In kthr.c, obtain the address of the PCB for threads that were running

on a core, when the core was stopped, by calling kgdb_trgt_core_pcb().
This has 2 advantages:
1.  We don't need to include a machine-specific header anymore and as
    such kthr.c is truly machine independent. This allows the code to
    be used in a cross-debugger.
2.  We don't need to lookup stoppcbs in generic code when it's an
    inherently target-spicific symbol. It does not exist for ia64.

Implement kgdb_trgt_core_pcb() for all architectures, except ia64, by
calling a common function called kgdb_trgt_stop_pcb(). This function
differs from kgdb_trgt_core_pcb() in that it gets the size of the PCB
structure as an argument and as such remains machine independent.

On ia64 the PCB for stopped cores is in the PCPU structure itself.
This for better scaling. The implementation of kgdb_trgt_core_pcb()
for ia64 uses the cpuid_to_pcpu[] array to to obtain the address of
the PCB structure.

gnu/usr.bin/gdb/kgdb/kgdb.h

@@ -49,6 +49,8 @@ extern struct kthr *curkthr;
 void initialize_kld_target(void);
 void initialize_kgdb_target(void);
 void kgdb_dmesg(void);
+CORE_ADDR kgdb_trgt_core_pcb(u_int);
+CORE_ADDR kgdb_trgt_stop_pcb(u_int, u_int);
 void kgdb_trgt_new_objfile(struct objfile *);
 void kgdb_trgt_fetch_registers(int);
 void kgdb_trgt_store_registers(int);

gnu/usr.bin/gdb/kgdb/kthr.c

@@ -44,12 +44,10 @@ __FBSDID("$FreeBSD$");
 #include <frame-unwind.h>
 
 #include "kgdb.h"
-#include <machine/pcb.h>
 
 static CORE_ADDR dumppcb;
 static int dumptid;
 
-static CORE_ADDR stoppcbs;
 static cpuset_t stopped_cpus;
 
 static struct kthr *first;
@@ -98,10 +96,9 @@ kgdb_thr_add_procs(uintptr_t paddr)
 			kt->kaddr = addr;
 			if (td.td_tid == dumptid)
 				kt->pcb = dumppcb;
-			else if (td.td_state == TDS_RUNNING && stoppcbs != 0 &&
+			else if (td.td_state == TDS_RUNNING &&
 			    CPU_ISSET(td.td_oncpu, &stopped_cpus))
-				kt->pcb = (uintptr_t)stoppcbs +
-				    sizeof(struct pcb) * td.td_oncpu;
+				kt->pcb = kgdb_trgt_core_pcb(td.td_oncpu);
 			else
 				kt->pcb = (uintptr_t)td.td_pcb;
 			kt->kstack = td.td_kstack;
@@ -152,8 +149,6 @@ kgdb_thr_init(void)
 	    addr != 0)
 		kvm_read(kvm, addr, &stopped_cpus, cpusetsize);
 
-	stoppcbs = kgdb_lookup("stoppcbs");
-
 	kgdb_thr_add_procs(paddr);
 	addr = kgdb_lookup("zombproc");
 	if (addr != 0) {

gnu/usr.bin/gdb/kgdb/trgt.c

@@ -53,6 +53,8 @@ __FBSDID("$FreeBSD$");
 
 #include "kgdb.h"
 
+static CORE_ADDR stoppcbs;
+
 static void	kgdb_core_cleanup(void *);
 
 static char *vmcore;
@@ -352,3 +354,18 @@ initialize_kgdb_target(void)
 	add_com ("tid", class_obscure, kgdb_set_tid_cmd,
 	   "Set current thread context");
 }
+
+CORE_ADDR
+kgdb_trgt_stop_pcb(u_int cpuid, u_int pcbsz)
+{
+	static int once = 0;
+
+	if (stoppcbs == 0 && !once) {
+		once = 1;
+		stoppcbs = kgdb_lookup("stoppcbs");
+	}
+	if (stoppcbs == 0)
+		return 0;
+
+	return (stoppcbs + pcbsz * cpuid);
+}

gnu/usr.bin/gdb/kgdb/trgt_amd64.c

@@ -44,6 +44,12 @@ __FBSDID("$FreeBSD$");
 
