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Diffstat (limited to 'kernel/arch/alpha/lib/stxcpy.S')
| -rw-r--r-- | kernel/arch/alpha/lib/stxcpy.S | 289 |
1 files changed, 289 insertions, 0 deletions
diff --git a/kernel/arch/alpha/lib/stxcpy.S b/kernel/arch/alpha/lib/stxcpy.S new file mode 100644 index 000000000..2a8d51bfc --- /dev/null +++ b/kernel/arch/alpha/lib/stxcpy.S @@ -0,0 +1,289 @@ +/* + * arch/alpha/lib/stxcpy.S + * Contributed by Richard Henderson (rth@tamu.edu) + * + * Copy a null-terminated string from SRC to DST. + * + * This is an internal routine used by strcpy, stpcpy, and strcat. + * As such, it uses special linkage conventions to make implementation + * of these public functions more efficient. + * + * On input: + * t9 = return address + * a0 = DST + * a1 = SRC + * + * On output: + * t12 = bitmask (with one bit set) indicating the last byte written + * a0 = unaligned address of the last *word* written + * + * Furthermore, v0, a3-a5, t11, and t12 are untouched. + */ + +#include <asm/regdef.h> + + .set noat + .set noreorder + + .text + +/* There is a problem with either gdb (as of 4.16) or gas (as of 2.7) that + doesn't like putting the entry point for a procedure somewhere in the + middle of the procedure descriptor. Work around this by putting the + aligned copy in its own procedure descriptor */ + + .ent stxcpy_aligned + .align 3 +stxcpy_aligned: + .frame sp, 0, t9 + .prologue 0 + + /* On entry to this basic block: + t0 == the first destination word for masking back in + t1 == the first source word. */ + + /* Create the 1st output word and detect 0's in the 1st input word. */ + lda t2, -1 # e1 : build a mask against false zero + mskqh t2, a1, t2 # e0 : detection in the src word + mskqh t1, a1, t3 # e0 : + ornot t1, t2, t2 # .. e1 : + mskql t0, a1, t0 # e0 : assemble the first output word + cmpbge zero, t2, t8 # .. e1 : bits set iff null found + or t0, t3, t1 # e0 : + bne t8, $a_eos # .. e1 : + + /* On entry to this basic block: + t0 == the first destination word for masking back in + t1 == a source word not containing a null. */ + +$a_loop: + stq_u t1, 0(a0) # e0 : + addq a0, 8, a0 # .. e1 : + ldq_u t1, 0(a1) # e0 : + addq a1, 8, a1 # .. e1 : + cmpbge zero, t1, t8 # e0 (stall) + beq t8, $a_loop # .. e1 (zdb) + + /* Take care of the final (partial) word store. + On entry to this basic block we have: + t1 == the source word containing the null + t8 == the cmpbge mask that found it. */ +$a_eos: + negq t8, t6 # e0 : find low bit set + and t8, t6, t12 # e1 (stall) + + /* For the sake of the cache, don't read a destination word + if we're not going to need it. */ + and t12, 0x80, t6 # e0 : + bne t6, 1f # .. e1 (zdb) + + /* We're doing a partial word store and so need to combine + our source and original destination words. */ + ldq_u t0, 0(a0) # e0 : + subq t12, 1, t6 # .. e1 : + zapnot t1, t6, t1 # e0 : clear src bytes >= null + or t12, t6, t8 # .. e1 : + zap t0, t8, t0 # e0 : clear dst bytes <= null + or t0, t1, t1 # e1 : + +1: stq_u t1, 0(a0) # e0 : + ret (t9) # .. e1 : + + .end stxcpy_aligned + + .align 3 + .ent __stxcpy + .globl __stxcpy +__stxcpy: + .frame sp, 0, t9 + .prologue 0 + + /* Are source and destination co-aligned? */ + xor a0, a1, t0 # e0 : + unop # : + and t0, 7, t0 # e0 : + bne t0, $unaligned # .. e1 : + + /* We are co-aligned; take care of a partial first word. */ + ldq_u t1, 0(a1) # e0 : load first src word + and a0, 7, t0 # .. e1 : take care not to load a word ... + addq a1, 8, a1 # e0 : + beq t0, stxcpy_aligned # .. e1 : ... if we wont need it + ldq_u t0, 0(a0) # e0 : + br stxcpy_aligned # .. e1 : + + +/* The source and destination are not co-aligned. Align the destination + and cope. We have to be very careful about not reading too much and + causing a SEGV. */ + + .align 3 +$u_head: + /* We know just enough now to be able to assemble the first + full source word. We can still find a zero at the end of it + that prevents us from outputting the whole thing. + + On entry to this basic block: + t0 == the first dest word, for masking back in, if needed else 0 + t1 == the low bits of the first source word + t6 == bytemask that is -1 in dest word bytes */ + + ldq_u t2, 8(a1) # e0 : + addq a1, 8, a1 # .. e1 : + + extql t1, a1, t1 # e0 : + extqh t2, a1, t4 # e0 : + mskql t0, a0, t0 # e0 : + or t1, t4, t1 # .. e1 : + mskqh t1, a0, t1 # e0 : + or t0, t1, t1 # e1 : + + or t1, t6, t6 # e0 : + cmpbge zero, t6, t8 # .. e1 : + lda t6, -1 # e0 : for masking just below + bne t8, $u_final # .. e1 : + + mskql t6, a1, t6 # e0 : mask out the bits we have + or t6, t2, t2 # e1 : already extracted before + cmpbge