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Subject[PATCH v3 2/4] LoongArch: Add prologue unwinder support
Date
It unwind the stack frame based on prologue code analyze.
CONFIG_KALLSYMS is needed, at least the address and length
of each function.

Three stages when we do unwind,
1) unwind_start(), the prapare of unwinding, fill unwind_state.
2) unwind_done(), judge whether the unwind process is finished or not.
3) unwind_next_frame(), unwind the next frame.

Dividing unwinder helps to add new unwinders in the future, eg:
unwind_frame, unwind_orc .etc

Signed-off-by: Qing Zhang <zhangqing@loongson.cn>
---
arch/loongarch/Kconfig.debug | 19 +++
arch/loongarch/include/asm/inst.h | 52 +++++++
arch/loongarch/include/asm/unwind.h | 12 +-
arch/loongarch/kernel/Makefile | 1 +
arch/loongarch/kernel/traps.c | 3 +
arch/loongarch/kernel/unwind_prologue.c | 172 ++++++++++++++++++++++++
6 files changed, 258 insertions(+), 1 deletion(-)
create mode 100644 arch/loongarch/kernel/unwind_prologue.c

diff --git a/arch/loongarch/Kconfig.debug b/arch/loongarch/Kconfig.debug
index 68634d4fa27b..57cdbe0cfd98 100644
--- a/arch/loongarch/Kconfig.debug
+++ b/arch/loongarch/Kconfig.debug
@@ -1,3 +1,11 @@
+choice
+ prompt "Choose kernel unwinder"
+ default UNWINDER_PROLOGUE if KALLSYMS
+ help
+ This determines which method will be used for unwinding kernel stack
+ traces for panics, oopses, bugs, warnings, perf, /proc/<pid>/stack,
+ lockdep, and more.
+
config UNWINDER_GUESS
bool "Guess unwinder"
help
@@ -7,3 +15,14 @@ config UNWINDER_GUESS

While this option often produces false positives, it can still be
useful in many cases.
+
+config UNWINDER_PROLOGUE
+ bool "Prologue unwinder"
+ depends on KALLSYMS
+ help
+ This option enables the "prologue" unwinder for unwinding kernel stack
+ traces. It unwind the stack frame based on prologue code analyze. Symbol
+ information is needed, at least the address and length of each function.
+ Some of the addresses it reports may be incorrect.
+
+endchoice
diff --git a/arch/loongarch/include/asm/inst.h b/arch/loongarch/include/asm/inst.h
index 575d1bb66ffb..b876907ca65a 100644
--- a/arch/loongarch/include/asm/inst.h
+++ b/arch/loongarch/include/asm/inst.h
@@ -23,12 +23,33 @@ enum reg1i20_op {
lu32id_op = 0x0b,
};

+enum reg1i21_op {
+ beqz_op = 0x10,
+ bnez_op = 0x11,
+};
+
enum reg2i12_op {
+ addiw_op = 0x0a,
+ addid_op = 0x0b,
lu52id_op = 0x0c,
+ ldb_op = 0xa0,
+ ldh_op = 0xa1,
+ ldw_op = 0xa2,
+ ldd_op = 0xa3,
+ stb_op = 0xa4,
+ sth_op = 0xa5,
+ stw_op = 0xa6,
+ std_op = 0xa7,
};

enum reg2i16_op {
jirl_op = 0x13,
+ beq_op = 0x16,
+ bne_op = 0x17,
+ blt_op = 0x18,
+ bge_op = 0x19,
+ bltu_op = 0x1a,
+ bgeu_op = 0x1b,
};

struct reg0i26_format {
@@ -110,6 +131,37 @@ enum loongarch_gpr {
LOONGARCH_GPR_MAX
};

