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x86/mem: Move memmove to out of line assembler

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When building ARCH=i386 with CONFIG_LTO_CLANG_FULL=y, it's possible
(depending on additional configs which I have not been able to isolate)
to observe a failure during register allocation:

  error: inline assembly requires more registers than available

when memmove is inlined into tcp_v4_fill_cb() or tcp_v6_fill_cb().

memmove is quite large and probably shouldn't be inlined due to size
alone. A noinline function attribute would be the simplest fix, but
there's a few things that stand out with the current definition:

In addition to having complex constraints that can't always be resolved,
the clobber list seems to be missing %bx. By using numbered operands
rather than symbolic operands, the constraints are quite obnoxious to
refactor.

Having a large function be 99% inline asm is a code smell that this
function should simply be written in stand-alone out-of-line assembler.

Moving this to out of line assembler guarantees that the
compiler cannot inline calls to memmove.

This has been done previously for 64b:
commit 9599ec0471 ("x86-64, mem: Convert memmove() to assembly file
and fix return value bug")

That gives the opportunity for other cleanups like fixing the
inconsistent use of tabs vs spaces and instruction suffixes, and the
label 3 appearing twice.  Symbolic operands, local labels, and
additional comments would provide this code with a fresh coat of paint.

Finally, add a test that tickles the `rep movsl` implementation to test
it for correctness, since it has implicit operands.

Suggested-by: Ingo Molnar <mingo@kernel.org>
Suggested-by: David Laight <David.Laight@aculab.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Tested-by: Kees Cook <keescook@chromium.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/all/20221018172155.287409-1-ndesaulniers%40google.com
This commit is contained in:
Nick Desaulniers 2022-10-18 10:21:55 -07:00 committed by Dave Hansen
parent 30a0b95b13
commit bce5a1e8a3
4 changed files with 223 additions and 187 deletions
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1
arch/x86/lib/Makefile
View file

@ -60,6 +60,7 @@ ifeq ($(CONFIG_X86_32),y)
lib-y += checksum_32.o
lib-y += strstr_32.o
lib-y += string_32.o
lib-y += memmove_32.o
ifneq ($(CONFIG_X86_CMPXCHG64),y)
lib-y += cmpxchg8b_emu.o atomic64_386_32.o
endif

