Commit c9343637 authored by Vasily Gorbik's avatar Vasily Gorbik Committed by Heiko Carstens
Browse files

s390/ftrace: assume -mhotpatch or -mrecord-mcount always available 



Currently the kernel minimal compiler requirement is gcc 4.9 or
clang 10.0.1.
* gcc -mhotpatch option is supported since 4.8.
* A combination of -pg -mrecord-mcount -mnop-mcount -mfentry flags is
supported since gcc 9 and since clang 10.

Drop support for old -pg function prologues. Which leaves binary
compatible -mhotpatch / -mnop-mcount -mfentry prologues in a form:
	brcl	0,0
Which are also do not require initial nop optimization / conversion and
presence of _mcount symbol.

Signed-off-by: default avatarVasily Gorbik <gor@linux.ibm.com>
Reviewed-by: default avatarHeiko Carstens <hca@linux.ibm.com>
Signed-off-by: default avatarHeiko Carstens <hca@linux.ibm.com>
parent 73045a08

arch/s390/include/asm/ftrace.h

+10 −21
Original line number Diff line number Diff line
@@ -2,16 +2,9 @@ 
#ifndef _ASM_S390_FTRACE_H

#define _ASM_S390_FTRACE_H



#define HAVE_FUNCTION_GRAPH_RET_ADDR_PTR

#define ARCH_SUPPORTS_FTRACE_OPS 1



#if defined(CC_USING_HOTPATCH) || defined(CC_USING_NOP_MCOUNT)

#define MCOUNT_INSN_SIZE	6

#else

#define MCOUNT_INSN_SIZE	24

#define MCOUNT_RETURN_FIXUP	18

#endif



#define HAVE_FUNCTION_GRAPH_RET_ADDR_PTR



#ifndef __ASSEMBLY__
@@ -22,7 +15,6 @@ 
#define ftrace_return_address(n) __builtin_return_address(n)

#endif



void _mcount(void);

void ftrace_caller(void);



extern char ftrace_graph_caller_end;
@@ -30,12 +22,20 @@ extern unsigned long ftrace_plt; 


struct dyn_arch_ftrace { };



#define MCOUNT_ADDR ((unsigned long)_mcount)

#define MCOUNT_ADDR 0

#define FTRACE_ADDR ((unsigned long)ftrace_caller)



#define KPROBE_ON_FTRACE_NOP	0

#define KPROBE_ON_FTRACE_CALL	1



struct module;

struct dyn_ftrace;

/*

 * Either -mhotpatch or -mnop-mcount is used - no explicit init is required

 */

static inline int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec) { return 0; }

#define ftrace_init_nop ftrace_init_nop



static inline unsigned long ftrace_call_adjust(unsigned long addr)

{

	return addr;
@@ -49,28 +49,17 @@ struct ftrace_insn { 
static inline void ftrace_generate_nop_insn(struct ftrace_insn *insn)

{

#ifdef CONFIG_FUNCTION_TRACER

#if defined(CC_USING_HOTPATCH) || defined(CC_USING_NOP_MCOUNT)

	/* brcl 0,0 */

	insn->opc = 0xc004;

	insn->disp = 0;

#else

	/* jg .+24 */

	insn->opc = 0xc0f4;

	insn->disp = MCOUNT_INSN_SIZE / 2;

#endif

#endif

}



static inline int is_ftrace_nop(struct ftrace_insn *insn)

{

#ifdef CONFIG_FUNCTION_TRACER

#if defined(CC_USING_HOTPATCH) || defined(CC_USING_NOP_MCOUNT)

	if (insn->disp == 0)

		return 1;

#else

	if (insn->disp == MCOUNT_INSN_SIZE / 2)

		return 1;

#endif

#endif

	return 0;

}

arch/s390/kernel/ftrace.c

+14 −49
Original line number Diff line number Diff line
@@ -22,56 +22,26 @@ 
#include "entry.h"



/*

 * The mcount code looks like this:

 *	stg	%r14,8(%r15)		# offset 0

 *	larl	%r1,<&counter>		# offset 6

 *	brasl	%r14,_mcount		# offset 12

 *	lg	%r14,8(%r15)		# offset 18

 * Total length is 24 bytes. Only the first instruction will be patched

 * by ftrace_make_call / ftrace_make_nop.

 * The enabled ftrace code block looks like this:

 * To generate function prologue either gcc's hotpatch feature (since gcc 4.8)

 * or a combination of -pg -mrecord-mcount -mnop-mcount -mfentry flags

 * (since gcc 9 / clang 10) is used.