+#define is_imm12_negative(val) is_imm_negative(val, 12)
+
+static inline bool is_imm_negative(unsigned long val, unsigned int bit)
+{
+ return val & (1UL << (bit - 1));
+}
+
+static inline bool is_stack_alloc_ins(union loongarch_instruction *ip)
+{
+ /* addi.d $sp, $sp, -imm */
+ return ip->reg2i12_format.opcode == addid_op &&
+ ip->reg2i12_format.rj == LOONGARCH_GPR_SP &&
+ ip->reg2i12_format.rd == LOONGARCH_GPR_SP &&
+ is_imm12_negative(ip->reg2i12_format.immediate);
+}
+
+static inline bool is_ra_save_ins(union loongarch_instruction *ip)
+{
+ /* st.d $ra, $sp, offset */
+ return ip->reg2i12_format.opcode == std_op &&
+ ip->reg2i12_format.rj == LOONGARCH_GPR_SP &&
+ ip->reg2i12_format.rd == LOONGARCH_GPR_RA &&
+ !is_imm12_negative(ip->reg2i12_format.immediate);
+}
+
+static inline bool is_branch_insn(union loongarch_instruction insn)
+{
+ return insn.reg1i21_format.opcode >= beqz_op &&
+ insn.reg1i21_format.opcode <= bgeu_op;
+}
+
u32 larch_insn_gen_lu32id(enum loongarch_gpr rd, int imm);
u32 larch_insn_gen_lu52id(enum loongarch_gpr rd, enum loongarch_gpr rj, int imm);
u32 larch_insn_gen_jirl(enum loongarch_gpr rd, enum loongarch_gpr rj, unsigned long pc, unsigned long dest);
diff --git a/arch/loongarch/include/asm/unwind.h b/arch/loongarch/include/asm/unwind.h
index 243330b39d0d..67e542e136af 100644
--- a/arch/loongarch/include/asm/unwind.h
+++ b/arch/loongarch/include/asm/unwind.h
@@ -11,10 +11,20 @@

#include <asm/stacktrace.h>

+enum unwinder_type {
+ UNWINDER_GUESS,
+ UNWINDER_PROLOGURE,
+};
+
struct unwind_state {
+ /*
+ * UNWINDER_PROLOGURE is the prologue analysis method
+ * UNWINDER_GUESS is the way to guess.
+ */
+ char type;
struct stack_info stack_info;
struct task_struct *task;
- unsigned long sp, pc;
+ unsigned long sp, pc, ra;
bool first;
bool error;
};
diff --git a/arch/loongarch/kernel/Makefile b/arch/loongarch/kernel/Makefile
index c5fa4adb23b6..918600e7b30f 100644
--- a/arch/loongarch/kernel/Makefile
+++ b/arch/loongarch/kernel/Makefile
@@ -23,5 +23,6 @@ obj-$(CONFIG_SMP) += smp.o
obj-$(CONFIG_NUMA) += numa.o

obj-$(CONFIG_UNWINDER_GUESS) += unwind_guess.o
+obj-$(CONFIG_UNWINDER_PROLOGUE) += unwind_prologue.o

CPPFLAGS_vmlinux.lds := $(KBUILD_CFLAGS)
diff --git a/arch/loongarch/kernel/traps.c b/arch/loongarch/kernel/traps.c
index f65fdf90d29e..aa1c95aaf595 100644
--- a/arch/loongarch/kernel/traps.c
+++ b/arch/loongarch/kernel/traps.c
@@ -71,6 +71,9 @@ static void show_backtrace(struct task_struct *task, const struct pt_regs *regs,
if (!task)
task = current;

