x86/debug: Remove perpetually broken, unmaintainable dwarf annotations

So the dwarf2 annotations in low level assembly code have
become an increasing hindrance: unreadable, messy macros
mixed into some of the most security sensitive code paths
of the Linux kernel.

These debug info annotations don't even buy the upstream
kernel anything: dwarf driven stack unwinding has caused
problems in the past so it's out of tree, and the upstream
kernel only uses the much more robust framepointers based
stack unwinding method.

In addition to that there's a steady, slow bitrot going
on with these annotations, requiring frequent fixups.
There's no tooling and no functionality upstream that
keeps it correct.

So burn down the sick forest, allowing new, healthier growth:

   27 files changed, 350 insertions(+), 1101 deletions(-)

Someone who has the willingness and time to do this
properly can attempt to reintroduce dwarf debuginfo in x86
assembly code plus dwarf unwinding from first principles,
with the following conditions:

 - it should be maximally readable, and maximally low-key to
   'ordinary' code reading and maintenance.

 - find a build time method to insert dwarf annotations
   automatically in the most common cases, for pop/push
   instructions that manipulate the stack pointer. This could
   be done for example via a preprocessing step that just
   looks for common patterns - plus special annotations for
   the few cases where we want to depart from the default.
   We have hundreds of CFI annotations, so automating most of
   that makes sense.

 - it should come with build tooling checks that ensure that
   CFI annotations are sensible. We've seen such efforts from
   the framepointer side, and there's no reason it couldn't be
   done on the dwarf side.

Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Frédéric Weisbecker <fweisbec@gmail.com
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jan Beulich <JBeulich@suse.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 32 insertions, 101 deletions

diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S
index 63450a596800..2be23c734db5 100644
--- a/arch/x86/ia32/ia32entry.S
+++ b/arch/x86/ia32/ia32entry.S
@@ -4,7 +4,6 @@
  * Copyright 2000-2002 Andi Kleen, SuSE Labs.
  */		 
 
-#include <asm/dwarf2.h>
 #include <asm/calling.h>
 #include <asm/asm-offsets.h>
 #include <asm/current.h>
@@ -60,17 +59,6 @@
 	movl %eax,%eax			/* zero extension */
 	.endm
 	
-	.macro CFI_STARTPROC32 simple
-	CFI_STARTPROC	\simple
-	CFI_UNDEFINED	r8
-	CFI_UNDEFINED	r9
-	CFI_UNDEFINED	r10
-	CFI_UNDEFINED	r11
-	CFI_UNDEFINED	r12
-	CFI_UNDEFINED	r13
-	CFI_UNDEFINED	r14
-	CFI_UNDEFINED	r15
-	.endm
 
 #ifdef CONFIG_PARAVIRT
 ENTRY(native_usergs_sysret32)
@@ -102,11 +90,6 @@ ENDPROC(native_usergs_sysret32)
  * with the int 0x80 path.
  */
 ENTRY(ia32_sysenter_target)
-	CFI_STARTPROC32	simple
-	CFI_SIGNAL_FRAME
-	CFI_DEF_CFA	rsp,0
-	CFI_REGISTER	rsp,rbp
-
 	/*
 	 * Interrupts are off on entry.
 	 * We do not frame this tiny irq-off block with TRACE_IRQS_OFF/ON,
@@ -121,25 +104,21 @@ ENTRY(ia32_sysenter_target)
 	movl	%eax, %eax
 