187
arch/x86/lib/memcpy_32.c
View file

@ -17,190 +17,3 @@ __visible void *memset(void *s, int c, size_t count)
return __memset(s, c, count);
}
EXPORT_SYMBOL(memset);
__visible void *memmove(void *dest, const void *src, size_t n)
{
int d0,d1,d2,d3,d4,d5;
char *ret = dest;
__asm__ __volatile__(
/* Handle more 16 bytes in loop */
"cmp $0x10, %0\n\t"
"jb 1f\n\t"
/* Decide forward/backward copy mode */
"cmp %2, %1\n\t"
"jb 2f\n\t"
/*
* movs instruction have many startup latency
* so we handle small size by general register.
*/
"cmp $680, %0\n\t"
"jb 3f\n\t"
/*
* movs instruction is only good for aligned case.
*/
"mov %1, %3\n\t"
"xor %2, %3\n\t"
"and $0xff, %3\n\t"
"jz 4f\n\t"
"3:\n\t"
"sub $0x10, %0\n\t"
/*
* We gobble 16 bytes forward in each loop.
*/
"3:\n\t"
"sub $0x10, %0\n\t"
"mov 0*4(%1), %3\n\t"
"mov 1*4(%1), %4\n\t"
"mov %3, 0*4(%2)\n\t"
"mov %4, 1*4(%2)\n\t"
"mov 2*4(%1), %3\n\t"
"mov 3*4(%1), %4\n\t"
"mov %3, 2*4(%2)\n\t"
"mov %4, 3*4(%2)\n\t"
"lea 0x10(%1), %1\n\t"
"lea 0x10(%2), %2\n\t"
"jae 3b\n\t"
"add $0x10, %0\n\t"
"jmp 1f\n\t"
/*
* Handle data forward by movs.
*/
".p2align 4\n\t"
"4:\n\t"
"mov -4(%1, %0), %3\n\t"
"lea -4(%2, %0), %4\n\t"
"shr $2, %0\n\t"
"rep movsl\n\t"
"mov %3, (%4)\n\t"
"jmp 11f\n\t"
/*
* Handle data backward by movs.
*/
".p2align 4\n\t"
"6:\n\t"
"mov (%1), %3\n\t"
"mov %2, %4\n\t"
"lea -4(%1, %0), %1\n\t"
"lea -4(%2, %0), %2\n\t"
"shr $2, %0\n\t"
"std\n\t"
"rep movsl\n\t"
"mov %3,(%4)\n\t"
"cld\n\t"
"jmp 11f\n\t"
/*
* Start to prepare for backward copy.
*/
".p2align 4\n\t"
"2:\n\t"
"cmp $680, %0\n\t"
"jb 5f\n\t"
"mov %1, %3\n\t"
"xor %2, %3\n\t"
"and $0xff, %3\n\t"
"jz 6b\n\t"
/*
* Calculate copy position to tail.
*/
"5:\n\t"
"add %0, %1\n\t"
"add %0, %2\n\t"
"sub $0x10, %0\n\t"
/*
* We gobble 16 bytes backward in each loop.
*/
"7:\n\t"
"sub $0x10, %0\n\t"
"mov -1*4(%1), %3\n\t"
"mov -2*4(%1), %4\n\t"
"mov %3, -1*4(%2)\n\t"
"mov %4, -2*4(%2)\n\t"
"mov -3*4(%1), %3\n\t"
"mov -4*4(%1), %4\n\t"
"mov %3, -3*4(%2)\n\t"
"mov %4, -4*4(%2)\n\t"
"lea -0x10(%1), %1\n\t"
"lea -0x10(%2), %2\n\t"
"jae 7b\n\t"
/*
* Calculate copy position to head.
*/
"add $0x10, %0\n\t"
"sub %0, %1\n\t"
"sub %0, %2\n\t"
/*
* Move data from 8 bytes to 15 bytes.
*/
".p2align 4\n\t"
"1:\n\t"
"cmp $8, %0\n\t"
"jb 8f\n\t"
"mov 0*4(%1), %3\n\t"
"mov 1*4(%1), %4\n\t"
"mov -2*4(%1, %0), %5\n\t"
"mov -1*4(%1, %0), %1\n\t"
"mov %3, 0*4(%2)\n\t"
"mov %4, 1*4(%2)\n\t"
"mov %5, -2*4(%2, %0)\n\t"
"mov %1, -1*4(%2, %0)\n\t"
"jmp 11f\n\t"
/*
* Move data from 4 bytes to 7 bytes.
*/
".p2align 4\n\t"
"8:\n\t"
"cmp $4, %0\n\t"
"jb 9f\n\t"
"mov 0*4(%1), %3\n\t"
"mov -1*4(%1, %0), %4\n\t"
"mov %3, 0*4(%2)\n\t"
"mov %4, -1*4(%2, %0)\n\t"
"jmp 11f\n\t"
/*
* Move data from 2 bytes to 3 bytes.
*/
".p2align 4\n\t"
"9:\n\t"
"cmp $2, %0\n\t"
"jb 10f\n\t"
"movw 0*2(%1), %%dx\n\t"
"movw -1*2(%1, %0), %%bx\n\t"
"movw %%dx, 0*2(%2)\n\t"
"movw %%bx, -1*2(%2, %0)\n\t"
"jmp 11f\n\t"
/*
* Move data for 1 byte.
*/
".p2align 4\n\t"
"10:\n\t"
"cmp $1, %0\n\t"
"jb 11f\n\t"
"movb (%1), %%cl\n\t"
"movb %%cl, (%2)\n\t"
".p2align 4\n\t"
"11:"
: "=&c" (d0), "=&S" (d1), "=&D" (d2),
"=r" (d3),"=r" (d4), "=r"(d5)
:"0" (n),
"1" (src),
"2" (dest)
:"memory");
return ret;
}
EXPORT_SYMBOL(memmove);

