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// SPDX-License-Identifier: GPL-2.0
/*
* Dynamic function tracer architecture backend.
*
* Copyright IBM Corp. 2009,2014
*
* Author(s): Heiko Carstens <heiko.carstens@de.ibm.com>,
* Martin Schwidefsky <schwidefsky@de.ibm.com>
*/
#include <linux/moduleloader.h>
#include <linux/hardirq.h>
#include <linux/uaccess.h>
#include <linux/ftrace.h>
#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/kprobes.h>
#include <trace/syscall.h>
#include <asm/asm-offsets.h>
#include <asm/cacheflush.h>
#include <asm/set_memory.h>
#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:
* > brasl %r0,ftrace_caller # offset 0
* larl %r1,<&counter> # offset 6
* brasl %r14,_mcount # offset 12
* lg %r14,8(%r15) # offset 18
* 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)
{
return 0;
}
int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
unsigned long addr)
{
struct ftrace_insn orig, new, old;
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;
s390_kernel_write((void *) rec->ip, &new, sizeof(new));
return 0;
}
int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
{
struct ftrace_insn orig, new, old;
if (copy_from_kernel_nofault(&old, (void *) rec->ip, sizeof(old)))
return -EFAULT;
/* Replace nop with an ftrace call. */
ftrace_generate_nop_insn(&orig);
ftrace_generate_call_insn(&new, rec->ip);
/* Verify that the to be replaced code matches what we expect. */
if (memcmp(&orig, &old, sizeof(old)))
return -EINVAL;
s390_kernel_write((void *) rec->ip, &new, sizeof(new));
return 0;
}
int ftrace_update_ftrace_func(ftrace_func_t func)
{
return 0;
}
int __init ftrace_dyn_arch_init(void)
{
return 0;
}
#ifdef CONFIG_MODULES
static int __init ftrace_plt_init(void)
{
unsigned int *ip;
ftrace_plt = (unsigned long) module_alloc(PAGE_SIZE);
if (!ftrace_plt)
panic("cannot allocate ftrace plt\n");
ip = (unsigned int *) ftrace_plt;
ip[0] = 0x0d10e310; /* basr 1,0; lg 1,10(1); br 1 */
ip[1] = 0x100a0004;
ip[2] = 0x07f10000;
ip[3] = FTRACE_ADDR >> 32;
ip[4] = FTRACE_ADDR & 0xffffffff;
set_memory_ro(ftrace_plt, 1);
return 0;
}
device_initcall(ftrace_plt_init);
#endif /* CONFIG_MODULES */
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
/*
* Hook the return address and push it in the stack of return addresses
* in current thread info.
*/
unsigned long prepare_ftrace_return(unsigned long ra, unsigned long sp,
unsigned long ip)
{
if (unlikely(ftrace_graph_is_dead()))
goto out;
if (unlikely(atomic_read(¤t->tracing_graph_pause)))
goto out;
ip -= MCOUNT_INSN_SIZE;
if (!function_graph_enter(ra, ip, 0, (void *) sp))
ra = (unsigned long) return_to_handler;
out:
return ra;
}
NOKPROBE_SYMBOL(prepare_ftrace_return);
/*
* Patch the kernel code at ftrace_graph_caller location. The instruction
* there is branch relative on condition. To enable the ftrace graph code
* block, we simply patch the mask field of the instruction to zero and
* turn the instruction into a nop.
* To disable the ftrace graph code the mask field will be patched to
* all ones, which turns the instruction into an unconditional branch.
*/
int ftrace_enable_ftrace_graph_caller(void)
{
u8 op = 0x04; /* set mask field to zero */
s390_kernel_write(__va(ftrace_graph_caller)+1, &op, sizeof(op));
return 0;
}
int ftrace_disable_ftrace_graph_caller(void)
{
u8 op = 0xf4; /* set mask field to all ones */
s390_kernel_write(__va(ftrace_graph_caller)+1, &op, sizeof(op));
return 0;
}
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
#ifdef CONFIG_KPROBES_ON_FTRACE
void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
struct ftrace_ops *ops, struct pt_regs *regs)
{
struct kprobe_ctlblk *kcb;
struct kprobe *p = get_kprobe((kprobe_opcode_t *)ip);
if (unlikely(!p) || kprobe_disabled(p))
return;
if (kprobe_running()) {
kprobes_inc_nmissed_count(p);
return;
}
__this_cpu_write(current_kprobe, p);
kcb = get_kprobe_ctlblk();
kcb->kprobe_status = KPROBE_HIT_ACTIVE;
instruction_pointer_set(regs, ip);
if (!p->pre_handler || !p->pre_handler(p, regs)) {
instruction_pointer_set(regs, ip + MCOUNT_INSN_SIZE);
if (unlikely(p->post_handler)) {
kcb->kprobe_status = KPROBE_HIT_SSDONE;
p->post_handler(p, regs, 0);
}
}
__this_cpu_write(current_kprobe, NULL);
}
NOKPROBE_SYMBOL(kprobe_ftrace_handler);
int arch_prepare_kprobe_ftrace(struct kprobe *p)
{
p->ainsn.insn = NULL;
return 0;
}
#endif
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