Remove stack unwinder for now

It has caused more problems than it ever really solved, and is
apparently not getting cleaned up and fixed.  We can put it back when
it's stable and isn't likely to make warning or bug events worse.

In the meantime, enable frame pointers for more readable stack traces.

Signed-off-by: Linus Torvalds <[email protected]>

Makefile

@@ -496,11 +496,6 @@ else
 CFLAGS		+= -fomit-frame-pointer
 endif
 
-ifdef CONFIG_UNWIND_INFO
-CFLAGS		+= -fasynchronous-unwind-tables
-LDFLAGS_vmlinux	+= --eh-frame-hdr
-endif
-
 ifdef CONFIG_DEBUG_INFO
 CFLAGS		+= -g
 endif

arch/i386/defconfig

@@ -1493,8 +1493,6 @@ CONFIG_DEBUG_BUGVERBOSE=y
 # CONFIG_DEBUG_VM is not set
 # CONFIG_DEBUG_LIST is not set
 # CONFIG_FRAME_POINTER is not set
-CONFIG_UNWIND_INFO=y
-CONFIG_STACK_UNWIND=y
 # CONFIG_FORCED_INLINING is not set
 # CONFIG_HEADERS_CHECK is not set
 # CONFIG_RCU_TORTURE_TEST is not set

arch/i386/kernel/entry.S

@@ -979,38 +979,6 @@ ENTRY(spurious_interrupt_bug)
 	jmp error_code
 	CFI_ENDPROC
 
-#ifdef CONFIG_STACK_UNWIND
-ENTRY(arch_unwind_init_running)
-	CFI_STARTPROC
-	movl	4(%esp), %edx
-	movl	(%esp), %ecx
-	leal	4(%esp), %eax
-	movl	%ebx, PT_EBX(%edx)
-	xorl	%ebx, %ebx
-	movl	%ebx, PT_ECX(%edx)
-	movl	%ebx, PT_EDX(%edx)
-	movl	%esi, PT_ESI(%edx)
-	movl	%edi, PT_EDI(%edx)
-	movl	%ebp, PT_EBP(%edx)
-	movl	%ebx, PT_EAX(%edx)
-	movl	$__USER_DS, PT_DS(%edx)
-	movl	$__USER_DS, PT_ES(%edx)
-	movl	$0, PT_GS(%edx)
-	movl	%ebx, PT_ORIG_EAX(%edx)
-	movl	%ecx, PT_EIP(%edx)
-	movl	12(%esp), %ecx
-	movl	$__KERNEL_CS, PT_CS(%edx)
-	movl	%ebx, PT_EFLAGS(%edx)
-	movl	%eax, PT_OLDESP(%edx)
-	movl	8(%esp), %eax
-	movl	%ecx, 8(%esp)
-	movl	PT_EBX(%edx), %ebx
-	movl	$__KERNEL_DS, PT_OLDSS(%edx)
-	jmpl	*%eax
-	CFI_ENDPROC
-ENDPROC(arch_unwind_init_running)
-#endif
-
 ENTRY(kernel_thread_helper)
 	pushl $0		# fake return address for unwinder
 	CFI_STARTPROC

arch/i386/kernel/traps.c

@@ -94,11 +94,6 @@ asmlinkage void spurious_interrupt_bug(void);
 asmlinkage void machine_check(void);
 
 int kstack_depth_to_print = 24;
-#ifdef CONFIG_STACK_UNWIND
-static int call_trace = 1;
-#else
-#define call_trace (-1)
-#endif
 ATOMIC_NOTIFIER_HEAD(i386die_chain);
 
 int register_die_notifier(struct notifier_block *nb)
@@ -152,33 +147,6 @@ static inline unsigned long print_context_stack(struct thread_info *tinfo,
 	return ebp;
 }
 
