Re: [PATCH 1/9] LoongArch/ftrace: Add basic support
From: Jinyang He
Date: Fri Aug 19 2022 - 05:29:50 EST
Hi, Qing
On 2022/8/19 16:13, Qing Zhang wrote:
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 open stack before `call _mcount`.
Find `open 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@xxxxxxxxxxx>
Signed-off-by: Jinyang He <hejinyang@xxxxxxxxxxx>
Signed-off-by: Qing Zhang <zhangqing@xxxxxxxxxxx>
---
arch/loongarch/Kconfig | 2 +
arch/loongarch/Makefile | 5 ++
arch/loongarch/include/asm/ftrace.h | 18 ++++++
arch/loongarch/kernel/Makefile | 8 +++
arch/loongarch/kernel/ftrace.c | 74 +++++++++++++++++++++++
arch/loongarch/kernel/mcount.S | 94 +++++++++++++++++++++++++++++
6 files changed, 201 insertions(+)
create mode 100644 arch/loongarch/include/asm/ftrace.h
create mode 100644 arch/loongarch/kernel/ftrace.c
create mode 100644 arch/loongarch/kernel/mcount.S
diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
index 4abc9a28aba4..703a2c3a8e0d 100644
--- a/arch/loongarch/Kconfig
+++ b/arch/loongarch/Kconfig
@@ -84,6 +84,8 @@ config LOONGARCH
select HAVE_DMA_CONTIGUOUS
select HAVE_EXIT_THREAD
select HAVE_FAST_GUP
+ select HAVE_FUNCTION_GRAPH_TRACER
+ select HAVE_FUNCTION_TRACER
select HAVE_GENERIC_VDSO
select HAVE_IOREMAP_PROT
select HAVE_IRQ_EXIT_ON_IRQ_STACK
diff --git a/arch/loongarch/Makefile b/arch/loongarch/Makefile
index ec3de6191276..44f11a2937e9 100644
--- a/arch/loongarch/Makefile
+++ b/arch/loongarch/Makefile
@@ -29,6 +29,11 @@ ifneq ($(SUBARCH),$(ARCH))
endif
endif
+ifdef CONFIG_DYNAMIC_FTRACE
+ KBUILD_CPPFLAGS += -DCC_USING_PATCHABLE_FUNCTION_ENTRY
+ CC_FLAGS_FTRACE := -fpatchable-function-entry=2
+endif
+
It seems this patch adds non-dynamic ftrace, this code should not
appear here.
BTW is it really necessary for non-dynamic ftrace? I do not use it
directly and frequently, IMHO, non-dynamic can be completely
replaced dynamic?
ifdef CONFIG_64BIT
ld-emul = $(64bit-emul)
cflags-y += -mabi=lp64s
diff --git a/arch/loongarch/include/asm/ftrace.h b/arch/loongarch/include/asm/ftrace.h
new file mode 100644
index 000000000000..6a3e76234618
--- /dev/null
+++ b/arch/loongarch/include/asm/ftrace.h
@@ -0,0 +1,18 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2022 Loongson Technology Corporation Limited
+ */
+
+#ifndef _ASM_LOONGARCH_FTRACE_H
+#define _ASM_LOONGARCH_FTRACE_H
+
+#ifdef CONFIG_FUNCTION_TRACER
+#define MCOUNT_INSN_SIZE 4 /* sizeof mcount call */
+
+#ifndef __ASSEMBLY__
+extern void _mcount(void);
+#define mcount _mcount
+
+#endif /* __ASSEMBLY__ */
+#endif /* CONFIG_FUNCTION_TRACER */
+#endif /* _ASM_LOONGARCH_FTRACE_H */
diff --git a/arch/loongarch/kernel/Makefile b/arch/loongarch/kernel/Makefile
index e5be17009fe8..0a745d24d3e5 100644
--- a/arch/loongarch/kernel/Makefile
+++ b/arch/loongarch/kernel/Makefile
@@ -14,6 +14,14 @@ obj-$(CONFIG_EFI) += efi.o
obj-$(CONFIG_CPU_HAS_FPU) += fpu.o
+ifdef CONFIG_FUNCTION_TRACER
+ obj-y += mcount.o ftrace.o
+ CFLAGS_REMOVE_ftrace.o = $(CC_FLAGS_FTRACE)
+ CFLAGS_REMOVE_inst.o = $(CC_FLAGS_FTRACE)
+ CFLAGS_REMOVE_time.o = $(CC_FLAGS_FTRACE)
+ CFLAGS_REMOVE_perf_event.o = $(CC_FLAGS_FTRACE)
+endif
+
obj-$(CONFIG_MODULES) += module.o module-sections.o
obj-$(CONFIG_STACKTRACE) += stacktrace.o
diff --git a/arch/loongarch/kernel/ftrace.c b/arch/loongarch/kernel/ftrace.c
