Sergei Shtylyov wrote:
Hm... yet the kernel I was booting was UP. The same happened with
SMP kernel I've just tried. Now I'm confused. :-/
something was broken WRT handling of the h/w breask as being per-CPU
resource but not seeing anything obvious...
The piece that clears DR7 is called _cpu_init().
It seems that we'll have to patch this to contain the state of the hw
registers from KGDB. Part of this is due to the lazy way the kernel
handles the breakpoints today. My thoughts are that other debuggers or
tools besides kgdb should be able to make use of this so it should be
done in a platform independent way and the initialization values should
perhaps be globals, or that there should be a kernel space version of
the registers. Doing this would be useful to in that you could check it
on the task swap and set it on the jump from user to kernel space if you
really wanted to have complete control.
An initial work around might be the attached patch. And of course you
will want to make sure your cvs tree is up todate as this is against the
2.6.21 branch.
Jason.
---
arch/i386/kernel/cpu/common.c | 14 ++++++++------
arch/i386/kernel/kgdb.c | 14 ++++++++++----
include/asm-i386/cpu.h | 2 ++
3 files changed, 20 insertions(+), 10 deletions(-)
Index: linux-2.6.21-standard/arch/i386/kernel/cpu/common.c
===================================================================
--- linux-2.6.21-standard.orig/arch/i386/kernel/cpu/common.c
+++ linux-2.6.21-standard/arch/i386/kernel/cpu/common.c
@@ -721,6 +721,8 @@ void __cpuinit cpu_set_gdt(int cpu)
set_kernel_fs();
}
+unsigned long kernel_debugreg[8];
+
/* Common CPU init for both boot and secondary CPUs */
static void __cpuinit _cpu_init(int cpu, struct task_struct *curr)
{
@@ -768,12 +770,12 @@ static void __cpuinit _cpu_init(int cpu,
asm volatile ("mov %0, %%gs" : : "r" (0));
/* Clear all 6 debug registers: */
- set_debugreg(0, 0);
- set_debugreg(0, 1);
- set_debugreg(0, 2);
- set_debugreg(0, 3);
- set_debugreg(0, 6);
- set_debugreg(0, 7);
+ set_debugreg(kernel_debugreg[0], 0);
+ set_debugreg(kernel_debugreg[1], 1);
+ set_debugreg(kernel_debugreg[2], 2);
+ set_debugreg(kernel_debugreg[3], 3);
+ set_debugreg(kernel_debugreg[6], 6);
+ set_debugreg(kernel_debugreg[7], 7);
/*
* Force FPU initialization:
Index: linux-2.6.21-standard/arch/i386/kernel/kgdb.c
===================================================================
--- linux-2.6.21-standard.orig/arch/i386/kernel/kgdb.c
+++ linux-2.6.21-standard/arch/i386/kernel/kgdb.c
@@ -43,6 +43,7 @@
#include <asm/apicdef.h>
#include <asm/desc.h>
#include <asm/kdebug.h>
+#include <asm/cpu.h>
#include "mach_ipi.h"
@@ -129,6 +130,11 @@ static struct hw_breakpoint {
{ .enabled = 0 },
};
+#define kgdb_set_debugreg(val, num) { \
+ kernel_debugreg[num] = val; \
+ set_debugreg(val, num); \
+}
+
static void kgdb_correct_hw_break(void)
{
int breakno;
@@ -148,19 +154,19 @@ static void kgdb_correct_hw_break(void)
((breakno << 2) + 16);
switch (breakno) {
case 0:
- set_debugreg(breakinfo[0].addr, 0);
+ kgdb_set_debugreg(breakinfo[0].addr, 0);
break;
case 1:
- set_debugreg(breakinfo[1].addr, 1);
+ kgdb_set_debugreg(breakinfo[1].addr, 1);
break;
case 2:
- set_debugreg(breakinfo[2].addr, 2);
+ kgdb_set_debugreg(breakinfo[2].addr, 2);
break;
case 3:
- set_debugreg(breakinfo[3].addr, 3);
+ kgdb_set_debugreg(breakinfo[3].addr, 3);
break;
}
} else if ((dr7 & breakbit) && !breakinfo[breakno].enabled) {
Index: linux-2.6.21-standard/include/asm-i386/cpu.h
===================================================================
--- linux-2.6.21-standard.orig/include/asm-i386/cpu.h
+++ linux-2.6.21-standard/include/asm-i386/cpu.h
@@ -18,5 +18,7 @@ extern int enable_cpu_hotplug;
#define enable_cpu_hotplug 0
#endif
+extern unsigned long *kernel_debugreg;
+
DECLARE_PER_CPU(int, cpu_state);
#endif /* _ASM_I386_CPU_H_ */
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