/*
* Copyright 2010 Tilera Corporation. All Rights Reserved.
*
* 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, version 2.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
* NON INFRINGEMENT. See the GNU General Public License for
* more details.
*/
#include <arch/chip.h>
/*
* This file shares the implementation of the userspace memcpy and
* the kernel's memcpy, copy_to_user and copy_from_user.
*/
#include <linux/linkage.h>
/* On TILE64, we wrap these functions via arch/tile/lib/memcpy_tile64.c */
#if !CHIP_HAS_COHERENT_LOCAL_CACHE()
#define memcpy __memcpy_asm
#define __copy_to_user_inatomic __copy_to_user_inatomic_asm
#define __copy_from_user_inatomic __copy_from_user_inatomic_asm
#define __copy_from_user_zeroing __copy_from_user_zeroing_asm
#endif
#define IS_MEMCPY 0
#define IS_COPY_FROM_USER 1
#define IS_COPY_FROM_USER_ZEROING 2
#define IS_COPY_TO_USER -1
.section .text.memcpy_common, "ax"
.align 64
/* Use this to preface each bundle that can cause an exception so
* the kernel can clean up properly. The special cleanup code should
* not use these, since it knows what it is doing.
*/
#define EX \
.pushsection __ex_table, "a"; \
.word 9f, memcpy_common_fixup; \
.popsection; \
9
/* __copy_from_user_inatomic takes the kernel target address in r0,
* the user source in r1, and the bytes to copy in r2.
* It returns the number of uncopiable bytes (hopefully zero) in r0.
*/
ENTRY(__copy_from_user_inatomic)
.type __copy_from_user_inatomic, @function
FEEDBACK_ENTER_EXPLICIT(__copy_from_user_inatomic, \
.text.memcpy_common, \
.Lend_memcpy_common - __copy_from_user_inatomic)
{ movei r29, IS_COPY_FROM_USER; j memcpy_common }
.size __copy_from_user_inatomic, . - __copy_from_user_inatomic
/* __copy_from_user_zeroing is like __copy_from_user_inatomic, but
* any uncopiable bytes are zeroed in the target.
*/
ENTRY(__copy_from_user_zeroing)
.type __copy_from_user_zeroing, @function
FEEDBACK_REENTER(__copy_from_user_inatomic)
{ movei r29, IS_COPY_FROM_USER_ZEROING; j memcpy_common }
.size __copy_from_user_zeroing, . - __copy_from_user_zeroing
/* __copy_to_user_inatomic takes the user target address in r0,
* the kernel source in r1, and the bytes to copy in r2.
* It returns the number of uncopiable bytes (hopefully zero) in r0.
*/
ENTRY(__copy_to_user_inatomic)
.type __copy_to_user_inatomic, @function
FEEDBACK_REENTER(__copy_from_user_inatomic)
{ movei r29, IS_COPY_TO_USER; j memcpy_common }
.size __copy_to_user_inatomic, . - __copy_to_user_inatomic
ENTRY(memcpy)
.type memcpy, @function
FEEDBACK_REENTER(__copy_from_user_inatomic)
{ movei r29, IS_MEMCPY }
.size memcpy, . - memcpy
/* Fall through */
.type memcpy_common, @function
memcpy_common:
/* On entry, r29 holds one of the IS_* macro values from above. */
/* r0 is the dest, r1 is the source, r2 is the size. */
/* Save aside original dest so we can return it at the end. */
{ sw sp, lr; move r23, r0; or r4, r0, r1 }
/* Check for an empty size. */
{ bz r2, .Ldone; andi r4, r4, 3 }
/* Save aside original values in case of a fault. */
{ move r24, r1; move r25, r2 }
move r27, lr
/* Check for an unaligned source or dest. */
{ bnz r4, .Lcopy_unaligned_maybe_many; addli r4, r2, -256 }
.Lcheck_aligned_copy_size:
/* If we are copying < 256 bytes, branch to simple case. */
{ blzt r4, .Lcopy_8_check; slti_u r8, r2, 8 }
/* Copying >= 256 bytes, so jump to complex prefetching loop. */
{ andi r6, r1, 63; j .Lcopy_many }
/*
*
* Aligned 4 byte at a time copy loop
*
*/
.Lcopy_8_loop:
/* Copy two words at a time to hide load latency. */
EX: { lw r3, r1; addi r1, r1, 4; slti_u r8, r2, 16 }
EX: { lw r4, r1; addi r1, r1, 4 }
EX: { sw r0, r3; addi r0, r0, 4; addi r2, r2, -4 }
EX: { sw r0, r4; addi r0, r0, 4; addi r2, r2, -4 }
.Lcopy_8_check:
{ bzt r8, .Lcopy_8_loop; slti_u r4, r2, 4 }
/* Copy odd leftover word, if any. */
{ bnzt r4, .Lcheck_odd_stragglers }
EX: { lw r3, r1; addi r1, r1, 4 }
EX: { sw r0, r3; addi r0, r0, 4; addi r2, r2, -4 }
.Lcheck_odd_stragglers:
{ bnz r2, .Lcopy_unaligned_few }
.Ldone:
/* For memcpy return original dest address, else zero. */
{ mz r0, r29, r23; jrp lr }
/*
*
* Prefetching multiple cache line copy handler (for large transfers).