new file mode 100644
index 000000000000..c8ddc5f11f32
--- /dev/null
+++ b/arch/loongarch/kernel/ftrace.c
@@ -0,0 +1,74 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2022 Loongson Technology Corporation Limited
+ */
+
+#include <linux/uaccess.h>
+#include <linux/init.h>
+#include <linux/ftrace.h>
+#include <linux/syscalls.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/unistd.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)
+{
+ union loongarch_instruction *insn;
+ int limit = 32;
+
+ 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(¤t->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 */
diff --git a/arch/loongarch/kernel/mcount.S b/arch/loongarch/kernel/mcount.S
new file mode 100644
index 000000000000..f1c1cc1a629e
--- /dev/null
+++ b/arch/loongarch/kernel/mcount.S
@@ -0,0 +1,94 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * LoongArch specific _mcount support
+ *
+ * Copyright (C) 2022 Loongson Technology Corporation Limited
+ */
+
+#include <asm/export.h>
+#include <asm/regdef.h>
+#include <asm/stackframe.h>
+#include <asm/ftrace.h>
+
+ .text
+
+#define MCOUNT_STACK_SIZE (2 * SZREG)
+#define MCOUNT_S0_OFFSET (0)
+#define MCOUNT_RA_OFFSET (SZREG)
+
+ .macro MCOUNT_SAVE_REGS
+ PTR_ADDI sp, sp, -MCOUNT_STACK_SIZE
+ PTR_S s0, sp, MCOUNT_S0_OFFSET
+ PTR_S ra, sp, MCOUNT_RA_OFFSET
+ move s0, a0
+ .endm
+
+ .macro MCOUNT_RESTORE_REGS
+ move a0, s0
+ PTR_L ra, sp, MCOUNT_RA_OFFSET
+ PTR_L s0, sp, MCOUNT_S0_OFFSET
+ PTR_ADDI sp, sp, MCOUNT_STACK_SIZE
+ .endm
+
+
+SYM_FUNC_START(_mcount)
+ la t1, ftrace_stub
+ la t2, ftrace_trace_function /* Prepare t2 for (1) */
'la.pcrel' is preferred here while 'la' should be deprecated.
+ PTR_L t2, t2, 0
+ beq t1, t2, fgraph_trace
+
+ MCOUNT_SAVE_REGS
+
+ move a0, ra /* arg0: self return address */
+ move a1, s0 /* arg1: parent's return address */
+ jirl ra, t2, 0 /* (1) call *ftrace_trace_function */
+
+ MCOUNT_RESTORE_REGS
+
+fgraph_trace:
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+ la t1, ftrace_stub
+ la t3, ftrace_graph_return
+ PTR_L t3, t3, 0
+ bne t1, t3, ftrace_graph_caller
+ la t1, ftrace_graph_entry_stub
+ la t3, ftrace_graph_entry
+ PTR_L t3, t3, 0
+ bne t1, t3, ftrace_graph_caller
+#endif
+
+ .globl ftrace_stub
+ftrace_stub:
+ jirl zero, ra, 0
+SYM_FUNC_END(_mcount)
+EXPORT_SYMBOL(_mcount)
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+SYM_FUNC_START(ftrace_graph_caller)
+ MCOUNT_SAVE_REGS
+
+ PTR_ADDI a0, ra, -4 /* arg0: Callsite self return addr */
+ PTR_ADDI a1, sp, MCOUNT_STACK_SIZE /* arg1: Callsite sp */
+ move a2, s0 /* arg2: Callsite parent ra */
+ bl prepare_ftrace_return
+
+ MCOUNT_RESTORE_REGS
+ jirl zero, ra, 0
We know Xuerui had done a lot works to keep asm code normalize.
So I think we should replace 'jirl zero,ra,0' with 'jr ra'. The basic
rule is use assembly macro as possible, I think.
Thanks,
Jinyang
+SYM_FUNC_END(ftrace_graph_caller)
+
+SYM_FUNC_START(return_to_handler)
+ PTR_ADDI sp, sp, -2 * SZREG
+ PTR_S a0, sp, 0
+ PTR_S a1, sp, SZREG
+
+ bl ftrace_return_to_handler
+
+ /* restore the real parent address: a0 -> ra */
+ move ra, a0
+
+ PTR_L a0, sp, 0
+ PTR_L a1, sp, SZREG
+ PTR_ADDI sp, sp, 2 * SZREG
+ jirl zero, ra, 0
+SYM_FUNC_END(return_to_handler)
+#endif /* CONFIG_FUNCTION_GRAPH_TRACER */