-undermydesk-freebsd"...
panic messages:
---
---
warning: skipping first file (kernel)
Reading symbols from /boot/kernel/ufs.ko...done.
Loaded symbols for /boot/kernel/ufs.ko
Reading symbols from /boot/kernel/md.ko...done.
Loaded symbols for /boot/kernel/md.ko
Reading symbols from /boot/kernel/vinum.ko...done.
Loaded symbols for /boot/kernel/vinum.ko
#0 mi_switch () at ../../../kern/kern_synch.c:849
849 td->td_kse->ke_oncpu = PCPU_GET(cpuid);
(kgdb) info sharedlibrary
warning: skipping first file (kernel)
From To Syms Read Shared Object Library
0xc1098dd0 0xc10bfc10 Yes /boot/kernel/ufs.ko
0xc11e24d0 0xc11e4270 Yes /boot/kernel/md.ko
0xc10cf940 0xc10ddc30 Yes /boot/kernel/vinum.ko
(kgdb) proc 316
(kgdb) bt
#0 mi_switch () at ../../../kern/kern_synch.c:849
#1 0xc01b7d14 in msleep (ident=0xc1292e00, mtx=0x0, priority=76, wmesg=0x0,
timo=0) at ../../../kern/kern_synch.c:559
#2 0xc11e3052 in md_kthread (arg=0xc1292e00) at /usr/src/sys/dev/md/md.c:578
#3 0xc019d2e5 in fork_exit (callout=0xc11e2fd0 <md_kthread>, arg=0x0,
frame=0x0) at ../../../kern/kern_fork.c:853
(kgdb)
Index: Makefile
===================================================================
RCS file: /dump/FreeBSD-CVS/src/gnu/usr.bin/binutils/gdb/Makefile,v
retrieving revision 1.61
diff -u -r1.61 Makefile
--- Makefile 29 Jun 2002 03:16:10 -0000 1.61
+++ Makefile 7 Oct 2002 10:31:41 -0000
@@ -37,7 +37,7 @@
ui-file.c ui-out.c wrapper.c cli-out.c \
cli-cmds.c cli-cmds.h cli-decode.c cli-decode.h cli-script.c \
cli-script.h cli-setshow.c cli-setshow.h cli-utils.c cli-utils.h
-XSRCS+= freebsd-uthread.c kvm-fbsd.c
+XSRCS+= freebsd-uthread.c kvm-fbsd.c solib-fbsd-kld.c
SRCS= init.c ${XSRCS} nm.h tm.h xm.h gdbversion.c xregex.h
.if exists(${.CURDIR}/Makefile.${TARGET_ARCH})
Index: fbsd-kgdb.h
===================================================================
RCS file: /dump/FreeBSD-CVS/src/gnu/usr.bin/binutils/gdb/fbsd-kgdb.h,v
retrieving revision 1.3
diff -u -r1.3 fbsd-kgdb.h
--- fbsd-kgdb.h 18 Sep 2002 16:20:49 -0000 1.3
+++ fbsd-kgdb.h 6 Oct 2002 23:32:14 -0000
@@ -7,6 +7,7 @@
extern int kernel_debugging;
extern int kernel_writablecore;
+extern struct target_so_ops kgdb_so_ops;
#define ADDITIONAL_OPTIONS \
{"kernel", no_argument, &kernel_debugging, 1}, \
Index: kvm-fbsd.c
===================================================================
RCS file: /dump/FreeBSD-CVS/src/gnu/usr.bin/binutils/gdb/kvm-fbsd.c,v
retrieving revision 1.42
diff -u -r1.42 kvm-fbsd.c
--- kvm-fbsd.c 18 Sep 2002 16:19:05 -0000 1.42
+++ kvm-fbsd.c 6 Oct 2002 23:41:56 -0000
@@ -56,6 +56,7 @@
#include "bfd.h"
#include "target.h"
#include "gdbcore.h"
+#include "solist.h"
static void
kcore_files_info (struct target_ops *);
@@ -72,6 +73,10 @@
static int
xfer_umem (CORE_ADDR, char *, int, int);
+#ifdef SOLIB_ADD
+static int kcore_solib_add_stub (PTR);
+#endif
+
static char *core_file;
static kvm_t *core_kd;
static struct pcb cur_pcb;
@@ -209,6 +214,12 @@
inferior_ptid = null_ptid; /* Avoid confusion from thread stuff. */
+ /* Clear out solib state while the bfd is still open. See
+ comments in clear_solib in solib.c. */
+#ifdef CLEAR_SOLIB
+ CLEAR_SOLIB ();
+#endif
+
if (core_kd)
{
kvm_close (core_kd);
@@ -305,7 +316,16 @@
printf ("---\n");
}
- if (!ontop)
+ if (ontop)
+ {
+ /* Add symbols and section mappings for any kernel modules. */
+#ifdef SOLIB_ADD
+ current_target_so_ops = &kgdb_so_ops;
+ catch_errors (kcore_solib_add_stub, &from_tty, (char *) 0,
+ RETURN_MASK_ALL);
+#endif
+ }
+ else
{
warning ("you won't be able to access this core file until you terminate\n"
"your %s; do ``info files''", target_longname);
@@ -651,6 +671,15 @@
if (set_context ((CORE_ADDR) val))
error ("invalid proc address");
}
+
+#ifdef SOLIB_ADD
+static int
+kcore_solib_add_stub (PTR from_ttyp)
+{
+ SOLIB_ADD (NULL, *(int *) from_ttyp, ¤t_target, auto_solib_add);
+ return 0;
+}
+#endif /* SOLIB_ADD */
void
_initialize_kcorelow (void)
Index: solib-fbsd-kld.c
===================================================================
RCS file: solib-fbsd-kld.c
diff -N solib-fbsd-kld.c
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ solib-fbsd-kld.c 7 Oct 2002 10:39:48 -0000
@@ -0,0 +1,181 @@
+/* Handle FreeBSD kernel modules as shared libraries.
