Commit fbf6c73c authored by Mark Rutland's avatar Mark Rutland
Browse files

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: default avatarMark Rutland <mark.rutland@arm.com>
Reviewed-by: default avatarAmit Daniel Kachhap <amit.kachhap@arm.com>
Reviewed-by: default avatarArd Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: default avatarMiroslav Benes <mbenes@suse.cz>
Reviewed-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
Reviewed-by: default avatarTorsten Duwe <duwe@suse.de>
Tested-by: default avatarAmit Daniel Kachhap <amit.kachhap@arm.com>
Tested-by: default avatarSven Schnelle <svens@stackframe.org>
Tested-by: default avatarTorsten Duwe <duwe@suse.de>
Cc: Ingo Molnar <mingo@redhat.com>
parent 4f5cafb5

include/linux/ftrace.h

+32 −3
Original line number Diff line number Diff line
@@ -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

 *

kernel/trace/ftrace.c

+3 −3
Original line number Diff line number Diff line
@@ -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++;

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