linux/arch/x86/lib/atomic64_386_32.S
Ingo Molnar 131484c8da 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>
2015-06-02 07:57:48 +02:00

192 lines
2.5 KiB
ArmAsm

/*
* atomic64_t for 386/486
*
* Copyright © 2010 Luca Barbieri
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*/
#include <linux/linkage.h>
#include <asm/alternative-asm.h>
/* if you want SMP support, implement these with real spinlocks */
.macro LOCK reg
pushfl
cli
.endm
.macro UNLOCK reg
popfl
.endm
#define BEGIN(op) \
.macro endp; \
ENDPROC(atomic64_##op##_386); \
.purgem endp; \
.endm; \
ENTRY(atomic64_##op##_386); \
LOCK v;
#define ENDP endp
#define RET \
UNLOCK v; \
ret
#define RET_ENDP \
RET; \
ENDP
#define v %ecx
BEGIN(read)
movl (v), %eax
movl 4(v), %edx
RET_ENDP
#undef v
#define v %esi
BEGIN(set)
movl %ebx, (v)
movl %ecx, 4(v)
RET_ENDP
#undef v
#define v %esi
BEGIN(xchg)
movl (v), %eax
movl 4(v), %edx
movl %ebx, (v)
movl %ecx, 4(v)
RET_ENDP
#undef v
#define v %ecx
BEGIN(add)
addl %eax, (v)
adcl %edx, 4(v)
RET_ENDP
#undef v
#define v %ecx
BEGIN(add_return)
addl (v), %eax
adcl 4(v), %edx
movl %eax, (v)
movl %edx, 4(v)
RET_ENDP
#undef v
#define v %ecx
BEGIN(sub)
subl %eax, (v)
sbbl %edx, 4(v)
RET_ENDP
#undef v
#define v %ecx
BEGIN(sub_return)
negl %edx
negl %eax
sbbl $0, %edx
addl (v), %eax
adcl 4(v), %edx
movl %eax, (v)
movl %edx, 4(v)
RET_ENDP
#undef v
#define v %esi
BEGIN(inc)
addl $1, (v)
adcl $0, 4(v)
RET_ENDP
#undef v
#define v %esi
BEGIN(inc_return)
movl (v), %eax
movl 4(v), %edx
addl $1, %eax
adcl $0, %edx
movl %eax, (v)
movl %edx, 4(v)
RET_ENDP
#undef v
#define v %esi
BEGIN(dec)
subl $1, (v)
sbbl $0, 4(v)
RET_ENDP
#undef v
#define v %esi
BEGIN(dec_return)
movl (v), %eax
movl 4(v), %edx
subl $1, %eax
sbbl $0, %edx
movl %eax, (v)
movl %edx, 4(v)
RET_ENDP
#undef v
#define v %esi
BEGIN(add_unless)
addl %eax, %ecx
adcl %edx, %edi
addl (v), %eax
adcl 4(v), %edx
cmpl %eax, %ecx
je 3f
1:
movl %eax, (v)
movl %edx, 4(v)
movl $1, %eax
2:
RET
3:
cmpl %edx, %edi
jne 1b
xorl %eax, %eax
jmp 2b
ENDP
#undef v
#define v %esi
BEGIN(inc_not_zero)
movl (v), %eax
movl 4(v), %edx
testl %eax, %eax
je 3f
1:
addl $1, %eax
adcl $0, %edx
movl %eax, (v)
movl %edx, 4(v)
movl $1, %eax
2:
RET
3:
testl %edx, %edx
jne 1b
jmp 2b
ENDP
#undef v
#define v %esi
BEGIN(dec_if_positive)
movl (v), %eax
movl 4(v), %edx
subl $1, %eax
sbbl $0, %edx
js 1f
movl %eax, (v)
movl %edx, 4(v)
1:
RET_ENDP
#undef v