3 files changed, 94 insertions, 29 deletions

diff --git a/Documentation/DocBook/kgdb.tmpl b/Documentation/DocBook/kgdb.tmpl
index e8acd1f03456..372dec20c8da 100644
--- a/Documentation/DocBook/kgdb.tmpl
+++ b/Documentation/DocBook/kgdb.tmpl
@@ -98,6 +98,24 @@
     "Kernel debugging" select "KGDB: kernel debugging with remote gdb".
     </para>
     <para>
+    It is advised, but not required that you turn on the
+    CONFIG_FRAME_POINTER kernel option.  This option inserts code to
+    into the compiled executable which saves the frame information in
+    registers or on the stack at different points which will allow a
+    debugger such as gdb to more accurately construct stack back traces
+    while debugging the kernel.
+    </para>
+    <para>
+    If the architecture that you are using supports the kernel option
+    CONFIG_DEBUG_RODATA, you should consider turning it off.  This
+    option will prevent the use of software breakpoints because it
+    marks certain regions of the kernel's memory space as read-only.
+    If kgdb supports it for the architecture you are using, you can
+    use hardware breakpoints if you desire to run with the
+    CONFIG_DEBUG_RODATA option turned on, else you need to turn off
+    this option.
+    </para>
+    <para>
     Next you should choose one of more I/O drivers to interconnect debugging
     host and debugged target.  Early boot debugging requires a KGDB
     I/O driver that supports early debugging and the driver must be
diff --git a/kernel/kgdb.c b/kernel/kgdb.c
index 3ec23c3ec97f..eaa21fc9ad1d 100644
--- a/kernel/kgdb.c
+++ b/kernel/kgdb.c
@@ -56,12 +56,14 @@
 
 static int kgdb_break_asap;
 
+#define KGDB_MAX_THREAD_QUERY 17
 struct kgdb_state {
         int                     ex_vector;
         int                     signo;
         int                     err_code;
         int                     cpu;
         int                     pass_exception;
+        unsigned long           thr_query;
         unsigned long           threadid;
         long                    kgdb_usethreadid;
         struct pt_regs          *linux_regs;
@@ -166,13 +168,6 @@ early_param("nokgdbroundup", opt_nokgdbroundup);
  * Weak aliases for breakpoint management,
  * can be overriden by architectures when needed:
  */
-int __weak kgdb_validate_break_address(unsigned long addr)
-{
-        char tmp_variable[BREAK_INSTR_SIZE];
-
-        return probe_kernel_read(tmp_variable, (char *)addr, BREAK_INSTR_SIZE);
-}
-
 int __weak kgdb_arch_set_breakpoint(unsigned long addr, char *saved_instr)
 {
         int err;
@@ -191,6 +186,25 @@ int __weak kgdb_arch_remove_breakpoint(unsigned long addr, char *bundle)
                                   (char *)bundle, BREAK_INSTR_SIZE);
 }
 
+int __weak kgdb_validate_break_address(unsigned long addr)
+{
+        char tmp_variable[BREAK_INSTR_SIZE];
+        int err;
+        /* Validate setting the breakpoint and then removing it.  In the
+         * remove fails, the kernel needs to emit a bad message because we
+         * are deep trouble not being able to put things back the way we
+         * found them.
+         */
+        err = kgdb_arch_set_breakpoint(addr, tmp_variable);
+        if (err)
+                return err;
+        err = kgdb_arch_remove_breakpoint(addr, tmp_variable);
+        if (err)
+                printk(KERN_ERR "KGDB: Critical breakpoint error, kernel "
+                   "memory destroyed at: %lx", addr);
+        return err;
+}
+
 unsigned long __weak kgdb_arch_pc(int exception, struct pt_regs *regs)
 {
         return instruction_pointer(regs);
@@ -433,9 +447,14 @@ int kgdb_hex2long(char **ptr, unsigned long *long_val)
 {
         int hex_val;
         int num = 0;
+        int negate = 0;
 
         *long_val = 0;
 
+        if (**ptr == '-') {
+                negate = 1;
+                (*ptr)++;
+        }
         while (**ptr) {
                 hex_val = hex(**ptr);
                 if (hex_val < 0)
@@ -446,6 +465,9 @@ int kgdb_hex2long(char **ptr, unsigned long *long_val)
                 (*ptr)++;
         }
 
+        if (negate)
+                *long_val = -*long_val;
+
         return num;
 }
 
@@ -515,10 +537,16 @@ static void int_to_threadref(unsigned char *id, int value)
 static struct task_struct *getthread(struct pt_regs *regs, int tid)
 {
         /*
-         * Non-positive TIDs are remapped idle tasks:
+         * Non-positive TIDs are remapped to the cpu shadow information
          */
-        if (tid <= 0)
-                return idle_task(-tid);
+        if (tid == 0 || tid == -1)
+                tid = -atomic_read(&kgdb_active) - 2;
+        if (tid < 0) {
+                if (kgdb_info[-tid - 2].task)
+                        return kgdb_info[-tid - 2].task;
+                else
+                        return idle_task(-tid - 2);
+        }
 
