[PATCH 2/3] ARM: Add stack unwinding support

[Sascha Hauer <s.hauer@pengutronix.de>]

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
---
 arch/arm/Kconfig           |   10 ++
 arch/arm/Makefile          |    4 +
 arch/arm/cpu/interrupts.c  |    4 +
 arch/arm/lib/Makefile      |    2 +-
 arch/arm/lib/barebox.lds.S |   16 ++
 arch/arm/lib/unwind.c      |  344 ++++++++++++++++++++++++++++++++++++++++++++
 6 files changed, 379 insertions(+), 1 deletions(-)
 create mode 100644 arch/arm/lib/unwind.c

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index bc54e58..aae0e99 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -115,6 +115,16 @@ config ARM_OPTIMZED_STRING_FUNCTIONS
 	  These functions work much faster than the normal versions but
 	  increase your binary size.
 
+config ARM_UNWIND
+	bool "enable stack unwinding support"
+	depends on AEABI
+	help
+	  This option enables stack unwinding support in barebox
+	  using the information automatically generated by the
+	  compiler. The resulting kernel image is slightly bigger but
+	  the performance is not affected. Currently, this feature
+	  only works with EABI compilers. If unsure say Y.
+
 endmenu
 
 source common/Kconfig
diff --git a/arch/arm/Makefile b/arch/arm/Makefile
index d075efd..697c783 100644
--- a/arch/arm/Makefile
+++ b/arch/arm/Makefile
@@ -34,6 +34,10 @@ else
 CFLAGS_ABI	:=$(call cc-option,-mapcs-32,-mabi=apcs-gnu) $(call cc-option,-mno-thumb-interwork,)
 endif
 
+ifeq ($(CONFIG_ARM_UNWIND),y)
+CFLAGS_ABI	+=-funwind-tables
+endif
+
 CPPFLAGS += $(CFLAGS_ABI) $(arch-y) $(tune-y)
 AFLAGS   += -include asm/unified.h
 
diff --git a/arch/arm/cpu/interrupts.c b/arch/arm/cpu/interrupts.c
index 4a0b3f8..5168921 100644
--- a/arch/arm/cpu/interrupts.c
+++ b/arch/arm/cpu/interrupts.c
@@ -27,6 +27,7 @@
 
 #include <common.h>
 #include <asm/ptrace.h>
+#include <asm/unwind.h>
 
 void do_undefined_instruction (struct pt_regs *pt_regs);
 void do_software_interrupt (struct pt_regs *pt_regs);
@@ -115,6 +116,9 @@ void show_regs (struct pt_regs *regs)
 		fast_interrupts_enabled (regs) ? "on" : "off",
 		processor_modes[processor_mode (regs)],
 		thumb_mode (regs) ? " (T)" : "");
+#ifdef CONFIG_ARM_UNWIND
+	unwind_backtrace(regs);
+#endif
 }
 
 /**
diff --git a/arch/arm/lib/Makefile b/arch/arm/lib/Makefile
index 89cb72b..3a01083 100644
--- a/arch/arm/lib/Makefile
+++ b/arch/arm/lib/Makefile
@@ -14,7 +14,7 @@ obj-y	+= ashldi3.o
 obj-y	+= lshrdi3.o
 obj-$(CONFIG_ARM_OPTIMZED_STRING_FUNCTIONS)	+= memcpy.o
 obj-$(CONFIG_ARM_OPTIMZED_STRING_FUNCTIONS)	+= memset.o
-
+obj-$(CONFIG_ARM_UNWIND) += unwind.o
 obj-$(CONFIG_MODULES) += module.o
 extra-$(CONFIG_GENERIC_LINKER_SCRIPT) += barebox.lds
 
diff --git a/arch/arm/lib/barebox.lds.S b/arch/arm/lib/barebox.lds.S
index cc74b2f..7683f73 100644
--- a/arch/arm/lib/barebox.lds.S
+++ b/arch/arm/lib/barebox.lds.S
@@ -51,6 +51,22 @@ SECTIONS
 	. = ALIGN(4);
 	.rodata : { *(.rodata*) }
 