zero, t2, t8 # e0 : testing eos + bne t8, $u_late_head_exit # .. e1 (zdb) + + /* Finally, we've got all the stupid leading edge cases taken care + of and we can set up to enter the main loop. */ + + stq_u t1, 0(a0) # e0 : store first output word + addq a0, 8, a0 # .. e1 : + extql t2, a1, t0 # e0 : position ho-bits of lo word + ldq_u t2, 8(a1) # .. e1 : read next high-order source word + addq a1, 8, a1 # e0 : + cmpbge zero, t2, t8 # .. e1 : + nop # e0 : + bne t8, $u_eos # .. e1 : + + /* Unaligned copy main loop. In order to avoid reading too much, + the loop is structured to detect zeros in aligned source words. + This has, unfortunately, effectively pulled half of a loop + iteration out into the head and half into the tail, but it does + prevent nastiness from accumulating in the very thing we want + to run as fast as possible. + + On entry to this basic block: + t0 == the shifted high-order bits from the previous source word + t2 == the unshifted current source word + + We further know that t2 does not contain a null terminator. */ + + .align 3 +$u_loop: + extqh t2, a1, t1 # e0 : extract high bits for current word + addq a1, 8, a1 # .. e1 : + extql t2, a1, t3 # e0 : extract low bits for next time + addq a0, 8, a0 # .. e1 : + or t0, t1, t1 # e0 : current dst word now complete + ldq_u t2, 0(a1) # .. e1 : load high word for next time + stq_u t1, -8(a0) # e0 : save the current word + mov t3, t0 # .. e1 : + cmpbge zero, t2, t8 # e0 : test new word for eos + beq t8, $u_loop # .. e1 : + + /* We've found a zero somewhere in the source word we just read. + If it resides in the lower half, we have one (probably partial) + word to write out, and if it resides in the upper half, we + have one full and one partial word left to write out. + + On entry to this basic block: + t0 == the shifted high-order bits from the previous source word + t2 == the unshifted current source word. */ +$u_eos: + extqh t2, a1, t1 # e0 : + or t0, t1, t1 # e1 : first (partial) source word complete + + cmpbge zero, t1, t8 # e0 : is the null in this first bit? + bne t8, $u_final # .. e1 (zdb) + +$u_late_head_exit: + stq_u t1, 0(a0) # e0 : the null was in the high-order bits + addq a0, 8, a0 # .. e1 : + extql t2, a1, t1 # e0 : + cmpbge zero, t1, t8 # .. e1 : + + /* Take care of a final (probably partial) result word. + On entry to this basic block: + t1 == assembled source word + t8 == cmpbge mask that found the null. */ +$u_final: + negq t8, t6 # e0 : isolate low bit set + and t6, t8, t12 # e1 : + + and t12, 0x80, t6 # e0 : avoid dest word load if we can + bne t6, 1f # .. e1 (zdb) + + ldq_u t0, 0(a0) # e0 : + subq t12, 1, t6 # .. e1 : + or t6, t12, t8 # e0 : + zapnot t1, t6, t1 # .. e1 : kill source bytes >= null + zap t0, t8, t0 # e0 : kill dest bytes <= null + or t0, t1, t1 # e1 : + +1: stq_u t1, 0(a0) # e0 : + ret (t9) # .. e1 : + + /* Unaligned copy entry point. */ + .align 3 +$unaligned: + + ldq_u t1, 0(a1) # e0 : load first source word + + and a0, 7, t4 # .. e1 : find dest misalignment + and a1, 7, t5 # e0 : find src misalignment + + /* Conditionally load the first destination word and a bytemask + with 0xff indicating that the destination byte is sacrosanct. */ + + mov zero, t0 # .. e1 : + mov zero, t6 # e0 : + beq t4, 1f # .. e1 : + ldq_u t0, 0(a0) # e0 : + lda t6, -1 # .. e1 : + mskql t6, a0, t6 # e0 : +1: + subq a1, t4, a1 # .. e1 : sub dest misalignment from src addr + + /* If source misalignment is larger than dest misalignment, we need + extra startup checks to avoid SEGV. */ + + cmplt t4, t5, t12 # e0 : + beq t12, $u_head # .. e1 (zdb) + + lda t2, -1 # e1 : mask out leading garbage in source + mskqh t2, t5, t2 # e0 : + nop # e0 : + ornot t1, t2, t3 # .. e1 : + cmpbge zero, t3, t8 # e0 : is there a zero? + beq t8, $u_head # .. e1 (zdb) + + /* At this point we've found a zero in the first partial word of + the source. We need to isolate the valid source data and mask + it into the original destination data. (Incidentally, we know + that we'll need at least one byte of that original dest word.) */ + + ldq_u t0, 0(a0) # e0 : + + negq t8, t6 # .. e1 : build bitmask of bytes <= zero + and t6, t8, t12 # e0 : + and a1, 7, t5 # .. e1 : + subq t12, 1, t6 # e0 : + or t6, t12, t8 # e1 : + srl t12, t5, t12 # e0 : adjust final null return value + + zapnot t2, t8, t2 # .. e1 : prepare source word; mirror changes + and t1, t2, t1 # e1 : to source validity mask + extql t2, a1, t2 # .. e0 : + extql t1, a1, t1 # e0 : + + andnot t0, t2, t0 # .. e1 : zero place for source to reside + or t0, t1, t1 # e1 : and put it there + stq_u t1, 0(a0) # .. e0 : + ret (t9) # e1 : + + .end __stxcpy |