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>

diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
index 28d827c..72a41e0 100644 (file)
--- a/arch/loongarch/Kconfig
+++ b/arch/loongarch/Kconfig
@@ -90,6 +90,8 @@ config LOONGARCH
        select HAVE_EBPF_JIT
        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/include/asm/ftrace.h b/arch/loongarch/include/asm/ftrace.h
new file mode 100644 (file)
index 0000000..c3f5cde
--- /dev/null
+++ b/arch/loongarch/include/asm/ftrace.h
@@ -0,0 +1,21 @@
+/* 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__
+#define mcount _mcount
+extern void _mcount(void);
+extern void prepare_ftrace_return(unsigned long self_addr, unsigned long callsite_sp, unsigned long old);
+#endif /* __ASSEMBLY__ */
+
+#endif /* CONFIG_FUNCTION_TRACER */
+
+#endif /* _ASM_LOONGARCH_FTRACE_H */

diff --git a/arch/loongarch/kernel/Makefile b/arch/loongarch/kernel/Makefile
index 8674453..3f71bce 100644 (file)
--- a/arch/loongarch/kernel/Makefile
+++ b/arch/loongarch/kernel/Makefile
@@ -15,6 +15,14 @@ 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 (file)
index 0000000..8c3ec1b
--- /dev/null
+++ b/arch/loongarch/kernel/ftrace.c
@@ -0,0 +1,73 @@
+// 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 */

diff --git a/arch/loongarch/kernel/mcount.S b/arch/loongarch/kernel/mcount.S
new file mode 100644 (file)
index 0000000..8cdc156
--- /dev/null
+++ b/arch/loongarch/kernel/mcount.S
@@ -0,0 +1,96 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * LoongArch specific _mcount support
+ *
+ * Copyright (C) 2022 Loongson Technology Corporation Limited
+ */
+
+#include <asm/export.h>
+#include <asm/ftrace.h>
+#include <asm/regdef.h>
+#include <asm/stackframe.h>
+
+       .text
+
+#define MCOUNT_S0_OFFSET       (0)
+#define MCOUNT_RA_OFFSET       (SZREG)
+#define MCOUNT_STACK_SIZE      (2 * 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.pcrel        t1, ftrace_stub
+       la.pcrel        t2, ftrace_trace_function       /* Prepare t2 for (1) */
+       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.pcrel        t1, ftrace_stub
+       la.pcrel        t3, ftrace_graph_return
+       PTR_L           t3, t3, 0
+       bne             t1, t3, ftrace_graph_caller
+       la.pcrel        t1, ftrace_graph_entry_stub
+       la.pcrel        t3, ftrace_graph_entry
+       PTR_L           t3, t3, 0
+       bne             t1, t3, ftrace_graph_caller
+#endif
+
+SYM_INNER_LABEL(ftrace_stub, SYM_L_GLOBAL)
+       jr              ra
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+SYM_INNER_LABEL(ftrace_graph_func, SYM_L_GLOBAL)
+       bl              ftrace_stub
+#endif
+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
+       jr              ra
+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
+       jr              ra
+SYM_FUNC_END(return_to_handler)
+#endif /* CONFIG_FUNCTION_GRAPH_TRACER */