+#ifdef CONFIG_ARM_UNWIND
+	/*
+	 * Stack unwinding tables
+	 */
+	. = ALIGN(8);
+	.ARM.unwind_idx : {
+		__start_unwind_idx = .;
+		*(.ARM.exidx*)
+		__stop_unwind_idx = .;
+	}
+	.ARM.unwind_tab : {
+		__start_unwind_tab = .;
+		*(.ARM.extab*)
+		__stop_unwind_tab = .;
+	}
+#endif
 	_etext = .;			/* End of text and rodata section */
 
 	. = ALIGN(4);
diff --git a/arch/arm/lib/unwind.c b/arch/arm/lib/unwind.c
new file mode 100644
index 0000000..62d26af
--- /dev/null
+++ b/arch/arm/lib/unwind.c
@@ -0,0 +1,344 @@
+#include <common.h>
+#include <init.h>
+#include <asm/stacktrace.h>
+#include <asm/unwind.h>
+#include <asm-generic/sections.h>
+
+/* Dummy functions to avoid linker complaints */
+void __aeabi_unwind_cpp_pr0(void)
+{
+};
+EXPORT_SYMBOL(__aeabi_unwind_cpp_pr0);
+
+void __aeabi_unwind_cpp_pr1(void)
+{
+};
+EXPORT_SYMBOL(__aeabi_unwind_cpp_pr1);
+
+void __aeabi_unwind_cpp_pr2(void)
+{
+};
+EXPORT_SYMBOL(__aeabi_unwind_cpp_pr2);
+
+struct unwind_ctrl_block {
+	unsigned long vrs[16];		/* virtual register set */
+	unsigned long *insn;		/* pointer to the current instructions word */
+	int entries;			/* number of entries left to interpret */
+	int byte;			/* current byte number in the instructions word */
+};
+
+enum regs {
+	FP = 11,
+	SP = 13,
+	LR = 14,
+	PC = 15
+};
+
+#define THREAD_SIZE               8192
+
+extern struct unwind_idx __start_unwind_idx[];
+extern struct unwind_idx __stop_unwind_idx[];
+
+/* Convert a prel31 symbol to an absolute address */
+#define prel31_to_addr(ptr)				\
+({							\
+	/* sign-extend to 32 bits */			\
+	long offset = (((long)*(ptr)) << 1) >> 1;	\
+	(unsigned long)(ptr) + offset;			\
+})
+
+static inline int is_kernel_text(unsigned long addr)
+{
+	if ((addr >= (unsigned long)_stext && addr <= (unsigned long)_etext))
+		return 1;
+	return 0;
+}
+
+void dump_backtrace_entry(unsigned long where, unsigned long from, unsigned long frame)
+{
+#ifdef CONFIG_KALLSYMS
+	printk("[<%08lx>] (%pS) from [<%08lx>] (%pS)\n", where, (void *)where, from, (void *)from);
+#else
+	printk("Function entered at [<%08lx>] from [<%08lx>]\n", where, from);
+#endif
+}
+
+/*
+ * Binary search in the unwind index. The entries entries are
+ * guaranteed to be sorted in ascending order by the linker.
+ */
+static struct unwind_idx *search_index(unsigned long addr,
+				       struct unwind_idx *first,
+				       struct unwind_idx *last)
+{
+	pr_debug("%s(%08lx, %p, %p)\n", __func__, addr, first, last);
+
+	if (addr < first->addr) {
+		pr_warning("unwind: Unknown symbol address %08lx\n", addr);
+		return NULL;
+	} else if (addr >= last->addr)
+		return last;
+
+	while (first < last - 1) {
+		struct unwind_idx *mid = first + ((last - first + 1) >> 1);
+
+		if (addr < mid->addr)
+			last = mid;
+		else
+			first = mid;
+	}
+
+	return first;
+}
+
+static struct unwind_idx *unwind_find_idx(unsigned long addr)
+{
+	struct unwind_idx *idx = NULL;
+
+	pr_debug("%s(%08lx)\n", __func__, addr);
+
+	if (is_kernel_text(addr))
+		/* main unwind table */
+		idx = search_index(addr, __start_unwind_idx,