 	movl	ASM_THREAD_INFO(TI_sysenter_return, %rsp, 0), %r10d
-	CFI_REGISTER rip,r10
 
 	/* Construct struct pt_regs on stack */
-	pushq_cfi	$__USER32_DS		/* pt_regs->ss */
-	pushq_cfi	%rbp			/* pt_regs->sp */
-	CFI_REL_OFFSET	rsp,0
-	pushfq_cfi				/* pt_regs->flags */
-	pushq_cfi	$__USER32_CS		/* pt_regs->cs */
-	pushq_cfi	%r10 /* pt_regs->ip = thread_info->sysenter_return */
-	CFI_REL_OFFSET	rip,0
-	pushq_cfi_reg	rax			/* pt_regs->orig_ax */
-	pushq_cfi_reg	rdi			/* pt_regs->di */
-	pushq_cfi_reg	rsi			/* pt_regs->si */
-	pushq_cfi_reg	rdx			/* pt_regs->dx */
-	pushq_cfi_reg	rcx			/* pt_regs->cx */
-	pushq_cfi	$-ENOSYS		/* pt_regs->ax */
+	pushq	$__USER32_DS		/* pt_regs->ss */
+	pushq	%rbp			/* pt_regs->sp */
+	pushfq				/* pt_regs->flags */
+	pushq	$__USER32_CS		/* pt_regs->cs */
+	pushq	%r10 /* pt_regs->ip = thread_info->sysenter_return */
+	pushq	%rax			/* pt_regs->orig_ax */
+	pushq	%rdi			/* pt_regs->di */
+	pushq	%rsi			/* pt_regs->si */
+	pushq	%rdx			/* pt_regs->dx */
+	pushq	%rcx			/* pt_regs->cx */
+	pushq	$-ENOSYS		/* pt_regs->ax */
 	cld
 	sub	$(10*8),%rsp /* pt_regs->r8-11,bp,bx,r12-15 not saved */
-	CFI_ADJUST_CFA_OFFSET 10*8
 
 	/*
 	 * no need to do an access_ok check here because rbp has been
@@ -161,8 +140,8 @@ sysenter_flags_fixed:
 
 	orl     $TS_COMPAT, ASM_THREAD_INFO(TI_status, %rsp, SIZEOF_PTREGS)
 	testl   $_TIF_WORK_SYSCALL_ENTRY, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
-	CFI_REMEMBER_STATE
 	jnz  sysenter_tracesys
+
 sysenter_do_call:
 	/* 32bit syscall -> 64bit C ABI argument conversion */
 	movl	%edi,%r8d	/* arg5 */
@@ -193,14 +172,12 @@ sysexit_from_sys_call:
 	 */
 	andl    $~TS_COMPAT,ASM_THREAD_INFO(TI_status, %rsp, SIZEOF_PTREGS)
 	movl	RIP(%rsp),%ecx		/* User %eip */
-	CFI_REGISTER rip,rcx
 	RESTORE_RSI_RDI
 	xorl	%edx,%edx		/* avoid info leaks */
 	xorq	%r8,%r8
 	xorq	%r9,%r9
 	xorq	%r10,%r10
 	movl	EFLAGS(%rsp),%r11d	/* User eflags */
-	/*CFI_RESTORE rflags*/
 	TRACE_IRQS_ON
 
 	/*
@@ -231,8 +208,6 @@ sysexit_from_sys_call:
 	 */
 	USERGS_SYSRET32
 
-	CFI_RESTORE_STATE
-
 #ifdef CONFIG_AUDITSYSCALL
 	.macro auditsys_entry_common
 	movl %esi,%r8d			/* 5th arg: 4th syscall arg */
@@ -282,8 +257,8 @@ sysexit_audit:
 #endif
 
 sysenter_fix_flags:
-	pushq_cfi $(X86_EFLAGS_IF|X86_EFLAGS_FIXED)
-	popfq_cfi
+	pushq $(X86_EFLAGS_IF|X86_EFLAGS_FIXED)
+	popfq
 	jmp sysenter_flags_fixed
 
 sysenter_tracesys:
@@ -298,7 +273,6 @@ sysenter_tracesys:
 	LOAD_ARGS32  /* reload args from stack in case ptrace changed it */
 	RESTORE_EXTRA_REGS
 	jmp	sysenter_do_call
-	CFI_ENDPROC
 ENDPROC(ia32_sysenter_target)
 
 /*
@@ -332,12 +306,6 @@ ENDPROC(ia32_sysenter_target)
  * with the int 0x80 path.
  */
 ENTRY(ia32_cstar_target)
-	CFI_STARTPROC32	simple
-	CFI_SIGNAL_FRAME
-	CFI_DEF_CFA	rsp,0
-	CFI_REGISTER	rip,rcx
-	/*CFI_REGISTER	rflags,r11*/
-
 	/*
 	 * Interrupts are off on entry.
 	 * We do not frame this tiny irq-off block with TRACE_IRQS_OFF/ON,
@@ -345,7 +313,6 @@ ENTRY(ia32_cstar_target)
 	 */
 	SWAPGS_UNSAFE_STACK
 	movl	%esp,%r8d
-	CFI_REGISTER	rsp,r8
 	movq	PER_CPU_VAR(cpu_current_top_of_stack),%rsp
 	ENABLE_INTERRUPTS(CLBR_NONE)
 