-struct ops_and_data {
-	struct stacktrace_ops *ops;
-	void *data;
-};
-
-static asmlinkage int
-dump_trace_unwind(struct unwind_frame_info *info, void *data)
-{
-	struct ops_and_data *oad = (struct ops_and_data *)data;
-	int n = 0;
-	unsigned long sp = UNW_SP(info);
-
-	if (arch_unw_user_mode(info))
-		return -1;
-	while (unwind(info) == 0 && UNW_PC(info)) {
-		n++;
-		oad->ops->address(oad->data, UNW_PC(info));
-		if (arch_unw_user_mode(info))
-			break;
-		if ((sp & ~(PAGE_SIZE - 1)) == (UNW_SP(info) & ~(PAGE_SIZE - 1))
-		    && sp > UNW_SP(info))
-			break;
-		sp = UNW_SP(info);
-	}
-	return n;
-}
-
 #define MSG(msg) ops->warning(data, msg)
 
 void dump_trace(struct task_struct *task, struct pt_regs *regs,
@@ -190,41 +158,6 @@ void dump_trace(struct task_struct *task, struct pt_regs *regs,
 	if (!task)
 		task = current;
 
-	if (call_trace >= 0) {
-		int unw_ret = 0;
-		struct unwind_frame_info info;
-		struct ops_and_data oad = { .ops = ops, .data = data };
-
-		if (regs) {
-			if (unwind_init_frame_info(&info, task, regs) == 0)
-				unw_ret = dump_trace_unwind(&info, &oad);
-		} else if (task == current)
-			unw_ret = unwind_init_running(&info, dump_trace_unwind,
-						      &oad);
-		else {
-			if (unwind_init_blocked(&info, task) == 0)
-				unw_ret = dump_trace_unwind(&info, &oad);
-		}
-		if (unw_ret > 0) {
-			if (call_trace == 1 && !arch_unw_user_mode(&info)) {
-				ops->warning_symbol(data,
-					     "DWARF2 unwinder stuck at %s",
-					     UNW_PC(&info));
-				if (UNW_SP(&info) >= PAGE_OFFSET) {
-					MSG("Leftover inexact backtrace:");
-					stack = (void *)UNW_SP(&info);
-					if (!stack)
-						return;
-					ebp = UNW_FP(&info);
-				} else
-					MSG("Full inexact backtrace again:");
-			} else if (call_trace >= 1)
-				return;
-			else
-				MSG("Full inexact backtrace again:");
-		} else
-			MSG("Inexact backtrace:");
-	}
 	if (!stack) {
 		unsigned long dummy;
 		stack = &dummy;
@@ -1258,19 +1191,3 @@ static int __init kstack_setup(char *s)
 	return 1;
 }
 __setup("kstack=", kstack_setup);
-
-#ifdef CONFIG_STACK_UNWIND
-static int __init call_trace_setup(char *s)
-{
-	if (strcmp(s, "old") == 0)
-		call_trace = -1;
-	else if (strcmp(s, "both") == 0)
-		call_trace = 0;
-	else if (strcmp(s, "newfallback") == 0)
-		call_trace = 1;
-	else if (strcmp(s, "new") == 2)
-		call_trace = 2;
-	return 1;
-}
-__setup("call_trace=", call_trace_setup);
-#endif

arch/x86_64/Makefile

@@ -45,9 +45,7 @@ cflags-kernel-$(CONFIG_REORDER) += -ffunction-sections
 # actually it makes the kernel smaller too.
 cflags-y += -fno-reorder-blocks
 cflags-y += -Wno-sign-compare
-ifneq ($(CONFIG_UNWIND_INFO),y)
 cflags-y += -fno-asynchronous-unwind-tables
-endif
 ifneq ($(CONFIG_DEBUG_INFO),y)
 # -fweb shrinks the kernel a bit, but the difference is very small
 # it also messes up debugging, so don't use it for now.