+ if (user_mode(regs))
+ state.type = UNWINDER_GUESS;
+
printk("%sCall Trace:", loglvl);
for (unwind_start(&state, task, pregs);
!unwind_done(&state); unwind_next_frame(&state)) {
diff --git a/arch/loongarch/kernel/unwind_prologue.c b/arch/loongarch/kernel/unwind_prologue.c
new file mode 100644
index 000000000000..3860d17aad74
--- /dev/null
+++ b/arch/loongarch/kernel/unwind_prologue.c
@@ -0,0 +1,172 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2022 Loongson Technology Corporation Limited
+ */
+#include <linux/kallsyms.h>
+
+#include <asm/inst.h>
+#include <asm/ptrace.h>
+#include <asm/unwind.h>
+
+unsigned long unwind_get_return_address(struct unwind_state *state)
+{
+
+ if (unwind_done(state))
+ return 0;
+ else if (state->type)
+ return state->pc;
+ else if (state->first)
+ return state->pc;
+
+ return *(unsigned long *)(state->sp);
+
+}
+EXPORT_SYMBOL_GPL(unwind_get_return_address);
+
+static bool unwind_by_prologue(struct unwind_state *state)
+{
+ struct stack_info *info = &state->stack_info;
+ union loongarch_instruction *ip, *ip_end;
+ unsigned long frame_size = 0, frame_ra = -1;
+ unsigned long size, offset, pc = state->pc;
+
+ if (state->sp >= info->end || state->sp < info->begin)
+ return false;
+
+ if (!kallsyms_lookup_size_offset(pc, &size, &offset))
+ return false;
+
+ ip = (union loongarch_instruction *)(pc - offset);
+ ip_end = (union loongarch_instruction *)pc;
+
+ while (ip < ip_end) {
+ if (is_stack_alloc_ins(ip)) {
+ frame_size = (1 << 12) - ip->reg2i12_format.immediate;
+ ip++;
+ break;
+ }
+ ip++;
+ }
+
+ if (!frame_size) {
+ if (state->first)
+ goto first;
+
+ return false;
+ }
+
+ while (ip < ip_end) {
+ if (is_ra_save_ins(ip)) {
+ frame_ra = ip->reg2i12_format.immediate;
+ break;
+ }
+ if (is_branch_insn(*ip))
+ break;
+ ip++;
+ }
+
+ if (frame_ra < 0) {
+ if (state->first) {
+ state->sp = state->sp + frame_size;
+ goto first;
+ }
+ return false;
+ }
+
+ if (state->first)
+ state->first = false;
+
+ state->pc = *(unsigned long *)(state->sp + frame_ra);
+ state->sp = state->sp + frame_size;
+ return !!__kernel_text_address(state->pc);
+
+first:
+ state->first = false;
+ if (state->pc == state->ra)
+ return false;
+
+ state->pc = state->ra;
+
+ return !!__kernel_text_address(state->ra);
+}
+
+static bool unwind_by_guess(struct unwind_state *state)
+{
+ struct stack_info *info = &state->stack_info;
+ unsigned long addr;
+
+ for (state->sp += sizeof(unsigned long);
+ state->sp < info->end;
+ state->sp += sizeof(unsigned long)) {
+ addr = *(unsigned long *)(state->sp);
+ if (__kernel_text_address(addr))
+ return true;
+ }
+
+ return false;
+}
+
+void unwind_start(struct unwind_state *state, struct task_struct *task,
+ struct pt_regs *regs)
+{
+ memset(state, 0, sizeof(*state));
+
+ if (__kernel_text_address(regs->csr_era))
+ state->type = UNWINDER_PROLOGURE;
+
+ state->task = task;
+ state->pc = regs->csr_era;
+ state->sp = regs->regs[3];
+ state->ra = regs->regs[1];
+ state->first = true;
+
+ get_stack_info(state->sp, state->task, &state->stack_info);
+
+ if (!unwind_done(state) && !__kernel_text_address(state->pc))
+ unwind_next_frame(state);
+}
+EXPORT_SYMBOL_GPL(unwind_start);
+
+bool unwind_next_frame(struct unwind_state *state)
+{
+ struct stack_info *info = &state->stack_info;
+ struct pt_regs *regs;
+ unsigned long pc;
+
+ if (unwind_done(state))
+ return false;
+
+ do {
+ if (state->type) {
+ if (unwind_by_prologue(state))
+ return true;
+
+ if (info->type == STACK_TYPE_IRQ &&
+ info->end == state->sp) {
+ regs = (struct pt_regs *)info->next_sp;
+ pc = regs->csr_era;
+ if (user_mode(regs) || !__kernel_text_address(pc))
+ return false;
+
+ state->pc = pc;
+ state->sp = regs->regs[3];
+ state->ra = regs->regs[1];
+ state->first = true;
+ get_stack_info(state->sp, state->task, info);
+
+ return true;
+ }
+ } else {
+ if (state->first)
+ state->first = false;
+ else if (unwind_by_guess(state))
+ return true;
+ }
+
+ state->sp = info->next_sp;
+
+ } while (!get_stack_info(state->sp, state->task, info));
+
+ return false;
+}
+EXPORT_SYMBOL_GPL(unwind_next_frame);
--
2.20.1
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