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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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