@@ -353,22 +320,19 @@ ENTRY(ia32_cstar_target)
 	movl	%eax,%eax
 
 	/* Construct struct pt_regs on stack */
-	pushq_cfi	$__USER32_DS		/* pt_regs->ss */
-	pushq_cfi	%r8			/* pt_regs->sp */
-	CFI_REL_OFFSET rsp,0
-	pushq_cfi	%r11			/* pt_regs->flags */
-	pushq_cfi	$__USER32_CS		/* pt_regs->cs */
-	pushq_cfi	%rcx			/* pt_regs->ip */
-	CFI_REL_OFFSET rip,0
-	pushq_cfi_reg	rax			/* pt_regs->orig_ax */
-	pushq_cfi_reg	rdi			/* pt_regs->di */
-	pushq_cfi_reg	rsi			/* pt_regs->si */
-	pushq_cfi_reg	rdx			/* pt_regs->dx */
-	pushq_cfi_reg	rbp			/* pt_regs->cx */
+	pushq	$__USER32_DS		/* pt_regs->ss */
+	pushq	%r8			/* pt_regs->sp */
+	pushq	%r11			/* pt_regs->flags */
+	pushq	$__USER32_CS		/* pt_regs->cs */
+	pushq	%rcx			/* pt_regs->ip */
+	pushq	%rax			/* pt_regs->orig_ax */
+	pushq	%rdi			/* pt_regs->di */
+	pushq	%rsi			/* pt_regs->si */
+	pushq	%rdx			/* pt_regs->dx */
+	pushq	%rbp			/* pt_regs->cx */
 	movl	%ebp,%ecx
-	pushq_cfi	$-ENOSYS		/* pt_regs->ax */
+	pushq	$-ENOSYS		/* pt_regs->ax */
 	sub	$(10*8),%rsp /* pt_regs->r8-11,bp,bx,r12-15 not saved */
-	CFI_ADJUST_CFA_OFFSET 10*8
 
 	/*
 	 * no need to do an access_ok check here because r8 has been
@@ -380,8 +344,8 @@ ENTRY(ia32_cstar_target)
 	ASM_CLAC
 	orl     $TS_COMPAT, ASM_THREAD_INFO(TI_status, %rsp, SIZEOF_PTREGS)
 	testl   $_TIF_WORK_SYSCALL_ENTRY, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
-	CFI_REMEMBER_STATE
 	jnz   cstar_tracesys
+
 cstar_do_call:
 	/* 32bit syscall -> 64bit C ABI argument conversion */
 	movl	%edi,%r8d	/* arg5 */
@@ -403,15 +367,12 @@ sysretl_from_sys_call:
 	andl $~TS_COMPAT, ASM_THREAD_INFO(TI_status, %rsp, SIZEOF_PTREGS)
 	RESTORE_RSI_RDI_RDX
 	movl RIP(%rsp),%ecx
-	CFI_REGISTER rip,rcx
 	movl EFLAGS(%rsp),%r11d
-	/*CFI_REGISTER rflags,r11*/
 	xorq	%r10,%r10
 	xorq	%r9,%r9
 	xorq	%r8,%r8
 	TRACE_IRQS_ON
 	movl RSP(%rsp),%esp
-	CFI_RESTORE rsp
 	/*
 	 * 64bit->32bit SYSRET restores eip from ecx,
 	 * eflags from r11 (but RF and VM bits are forced to 0),
@@ -430,7 +391,6 @@ sysretl_from_sys_call:
 
 #ifdef CONFIG_AUDITSYSCALL
 cstar_auditsys:
-	CFI_RESTORE_STATE
 	movl %r9d,R9(%rsp)	/* register to be clobbered by call */
 	auditsys_entry_common
 	movl R9(%rsp),%r9d	/* reload 6th syscall arg */
@@ -460,7 +420,6 @@ ia32_badarg:
 	ASM_CLAC
 	movq $-EFAULT,%rax
 	jmp ia32_sysret
-	CFI_ENDPROC
 