arch/x86_64/defconfig

@@ -1523,8 +1523,6 @@ CONFIG_DEBUG_FS=y
 # CONFIG_DEBUG_VM is not set
 # CONFIG_DEBUG_LIST is not set
 # CONFIG_FRAME_POINTER is not set
-CONFIG_UNWIND_INFO=y
-CONFIG_STACK_UNWIND=y
 # CONFIG_FORCED_INLINING is not set
 # CONFIG_HEADERS_CHECK is not set
 # CONFIG_RCU_TORTURE_TEST is not set

arch/x86_64/kernel/entry.S

@@ -1155,36 +1155,3 @@ ENTRY(call_softirq)
 	ret
 	CFI_ENDPROC
 ENDPROC(call_softirq)
-
-#ifdef CONFIG_STACK_UNWIND
-ENTRY(arch_unwind_init_running)
-	CFI_STARTPROC
-	movq	%r15, R15(%rdi)
-	movq	%r14, R14(%rdi)
-	xchgq	%rsi, %rdx
-	movq	%r13, R13(%rdi)
-	movq	%r12, R12(%rdi)
-	xorl	%eax, %eax
-	movq	%rbp, RBP(%rdi)
-	movq	%rbx, RBX(%rdi)
-	movq	(%rsp), %rcx
-	movq	%rax, R11(%rdi)
-	movq	%rax, R10(%rdi)
-	movq	%rax, R9(%rdi)
-	movq	%rax, R8(%rdi)
-	movq	%rax, RAX(%rdi)
-	movq	%rax, RCX(%rdi)
-	movq	%rax, RDX(%rdi)
-	movq	%rax, RSI(%rdi)
-	movq	%rax, RDI(%rdi)
-	movq	%rax, ORIG_RAX(%rdi)
-	movq	%rcx, RIP(%rdi)
-	leaq	8(%rsp), %rcx
-	movq	$__KERNEL_CS, CS(%rdi)
-	movq	%rax, EFLAGS(%rdi)
-	movq	%rcx, RSP(%rdi)
-	movq	$__KERNEL_DS, SS(%rdi)
-	jmpq	*%rdx
-	CFI_ENDPROC
-ENDPROC(arch_unwind_init_running)
-#endif

arch/x86_64/kernel/traps.c

@@ -110,11 +110,6 @@ static inline void preempt_conditional_cli(struct pt_regs *regs)
 }
 
 int kstack_depth_to_print = 12;
-#ifdef CONFIG_STACK_UNWIND
-static int call_trace = 1;
-#else
-#define call_trace (-1)
-#endif
 
 #ifdef CONFIG_KALLSYMS
 void printk_address(unsigned long address)
@@ -217,32 +212,6 @@ static unsigned long *in_exception_stack(unsigned cpu, unsigned long stack,
 	return NULL;
 }
 
-struct ops_and_data {
-	struct stacktrace_ops *ops;
-	void *data;
-};
-
-static int dump_trace_unwind(struct unwind_frame_info *info, void *context)
-{
-	struct ops_and_data *oad = (struct ops_and_data *)context;
-	int n = 0;
-	unsigned long sp = UNW_SP(info);
-
-	if (arch_unw_user_mode(info))
-		return -1;
-	while (unwind(info) == 0 && UNW_PC(info)) {
-		n++;
-		oad->ops->address(oad->data, UNW_PC(info));
-		if (arch_unw_user_mode(info))
-			break;
-		if ((sp & ~(PAGE_SIZE - 1)) == (UNW_SP(info) & ~(PAGE_SIZE - 1))
-		    && sp > UNW_SP(info))
-			break;
-		sp = UNW_SP(info);
-	}
-	return n;
-}
-
 #define MSG(txt) ops->warning(data, txt)
 
 /*
@@ -270,40 +239,6 @@ void dump_trace(struct task_struct *tsk, struct pt_regs *regs,
 	if (!tsk)
 		tsk = current;
 
-	if (call_trace >= 0) {
-		int unw_ret = 0;
-		struct unwind_frame_info info;
-		struct ops_and_data oad = { .ops = ops, .data = data };
-
-		if (regs) {
-			if (unwind_init_frame_info(&info, tsk, regs) == 0)
-				unw_ret = dump_trace_unwind(&info, &oad);
-		} else if (tsk == current)
-			unw_ret = unwind_init_running(&info, dump_trace_unwind,
-						      &oad);
-		else {
-			if (unwind_init_blocked(&info, tsk) == 0)
-				unw_ret = dump_trace_unwind(&info, &oad);
-		}
-		if (unw_ret > 0) {
-			if (call_trace == 1 && !arch_unw_user_mode(&info)) {
-				ops->warning_symbol(data,
-					     "DWARF2 unwinder stuck at %s",
-					     UNW_PC(&info));
-				if ((long)UNW_SP(&info) < 0) {
-					MSG("Leftover inexact backtrace:");
-					stack = (unsigned long *)UNW_SP(&info);
-					if (!stack)
-						goto out;
-				} else
-					MSG("Full inexact backtrace again:");
-			} else if (call_trace >= 1)
-				goto out;
-			else
-				MSG("Full inexact backtrace again:");
-		} else
-			MSG("Inexact backtrace:");
-	}
 	if (!stack) {
 		unsigned long dummy;
 		stack = &dummy;
@@ -387,7 +322,6 @@ void dump_trace(struct task_struct *tsk, struct pt_regs *regs,
 	tinfo = current_thread_info();
 	HANDLE_STACK (valid_stack_ptr(tinfo, stack));
 #undef HANDLE_STACK
-out:
 	put_cpu();
 }
 EXPORT_SYMBOL(dump_trace);
@@ -1188,21 +1122,3 @@ static int __init kstack_setup(char *s)
 	return 0;
 }
 early_param("kstack", kstack_setup);
-
-#ifdef CONFIG_STACK_UNWIND
-static int __init call_trace_setup(char *s)
-{
-	if (!s)
-		return -EINVAL;
-	if (strcmp(s, "old") == 0)
-		call_trace = -1;
-	else if (strcmp(s, "both") == 0)
-		call_trace = 0;
-	else if (strcmp(s, "newfallback") == 0)
-		call_trace = 1;
-	else if (strcmp(s, "new") == 0)
-		call_trace = 2;
-	return 0;
-}
-early_param("call_trace", call_trace_setup);
-#endif

arch/x86_64/kernel/vmlinux.lds.S

@@ -221,9 +221,7 @@ SECTIONS
   /* Sections to be discarded */
   /DISCARD/ : {
 	*(.exitcall.exit)
-#ifndef CONFIG_UNWIND_INFO
 	*(.eh_frame)
-#endif
 	}
 
   STABS_DEBUG

include/asm-generic/vmlinux.lds.h

@@ -119,8 +119,6 @@
 		*(__ksymtab_strings)					\
 	}								\
 									\
-	EH_FRAME							\
-									\
 	/* Built-in module parameters. */				\
 	__param : AT(ADDR(__param) - LOAD_OFFSET) {			\
 		VMLINUX_SYMBOL(__start___param) = .;			\
@@ -160,26 +158,6 @@
 		*(.kprobes.text)					\
 		VMLINUX_SYMBOL(__kprobes_text_end) = .;
 
-#ifdef CONFIG_STACK_UNWIND
-#define EH_FRAME							\
-		/* Unwind data binary search table */			\
-		. = ALIGN(8);						\
-        	.eh_frame_hdr : AT(ADDR(.eh_frame_hdr) - LOAD_OFFSET) {	\
-			VMLINUX_SYMBOL(__start_unwind_hdr) = .;		\
-			*(.eh_frame_hdr)				\
-			VMLINUX_SYMBOL(__end_unwind_hdr) = .;		\
-		}							\
-		/* Unwind data */					\
-		. = ALIGN(8);						\
-		.eh_frame : AT(ADDR(.eh_frame) - LOAD_OFFSET) {		\
-			VMLINUX_SYMBOL(__start_unwind) = .;		\
-		  	*(.eh_frame)					\
-			VMLINUX_SYMBOL(__end_unwind) = .;		\
-		}
-#else
-#define EH_FRAME
-#endif
-
 		/* DWARF debug sections.
 		Symbols in the DWARF debugging sections are relative to
 		the beginning of the section so we begin them at 0.  */