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linux/arch/loongarch/kernel/ftrace.c
Qing Zhang dbe3ba3018 LoongArch/ftrace: Add basic support
This patch contains basic ftrace support for LoongArch. Specifically,
function tracer (HAVE_FUNCTION_TRACER), function graph tracer (HAVE_
FUNCTION_GRAPH_TRACER) are implemented following the instructions in
Documentation/trace/ftrace-design.txt.

Use `-pg` makes stub like a child function `void _mcount(void *ra)`.
Thus, it can be seen store RA and alloc stack before `call _mcount`.
Find `alloc stack` at first, and then find `store RA`.

Note that the functions in both inst.c and time.c should not be hooked
with the compiler's -pg option: to prevent infinite self-referencing for
the former, and to ignore early setup stuff for the latter.

Co-developed-by: Jinyang He <hejinyang@loongson.cn>
Signed-off-by: Jinyang He <hejinyang@loongson.cn>
Signed-off-by: Qing Zhang <zhangqing@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
2022-12-14 08:41:53 +08:00

74 lines
1.5 KiB
C

// SPDX-License-Identifier: GPL-2.0
/*
* Copyright (C) 2022 Loongson Technology Corporation Limited
*/
#include <linux/init.h>
#include <linux/ftrace.h>
#include <linux/syscalls.h>
#include <linux/uaccess.h>
#include <asm/asm.h>
#include <asm/asm-offsets.h>
#include <asm/cacheflush.h>
#include <asm/inst.h>
#include <asm/loongarch.h>
#include <asm/syscall.h>
#include <asm-generic/sections.h>
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
/*
* As `call _mcount` follows LoongArch psABI, ra-saved operation and
* stack operation can be found before this insn.
*/
static int ftrace_get_parent_ra_addr(unsigned long insn_addr, int *ra_off)
{
int limit = 32;
union loongarch_instruction *insn;
insn = (union loongarch_instruction *)insn_addr;
do {
insn--;
limit--;
if (is_ra_save_ins(insn))
*ra_off = -((1 << 12) - insn->reg2i12_format.immediate);
} while (!is_stack_alloc_ins(insn) && limit);
if (!limit)
return -EINVAL;
return 0;
}
void prepare_ftrace_return(unsigned long self_addr,
unsigned long callsite_sp, unsigned long old)
{
int ra_off;
unsigned long return_hooker = (unsigned long)&return_to_handler;
if (unlikely(ftrace_graph_is_dead()))
return;
if (unlikely(atomic_read(&current->tracing_graph_pause)))
return;
if (ftrace_get_parent_ra_addr(self_addr, &ra_off))
goto out;
if (!function_graph_enter(old, self_addr, 0, NULL))
*(unsigned long *)(callsite_sp + ra_off) = return_hooker;
return;
out:
ftrace_graph_stop();
WARN_ON(1);
}
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */