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powerpc/kgdb: Restore current_thread_info properly 

For powerpc BooKE and e200, singlestep is handled on the critical/dbg
exception stack. This causes current_thread_info() to fail for kgdb
internal, so previously We work around this issue by copying
the thread_info from the kernel stack before calling kgdb_handle_exception,
and copying it back afterwards.

But actually we don't do this properly. We should backup current_thread_info
then restore that when exit.

Signed-off-by: Tiejun Chen <tiejun.chen@windriver.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This commit is contained in:
Tiejun Chen 2012-08-22 16:10:20 +00:00 committed by Benjamin Herrenschmidt
parent 949616cf2d
commit 5f630401f9
1 changed files with 9 additions and 2 deletions
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11
arch/powerpc/kernel/kgdb.c
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@ -25,6 +25,7 @@
#include <asm/processor.h>
#include <asm/machdep.h>
#include <asm/debug.h>
#include <linux/slab.h>
/*
* This table contains the mapping between PowerPC hardware trap types, and
@ -153,6 +154,8 @@ static int kgdb_handle_breakpoint(struct pt_regs *regs)
static int kgdb_singlestep(struct pt_regs *regs)
{
struct thread_info *thread_info, *exception_thread_info;
struct thread_info *backup_current_thread_info = \
(struct thread_info *)kmalloc(sizeof(struct thread_info), GFP_KERNEL);
if (user_mode(regs))
return 0;
@ -170,13 +173,17 @@ static int kgdb_singlestep(struct pt_regs *regs)
thread_info = (struct thread_info *)(regs->gpr[1] & ~(THREAD_SIZE-1));
exception_thread_info = current_thread_info();
if (thread_info != exception_thread_info)
if (thread_info != exception_thread_info) {
/* Save the original current_thread_info. */
memcpy(backup_current_thread_info, exception_thread_info, sizeof *thread_info);
memcpy(exception_thread_info, thread_info, sizeof *thread_info);
}
kgdb_handle_exception(0, SIGTRAP, 0, regs);
if (thread_info != exception_thread_info)
memcpy(thread_info, exception_thread_info, sizeof *thread_info);
/* Restore current_thread_info lastly. */
memcpy(exception_thread_info, backup_current_thread_info, sizeof *thread_info);
return 1;
}