*
*/
/* Copy words until r1 is cache-line-aligned. */
.Lalign_loop:
EX: { lw r3, r1; addi r1, r1, 4 }
{ andi r6, r1, 63 }
EX: { sw r0, r3; addi r0, r0, 4; addi r2, r2, -4 }
.Lcopy_many:
{ bnzt r6, .Lalign_loop; addi r9, r0, 63 }
{ addi r3, r1, 60; andi r9, r9, -64 }
#if CHIP_HAS_WH64()
/* No need to prefetch dst, we'll just do the wh64
* right before we copy a line.
*/
#endif
EX: { lw r5, r3; addi r3, r3, 64; movei r4, 1 }
/* Intentionally stall for a few cycles to leave L2 cache alone. */
{ bnzt zero, .; move r27, lr }
EX: { lw r6, r3; addi r3, r3, 64 }
/* Intentionally stall for a few cycles to leave L2 cache alone. */
{ bnzt zero, . }
EX: { lw r7, r3; addi r3, r3, 64 }
#if !CHIP_HAS_WH64()
/* Prefetch the dest */
/* Intentionally stall for a few cycles to leave L2 cache alone. */
{ bnzt zero, . }
/* Use a real load to cause a TLB miss if necessary. We aren't using
* r28, so this should be fine.
*/
EX: { lw r28, r9; addi r9, r9, 64 }
/* Intentionally stall for a few cycles to leave L2 cache alone. */
{ bnzt zero, . }
{ prefetch r9; addi r9, r9, 64 }
/* Intentionally stall for a few cycles to leave L2 cache alone. */
{ bnzt zero, . }
{ prefetch r9; addi r9, r9, 64 }
#endif
/* Intentionally stall for a few cycles to leave L2 cache alone. */
{ bz zero, .Lbig_loop2 }
/* On entry to this loop:
* - r0 points to the start of dst line 0
* - r1 points to start of src line 0
* - r2 >= (256 - 60), only the first time the loop trips.
* - r3 contains r1 + 128 + 60 [pointer to end of source line 2]
* This is our prefetch address. When we get near the end
* rather than prefetching off the end this is changed to point
* to some "safe" recently loaded address.
* - r5 contains *(r1 + 60) [i.e. last word of source line 0]
* - r6 contains *(r1 + 64 + 60) [i.e. last word of source line 1]
* - r9 contains ((r0 + 63) & -64)
* [start of next dst cache line.]
*/
.Lbig_loop:
{ jal .Lcopy_line2; add r15, r1, r2 }
.Lbig_loop2:
/* Copy line 0, first stalling until r5 is ready. */
EX: { move r12, r5; lw r16, r1 }
{ bz r4, .Lcopy_8_check; slti_u r8, r2, 8 }
/* Prefetch several lines ahead. */
EX: { lw r5, r3; addi r3, r3, 64 }
{ jal .Lcopy_line }
/* Copy line 1, first stalling until r6 is ready. */
EX: { move r12, r6; lw r16, r1 }
{ bz r4, .Lcopy_8_check; slti_u r8, r2, 8 }
/* Prefetch several lines ahead. */
EX: { lw r6, r3; addi r3, r3, 64 }
{ jal .Lcopy_line }
/* Copy line 2, first stalling until r7 is ready. */
EX: { move r12, r7; lw r16, r1 }
{ bz r4, .Lcopy_8_check; slti_u r8, r2, 8 }
/* Prefetch several lines ahead. */
EX: { lw r7, r3; addi r3, r3, 64 }
/* Use up a caches-busy cycle by jumping back to the top of the
* loop. Might as well get it out of the way now.
