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    SubjectRe: [PATCH] dump_stack: convert generic dump_stack into a weak symbol
    On Mon 2018-03-05 14:37:42, Sergey Senozhatsky wrote:
    > We want to move dump_stack related functions out of printk C
    > code and consolidate them in lib/dump_stack file. The reason why
    > dump_stack_print_info()/etc ended up in printk.c was a "generic"
    > (dummy) lib dump_stack() function, which archs can override.
    > For example, blackfin and nds32, define their own EXPORT_SYMBOL
    > dump_stack() functions.
    >
    > In case of blackfin that arch-specific dump_stack() symbol invokes
    > a global dump_stack_print_info() function. So we can't easily move
    > dump_stack_print_info() to lib/dump_stack, because this way we will
    > link with lib/dump_stack.o file, which will bring in a generic
    > dump_stack() symbol with it, causing a multiple definitions error:
    > - one dump_stack() from arch/blackfin/dumpstack
    > - the other one from lib/dump_stack
    >
    > Convert generic dump_stack() into a weak symbol. So we will be
    > able link with lib/dump_stack and at the same time archs will
    > be able to override dump_stack(). It also opens up a way for us
    > to move dump_stack_set_arch_desc(), dump_stack_print_info() and
    > show_regs_print_info() to lib/dump_stack.
    >
    > Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
    > ---
    > arch/blackfin/kernel/dumpstack.c | 1 -
    > arch/nds32/kernel/traps.c | 2 --
    > lib/dump_stack.c | 4 ++--
    > 3 files changed, 2 insertions(+), 5 deletions(-)
    >
    > diff --git a/arch/blackfin/kernel/dumpstack.c b/arch/blackfin/kernel/dumpstack.c
    > index 3c992c1f8ef2..61af017130cd 100644
    > --- a/arch/blackfin/kernel/dumpstack.c
    > +++ b/arch/blackfin/kernel/dumpstack.c
    > @@ -174,4 +174,3 @@ void dump_stack(void)
    > show_stack(current, &stack);
    > trace_buffer_restore(tflags);
    > }
    > -EXPORT_SYMBOL(dump_stack);

    I was afraid that blackfin modules would not longer be able
    to use arch-specific dump_stack symbol. But it seems that only
    the symbol name is important. Alos the list of symbols look
    promissing:

    before:

    $> objdump -x vmlinux | less | grep dump_stack
    00248530 l O __ksymtab 00000008 ___ksymtab_dump_stack
    002500d4 l O __ksymtab_strings 0000000c ___kstrtab_dump_stack
    00272bb6 l O .bss 00000080 _dump_stack_arch_desc_str
    000051a8 g F .text 00000042 _dump_stack
    002ab05c g F .init.text 0000002a _dump_stack_set_arch_desc
    0003051c g F .text 000000a4 _dump_stack_print_info


    after:

    $> objdump -x vmlinux.patched | less | grep dump_stack
    00000000 l df *ABS* 00000000 lib/dump_stack.c
    0027c3e8 l O .bss 00000080 _dump_stack_arch_desc_str
    00248580 l O __ksymtab 00000008 ___ksymtab_dump_stack
    002653d4 l O __ksymtab_strings 0000000c ___kstrtab_dump_stack
    000051a8 g F .text 00000042 _dump_stack
    002b69dc g F .init.text 0000002a _dump_stack_set_arch_desc
    001c2a90 g F .text 000000a4 _dump_stack_print_info

    I hope that I did not miss anything. I could not try this at
    runtime. I could just cross-compile.

    Anyway, from my side:

    Reviewed-by: Petr Mladek <pmladek@suse.com>

    I'll wait a bit and push it into printk.git for-4.17.


    Greentime Hu, you tested this on nds32. Could I use your Tested-by,
    please?

    Best Regards,
    Petr

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