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Subject[PATCH 3/8] x86,kgdb: Implement early hardware breakpoint debugging
Date
It is not possible to use the hw_breakpoint.c API prior to mm_init(),
but it is possible to use hardware breakpoints with the kernel
debugger.

Prior to smp_init() it is possible to simply write to the dr registers
of the boot cpu directly. This can be used up until the
kgdb_arch_late() is invoked, at which point the standard hw_breakpoint.c
API will get used.

CC: Frederic Weisbecker <fweisbec@gmail.com>
CC: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
---
arch/x86/kernel/kgdb.c | 30 ++++++++++++++++++++++++++++--
1 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/kgdb.c b/arch/x86/kernel/kgdb.c
index 896874a..8e79fea 100644
--- a/arch/x86/kernel/kgdb.c
+++ b/arch/x86/kernel/kgdb.c
@@ -199,6 +199,8 @@ static struct hw_breakpoint {
struct perf_event **pev;
} breakinfo[4];

+static unsigned long early_dr7;
+
static void kgdb_correct_hw_break(void)
{
int breakno;
@@ -210,6 +212,14 @@ static void kgdb_correct_hw_break(void)
int cpu = raw_smp_processor_id();
if (!breakinfo[breakno].enabled)
continue;
+ if (dbg_is_early) {
+ set_debugreg(breakinfo[breakno].addr, breakno);
+ early_dr7 |= encode_dr7(breakno,
+ breakinfo[breakno].len,
+ breakinfo[breakno].type);
+ set_debugreg(early_dr7, 7);
+ continue;
+ }
bp = *per_cpu_ptr(breakinfo[breakno].pev, cpu);
info = counter_arch_bp(bp);
if (bp->attr.disabled != 1)
@@ -224,7 +234,8 @@ static void kgdb_correct_hw_break(void)
if (!val)
bp->attr.disabled = 0;
}
- hw_breakpoint_restore();
+ if (!dbg_is_early)
+ hw_breakpoint_restore();
}

static int hw_break_reserve_slot(int breakno)
@@ -233,6 +244,9 @@ static int hw_break_reserve_slot(int breakno)
int cnt = 0;
struct perf_event **pevent;

+ if (dbg_is_early)
+ return 0;
+
for_each_online_cpu(cpu) {
cnt++;
pevent = per_cpu_ptr(breakinfo[breakno].pev, cpu);
@@ -258,6 +272,9 @@ static int hw_break_release_slot(int breakno)
struct perf_event **pevent;
int cpu;

+ if (dbg_is_early)
+ return 0;
+
for_each_online_cpu(cpu) {
pevent = per_cpu_ptr(breakinfo[breakno].pev, cpu);
if (dbg_release_bp_slot(*pevent))
@@ -302,7 +319,11 @@ static void kgdb_remove_all_hw_break(void)
bp = *per_cpu_ptr(breakinfo[i].pev, cpu);
if (bp->attr.disabled == 1)
continue;
- arch_uninstall_hw_breakpoint(bp);
+ if (dbg_is_early)
+ early_dr7 &= ~encode_dr7(i, breakinfo[i].len,
+ breakinfo[i].type);
+ else
+ arch_uninstall_hw_breakpoint(bp);
bp->attr.disabled = 1;
}
}
@@ -379,6 +400,11 @@ void kgdb_disable_hw_debug(struct pt_regs *regs)
for (i = 0; i < 4; i++) {
if (!breakinfo[i].enabled)
continue;
+ if (dbg_is_early) {
+ early_dr7 &= ~encode_dr7(i, breakinfo[i].len,
+ breakinfo[i].type);
+ continue;
+ }
bp = *per_cpu_ptr(breakinfo[i].pev, cpu);
if (bp->attr.disabled == 1)
continue;
--
1.6.4.rc1


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