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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: Vasily Gorbik <gor@linux.ibm.com>
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
This commit is contained in:
Vasily Gorbik 2020-11-12 15:54:47 +01:00 committed by Heiko Carstens
parent 73045a08cf
commit c9343637d6
4 changed files with 25 additions and 82 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

33
arch/s390/include/asm/ftrace.h
View File

@ -2,16 +2,9 @@
#ifndef _ASM_S390_FTRACE_H
#define _ASM_S390_FTRACE_H
#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
#define ARCH_SUPPORTS_FTRACE_OPS 1
#define MCOUNT_INSN_SIZE 6
#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;
}

63
arch/s390/kernel/ftrace.c
View File

@ -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);
}
/* 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;

8
arch/s390/kernel/mcount.S
View File

@ -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)

3
scripts/recordmcount.pl
View File

@ -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";