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, 0 insertions, 170 deletions

diff --git a/arch/x86/include/asm/dwarf2.h b/arch/x86/include/asm/dwarf2.h
deleted file mode 100644
index de1cdaf4d743..000000000000
--- a/arch/x86/include/asm/dwarf2.h
+++ /dev/null
@@ -1,170 +0,0 @@
-#ifndef _ASM_X86_DWARF2_H
-#define _ASM_X86_DWARF2_H
-
-#ifndef __ASSEMBLY__
-#warning "asm/dwarf2.h should be only included in pure assembly files"
-#endif
-
-/*
- * Macros for dwarf2 CFI unwind table entries.
- * See "as.info" for details on these pseudo ops. Unfortunately
- * they are only supported in very new binutils, so define them
- * away for older version.
- */
-
-#ifdef CONFIG_AS_CFI
-
-#define CFI_STARTPROC		.cfi_startproc
-#define CFI_ENDPROC		.cfi_endproc
-#define CFI_DEF_CFA		.cfi_def_cfa
-#define CFI_DEF_CFA_REGISTER	.cfi_def_cfa_register
-#define CFI_DEF_CFA_OFFSET	.cfi_def_cfa_offset
-#define CFI_ADJUST_CFA_OFFSET	.cfi_adjust_cfa_offset
-#define CFI_OFFSET		.cfi_offset
-#define CFI_REL_OFFSET		.cfi_rel_offset
-#define CFI_REGISTER		.cfi_register
-#define CFI_RESTORE		.cfi_restore
-#define CFI_REMEMBER_STATE	.cfi_remember_state
-#define CFI_RESTORE_STATE	.cfi_restore_state
-#define CFI_UNDEFINED		.cfi_undefined
-#define CFI_ESCAPE		.cfi_escape
-
-#ifdef CONFIG_AS_CFI_SIGNAL_FRAME
-#define CFI_SIGNAL_FRAME	.cfi_signal_frame
-#else
-#define CFI_SIGNAL_FRAME
-#endif
-
-#if defined(CONFIG_AS_CFI_SECTIONS) && defined(__ASSEMBLY__)
-	/*
-	 * Emit CFI data in .debug_frame sections, not .eh_frame sections.
-	 * The latter we currently just discard since we don't do DWARF
-	 * unwinding at runtime.  So only the offline DWARF information is
-	 * useful to anyone.  Note we should not use this directive if this
-	 * file is used in the vDSO assembly, or if vmlinux.lds.S gets
-	 * changed so it doesn't discard .eh_frame.
-	 */
-	.cfi_sections .debug_frame
-#endif
-
-#else
-
-/*
- * Due to the structure of pre-exisiting code, don't use assembler line
- * comment character # to ignore the arguments. Instead, use a dummy macro.
- */
-.macro cfi_ignore a=0, b=0, c=0, d=0
-.endm
-
-#define CFI_STARTPROC		cfi_ignore
-#define CFI_ENDPROC		cfi_ignore
-#define CFI_DEF_CFA		cfi_ignore
-#define CFI_DEF_CFA_REGISTER	cfi_ignore
-#define CFI_DEF_CFA_OFFSET	cfi_ignore
-#define CFI_ADJUST_CFA_OFFSET	cfi_ignore
-#define CFI_OFFSET		cfi_ignore
-#define CFI_REL_OFFSET		cfi_ignore
-#define CFI_REGISTER		cfi_ignore
-#define CFI_RESTORE		cfi_ignore
-#define CFI_REMEMBER_STATE	cfi_ignore
-#define CFI_RESTORE_STATE	cfi_ignore
-#define CFI_UNDEFINED		cfi_ignore
-#define CFI_ESCAPE		cfi_ignore
-#define CFI_SIGNAL_FRAME	cfi_ignore
-
-#endif
-
-/*
- * An attempt to make CFI annotations more or less
- * correct and shorter. It is implied that you know
- * what you're doing if you use them.
- */
-#ifdef __ASSEMBLY__
-#ifdef CONFIG_X86_64
-	.macro pushq_cfi reg
-	pushq \reg
-	CFI_ADJUST_CFA_OFFSET 8
-	.endm
-
-	.macro pushq_cfi_reg reg
-	pushq %\reg
-	CFI_ADJUST_CFA_OFFSET 8
-	CFI_REL_OFFSET \reg, 0
-	.endm
-
-	.macro popq_cfi reg
-	popq \reg
-	CFI_ADJUST_CFA_OFFSET -8
-	.endm
-
-	.macro popq_cfi_reg reg
-	popq %\reg
-	CFI_ADJUST_CFA_OFFSET -8
-	CFI_RESTORE \reg
-	.endm
-
-	.macro pushfq_cfi
-	pushfq
-	CFI_ADJUST_CFA_OFFSET 8
-	.endm
-
-	.macro popfq_cfi
-	popfq
-	CFI_ADJUST_CFA_OFFSET -8
-	.endm
-
-	.macro movq_cfi reg offset=0
-	movq %\reg, \offset(%rsp)
-	CFI_REL_OFFSET \reg, \offset
-	.endm
-
-	.macro movq_cfi_restore offset reg
-	movq \offset(%rsp), %\reg
-	CFI_RESTORE \reg
-	.endm
-#else /*!CONFIG_X86_64*/
-	.macro pushl_cfi reg
-	pushl \reg
-	CFI_ADJUST_CFA_OFFSET 4
-	.endm
-
-	.macro pushl_cfi_reg reg
-	pushl %\reg
-	CFI_ADJUST_CFA_OFFSET 4
-	CFI_REL_OFFSET \reg, 0
-	.endm
-
-	.macro popl_cfi reg
-	popl \reg
-	CFI_ADJUST_CFA_OFFSET -4
-	.endm
-
-	.macro popl_cfi_reg reg
-	popl %\reg
-	CFI_ADJUST_CFA_OFFSET -4
-	CFI_RESTORE \reg
-	.endm
-
-	.macro pushfl_cfi
-	pushfl
-	CFI_ADJUST_CFA_OFFSET 4
-	.endm
-
-	.macro popfl_cfi
-	popfl
-	CFI_ADJUST_CFA_OFFSET -4
-	.endm
-
-	.macro movl_cfi reg offset=0
-	movl %\reg, \offset(%esp)
-	CFI_REL_OFFSET \reg, \offset
-	.endm
-
-	.macro movl_cfi_restore offset reg
-	movl \offset(%esp), %\reg
-	CFI_RESTORE \reg
-	.endm
-#endif /*!CONFIG_X86_64*/
-#endif /*__ASSEMBLY__*/
-
-#endif /* _ASM_X86_DWARF2_H */