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s390/ftrace: hotpatch support for function tracing 

Make use of gcc's hotpatch support to generate better code for ftrace
function tracing.
The generated code now contains only a six byte nop in each function
prologue instead of a 24 byte code block which will be runtime patched to
support function tracing.
With the new code generation the runtime overhead for supporting function
tracing is close to zero, while the original code did show a significant
performance impact.

Acked-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Heiko Carstens 2015-01-09 13:08:28 +01:00 committed by Martin Schwidefsky
parent 61f552141c
commit e6d60b368b
8 changed files with 52 additions and 7 deletions
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1
arch/s390/Kconfig
View File

@ -117,7 +117,6 @@ config S390
select HAVE_BPF_JIT if 64BIT && PACK_STACK
select HAVE_CMPXCHG_DOUBLE
select HAVE_CMPXCHG_LOCAL
select HAVE_C_RECORDMCOUNT
select HAVE_DEBUG_KMEMLEAK
select HAVE_DYNAMIC_FTRACE if 64BIT
select HAVE_DYNAMIC_FTRACE_WITH_REGS if 64BIT

10
arch/s390/Makefile
View File

@ -87,6 +87,16 @@ ifeq ($(call cc-option-yn,-mwarn-dynamicstack),y)
cflags-$(CONFIG_WARN_DYNAMIC_STACK) += -mwarn-dynamicstack
endif
ifdef CONFIG_FUNCTION_TRACER
# make use of hotpatch feature if the compiler supports it
cc_hotpatch := -mhotpatch=0,3
ifeq ($(call cc-option-yn,$(cc_hotpatch)),y)
CC_FLAGS_FTRACE := $(cc_hotpatch)
KBUILD_AFLAGS += -DCC_USING_HOTPATCH
KBUILD_CFLAGS += -DCC_USING_HOTPATCH
endif
endif
KBUILD_CFLAGS += -mbackchain -msoft-float $(cflags-y)
KBUILD_CFLAGS += -pipe -fno-strength-reduce -Wno-sign-compare
KBUILD_AFLAGS += $(aflags-y)

15
arch/s390/include/asm/ftrace.h
View File

@ -3,8 +3,12 @@
#define ARCH_SUPPORTS_FTRACE_OPS 1
#ifdef CC_USING_HOTPATCH
#define MCOUNT_INSN_SIZE 6
#else
#define MCOUNT_INSN_SIZE 24
#define MCOUNT_RETURN_FIXUP 18
#endif
#ifndef __ASSEMBLY__
@ -37,17 +41,28 @@ struct ftrace_insn {
static inline void ftrace_generate_nop_insn(struct ftrace_insn *insn)
{
#ifdef CONFIG_FUNCTION_TRACER
#ifdef CC_USING_HOTPATCH
/* 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
#ifdef CC_USING_HOTPATCH
if (insn->disp == 0)
return 1;
#else
if (insn->disp == MCOUNT_INSN_SIZE / 2)
return 1;
#endif
#endif
return 0;
}

4
arch/s390/kernel/Makefile
View File

@ -4,8 +4,8 @@
ifdef CONFIG_FUNCTION_TRACER
# Don't trace early setup code and tracing code
CFLAGS_REMOVE_early.o = -pg
CFLAGS_REMOVE_ftrace.o = -pg
CFLAGS_REMOVE_early.o = $(CC_FLAGS_FTRACE)
CFLAGS_REMOVE_ftrace.o = $(CC_FLAGS_FTRACE)
endif
#

15
arch/s390/kernel/ftrace.c
View File

@ -46,6 +46,13 @@
* 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;
@ -64,9 +71,15 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
if (probe_kernel_read(&old, (void *) rec->ip, sizeof(old)))
return -EFAULT;
if (addr == MCOUNT_ADDR) {
/* Initial code replacement; we expect to see stg r14,8(r15) */
/* Initial code replacement */
#ifdef CC_USING_HOTPATCH
/* We expect to see brcl 0,0 */
ftrace_generate_nop_insn(&orig);
#else
/* We expect to see stg r14,8(r15) */
orig.opc = 0xe3e0;
orig.disp = 0xf0080024;
#endif
ftrace_generate_nop_insn(&new);
} else if (old.opc == BREAKPOINT_INSTRUCTION) {
/*

3
arch/s390/kernel/kprobes.c
View File

@ -69,7 +69,8 @@ static void copy_instruction(struct kprobe *p)
/*
* If kprobes patches the instruction that is morphed by
* ftrace make sure that kprobes always sees the branch
* "jg .+24" that skips the mcount block
* "jg .+24" that skips the mcount block or the "brcl 0,0"
* in case of hotpatch.
*/
ftrace_generate_nop_insn((struct ftrace_insn *)p->ainsn.insn);
p->ainsn.is_ftrace_insn = 1;

2
arch/s390/kernel/mcount.S
View File

@ -27,7 +27,9 @@ ENTRY(ftrace_caller)
.globl ftrace_regs_caller
.set ftrace_regs_caller,ftrace_caller
lgr %r1,%r15
#ifndef CC_USING_HOTPATCH
aghi %r0,MCOUNT_RETURN_FIXUP
#endif
aghi %r15,-STACK_FRAME_SIZE
stg %r1,__SF_BACKCHAIN(%r15)
stg %r1,(STACK_PTREGS_GPRS+15*8)(%r15)

9
scripts/recordmcount.pl
View File

@ -242,8 +242,13 @@ if ($arch eq "x86_64") {
$cc .= " -m32";
} elsif ($arch eq "s390" && $bits == 64) {
$mcount_regex = "^\\s*([0-9a-fA-F]+):\\s*R_390_(PC|PLT)32DBL\\s+_mcount\\+0x2\$";
$mcount_adjust = -14;
if ($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";
$ld .= " -m elf64_s390";