+ Copyright 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998, 1999, 2000,
+ 2001
+ Free Software Foundation, Inc.
+
+ This file is part of GDB.
+
+ This program is free software; you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation; either version 2 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program; if not, write to the Free Software
+ Foundation, Inc., 59 Temple Place - Suite 330,
+ Boston, MA 02111-1307, USA. */
+
+#include <sys/param.h>
+#include <sys/queue.h>
+#define _KERNEL
+#include <sys/linker.h>
+#undef _KERNEL
+
+#include "defs.h"
+#include "symtab.h"
+#include "bfd.h"
+#include "symfile.h"
+#include "objfiles.h"
+#include "gdbcore.h"
+#include "target.h"
+#include "inferior.h"
+
+#include "solist.h"
+
+struct lm_info
+ {
+ CORE_ADDR address;
+ };
+
+static void
+kgdb_relocate_section_addresses (struct so_list *so,
+ struct section_table *sec)
+{
+ sec->addr += so->lm_info->address;
+ sec->endaddr += so->lm_info->address;
+}
+
+static int
+kgdb_open_symbol_file_object (void *from_ttyp)
+{
+ warning ("kgdb_open_symbol_file_object called\n");
+ return 0;
+}
+
+static struct so_list *
+kgdb_current_sos (void)
+{
+ linker_file_list_t linker_files;
+ struct linker_file lfile;
+ struct minimal_symbol *msymbol;
+ struct linker_file *lfilek;
+ struct so_list *head = NULL;
+ struct so_list **link_ptr = &head;
+
+ CORE_ADDR lfiles_addr;
+
+ msymbol = lookup_minimal_symbol ("linker_files", NULL, symfile_objfile);
+ if (msymbol == NULL || SYMBOL_VALUE_ADDRESS (msymbol) == 0)
+ {
+ warning ("failed to find linker_files symbol\n");
+ return 0;
+ }
+ lfiles_addr = SYMBOL_VALUE_ADDRESS (msymbol);
+ if (target_read_memory (lfiles_addr, (char *)&linker_files,
+ sizeof (linker_files)))
+ {
+ warning ("failed to read linker_files data\n");
+ return 0;
+ }
+ for (lfilek = TAILQ_FIRST (&linker_files); lfilek != NULL;
+ lfilek = TAILQ_NEXT (&lfile, link))
+ {
+ struct so_list *new;
+ struct cleanup *old_chain;
+ char *buf;
+ int errcode;
+
+ if (target_read_memory ((CORE_ADDR) lfilek, (char *) &lfile,
+ sizeof (lfile)))
+ {
+ warning ("failed to read linker file data at %p\n", lfilek);
+ return 0;
+ }
+ target_read_string ((CORE_ADDR) lfile.filename, &buf,
+ SO_NAME_MAX_PATH_SIZE - 1, &errcode);
+ if (errcode != 0)
+ {
+ warning ("cannot read linker file pathname: %s\n",
+ safe_strerror (errcode));
+ return 0;
+ }
+ if (lfilek == TAILQ_FIRST (&linker_files)) /* XXX kernel always first? */
+ {
+ warning ("skipping first file (%s)\n", buf);
+ xfree (buf);
+ continue;
+ }
+
+ new = (struct so_list *) xmalloc (sizeof (struct so_list));
+ old_chain = make_cleanup (xfree, new);
+
+ memset (new, 0, sizeof (*new));
+
+ new->lm_info = xmalloc (sizeof (struct lm_info));
+ make_cleanup (xfree, new->lm_info);
+
+ new->lm_info->address = (CORE_ADDR) lfile.address;
+
+ strncpy (new->so_original_name, buf, SO_NAME_MAX_PATH_SIZE - 1);
+ new->so_original_name[SO_NAME_MAX_PATH_SIZE - 1] = '\0';
+ xfree (buf);
+ snprintf (new->so_name, SO_NAME_MAX_PATH_SIZE, "/boot/kernel/%s",
+ new->so_original_name);
+
+ new->next = NULL;
+ *link_ptr = new;
+ link_ptr = &new->next;
+
+ discard_cleanups (old_chain);
+ }
+ return head;
+}
+
+static int
+kgdb_in_dynsym_resolve_code (CORE_ADDR pc)
+{
+ warning ("kgdb_in_dynsym_resolve_code called\n");
+ return 0;
+}
+
+static void
+kgdb_special_symbol_handling (void)
+{
+}
+
+static void
+kgdb_solib_create_inferior_hook (void)
+{
+ warning ("kgdb_solib_create_inferior_hook called\n");
+}
+
+static void
+kgdb_clear_solib (void)
+{
+}
+
+static void
+kgdb_free_so (struct so_list *so)
+{
+ xfree (so->lm_info);
+}
+
+struct target_so_ops kgdb_so_ops;
+
+void
+_initialize_kgdb_solib (void)
+{
+ kgdb_so_ops.relocate_section_addresses = kgdb_relocate_section_addresses;
+ kgdb_so_ops.free_so = kgdb_free_so;
+ kgdb_so_ops.clear_solib = kgdb_clear_solib;
+ kgdb_so_ops.solib_create_inferior_hook = kgdb_solib_create_inferior_hook;
+ kgdb_so_ops.special_symbol_handling = kgdb_special_symbol_handling;
+ kgdb_so_ops.current_sos = kgdb_current_sos;
+ kgdb_so_ops.open_symbol_file_object = kgdb_open_symbol_file_object;
+ kgdb_so_ops.in_dynsym_resolve_code = kgdb_in_dynsym_resolve_code;
+}
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