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MIPS: ftrace: Reword prepare_ftrace_return() comment block 

Improve the comment block for prepare_ftrace_return().

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: James Hogan <jhogan@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: linux-mips@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
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Geert Uytterhoeven 2019-06-07 13:36:40 +02:00 committed by Paul Burton
parent d171df6b73
commit 4f85c9566c
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1 changed files with 12 additions and 11 deletions
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23
arch/mips/kernel/ftrace.c
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@ -333,20 +333,21 @@ void prepare_ftrace_return(unsigned long *parent_ra_addr, unsigned long self_ra,
return;
/*
* "parent_ra_addr" is the stack address saved the return address of
* the caller of _mcount.
* "parent_ra_addr" is the stack address where the return address of
* the caller of _mcount is saved.
*
* if the gcc < 4.5, a leaf function does not save the return address
* in the stack address, so, we "emulate" one in _mcount's stack space,
* and hijack it directly, but for a non-leaf function, it save the
* return address to the its own stack space, we can not hijack it
* directly, but need to find the real stack address,
* ftrace_get_parent_addr() does it!
* If gcc < 4.5, a leaf function does not save the return address
* in the stack address, so we "emulate" one in _mcount's stack space,
* and hijack it directly.
* For a non-leaf function, it does save the return address to its own
* stack space, so we can not hijack it directly, but need to find the
* real stack address, which is done by ftrace_get_parent_addr().
*
* if gcc>= 4.5, with the new -mmcount-ra-address option, for a
* If gcc >= 4.5, with the new -mmcount-ra-address option, for a
* non-leaf function, the location of the return address will be saved
* to $12 for us, and for a leaf function, only put a zero into $12. we
* do it in ftrace_graph_caller of mcount.S.
* to $12 for us.
* For a leaf function, it just puts a zero into $12, so we handle
* it in ftrace_graph_caller() of mcount.S.
*/
/* old_parent_ra = *parent_ra_addr; */