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SubjectRe: [patch] i386: fix one case of stuck dwarf2 unwinder II
>> So it would seem to me. Nevertheless, in my opinion the proper fix is
to annotate the call site
>> (in head.S) to specify a zero EIP as return address (which denotes
the bottom of a frame).
>
>Can you please send a patch to do that?
>
>That seems to be missing in some other places too, e.g. i386 sysenter
path, x86-64 kernel_thread,
>more?

Attaching both an i386 version (boot/idle thread only, you did
kernel_thread already)
and an x86-64 one (boot/idle and kernel_thread). The i386 sysenter path
is a different
thing, there we have an actual caller (though outside of the kernel),
which I'd like to
continue to reflect/catch through arch_unw_user_mode().

Jan
Add kernel thread stack frame termination for properly stopping stack
unwinds.

One open question: Should these added pushes perhaps be made
conditional upon CONFIG_STACK_UNWIND or CONFIG_UNWIND_INFO?

Signed-off-by: Jan Beulich <jbeulich@novell.com>

--- linux-2.6.18-rc4/arch/x86_64/kernel/entry.S 2006-08-15 11:29:41.000000000 +0200
+++ 2.6.18-rc4-unwind-x86_64-term/arch/x86_64/kernel/entry.S 2006-08-15 10:15:40.000000000 +0200
@@ -973,6 +973,8 @@ ENTRY(kernel_thread)
ENDPROC(kernel_thread)

child_rip:
+ pushq $0 # fake return address
+ CFI_STARTPROC
/*
* Here we are in the child and the registers are set as they were
* at kernel_thread() invocation in the parent.
@@ -983,6 +985,7 @@ child_rip:
# exit
xorl %edi, %edi
call do_exit
+ CFI_ENDPROC
ENDPROC(child_rip)

/*
--- linux-2.6.18-rc4/arch/x86_64/kernel/head.S 2006-06-18 03:49:35.000000000 +0200
+++ 2.6.18-rc4-unwind-x86_64-term/arch/x86_64/kernel/head.S 2006-08-15 11:05:13.000000000 +0200
@@ -191,6 +191,7 @@ startup_64:
* jump
*/
movq initial_code(%rip),%rax
+ pushq $0 # fake return address
jmp *%rax

/* SMP bootup changes these two */Add boot/idle kernel thread stack frame termination for properly
stopping stack unwinds.

One open question: Should this added push perhaps be made conditional
upon CONFIG_STACK_UNWIND or CONFIG_UNWIND_INFO?

Signed-off-by: Jan Beulich <jbeulich@novell.com>

--- linux-2.6.18-rc4/arch/i386/kernel/head.S 2006-08-15 11:32:08.000000000 +0200
+++ 2.6.18-rc4-unwind-i386-term/arch/i386/kernel/head.S 2006-08-15 11:06:03.000000000 +0200
@@ -317,20 +317,14 @@ is386: movl $2,%ecx # set MP
movl %eax,%gs
lldt %ax
cld # gcc2 wants the direction flag cleared at all times
+ pushl %eax # fake return address
#ifdef CONFIG_SMP
movb ready, %cl
movb $1, ready
- cmpb $0,%cl
- je 1f # the first CPU calls start_kernel
- # all other CPUs call initialize_secondary
- call initialize_secondary
- jmp L6
-1:
+ cmpb $0,%cl # the first CPU calls start_kernel
+ jne initialize_secondary # all other CPUs call initialize_secondary
#endif /* CONFIG_SMP */
- call start_kernel
-L6:
- jmp L6 # main should never return here, but
- # just in case, we know what happens.
+ jmp start_kernel

/*
* We depend on ET to be correct. This checks for 287/387.
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