*/
{ j .Lbig_loop }
/* On entry:
* - r0 points to the destination line.
* - r1 points to the source line.
* - r3 is the next prefetch address.
* - r9 holds the last address used for wh64.
* - r12 = WORD_15
* - r16 = WORD_0.
* - r17 == r1 + 16.
* - r27 holds saved lr to restore.
*
* On exit:
* - r0 is incremented by 64.
* - r1 is incremented by 64, unless that would point to a word
* beyond the end of the source array, in which case it is redirected
* to point to an arbitrary word already in the cache.
* - r2 is decremented by 64.
* - r3 is unchanged, unless it points to a word beyond the
* end of the source array, in which case it is redirected
* to point to an arbitrary word already in the cache.
* Redirecting is OK since if we are that close to the end
* of the array we will not come back to this subroutine
* and use the contents of the prefetched address.
* - r4 is nonzero iff r2 >= 64.
* - r9 is incremented by 64, unless it points beyond the
* end of the last full destination cache line, in which
* case it is redirected to a "safe address" that can be
* clobbered (sp - 64)
* - lr contains the value in r27.
*/
/* r26 unused */
.Lcopy_line:
/* TODO: when r3 goes past the end, we would like to redirect it
* to prefetch the last partial cache line (if any) just once, for the
* benefit of the final cleanup loop. But we don't want to
* prefetch that line more than once, or subsequent prefetches
* will go into the RTF. But then .Lbig_loop should unconditionally
* branch to top of loop to execute final prefetch, and its
* nop should become a conditional branch.
*/
/* We need two non-memory cycles here to cover the resources
* used by the loads initiated by the caller.
*/
{ add r15, r1, r2 }
.Lcopy_line2:
{ slt_u r13, r3, r15; addi r17, r1, 16 }
/* NOTE: this will stall for one cycle as L1 is busy. */
/* Fill second L1D line. */
EX: { lw r17, r17; addi r1, r1, 48; mvz r3, r13, r1 } /* r17 = WORD_4 */
#if CHIP_HAS_WH64()
/* Prepare destination line for writing. */
EX: { wh64 r9; addi r9, r9, 64 }
#else
/* Prefetch dest line */
{ prefetch r9; addi r9, r9, 64 }
#endif
/* Load seven words that are L1D hits to cover wh64 L2 usage. */
/* Load the three remaining words from the last L1D line, which
* we know has already filled the L1D.
*/
EX: { lw r4, r1; addi r1, r1, 4; addi r20, r1, 16 } /* r4 = WORD_12 */
EX: { lw r8, r1; addi r1, r1, 4; slt_u r13, r20, r15 }/* r8 = WORD_13 */
EX: { lw r11, r1; addi r1, r1, -52; mvz r20, r13, r1 } /* r11 = WORD_14 */
/* Load the three remaining words from the first L1D line, first
* stalling until it has filled by "looking at" r16.
*/
EX: { lw r13, r1; addi r1, r1, 4; move zero, r16 } /* r13 = WORD_1 */
EX: { lw r14, r1; addi r1, r1, 4 } /* r14 = WORD_2 */
EX: { lw r15, r1; addi r1, r1, 8; addi r10, r0, 60 } /* r15 = WORD_3 */
/* Load second word from the second L1D line, first
* stalling until it has filled by "looking at" r17.
*/
EX: { lw r19, r1; addi r1, r1, 4; move zero, r17 } /* r19 = WORD_5 */
/* Store last word to the destination line, potentially dirtying it
* for the first time, which keeps the L2 busy for two cycles.
