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linux/arch/x86/lib/csum-copy_64.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

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/*
* Copyright 2002, 2003 Andi Kleen, SuSE Labs.
*
* This file is subject to the terms and conditions of the GNU General Public
* License. See the file COPYING in the main directory of this archive
* for more details. No warranty for anything given at all.
*/
#include <linux/linkage.h>
#include <asm/errno.h>
#include <asm/asm.h>
/*
* Checksum copy with exception handling.
* On exceptions src_err_ptr or dst_err_ptr is set to -EFAULT and the
* destination is zeroed.
*
* Input
* rdi source
* rsi destination
* edx len (32bit)
* ecx sum (32bit)
* r8 src_err_ptr (int)
* r9 dst_err_ptr (int)
*
* Output
* eax 64bit sum. undefined in case of exception.
*
* Wrappers need to take care of valid exception sum and zeroing.
* They also should align source or destination to 8 bytes.
*/
.macro source
10:
_ASM_EXTABLE(10b, .Lbad_source)
.endm
.macro dest
20:
_ASM_EXTABLE(20b, .Lbad_dest)
.endm
.macro ignore L=.Lignore
30:
_ASM_EXTABLE(30b, \L)
.endm
ENTRY(csum_partial_copy_generic)
cmpl $3*64, %edx
jle .Lignore
.Lignore:
subq $7*8, %rsp
movq %rbx, 2*8(%rsp)
movq %r12, 3*8(%rsp)
movq %r14, 4*8(%rsp)
movq %r13, 5*8(%rsp)
movq %rbp, 6*8(%rsp)
movq %r8, (%rsp)
movq %r9, 1*8(%rsp)
movl %ecx, %eax
movl %edx, %ecx
xorl %r9d, %r9d
movq %rcx, %r12
shrq $6, %r12
jz .Lhandle_tail /* < 64 */
clc
/* main loop. clear in 64 byte blocks */
/* r9: zero, r8: temp2, rbx: temp1, rax: sum, rcx: saved length */
/* r11: temp3, rdx: temp4, r12 loopcnt */
/* r10: temp5, rbp: temp6, r14 temp7, r13 temp8 */
.p2align 4
.Lloop:
source
movq (%rdi), %rbx
source
movq 8(%rdi), %r8
source
movq 16(%rdi), %r11
source
movq 24(%rdi), %rdx
source
movq 32(%rdi), %r10
source
movq 40(%rdi), %rbp
source
movq 48(%rdi), %r14
source
movq 56(%rdi), %r13
ignore 2f
prefetcht0 5*64(%rdi)
2:
adcq %rbx, %rax
adcq %r8, %rax
adcq %r11, %rax
adcq %rdx, %rax
adcq %r10, %rax
adcq %rbp, %rax
adcq %r14, %rax
adcq %r13, %rax
decl %r12d
dest
movq %rbx, (%rsi)
dest
movq %r8, 8(%rsi)
dest
movq %r11, 16(%rsi)
dest
movq %rdx, 24(%rsi)
dest
movq %r10, 32(%rsi)
dest
movq %rbp, 40(%rsi)
dest
movq %r14, 48(%rsi)
dest
movq %r13, 56(%rsi)
3:
leaq 64(%rdi), %rdi
leaq 64(%rsi), %rsi
jnz .Lloop
adcq %r9, %rax
/* do last up to 56 bytes */
.Lhandle_tail:
/* ecx: count */
movl %ecx, %r10d
andl $63, %ecx
shrl $3, %ecx
jz .Lfold
clc
.p2align 4
.Lloop_8:
source
movq (%rdi), %rbx
adcq %rbx, %rax
decl %ecx
dest
movq %rbx, (%rsi)
leaq 8(%rsi), %rsi /* preserve carry */
leaq 8(%rdi), %rdi
jnz .Lloop_8
adcq %r9, %rax /* add in carry */
.Lfold:
/* reduce checksum to 32bits */
movl %eax, %ebx
shrq $32, %rax
addl %ebx, %eax
adcl %r9d, %eax
/* do last up to 6 bytes */
.Lhandle_7:
movl %r10d, %ecx
andl $7, %ecx
shrl $1, %ecx
jz .Lhandle_1
movl $2, %edx
xorl %ebx, %ebx
clc
.p2align 4
.Lloop_1:
source
movw (%rdi), %bx
adcl %ebx, %eax
decl %ecx
dest
movw %bx, (%rsi)
leaq 2(%rdi), %rdi
leaq 2(%rsi), %rsi
jnz .Lloop_1
adcl %r9d, %eax /* add in carry */
/* handle last odd byte */
.Lhandle_1:
testb $1, %r10b
jz .Lende
xorl %ebx, %ebx
source
movb (%rdi), %bl
dest
movb %bl, (%rsi)
addl %ebx, %eax
adcl %r9d, %eax /* carry */
.Lende:
movq 2*8(%rsp), %rbx
movq 3*8(%rsp), %r12
movq 4*8(%rsp), %r14
movq 5*8(%rsp), %r13
movq 6*8(%rsp), %rbp
addq $7*8, %rsp
ret
/* Exception handlers. Very simple, zeroing is done in the wrappers */
.Lbad_source:
movq (%rsp), %rax
testq %rax, %rax
jz .Lende
movl $-EFAULT, (%rax)
jmp .Lende
.Lbad_dest:
movq 8(%rsp), %rax
testq %rax, %rax
jz .Lende
movl $-EFAULT, (%rax)
jmp .Lende
ENDPROC(csum_partial_copy_generic)
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