On 6/28/11, Catalin Marinas [off-list ref] wrote:

On Tue, Jun 28, 2011 at 04:45:52PM +0100, Dmitry Eremin-Solenikov wrote:

quoted

Here is a part of gdb log generated using the attached patch:

[...]

quoted

#11 0xc0033810 in kernel_thread_helper ()
#12 0xc0033810 in kernel_thread_helper ()
Backtrace stopped: previous frame identical to this frame (corrupt stack?)

Maybe you can add something similar to the kernel_thread_helper in
arch/arm/kernel/process.c? I'm not sure whether there is something like
.cantunwind (as for the kernel unwinding information).

quoted

diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index e8d8856..44daf40 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S

@@ -28,6 +28,7 @@
 #include "entry-header.S"
 #include <asm/entry-macro-multi.S>

+	.cfi_sections	.debug_frame
 /*
  * Interrupt handling.  Preserves r7, r8, r9
  */

@@ -113,6 +114,7 @@ ENDPROC(__und_invalid)

 	.macro	svc_entry, stack_hole=0
  UNWIND(.fnstart		)
+	.cfi_startproc
  UNWIND(.save {r0 - pc}		)
 	sub	sp, sp, #(S_FRAME_SIZE + \stack_hole - 4)
 #ifdef CONFIG_THUMB2_KERNEL

@@ -146,6 +148,24 @@ ENDPROC(__und_invalid)
 	@  r4 - orig_r0 (see pt_regs definition in ptrace.h)
 	@
 	stmia	r5, {r0 - r4}
+	.cfi_def_cfa_offset S_PC + 4
+	.cfi_offset 14, -4
+#define	CFI_REG_OFF(r) .cfi_offset r, (r - 16) * 4
+	CFI_REG_OFF(13)
+	CFI_REG_OFF(12)
+	CFI_REG_OFF(11)
+	CFI_REG_OFF(10)
+	CFI_REG_OFF(9)
+	CFI_REG_OFF(8)
+	CFI_REG_OFF(7)
+	CFI_REG_OFF(6)
+	CFI_REG_OFF(5)
+	CFI_REG_OFF(4)
+	CFI_REG_OFF(3)
+	CFI_REG_OFF(2)
+	CFI_REG_OFF(1)
+	CFI_REG_OFF(0)
+#undef CFI_REG_OFF
 	.endm

Do we need all the registers in here for gdb stack unwinding? In general
we would only need LR, SP and FP.

CFI info isn't only related to stack unwinding. IIUC (I'll have to run
more experiments)
these instrutions will help me to get correct variables/arguments
values in the before-exception stack frames.

--
Catalin

-- 
With best wishes
Dmitry