linux-kernel - [PATCH] dump_stack: convert generic dump

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Date:   Mon,  5 Mar 2018 14:37:42 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Petr Mladek <pmladek@...e.com>, Tejun Heo <tj@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Dave Young <dyoung@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Greentime Hu <green.hu@...il.com>,
        Vincent Chen <deanbo422@...il.com>,
        Arnd Bergmann <arnd@...db.de>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        adi-buildroot-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: [PATCH] dump_stack: convert generic dump_stack into a weak symbol

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@...il.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);
diff --git a/arch/nds32/kernel/traps.c b/arch/nds32/kernel/traps.c
index 8828b4aeb72b..455bb0787367 100644
--- a/arch/nds32/kernel/traps.c
+++ b/arch/nds32/kernel/traps.c
@@ -166,8 +166,6 @@ void dump_stack(void)
 	__dump(NULL, base_reg);
 }
 
-EXPORT_SYMBOL(dump_stack);
-
 void show_stack(struct task_struct *tsk, unsigned long *sp)
 {
 	unsigned long *base_reg;
diff --git a/lib/dump_stack.c b/lib/dump_stack.c
index c5edbedd364d..02a8ad163760 100644
--- a/lib/dump_stack.c
+++ b/lib/dump_stack.c
@@ -25,7 +25,7 @@ static void __dump_stack(void)
 #ifdef CONFIG_SMP
 static atomic_t dump_lock = ATOMIC_INIT(-1);
 
-asmlinkage __visible void dump_stack(void)
+asmlinkage __weak __visible void dump_stack(void)
 {
 	unsigned long flags;
 	int was_locked;
@@ -58,7 +58,7 @@ asmlinkage __visible void dump_stack(void)
 	local_irq_restore(flags);
 }
 #else
-asmlinkage __visible void dump_stack(void)
+asmlinkage __weak __visible void dump_stack(void)
 {
 	__dump_stack();
 }
-- 
2.16.2