 /*
  * Emulated IA32 system calls via int 0x80.
@@ -484,15 +443,6 @@ ia32_badarg:
  */
 
 ENTRY(ia32_syscall)
-	CFI_STARTPROC32	simple
-	CFI_SIGNAL_FRAME
-	CFI_DEF_CFA	rsp,5*8
-	/*CFI_REL_OFFSET	ss,4*8 */
-	CFI_REL_OFFSET	rsp,3*8
-	/*CFI_REL_OFFSET	rflags,2*8 */
-	/*CFI_REL_OFFSET	cs,1*8 */
-	CFI_REL_OFFSET	rip,0*8
-
 	/*
 	 * Interrupts are off on entry.
 	 * We do not frame this tiny irq-off block with TRACE_IRQS_OFF/ON,
@@ -506,15 +456,14 @@ ENTRY(ia32_syscall)
 	movl	%eax,%eax
 
 	/* Construct struct pt_regs on stack (iret frame is already on stack) */
-	pushq_cfi_reg	rax			/* pt_regs->orig_ax */
-	pushq_cfi_reg	rdi			/* pt_regs->di */
-	pushq_cfi_reg	rsi			/* pt_regs->si */
-	pushq_cfi_reg	rdx			/* pt_regs->dx */
-	pushq_cfi_reg	rcx			/* pt_regs->cx */
-	pushq_cfi	$-ENOSYS		/* pt_regs->ax */
+	pushq	%rax			/* pt_regs->orig_ax */
+	pushq	%rdi			/* pt_regs->di */
+	pushq	%rsi			/* pt_regs->si */
+	pushq	%rdx			/* pt_regs->dx */
+	pushq	%rcx			/* pt_regs->cx */
+	pushq	$-ENOSYS		/* pt_regs->ax */
 	cld
 	sub	$(10*8),%rsp /* pt_regs->r8-11,bp,bx,r12-15 not saved */
-	CFI_ADJUST_CFA_OFFSET 10*8
 
 	orl $TS_COMPAT, ASM_THREAD_INFO(TI_status, %rsp, SIZEOF_PTREGS)
 	testl $_TIF_WORK_SYSCALL_ENTRY, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
@@ -544,7 +493,6 @@ ia32_tracesys:
 	LOAD_ARGS32	/* reload args from stack in case ptrace changed it */
 	RESTORE_EXTRA_REGS
 	jmp ia32_do_call
-	CFI_ENDPROC
 END(ia32_syscall)
 
 	.macro PTREGSCALL label, func
@@ -554,8 +502,6 @@ GLOBAL(\label)
 	jmp  ia32_ptregs_common	
 	.endm
 
-	CFI_STARTPROC32
-
 	PTREGSCALL stub32_rt_sigreturn, sys32_rt_sigreturn
 	PTREGSCALL stub32_sigreturn, sys32_sigreturn
 	PTREGSCALL stub32_fork, sys_fork
@@ -569,23 +515,8 @@ GLOBAL(stub32_clone)
 
 	ALIGN
 ia32_ptregs_common:
-	CFI_ENDPROC
-	CFI_STARTPROC32	simple
-	CFI_SIGNAL_FRAME
-	CFI_DEF_CFA	rsp,SIZEOF_PTREGS
-	CFI_REL_OFFSET	rax,RAX
-	CFI_REL_OFFSET	rcx,RCX
-	CFI_REL_OFFSET	rdx,RDX
-	CFI_REL_OFFSET	rsi,RSI
-	CFI_REL_OFFSET	rdi,RDI
-	CFI_REL_OFFSET	rip,RIP
-/*	CFI_REL_OFFSET	cs,CS*/
-/*	CFI_REL_OFFSET	rflags,EFLAGS*/
-	CFI_REL_OFFSET	rsp,RSP
-/*	CFI_REL_OFFSET	ss,SS*/
 	SAVE_EXTRA_REGS 8
 	call *%rax
 	RESTORE_EXTRA_REGS 8
 	ret
-	CFI_ENDPROC
 END(ia32_ptregs_common)