200
arch/x86/lib/memmove_32.S Normal file
View file

@ -0,0 +1,200 @@
/* SPDX-License-Identifier: GPL-2.0 */
#include <linux/linkage.h>
#include <asm/export.h>
SYM_FUNC_START(memmove)
/*
* void *memmove(void *dest_in, const void *src_in, size_t n)
* -mregparm=3 passes these in registers:
* dest_in: %eax
* src_in: %edx
* n: %ecx
* See also: arch/x86/entry/calling.h for description of the calling convention.
*
* n can remain in %ecx, but for `rep movsl`, we'll need dest in %edi and src
* in %esi.
*/
.set dest_in, %eax
.set dest, %edi
.set src_in, %edx
.set src, %esi
.set n, %ecx
.set tmp0, %edx
.set tmp0w, %dx
.set tmp1, %ebx
.set tmp1w, %bx
.set tmp2, %eax
.set tmp3b, %cl
/*
* Save all callee-saved registers, because this function is going to clobber
* all of them:
*/
pushl %ebp
movl %esp, %ebp // set standard frame pointer
pushl %ebx
pushl %edi
pushl %esi
pushl %eax // save 'dest_in' parameter [eax] as the return value
movl src_in, src
movl dest_in, dest
/* Handle more 16 bytes in loop */
cmpl $0x10, n
jb .Lmove_16B
/* Decide forward/backward copy mode */
cmpl dest, src
jb .Lbackwards_header
/*
* movs instruction have many startup latency
* so we handle small size by general register.
*/
cmpl $680, n
jb .Ltoo_small_forwards
/* movs instruction is only good for aligned case. */
movl src, tmp0
xorl dest, tmp0
andl $0xff, tmp0
jz .Lforward_movs
.Ltoo_small_forwards:
subl $0x10, n
/* We gobble 16 bytes forward in each loop. */
.Lmove_16B_forwards_loop:
subl $0x10, n
movl 0*4(src), tmp0
movl 1*4(src), tmp1
movl tmp0, 0*4(dest)
movl tmp1, 1*4(dest)
movl 2*4(src), tmp0
movl 3*4(src), tmp1
movl tmp0, 2*4(dest)
movl tmp1, 3*4(dest)
leal 0x10(src), src
leal 0x10(dest), dest
jae .Lmove_16B_forwards_loop
addl $0x10, n
jmp .Lmove_16B
/* Handle data forward by movs. */
.p2align 4
.Lforward_movs:
movl -4(src, n), tmp0
leal -4(dest, n), tmp1
shrl $2, n
rep movsl
movl tmp0, (tmp1)
jmp .Ldone
/* Handle data backward by movs. */
.p2align 4
.Lbackwards_movs:
movl (src), tmp0
movl dest, tmp1
leal -4(src, n), src
leal -4(dest, n), dest
shrl $2, n
std
rep movsl
movl tmp0,(tmp1)
cld
jmp .Ldone
/* Start to prepare for backward copy. */
.p2align 4
.Lbackwards_header:
cmpl $680, n
jb .Ltoo_small_backwards
movl src, tmp0
xorl dest, tmp0
andl $0xff, tmp0
jz .Lbackwards_movs
/* Calculate copy position to tail. */
.Ltoo_small_backwards:
addl n, src
addl n, dest
subl $0x10, n
/* We gobble 16 bytes backward in each loop. */
.Lmove_16B_backwards_loop:
subl $0x10, n
movl -1*4(src), tmp0
movl -2*4(src), tmp1
movl tmp0, -1*4(dest)
movl tmp1, -2*4(dest)
movl -3*4(src), tmp0
movl -4*4(src), tmp1
movl tmp0, -3*4(dest)
movl tmp1, -4*4(dest)
leal -0x10(src), src
leal -0x10(dest), dest
jae .Lmove_16B_backwards_loop
/* Calculate copy position to head. */
addl $0x10, n
subl n, src
subl n, dest
/* Move data from 8 bytes to 15 bytes. */
.p2align 4
.Lmove_16B:
cmpl $8, n
jb .Lmove_8B
movl 0*4(src), tmp0
movl 1*4(src), tmp1
movl -2*4(src, n), tmp2
movl -1*4(src, n), src
movl tmp0, 0*4(dest)
movl tmp1, 1*4(dest)
movl tmp2, -2*4(dest, n)
movl src, -1*4(dest, n)
jmp .Ldone
/* Move data from 4 bytes to 7 bytes. */
.p2align 4
.Lmove_8B:
cmpl $4, n
jb .Lmove_4B
movl 0*4(src), tmp0
movl -1*4(src, n), tmp1
movl tmp0, 0*4(dest)
movl tmp1, -1*4(dest, n)
jmp .Ldone
/* Move data from 2 bytes to 3 bytes. */
.p2align 4
.Lmove_4B:
cmpl $2, n
jb .Lmove_1B
movw 0*2(src), tmp0w
movw -1*2(src, n), tmp1w
movw tmp0w, 0*2(dest)
movw tmp1w, -1*2(dest, n)
jmp .Ldone
/* Move data for 1 byte. */
.p2align 4
.Lmove_1B:
cmpl $1, n
jb .Ldone
movb (src), tmp3b
movb tmp3b, (dest)
.p2align 4
.Ldone:
popl dest_in // restore 'dest_in' [eax] as the return value
/* Restore all callee-saved registers: */
popl %esi
popl %edi
popl %ebx
popl %ebp
RET
SYM_FUNC_END(memmove)
EXPORT_SYMBOL(memmove)

22
lib/memcpy_kunit.c
View file

@ -105,6 +105,8 @@ static void memcpy_test(struct kunit *test)
#undef TEST_OP
}
static unsigned char larger_array [2048];
static void memmove_test(struct kunit *test)
{
#define TEST_OP "memmove"
@ -179,6 +181,26 @@ static void memmove_test(struct kunit *test)
ptr = &overlap.data[2];
memmove(ptr, overlap.data, 5);
compare("overlapping write", overlap, overlap_expected);
/* Verify larger overlapping moves. */
larger_array[256] = 0xAAu;
/*
* Test a backwards overlapping memmove first. 256 and 1024 are
* important for i386 to use rep movsl.
*/
memmove(larger_array, larger_array + 256, 1024);
KUNIT_ASSERT_EQ(test, larger_array[0], 0xAAu);
KUNIT_ASSERT_EQ(test, larger_array[256], 0x00);
KUNIT_ASSERT_NULL(test,
memchr(larger_array + 1, 0xaa, ARRAY_SIZE(larger_array) - 1));
/* Test a forwards overlapping memmove. */
larger_array[0] = 0xBBu;
memmove(larger_array + 256, larger_array, 1024);
KUNIT_ASSERT_EQ(test, larger_array[0], 0xBBu);
KUNIT_ASSERT_EQ(test, larger_array[256], 0xBBu);
KUNIT_ASSERT_NULL(test, memchr(larger_array + 1, 0xBBu, 256 - 1));
KUNIT_ASSERT_NULL(test,
memchr(larger_array + 257, 0xBBu, ARRAY_SIZE(larger_array) - 257));
#undef TEST_OP
}