+				   __stop_unwind_idx - 1);
+	else {
+		/* module unwinding not supported */
+	}
+
+	pr_debug("%s: idx = %p\n", __func__, idx);
+	return idx;
+}
+
+static unsigned long unwind_get_byte(struct unwind_ctrl_block *ctrl)
+{
+	unsigned long ret;
+
+	if (ctrl->entries <= 0) {
+		pr_warning("unwind: Corrupt unwind table\n");
+		return 0;
+	}
+
+	ret = (*ctrl->insn >> (ctrl->byte * 8)) & 0xff;
+
+	if (ctrl->byte == 0) {
+		ctrl->insn++;
+		ctrl->entries--;
+		ctrl->byte = 3;
+	} else
+		ctrl->byte--;
+
+	return ret;
+}
+
+/*
+ * Execute the current unwind instruction.
+ */
+static int unwind_exec_insn(struct unwind_ctrl_block *ctrl)
+{
+	unsigned long insn = unwind_get_byte(ctrl);
+
+	pr_debug("%s: insn = %08lx\n", __func__, insn);
+
+	if ((insn & 0xc0) == 0x00)
+		ctrl->vrs[SP] += ((insn & 0x3f) << 2) + 4;
+	else if ((insn & 0xc0) == 0x40)
+		ctrl->vrs[SP] -= ((insn & 0x3f) << 2) + 4;
+	else if ((insn & 0xf0) == 0x80) {
+		unsigned long mask;
+		unsigned long *vsp = (unsigned long *)ctrl->vrs[SP];
+		int load_sp, reg = 4;
+
+		insn = (insn << 8) | unwind_get_byte(ctrl);
+		mask = insn & 0x0fff;
+		if (mask == 0) {
+			pr_warning("unwind: 'Refuse to unwind' instruction %04lx\n",
+				   insn);
+			return -URC_FAILURE;
+		}
+
+		/* pop R4-R15 according to mask */
+		load_sp = mask & (1 << (13 - 4));
+		while (mask) {
+			if (mask & 1)
+				ctrl->vrs[reg] = *vsp++;
+			mask >>= 1;
+			reg++;
+		}
+		if (!load_sp)
+			ctrl->vrs[SP] = (unsigned long)vsp;
+	} else if ((insn & 0xf0) == 0x90 &&
+		   (insn & 0x0d) != 0x0d)
+		ctrl->vrs[SP] = ctrl->vrs[insn & 0x0f];
+	else if ((insn & 0xf0) == 0xa0) {
+		unsigned long *vsp = (unsigned long *)ctrl->vrs[SP];
+		int reg;
+
+		/* pop R4-R[4+bbb] */
+		for (reg = 4; reg <= 4 + (insn & 7); reg++)
+			ctrl->vrs[reg] = *vsp++;
+		if (insn & 0x80)
+			ctrl->vrs[14] = *vsp++;
+		ctrl->vrs[SP] = (unsigned long)vsp;
+	} else if (insn == 0xb0) {
+		if (ctrl->vrs[PC] == 0)
+			ctrl->vrs[PC] = ctrl->vrs[LR];
+		/* no further processing */
+		ctrl->entries = 0;
+	} else if (insn == 0xb1) {
+		unsigned long mask = unwind_get_byte(ctrl);
+		unsigned long *vsp = (unsigned long *)ctrl->vrs[SP];
+		int reg = 0;
+
+		if (mask == 0 || mask & 0xf0) {
+			pr_warning("unwind: Spare encoding %04lx\n",
+			       (insn << 8) | mask);
+			return -URC_FAILURE;
+		}
+
+		/* pop R0-R3 according to mask */
+		while (mask) {
+			if (mask & 1)
+				ctrl->vrs[reg] = *vsp++;
+			mask >>= 1;
+			reg++;
+		}
+		ctrl->vrs[SP] = (unsigned long)vsp;
+	} else if (insn == 0xb2) {
+		unsigned long uleb128 = unwind_get_byte(ctrl);
+
+		ctrl->vrs[SP] += 0x204 + (uleb128 << 2);
+	} else {
+		pr_warning("unwind: Unhandled instruction %02lx\n", insn);
+		return -URC_FAILURE;
+	}
+
+	pr_debug("%s: fp = %08lx sp = %08lx lr = %08lx pc = %08lx\n", __func__,
+		 ctrl->vrs[FP], ctrl->vrs[SP], ctrl->vrs[LR], ctrl->vrs[PC]);
+
+	return URC_OK;
+}
+
+/*
+ * Unwind a single frame starting with *sp for the symbol at *pc. It
+ * updates the *pc and *sp with the new values.
+ */
+int unwind_frame(struct stackframe *frame)
