linux/arch/x86/lib/atomic64_cx8_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

185 lines
2.7 KiB
ArmAsm

/*
* atomic64_t for 586+
*
* 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>
.macro read64 reg
movl %ebx, %eax
movl %ecx, %edx
/* we need LOCK_PREFIX since otherwise cmpxchg8b always does the write */
LOCK_PREFIX
cmpxchg8b (\reg)
.endm
ENTRY(atomic64_read_cx8)
read64 %ecx
ret
ENDPROC(atomic64_read_cx8)
ENTRY(atomic64_set_cx8)
1:
/* we don't need LOCK_PREFIX since aligned 64-bit writes
* are atomic on 586 and newer */
cmpxchg8b (%esi)
jne 1b
ret
ENDPROC(atomic64_set_cx8)
ENTRY(atomic64_xchg_cx8)
1:
LOCK_PREFIX
cmpxchg8b (%esi)
jne 1b
ret
ENDPROC(atomic64_xchg_cx8)
.macro addsub_return func ins insc
ENTRY(atomic64_\func\()_return_cx8)
pushl %ebp
pushl %ebx
pushl %esi
pushl %edi
movl %eax, %esi
movl %edx, %edi
movl %ecx, %ebp
read64 %ecx
1:
movl %eax, %ebx
movl %edx, %ecx
\ins\()l %esi, %ebx
\insc\()l %edi, %ecx
LOCK_PREFIX
cmpxchg8b (%ebp)
jne 1b
10:
movl %ebx, %eax
movl %ecx, %edx
popl %edi
popl %esi
popl %ebx
popl %ebp
ret
ENDPROC(atomic64_\func\()_return_cx8)
.endm
addsub_return add add adc
addsub_return sub sub sbb
.macro incdec_return func ins insc
ENTRY(atomic64_\func\()_return_cx8)
pushl %ebx
read64 %esi
1:
movl %eax, %ebx
movl %edx, %ecx
\ins\()l $1, %ebx
\insc\()l $0, %ecx
LOCK_PREFIX
cmpxchg8b (%esi)
jne 1b
10:
movl %ebx, %eax
movl %ecx, %edx
popl %ebx
ret
ENDPROC(atomic64_\func\()_return_cx8)
.endm
incdec_return inc add adc
incdec_return dec sub sbb
ENTRY(atomic64_dec_if_positive_cx8)
pushl %ebx
read64 %esi
1:
movl %eax, %ebx
movl %edx, %ecx
subl $1, %ebx
sbb $0, %ecx
js 2f
LOCK_PREFIX
cmpxchg8b (%esi)
jne 1b
2:
movl %ebx, %eax
movl %ecx, %edx
popl %ebx
ret
ENDPROC(atomic64_dec_if_positive_cx8)
ENTRY(atomic64_add_unless_cx8)
pushl %ebp
pushl %ebx
/* these just push these two parameters on the stack */
pushl %edi
pushl %ecx
movl %eax, %ebp
movl %edx, %edi
read64 %esi
1:
cmpl %eax, 0(%esp)
je 4f
2:
movl %eax, %ebx
movl %edx, %ecx
addl %ebp, %ebx
adcl %edi, %ecx
LOCK_PREFIX
cmpxchg8b (%esi)
jne 1b
movl $1, %eax
3:
addl $8, %esp
popl %ebx
popl %ebp
ret
4:
cmpl %edx, 4(%esp)
jne 2b
xorl %eax, %eax
jmp 3b
ENDPROC(atomic64_add_unless_cx8)
ENTRY(atomic64_inc_not_zero_cx8)
pushl %ebx
read64 %esi
1:
movl %eax, %ecx
orl %edx, %ecx
jz 3f
movl %eax, %ebx
xorl %ecx, %ecx
addl $1, %ebx
adcl %edx, %ecx
LOCK_PREFIX
cmpxchg8b (%esi)
jne 1b
movl $1, %eax
3:
popl %ebx
ret
ENDPROC(atomic64_inc_not_zero_cx8)