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ftrace: add ftrace_init_nop() 

Architectures may need to perform special initialization of ftrace
callsites, and today they do so by special-casing ftrace_make_nop() when
the expected branch address is MCOUNT_ADDR. In some cases (e.g. for
patchable-function-entry), we don't have an mcount-like symbol and don't
want a synthetic MCOUNT_ADDR, but we may need to perform some
initialization of callsites.

To make it possible to separate initialization from runtime
modification, and to handle cases without an mcount-like symbol, this
patch adds an optional ftrace_init_nop() function that architectures can
implement, which does not pass a branch address.

Where an architecture does not provide ftrace_init_nop(), we will fall
back to the existing behaviour of calling ftrace_make_nop() with
MCOUNT_ADDR.

At the same time, ftrace_code_disable() is renamed to
ftrace_nop_initialize() to make it clearer that it is intended to
intialize a callsite into a disabled state, and is not for disabling a
callsite that has been runtime enabled. The kerneldoc description of rec
arguments is updated to cover non-mcount callsites.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Reviewed-by: Torsten Duwe <duwe@suse.de>
Tested-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Tested-by: Sven Schnelle <svens@stackframe.org>
Tested-by: Torsten Duwe <duwe@suse.de>
Cc: Ingo Molnar <mingo@redhat.com>
This commit is contained in:
Mark Rutland 2019-10-16 17:51:10 +01:00
parent 4f5cafb5cb
commit fbf6c73c5b
2 changed files with 35 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

35
include/linux/ftrace.h
View File

@ -499,7 +499,7 @@ static inline int ftrace_disable_ftrace_graph_caller(void) { return 0; }
/**
* ftrace_make_nop - convert code into nop
* @mod: module structure if called by module load initialization
* @rec: the mcount call site record
* @rec: the call site record (e.g. mcount/fentry)
* @addr: the address that the call site should be calling
*
* This is a very sensitive operation and great care needs
@ -520,9 +520,38 @@ static inline int ftrace_disable_ftrace_graph_caller(void) { return 0; }
extern int ftrace_make_nop(struct module *mod,
struct dyn_ftrace *rec, unsigned long addr);
/**
* ftrace_init_nop - initialize a nop call site
* @mod: module structure if called by module load initialization
* @rec: the call site record (e.g. mcount/fentry)
*
* This is a very sensitive operation and great care needs
* to be taken by the arch. The operation should carefully
* read the location, check to see if what is read is indeed
* what we expect it to be, and then on success of the compare,
* it should write to the location.
*
* The code segment at @rec->ip should contain the contents created by
* the compiler
*
* Return must be:
* 0 on success
* -EFAULT on error reading the location
* -EINVAL on a failed compare of the contents
* -EPERM on error writing to the location
* Any other value will be considered a failure.
*/
#ifndef ftrace_init_nop
static inline int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
{
return ftrace_make_nop(mod, rec, MCOUNT_ADDR);
}
#endif
/**
* ftrace_make_call - convert a nop call site into a call to addr
* @rec: the mcount call site record
* @rec: the call site record (e.g. mcount/fentry)
* @addr: the address that the call site should call
*
* This is a very sensitive operation and great care needs
@ -545,7 +574,7 @@ extern int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr);
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
/**
* ftrace_modify_call - convert from one addr to another (no nop)
* @rec: the mcount call site record
* @rec: the call site record (e.g. mcount/fentry)
* @old_addr: the address expected to be currently called to
* @addr: the address to change to
*

6
kernel/trace/ftrace.c
View File

@ -2494,14 +2494,14 @@ struct dyn_ftrace *ftrace_rec_iter_record(struct ftrace_rec_iter *iter)
}
static int
ftrace_code_disable(struct module *mod, struct dyn_ftrace *rec)
ftrace_nop_initialize(struct module *mod, struct dyn_ftrace *rec)
{
int ret;
if (unlikely(ftrace_disabled))
return 0;
ret = ftrace_make_nop(mod, rec, MCOUNT_ADDR);
ret = ftrace_init_nop(mod, rec);
if (ret) {
ftrace_bug_type = FTRACE_BUG_INIT;
ftrace_bug(ret, rec);
@ -2943,7 +2943,7 @@ static int ftrace_update_code(struct module *mod, struct ftrace_page *new_pgs)
* to the NOP instructions.
*/
if (!__is_defined(CC_USING_NOP_MCOUNT) &&
!ftrace_code_disable(mod, p))
!ftrace_nop_initialize(mod, p))
break;
update_cnt++;