*/
EX: { sw r10, r12 } /* store(WORD_15) */
/* Use two L1D hits to cover the sw L2 access above. */
EX: { lw r10, r1; addi r1, r1, 4 } /* r10 = WORD_6 */
EX: { lw r12, r1; addi r1, r1, 4 } /* r12 = WORD_7 */
/* Fill third L1D line. */
EX: { lw r18, r1; addi r1, r1, 4 } /* r18 = WORD_8 */
/* Store first L1D line. */
EX: { sw r0, r16; addi r0, r0, 4; add r16, r0, r2 } /* store(WORD_0) */
EX: { sw r0, r13; addi r0, r0, 4; andi r16, r16, -64 } /* store(WORD_1) */
EX: { sw r0, r14; addi r0, r0, 4; slt_u r16, r9, r16 } /* store(WORD_2) */
#if CHIP_HAS_WH64()
EX: { sw r0, r15; addi r0, r0, 4; addi r13, sp, -64 } /* store(WORD_3) */
#else
/* Back up the r9 to a cache line we are already storing to
* if it gets past the end of the dest vector. Strictly speaking,
* we don't need to back up to the start of a cache line, but it's free
* and tidy, so why not?
*/
EX: { sw r0, r15; addi r0, r0, 4; andi r13, r0, -64 } /* store(WORD_3) */
#endif
/* Store second L1D line. */
EX: { sw r0, r17; addi r0, r0, 4; mvz r9, r16, r13 }/* store(WORD_4) */
EX: { sw r0, r19; addi r0, r0, 4 } /* store(WORD_5) */
EX: { sw r0, r10; addi r0, r0, 4 } /* store(WORD_6) */
EX: { sw r0, r12; addi r0, r0, 4 } /* store(WORD_7) */
EX: { lw r13, r1; addi r1, r1, 4; move zero, r18 } /* r13 = WORD_9 */
EX: { lw r14, r1; addi r1, r1, 4 } /* r14 = WORD_10 */
EX: { lw r15, r1; move r1, r20 } /* r15 = WORD_11 */
/* Store third L1D line. */
EX: { sw r0, r18; addi r0, r0, 4 } /* store(WORD_8) */
EX: { sw r0, r13; addi r0, r0, 4 } /* store(WORD_9) */
EX: { sw r0, r14; addi r0, r0, 4 } /* store(WORD_10) */
EX: { sw r0, r15; addi r0, r0, 4 } /* store(WORD_11) */
/* Store rest of fourth L1D line. */
EX: { sw r0, r4; addi r0, r0, 4 } /* store(WORD_12) */
{
EX: sw r0, r8 /* store(WORD_13) */
addi r0, r0, 4
/* Will r2 be > 64 after we subtract 64 below? */
shri r4, r2, 7
}
{
EX: sw r0, r11 /* store(WORD_14) */
addi r0, r0, 8
/* Record 64 bytes successfully copied. */
addi r2, r2, -64
}
{ jrp lr; move lr, r27 }
/* Convey to the backtrace library that the stack frame is size
* zero, and the real return address is on the stack rather than
* in 'lr'.
*/
{ info 8 }
.align 64
.Lcopy_unaligned_maybe_many:
/* Skip the setup overhead if we aren't copying many bytes. */
{ slti_u r8, r2, 20; sub r4, zero, r0 }
{ bnzt r8, .Lcopy_unaligned_few; andi r4, r4, 3 }
{ bz r4, .Ldest_is_word_aligned; add r18, r1, r2 }
/*
*
* unaligned 4 byte at a time copy handler.
*
*/
/* Copy single bytes until r0 == 0 mod 4, so we can store words. */
.Lalign_dest_loop:
EX: { lb_u r3, r1; addi r1, r1, 1; addi r4, r4, -1 }
EX: { sb r0, r3; addi r0, r0, 1; addi r2, r2, -1 }
{ bnzt r4, .Lalign_dest_loop; andi r3, r1, 3 }
/* If source and dest are now *both* aligned, do an aligned copy. */
{ bz r3, .Lcheck_aligned_copy_size; addli r4, r2, -256 }
.Ldest_is_word_aligned:
#if CHIP_HAS_DWORD_ALIGN()
EX: { andi r8, r0, 63; lwadd_na r6, r1, 4}
{ slti_u r9, r2, 64; bz r8, .Ldest_is_L2_line_aligned }
/* This copies unaligned words until either there are fewer
* than 4 bytes left to copy, or until the destination pointer
* is cache-aligned, whichever comes first.
*
* On entry:
* - r0 is the next store address.
* - r1 points 4 bytes past the load address corresponding to r0.