+{
+	unsigned long high, low;
+	struct unwind_idx *idx;
+	struct unwind_ctrl_block ctrl;
+
+	/* only go to a higher address on the stack */
+	low = frame->sp;
+	high = ALIGN(low, THREAD_SIZE);
+
+	pr_debug("%s(pc = %08lx lr = %08lx sp = %08lx)\n", __func__,
+		 frame->pc, frame->lr, frame->sp);
+
+	if (!is_kernel_text(frame->pc))
+		return -URC_FAILURE;
+
+	idx = unwind_find_idx(frame->pc);
+	if (!idx) {
+		pr_warning("unwind: Index not found %08lx\n", frame->pc);
+		return -URC_FAILURE;
+	}
+
+	ctrl.vrs[FP] = frame->fp;
+	ctrl.vrs[SP] = frame->sp;
+	ctrl.vrs[LR] = frame->lr;
+	ctrl.vrs[PC] = 0;
+
+	if (idx->insn == 1)
+		/* can't unwind */
+		return -URC_FAILURE;
+	else if ((idx->insn & 0x80000000) == 0)
+		/* prel31 to the unwind table */
+		ctrl.insn = (unsigned long *)prel31_to_addr(&idx->insn);
+	else if ((idx->insn & 0xff000000) == 0x80000000)
+		/* only personality routine 0 supported in the index */
+		ctrl.insn = &idx->insn;
+	else {
+		pr_warning("unwind: Unsupported personality routine %08lx in the index at %p\n",
+			   idx->insn, idx);
+		return -URC_FAILURE;
+	}
+
+	/* check the personality routine */
+	if ((*ctrl.insn & 0xff000000) == 0x80000000) {
+		ctrl.byte = 2;
+		ctrl.entries = 1;
+	} else if ((*ctrl.insn & 0xff000000) == 0x81000000) {
+		ctrl.byte = 1;
+		ctrl.entries = 1 + ((*ctrl.insn & 0x00ff0000) >> 16);
+	} else {
+		pr_warning("unwind: Unsupported personality routine %08lx at %p\n",
+			   *ctrl.insn, ctrl.insn);
+		return -URC_FAILURE;
+	}
+
+	while (ctrl.entries > 0) {
+		int urc = unwind_exec_insn(&ctrl);
+		if (urc < 0)
+			return urc;
+		if (ctrl.vrs[SP] < low || ctrl.vrs[SP] >= high)
+			return -URC_FAILURE;
+	}
+
+	if (ctrl.vrs[PC] == 0)
+		ctrl.vrs[PC] = ctrl.vrs[LR];
+
+	/* check for infinite loop */
+	if (frame->pc == ctrl.vrs[PC])
+		return -URC_FAILURE;
+
+	frame->fp = ctrl.vrs[FP];
+	frame->sp = ctrl.vrs[SP];
+	frame->lr = ctrl.vrs[LR];
+	frame->pc = ctrl.vrs[PC];
+
+	return URC_OK;
+}
+
+void unwind_backtrace(struct pt_regs *regs)
+{
+	struct stackframe frame;
+	register unsigned long current_sp asm ("sp");
+
+	pr_debug("%s\n", __func__);
+
+	if (regs) {
+		frame.fp = regs->ARM_fp;
+		frame.sp = regs->ARM_sp;
+		frame.lr = regs->ARM_lr;
+		/* PC might be corrupted, use LR in that case. */
+		frame.pc = is_kernel_text(regs->ARM_pc)
+			 ? regs->ARM_pc : regs->ARM_lr;
+	} else {
+		frame.sp = current_sp;
+		frame.lr = (unsigned long)__builtin_return_address(0);
+		frame.pc = (unsigned long)unwind_backtrace;
+	}
+
+	while (1) {
+		int urc;
+		unsigned long where = frame.pc;
+
+		urc = unwind_frame(&frame);
+		if (urc < 0)
+			break;
+		dump_backtrace_entry(where, frame.pc, frame.sp - 4);
+	}
+}
+
+static int unwind_init(void)
+{
+	struct unwind_idx *idx;
+
+	/* Convert the symbol addresses to absolute values */
+	for (idx = __start_unwind_idx; idx < __stop_unwind_idx; idx++)
+		idx->addr = prel31_to_addr(&idx->addr);
+
+	return 0;
+}
+core_initcall(unwind_init);
-- 
1.7.2.3


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