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Message-ID: <1332352536-29186-3-git-send-email-jason.wessel@windriver.com>
Date: Wed, 21 Mar 2012 12:55:36 -0500
From: Jason Wessel <jason.wessel@...driver.com>
To: <linux-kernel@...r.kernel.org>
CC: <kgdb-bugreport@...ts.sourceforge.net>,
<masami.hiramatsu.pt@...achi.com>, <tim.bird@...sony.com>
Subject: [PATCH 2/2] kgdb,debug_core,kgdbts: End DEBUG_RODATA limitation using kprobe breakpoints
There has long been a limitation using software breakpoints with a
kernel compiled with CONFIG_DEBUG_RODATA. The kprobe breakpoint code
has its own text_poke() function which accommodates writing a
breakpoint into a read-only page. The debug_core can make use of the
text_poke() capabilities by using the kprobes API, specifically
arch_arm_kprobe() and arch_disarm_kprobe(). For now it is safe to use
a single statically allocated kprobe structure to call the kprobes API
because the debug_core breakpoint API is only used when the kernel is
in the debug state.
The debug_core will first attempt to use the traditional
probe_kernel_write(), and next try using a kprobe breakpoint. The
kgdb test suite was updated to run all the software breakpoint tests
when using a kernel with built with CONFIG_DEBUG_RODATA.
Signed-off-by: Jason Wessel <jason.wessel@...driver.com>
---
drivers/misc/kgdbts.c | 13 -------------
include/linux/kgdb.h | 3 ++-
kernel/debug/debug_core.c | 40 +++++++++++++++++++++++++++++++++++++++-
3 files changed, 41 insertions(+), 15 deletions(-)
diff --git a/drivers/misc/kgdbts.c b/drivers/misc/kgdbts.c
index 3f7ad83..672b4a5 100644
--- a/drivers/misc/kgdbts.c
+++ b/drivers/misc/kgdbts.c
@@ -940,19 +940,6 @@ static void kgdbts_run_tests(void)
run_nmi_sleep_test(nmi_sleep);
}
-#ifdef CONFIG_DEBUG_RODATA
- /* Until there is an api to write to read-only text segments, use
- * HW breakpoints for the remainder of any tests, else print a
- * failure message if hw breakpoints do not work.
- */
- if (!(arch_kgdb_ops.flags & KGDB_HW_BREAKPOINT && hwbreaks_ok)) {
- eprintk("kgdbts: HW breakpoints do not work,"
- "skipping remaining tests\n");
- return;
- }
- force_hwbrks = 1;
-#endif /* CONFIG_DEBUG_RODATA */
-
/* If the do_fork test is run it will be the last test that is
* executed because a kernel thread will be spawned at the very
* end to unregister the debug hooks.
diff --git a/include/linux/kgdb.h b/include/linux/kgdb.h
index e5d689c..48f17d2 100644
--- a/include/linux/kgdb.h
+++ b/include/linux/kgdb.h
@@ -63,7 +63,8 @@ enum kgdb_bptype {
BP_HARDWARE_BREAKPOINT,
BP_WRITE_WATCHPOINT,
BP_READ_WATCHPOINT,
- BP_ACCESS_WATCHPOINT
+ BP_ACCESS_WATCHPOINT,
+ BP_KPROBE_BREAKPOINT,
};
enum kgdb_bpstate {
diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c
index a7e52ca..9051844 100644
--- a/kernel/debug/debug_core.c
+++ b/kernel/debug/debug_core.c
@@ -49,6 +49,7 @@
#include <linux/smp.h>
#include <linux/mm.h>
#include <linux/rcupdate.h>
+#include <linux/kprobes.h>
#include <asm/cacheflush.h>
#include <asm/byteorder.h>
@@ -108,6 +109,13 @@ module_param(kgdbreboot, int, 0644);
static struct kgdb_bkpt kgdb_break[KGDB_MAX_BREAKPOINTS] = {
[0 ... KGDB_MAX_BREAKPOINTS-1] = { .state = BP_UNDEFINED }
};
+/*
+ * probe_write_tmp is used to r/w breakpoints with the kprobe
+ * interface, it is not protected for reentrancy
+ */
+#if defined(CONFIG_KPROBES) && defined(CONFIG_DEBUG_RODATA)
+static struct kprobe probe_write_tmp;
+#endif /* CONFIG_KPROBES && CONFIG_DEBUG_RODATA */
/*
* The CPU# of the active CPU, or -1 if none:
@@ -165,17 +173,48 @@ int __weak kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt)
{
int err;
+ bpt->type = BP_BREAKPOINT;
err = probe_kernel_read(bpt->saved_instr, (char *)bpt->bpt_addr,
BREAK_INSTR_SIZE);
if (err)
return err;
err = probe_kernel_write((char *)bpt->bpt_addr,
arch_kgdb_ops.gdb_bpt_instr, BREAK_INSTR_SIZE);
+#if defined(CONFIG_KPROBES) && defined(CONFIG_DEBUG_RODATA)
+ if (!err)
+ return err;
+ probe_write_tmp.addr = (kprobe_opcode_t *)bpt->bpt_addr;
+ arch_arm_kprobe(&probe_write_tmp);
+ err = probe_kernel_read(&probe_write_tmp.opcode, (char *)bpt->bpt_addr,
+ BREAK_INSTR_SIZE);
+ if (err)
+ return err;
+ if (memcmp(&probe_write_tmp.opcode, arch_kgdb_ops.gdb_bpt_instr,
+ BREAK_INSTR_SIZE))
+ return -EINVAL;
+ bpt->type = BP_KPROBE_BREAKPOINT;
+#endif /* CONFIG_KPROBES && CONFIG_DEBUG_RODATA */
return err;
}
int __weak kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt)
{
+#if defined(CONFIG_KPROBES) && defined(CONFIG_DEBUG_RODATA)
+ int err;
+
+ if (bpt->type != BP_KPROBE_BREAKPOINT)
+ goto knl_write;
+ probe_write_tmp.addr = (kprobe_opcode_t *)bpt->bpt_addr;
+ memcpy(&probe_write_tmp.opcode, bpt->saved_instr, BREAK_INSTR_SIZE);
+ arch_disarm_kprobe(&probe_write_tmp);
+ err = probe_kernel_read(&probe_write_tmp.opcode, (char *)bpt->bpt_addr,
+ BREAK_INSTR_SIZE);
+ if (err ||
+ memcmp(&probe_write_tmp.opcode, bpt->saved_instr, BREAK_INSTR_SIZE))
+ goto knl_write;
+ return err;
+knl_write:
+#endif /* CONFIG_KPROBES && CONFIG_DEBUG_RODATA */
return probe_kernel_write((char *)bpt->bpt_addr,
(char *)bpt->saved_instr, BREAK_INSTR_SIZE);
}
@@ -294,7 +333,6 @@ int dbg_set_sw_break(unsigned long addr)
return -E2BIG;
kgdb_break[breakno].state = BP_SET;
- kgdb_break[breakno].type = BP_BREAKPOINT;
kgdb_break[breakno].bpt_addr = addr;
return 0;
--
1.7.5.4
--
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