* - r2 >= 4
* - r6 is the next aligned word loaded.
*/
.Lcopy_unaligned_src_words:
EX: { lwadd_na r7, r1, 4; slti_u r8, r2, 4 + 4 }
/* stall */
{ dword_align r6, r7, r1; slti_u r9, r2, 64 + 4 }
EX: { swadd r0, r6, 4; addi r2, r2, -4 }
{ bnz r8, .Lcleanup_unaligned_words; andi r8, r0, 63 }
{ bnzt r8, .Lcopy_unaligned_src_words; move r6, r7 }
/* On entry:
* - r0 is the next store address.
* - r1 points 4 bytes past the load address corresponding to r0.
* - r2 >= 4 (# of bytes left to store).
* - r6 is the next aligned src word value.
* - r9 = (r2 < 64U).
* - r18 points one byte past the end of source memory.
*/
.Ldest_is_L2_line_aligned:
{
/* Not a full cache line remains. */
bnz r9, .Lcleanup_unaligned_words
move r7, r6
}
/* r2 >= 64 */
/* Kick off two prefetches, but don't go past the end. */
{ addi r3, r1, 63 - 4; addi r8, r1, 64 + 63 - 4 }
{ prefetch r3; move r3, r8; slt_u r8, r8, r18 }
{ mvz r3, r8, r1; addi r8, r3, 64 }
{ prefetch r3; move r3, r8; slt_u r8, r8, r18 }
{ mvz r3, r8, r1; movei r17, 0 }
.Lcopy_unaligned_line:
/* Prefetch another line. */
{ prefetch r3; addi r15, r1, 60; addi r3, r3, 64 }
/* Fire off a load of the last word we are about to copy. */
EX: { lw_na r15, r15; slt_u r8, r3, r18 }
EX: { mvz r3, r8, r1; wh64 r0 }
/* This loop runs twice.
*
* On entry:
* - r17 is even before the first iteration, and odd before
* the second. It is incremented inside the loop. Encountering
* an even value at the end of the loop makes it stop.
*/
.Lcopy_half_an_unaligned_line:
EX: {
/* Stall until the last byte is ready. In the steady state this
* guarantees all words to load below will be in the L2 cache, which
* avoids shunting the loads to the RTF.
*/
move zero, r15
lwadd_na r7, r1, 16
}
EX: { lwadd_na r11, r1, 12 }
EX: { lwadd_na r14, r1, -24 }
EX: { lwadd_na r8, r1, 4 }
EX: { lwadd_na r9, r1, 4 }
EX: {
lwadd_na r10, r1, 8
/* r16 = (r2 < 64), after we subtract 32 from r2 below. */
slti_u r16, r2, 64 + 32
}
EX: { lwadd_na r12, r1, 4; addi r17, r17, 1 }
EX: { lwadd_na r13, r1, 8; dword_align r6, r7, r1 }
EX: { swadd r0, r6, 4; dword_align r7, r8, r1 }
EX: { swadd r0, r7, 4; dword_align r8, r9, r1 }
EX: { swadd r0, r8, 4; dword_align r9, r10, r1 }
EX: { swadd r0, r9, 4; dword_align r10, r11, r1 }
EX: { swadd r0, r10, 4; dword_align r11, r12, r1 }
EX: { swadd r0, r11, 4; dword_align r12, r13, r1 }
EX: { swadd r0, r12, 4; dword_align r13, r14, r1 }
EX: { swadd r0, r13, 4; addi r2, r2, -32 }
{ move r6, r14; bbst r17, .Lcopy_half_an_unaligned_line }
{ bzt r16, .Lcopy_unaligned_line; move r7, r6 }
/* On entry:
* - r0 is the next store address.
* - r1 points 4 bytes past the load address corresponding to r0.
* - r2 >= 0 (# of bytes left to store).
* - r7 is the next aligned src word value.
*/
.Lcleanup_unaligned_words:
/* Handle any trailing bytes. */
{ bz r2, .Lcopy_unaligned_done; slti_u r8, r2, 4 }
{ bzt r8, .Lcopy_unaligned_src_words; move r6, r7 }
/* Move r1 back to the point where it corresponds to r0. */
{ addi r1, r1, -4 }
#else /* !CHIP_HAS_DWORD_ALIGN() */
/* Compute right/left shift counts and load initial source words. */
{ andi r5, r1, -4; andi r3, r1, 3 }
EX: { lw r6, r5; addi r5, r5, 4; shli r3, r3, 3 }
EX: { lw r7, r5; addi r5, r5, 4; sub r4, zero, r3 }
/* Load and store one word at a time, using shifts and ORs
* to correct for the misaligned src.