         /*
          * find_task_by_pid_ns() does not take the tasklist lock anymore
@@ -725,14 +753,15 @@ setundefined:
 }
 
 /*
- * Remap normal tasks to their real PID, idle tasks to -1 ... -NR_CPUs:
+ * Remap normal tasks to their real PID,
+ * CPU shadow threads are mapped to -CPU - 2
  */
 static inline int shadow_pid(int realpid)
 {
         if (realpid)
                 return realpid;
 
-        return -1-raw_smp_processor_id();
+        return -raw_smp_processor_id() - 2;
 }
 
 static char gdbmsgbuf[BUFMAX + 1];
@@ -826,7 +855,7 @@ static void gdb_cmd_getregs(struct kgdb_state *ks)
                 local_debuggerinfo = kgdb_info[ks->cpu].debuggerinfo;
         } else {
                 local_debuggerinfo = NULL;
-                for (i = 0; i < NR_CPUS; i++) {
+                for_each_online_cpu(i) {
                         /*
                          * Try to find the task on some other
                          * or possibly this node if we do not
@@ -960,10 +989,13 @@ static int gdb_cmd_reboot(struct kgdb_state *ks)
 /* Handle the 'q' query packets */
 static void gdb_cmd_query(struct kgdb_state *ks)
 {
-        struct task_struct *thread;
+        struct task_struct *g;
+        struct task_struct *p;
         unsigned char thref[8];
         char *ptr;
         int i;
+        int cpu;
+        int finished = 0;
 
         switch (remcom_in_buffer[1]) {
         case 's':
@@ -973,22 +1005,34 @@ static void gdb_cmd_query(struct kgdb_state *ks)
                         break;
                 }
 
-                if (remcom_in_buffer[1] == 'f')
-                        ks->threadid = 1;
-
+                i = 0;
                 remcom_out_buffer[0] = 'm';
                 ptr = remcom_out_buffer + 1;
-
-                for (i = 0; i < 17; ks->threadid++) {
-                        thread = getthread(ks->linux_regs, ks->threadid);
-                        if (thread) {
-                                int_to_threadref(thref, ks->threadid);
+                if (remcom_in_buffer[1] == 'f') {
+                        /* Each cpu is a shadow thread */
+                        for_each_online_cpu(cpu) {
+                                ks->thr_query = 0;
+                                int_to_threadref(thref, -cpu - 2);
                                 pack_threadid(ptr, thref);
                                 ptr += BUF_THREAD_ID_SIZE;
                                 *(ptr++) = ',';
                                 i++;
                         }
                 }
+
+                do_each_thread(g, p) {
+                        if (i >= ks->thr_query && !finished) {
+                                int_to_threadref(thref, p->pid);
+                                pack_threadid(ptr, thref);
+                                ptr += BUF_THREAD_ID_SIZE;
+                                *(ptr++) = ',';
+                                ks->thr_query++;
+                                if (ks->thr_query % KGDB_MAX_THREAD_QUERY == 0)
+                                        finished = 1;
+                        }
+                        i++;
+                } while_each_thread(g, p);
+
                 *(--ptr) = '\0';
                 break;
 
@@ -1011,15 +1055,15 @@ static void gdb_cmd_query(struct kgdb_state *ks)
                         error_packet(remcom_out_buffer, -EINVAL);
                         break;
                 }
-                if (ks->threadid > 0) {
+                if ((int)ks->threadid > 0) {
                         kgdb_mem2hex(getthread(ks->linux_regs,
                                         ks->threadid)->comm,
                                         remcom_out_buffer, 16);
                 } else {
                         static char tmpstr[23 + BUF_THREAD_ID_SIZE];
 
-                        sprintf(tmpstr, "Shadow task %d for pid 0",
-                                        (int)(-ks->threadid-1));
+                        sprintf(tmpstr, "shadowCPU%d",
+                                        (int)(-ks->threadid - 2));
                         kgdb_mem2hex(tmpstr, remcom_out_buffer, strlen(tmpstr));
                 }
                 break;
diff --git a/lib/Kconfig.kgdb b/lib/Kconfig.kgdb
index 2cfd2721f7ed..9b5d1d7f2ef7 100644
--- a/lib/Kconfig.kgdb
+++ b/lib/Kconfig.kgdb
@@ -4,14 +4,17 @@ config HAVE_ARCH_KGDB
 
 menuconfig KGDB
         bool "KGDB: kernel debugging with remote gdb"
-        select FRAME_POINTER
         depends on HAVE_ARCH_KGDB
         depends on DEBUG_KERNEL && EXPERIMENTAL
         help
           If you say Y here, it will be possible to remotely debug the
-          kernel using gdb.  Documentation of kernel debugger is available
-          at http://kgdb.sourceforge.net as well as in DocBook form
-          in Documentation/DocBook/.  If unsure, say N.
+          kernel using gdb.  It is recommended but not required, that
+          you also turn on the kernel config option
+          CONFIG_FRAME_POINTER to aid in producing more reliable stack
+          backtraces in the external debugger.  Documentation of
+          kernel debugger is available at http://kgdb.sourceforge.net
+          as well as in DocBook form in Documentation/DocBook/.  If
+          unsure, say N.
 
 if KGDB