 #include "kgdb.h"
 
+CORE_ADDR
+kgdb_trgt_core_pcb(u_int cpuid)
+{
+	return (kgdb_trgt_stop_pcb(cpuid, sizeof(struct pcb)));
+}
+
 void
 kgdb_trgt_fetch_registers(int regno __unused)
 {

gnu/usr.bin/gdb/kgdb/trgt_arm.c

@@ -47,6 +47,12 @@ __FBSDID("$FreeBSD$");
 
 #include "kgdb.h"
 
+CORE_ADDR
+kgdb_trgt_core_pcb(u_int cpuid)
+{
+	return (kgdb_trgt_stop_pcb(cpuid, sizeof(struct pcb)));
+}
+
 void
 kgdb_trgt_fetch_registers(int regno __unused)
 {

gnu/usr.bin/gdb/kgdb/trgt_i386.c

@@ -49,6 +49,12 @@ __FBSDID("$FreeBSD$");
 
 static int ofs_fix;
 
+CORE_ADDR
+kgdb_trgt_core_pcb(u_int cpuid)
+{
+	return (kgdb_trgt_stop_pcb(cpuid, sizeof(struct pcb)));
+}
+
 void
 kgdb_trgt_fetch_registers(int regno __unused)
 {

gnu/usr.bin/gdb/kgdb/trgt_ia64.c

@@ -52,6 +52,18 @@ __FBSDID("$FreeBSD$");
 
 #include "kgdb.h"
 
+CORE_ADDR
+kgdb_trgt_core_pcb(u_int cpuid)
+{
+	CORE_ADDR addr;
+	char *expr;
+
+	asprintf(&expr, "&cpuid_to_pcpu[%d]->pc_md.pcb", cpuid);
+	addr = kgdb_parse(expr);
+	free(expr);
+	return (addr);
+}
+
 void
 kgdb_trgt_fetch_registers(int regno __unused)
 {

gnu/usr.bin/gdb/kgdb/trgt_mips.c

@@ -52,6 +52,12 @@ __FBSDID("$FreeBSD$");
 
 #include "kgdb.h"
 
+CORE_ADDR
+kgdb_trgt_core_pcb(u_int cpuid)
+{
+	return (kgdb_trgt_stop_pcb(cpuid, sizeof(struct pcb)));
+}
+
 void
 kgdb_trgt_fetch_registers(int regno __unused)
 {

gnu/usr.bin/gdb/kgdb/trgt_powerpc.c

@@ -49,6 +49,12 @@ __FBSDID("$FreeBSD$");
 
 #include "kgdb.h"
 
+CORE_ADDR
+kgdb_trgt_core_pcb(u_int cpuid)
+{
+	return (kgdb_trgt_stop_pcb(cpuid, sizeof(struct pcb)));
+}
+
 void
 kgdb_trgt_fetch_registers(int regno __unused)
 {

gnu/usr.bin/gdb/kgdb/trgt_powerpc64.c

@@ -44,6 +44,12 @@ __FBSDID("$FreeBSD$");
 
 #include "kgdb.h"
 
+CORE_ADDR
+kgdb_trgt_core_pcb(u_int cpuid)
+{
+	return (kgdb_trgt_stop_pcb(cpuid, sizeof(struct pcb)));
+}
+
 void
 kgdb_trgt_fetch_registers(int regno __unused)
 {

gnu/usr.bin/gdb/kgdb/trgt_sparc64.c

@@ -46,6 +46,12 @@ __FBSDID("$FreeBSD$");
 
 #include "kgdb.h"
 
+CORE_ADDR
+kgdb_trgt_core_pcb(u_int cpuid)
+{
+	return (kgdb_trgt_stop_pcb(cpuid, sizeof(struct pcb)));
+}
+
 void
 kgdb_trgt_fetch_registers(int regno __unused)
 {