*/
.Lcopy_unaligned_src_loop:
{ shr r6, r6, r3; shl r8, r7, r4 }
EX: { lw r7, r5; or r8, r8, r6; move r6, r7 }
EX: { sw r0, r8; addi r0, r0, 4; addi r2, r2, -4 }
{ addi r5, r5, 4; slti_u r8, r2, 8 }
{ bzt r8, .Lcopy_unaligned_src_loop; addi r1, r1, 4 }
{ bz r2, .Lcopy_unaligned_done }
#endif /* !CHIP_HAS_DWORD_ALIGN() */
/* Fall through */
/*
*
* 1 byte at a time copy handler.
*
*/
.Lcopy_unaligned_few:
EX: { lb_u r3, r1; addi r1, r1, 1 }
EX: { sb r0, r3; addi r0, r0, 1; addi r2, r2, -1 }
{ bnzt r2, .Lcopy_unaligned_few }
.Lcopy_unaligned_done:
/* For memcpy return original dest address, else zero. */
{ mz r0, r29, r23; jrp lr }
.Lend_memcpy_common:
.size memcpy_common, .Lend_memcpy_common - memcpy_common
.section .fixup,"ax"
memcpy_common_fixup:
.type memcpy_common_fixup, @function
/* Skip any bytes we already successfully copied.
* r2 (num remaining) is correct, but r0 (dst) and r1 (src)
* may not be quite right because of unrolling and prefetching.
* So we need to recompute their values as the address just
* after the last byte we are sure was successfully loaded and
* then stored.
*/
/* Determine how many bytes we successfully copied. */
{ sub r3, r25, r2 }
/* Add this to the original r0 and r1 to get their new values. */
{ add r0, r23, r3; add r1, r24, r3 }
{ bzt r29, memcpy_fixup_loop }
{ blzt r29, copy_to_user_fixup_loop }
copy_from_user_fixup_loop:
/* Try copying the rest one byte at a time, expecting a load fault. */
.Lcfu: { lb_u r3, r1; addi r1, r1, 1 }
{ sb r0, r3; addi r0, r0, 1; addi r2, r2, -1 }
{ bnzt r2, copy_from_user_fixup_loop }
.Lcopy_from_user_fixup_zero_remainder:
{ bbs r29, 2f } /* low bit set means IS_COPY_FROM_USER */
/* byte-at-a-time loop faulted, so zero the rest. */
{ move r3, r2; bz r2, 2f /* should be impossible, but handle it. */ }
1: { sb r0, zero; addi r0, r0, 1; addi r3, r3, -1 }
{ bnzt r3, 1b }
2: move lr, r27
{ move r0, r2; jrp lr }
copy_to_user_fixup_loop:
/* Try copying the rest one byte at a time, expecting a store fault. */
{ lb_u r3, r1; addi r1, r1, 1 }
.Lctu: { sb r0, r3; addi r0, r0, 1; addi r2, r2, -1 }
{ bnzt r2, copy_to_user_fixup_loop }
.Lcopy_to_user_fixup_done:
move lr, r27
{ move r0, r2; jrp lr }
memcpy_fixup_loop:
/* Try copying the rest one byte at a time. We expect a disastrous
* fault to happen since we are in fixup code, but let it happen.
*/
{ lb_u r3, r1; addi r1, r1, 1 }
{ sb r0, r3; addi r0, r0, 1; addi r2, r2, -1 }
{ bnzt r2, memcpy_fixup_loop }
/* This should be unreachable, we should have faulted again.
* But be paranoid and handle it in case some interrupt changed
* the TLB or something.
*/
move lr, r27
{ move r0, r23; jrp lr }
.size memcpy_common_fixup, . - memcpy_common_fixup
.section __ex_table,"a"
.word .Lcfu, .Lcopy_from_user_fixup_zero_remainder
.word .Lctu, .Lcopy_to_user_fixup_done
