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author | Qing Zhang <zhangqing@loongson.cn> | 2022-12-10 17:40:15 +0300 |
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committer | Huacai Chen <chenhuacai@loongson.cn> | 2022-12-14 03:41:53 +0300 |
commit | 4733f09d880745953b88c3358b49ad495aecd8e9 (patch) | |
tree | c53c7531fa72b908bab436f27cfb139f63d42ea5 /arch/loongarch/kernel/mcount_dyn.S | |
parent | a0a458fbd6f2317832e2d74acdbfa2451c3f4b8f (diff) | |
download | linux-4733f09d880745953b88c3358b49ad495aecd8e9.tar.xz |
LoongArch/ftrace: Add dynamic function tracer support
The compiler has inserted 2 NOPs before the regular function prologue.
T series registers are available and safe because of LoongArch's psABI.
At runtime, we can replace nop with bl to enable ftrace call and replace
bl with nop to disable ftrace call. The bl instruction requires us to
save the original RA value, so it saves RA at t0 here.
Details are:
| Compiled | Disabled | Enabled |
+------------+------------------------+------------------------+
| nop | move t0, ra | move t0, ra |
| nop | nop | bl ftrace_caller |
| func_body | func_body | func_body |
The RA value will be recovered by ftrace_regs_entry, and restored into
RA before returning to the regular function prologue. When a function is
not being traced, the "move t0, ra" is not harmful.
1) ftrace_make_call, ftrace_make_nop (in kernel/ftrace.c)
The two functions turn each recorded call site of filtered functions
into a call to ftrace_caller or nops.
2) ftracce_update_ftrace_func (in kernel/ftrace.c)
turns the nops at ftrace_call into a call to a generic entry for
function tracers.
3) ftrace_caller (in kernel/mcount_dyn.S)
The entry where each _mcount call sites calls to once they are
filtered to be traced.
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>
Diffstat (limited to 'arch/loongarch/kernel/mcount_dyn.S')
-rw-r--r-- | arch/loongarch/kernel/mcount_dyn.S | 85 |
1 files changed, 85 insertions, 0 deletions
diff --git a/arch/loongarch/kernel/mcount_dyn.S b/arch/loongarch/kernel/mcount_dyn.S new file mode 100644 index 000000000000..45ba88d2aacc --- /dev/null +++ b/arch/loongarch/kernel/mcount_dyn.S @@ -0,0 +1,85 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * Copyright (C) 2022 Loongson Technology Corporation Limited + */ + +#include <asm/export.h> +#include <asm/ftrace.h> +#include <asm/regdef.h> +#include <asm/stackframe.h> + + .text +/* + * Due to -fpatchable-function-entry=2: the compiler inserted 2 NOPs before the + * regular C function prologue. When PC arrived here, the last 2 instructions + * are as follows: + * move t0, ra + * bl callsite (for modules, callsite is a tramplione) + * + * modules trampoline is as follows: + * lu12i.w t1, callsite[31:12] + * lu32i.d t1, callsite[51:32] + * lu52i.d t1, t1, callsite[63:52] + * jirl zero, t1, callsite[11:0] >> 2 + * + * See arch/loongarch/kernel/ftrace_dyn.c for details. Here, pay attention to + * that the T series regs are available and safe because each C functions + * follows the LoongArch's psABI as well. + */ + + .macro ftrace_regs_entry + PTR_ADDI sp, sp, -PT_SIZE + PTR_S t0, sp, PT_R1 /* Save parent ra at PT_R1(RA) */ + PTR_S a0, sp, PT_R4 + PTR_S a1, sp, PT_R5 + PTR_S a2, sp, PT_R6 + PTR_S a3, sp, PT_R7 + PTR_S a4, sp, PT_R8 + PTR_S a5, sp, PT_R9 + PTR_S a6, sp, PT_R10 + PTR_S a7, sp, PT_R11 + PTR_S fp, sp, PT_R22 + PTR_S ra, sp, PT_ERA /* Save trace function ra at PT_ERA */ + PTR_ADDI t8, sp, PT_SIZE + PTR_S t8, sp, PT_R3 + .endm + +SYM_FUNC_START(ftrace_stub) + jr ra +SYM_FUNC_END(ftrace_stub) + +SYM_CODE_START(ftrace_common) + PTR_ADDI a0, ra, -8 /* arg0: ip */ + move a1, t0 /* arg1: parent_ip */ + la.pcrel t1, function_trace_op + PTR_L a2, t1, 0 /* arg2: op */ + move a3, sp /* arg3: regs */ + +SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL) + bl ftrace_stub +/* + * As we didn't use S series regs in this assmembly code and all calls + * are C function which will save S series regs by themselves, there is + * no need to restore S series regs. The T series is available and safe + * at the callsite, so there is no need to restore the T series regs. + */ +ftrace_common_return: + PTR_L ra, sp, PT_R1 + PTR_L a0, sp, PT_R4 + PTR_L a1, sp, PT_R5 + PTR_L a2, sp, PT_R6 + PTR_L a3, sp, PT_R7 + PTR_L a4, sp, PT_R8 + PTR_L a5, sp, PT_R9 + PTR_L a6, sp, PT_R10 + PTR_L a7, sp, PT_R11 + PTR_L fp, sp, PT_R22 + PTR_L t0, sp, PT_ERA + PTR_ADDI sp, sp, PT_SIZE + jr t0 +SYM_CODE_END(ftrace_common) + +SYM_CODE_START(ftrace_caller) + ftrace_regs_entry + b ftrace_common +SYM_CODE_END(ftrace_caller) |