 * In both cases the original and also the disabled function prologue contains

 * only a single six byte instruction and looks like this:

 * >	brcl	0,0			# offset 0

 * To enable ftrace the code gets patched like above and afterwards looks

 * like this:

 * >	brasl	%r0,ftrace_caller	# offset 0

 *	larl	%r1,<&counter>		# offset 6

 *	brasl	%r14,_mcount		# offset 12

 *	lg	%r14,8(%r15)		# offset 18

 *

 * The instruction will be patched by ftrace_make_call / ftrace_make_nop.

 * The ftrace function gets called with a non-standard C function call ABI

 * where r0 contains the return address. It is also expected that the called

 * function only clobbers r0 and r1, but restores r2-r15.

 * For module code we can't directly jump to ftrace caller, but need a

 * trampoline (ftrace_plt), which clobbers also r1.

 * The return point of the ftrace function has offset 24, so execution

 * continues behind the mcount block.

 * The disabled ftrace code block looks like this:

 * >	jg	.+24			# offset 0

 *	larl	%r1,<&counter>		# offset 6

 *	brasl	%r14,_mcount		# offset 12

 *	lg	%r14,8(%r15)		# offset 18

 * The jg instruction branches to offset 24 to skip as many instructions

 * as possible.

 * In case we use gcc's hotpatch feature the original and also the disabled

 * function prologue contains only a single six byte instruction and looks

 * like this:

 * >	brcl	0,0			# offset 0

 * To enable ftrace the code gets patched like above and afterwards looks

 * like this:

 * >	brasl	%r0,ftrace_caller	# offset 0

 */



unsigned long ftrace_plt;



static inline void ftrace_generate_orig_insn(struct ftrace_insn *insn)

{

#if defined(CC_USING_HOTPATCH) || defined(CC_USING_NOP_MCOUNT)

	/* brcl 0,0 */

	insn->opc = 0xc004;

	insn->disp = 0;

#else

	/* stg r14,8(r15) */

	insn->opc = 0xe3e0;

	insn->disp = 0xf0080024;

#endif

}



int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,

		       unsigned long addr)

{
@@ -85,15 +55,10 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, 


	if (copy_from_kernel_nofault(&old, (void *) rec->ip, sizeof(old)))

		return -EFAULT;

	if (addr == MCOUNT_ADDR) {

		/* Initial code replacement */

		ftrace_generate_orig_insn(&orig);

		ftrace_generate_nop_insn(&new);

	} else {

	/* Replace ftrace call with a nop. */

	ftrace_generate_call_insn(&orig, rec->ip);

	ftrace_generate_nop_insn(&new);

	}



	/* Verify that the to be replaced code matches what we expect. */

	if (memcmp(&orig, &old, sizeof(old)))

		return -EINVAL;

arch/s390/kernel/mcount.S

+0 −8
Original line number Diff line number Diff line
@@ -33,11 +33,6 @@ ENDPROC(ftrace_stub) 
#define TRACED_FUNC_FRAME_SIZE	STACK_FRAME_OVERHEAD

#endif



ENTRY(_mcount)

	BR_EX	%r14

ENDPROC(_mcount)

EXPORT_SYMBOL(_mcount)



ENTRY(ftrace_caller)

	.globl	ftrace_regs_caller

	.set	ftrace_regs_caller,ftrace_caller
@@ -46,9 +41,6 @@ ENTRY(ftrace_caller) 
	ipm	%r14				# don't put any instructions

	sllg	%r14,%r14,16			# clobbering CC before this point

	lgr	%r1,%r15

#if !(defined(CC_USING_HOTPATCH) || defined(CC_USING_NOP_MCOUNT))

	aghi	%r0,MCOUNT_RETURN_FIXUP

#endif

	# allocate stack frame for ftrace_caller to contain traced function

	aghi	%r15,-TRACED_FUNC_FRAME_SIZE

	stg	%r1,__SF_BACKCHAIN(%r15)

scripts/recordmcount.pl

+0 −3
Original line number Diff line number Diff line
@@ -254,9 +254,6 @@ if ($arch eq "x86_64") { 
    if ($cc =~ /-DCC_USING_HOTPATCH/) {

	$mcount_regex = "^\\s*([0-9a-fA-F]+):\\s*c0 04 00 00 00 00\\s*brcl\\s*0,[0-9a-f]+ <([^\+]*)>\$";

	$mcount_adjust = 0;

    } else {

	$mcount_regex = "^\\s*([0-9a-fA-F]+):\\s*R_390_(PC|PLT)32DBL\\s+_mcount\\+0x2\$";

	$mcount_adjust = -14;

    }

    $alignment = 8;

    $type = ".quad";