//
// Tuneable parameters
//
//
// arguments
//
//
// local registers
//
GLOBAL_ENTRY(__copy_user)
.prologue
.save ar.pfs, saved_pfs
alloc saved_pfs=ar.pfs,3,((2*PIPE_DEPTH+7)&~7),0,((2*PIPE_DEPTH+7)&~7)
.rotr val1[PIPE_DEPTH],val2[PIPE_DEPTH]
.rotp p[PIPE_DEPTH]
adds len2=-1,len // br.ctop is repeat/until
mov ret0=r0
;; // RAW of cfm when len=0
cmp.eq p8,p0=r0,len // check for zero length
.save ar.lc, saved_lc
mov saved_lc=ar.lc // preserve ar.lc (slow)
(p8) br.ret.spnt.many rp // empty mempcy()
;;
add enddst=dst,len // first byte after end of source
add endsrc=src,len // first byte after end of destination
.save pr, saved_pr
mov saved_pr=pr // preserve predicates
.body
mov dst1=dst // copy because of rotation
mov ar.ec=PIPE_DEPTH
mov pr.rot=1<<16 // p16=true all others are false
mov src1=src // copy because of rotation
mov ar.lc=len2 // initialize lc for small count
cmp.lt p10,p7=COPY_BREAK,len // if len > COPY_BREAK then long copy
xor tmp=src,dst // same alignment test prepare
(p10) br.cond.dptk .long_copy_user
;; // RAW pr.rot/p16 ?
//
// Now we do the byte by byte loop with software pipeline
//
// p7 is necessarily false by now
1:
EX(.failure_in_pipe1,(p16) ld1 val1[0]=[src1],1)
EX(.failure_out,(EPI) st1 [dst1]=val1[PIPE_DEPTH-1],1)
br.ctop.dptk.few 1b
;;
mov ar.lc=saved_lc
mov pr=saved_pr,0xffffffffffff0000
mov ar.pfs=saved_pfs // restore ar.ec
br.ret.sptk.many rp // end of short memcpy
//
// Not 8-byte aligned
//
.diff_align_copy_user:
// At this point we know we have more than 16 bytes to copy
// and also that src and dest do _not_ have the same alignment.
and src2=0x7,src1 // src offset
and dst2=0x7,dst1 // dst offset
;;
// The basic idea is that we copy byte-by-byte at the head so
// that we can reach 8-byte alignment for both src1 and dst1.
// Then copy the body using software pipelined 8-byte copy,
// shifting the two back-to-back words right and left, then copy
// the tail by copying byte-by-byte.
//
// Fault handling. If the byte-by-byte at the head fails on the
// load, then restart and finish the pipleline by copying zeros
// to the dst1. Then copy zeros for the rest of dst1.
// If 8-byte software pipeline fails on the load, do the same as
// failure_in3 does. If the byte-by-byte at the tail fails, it is
// handled simply by failure_in_pipe1.
//
// The case p14 represents the source has more bytes in the
// the first word (by the shifted part), whereas the p15 needs to
// copy some bytes from the 2nd word of the source that has the
// tail of the 1st of the destination.
//
//
// Optimization. If dst1 is 8-byte aligned (quite common), we don't need
// to copy the head to dst1, to start 8-byte copy software pipeline.
// We know src1 is not 8-byte aligned in this case.
//
cmp.eq p14,p15=r0,dst2
(p15) br.cond.spnt 1f
;;
sub t1=8,src2
mov t2=src2
;;
shl rshift=t2,3
sub len1=len,t1 // set len1
;;
sub lshift=64,rshift
;;
br.cond.spnt .word_copy_user
;;
1:
cmp.leu p14,p15=src2,dst2
sub t1=dst2,src2
;;
.pred.rel "mutex", p14, p15
(p14) sub word1=8,src2 // (8 - src offset)
(p15) sub t1=r0,t1 // absolute value
(p15) sub word1=8,dst2 // (8 - dst offset)
;;
// For the case p14, we don't need to copy the shifted part to
// the 1st word of destination.
sub t2=8,t1
(p14) sub word1=word1,t1
;;
sub len1=len,word1 // resulting len
(p15) shl rshift=t1,3 // in bits
(p14) shl rshift=t2,3
;;
(p14) sub len1=len1,t1
adds cnt=-1,word1
;;
sub lshift=64,rshift
mov ar.ec=PIPE_DEPTH
mov pr.rot=1<<16 // p16=true all others are false
mov ar.lc=cnt
;;
2:
EX(.failure_in_pipe2,(p16) ld1 val1[0]=[src1],1)
EX(.failure_out,(EPI) st1 [dst1]=val1[PIPE_DEPTH-1],1)
br.ctop.dptk.few 2b
;;
clrrrb
;;
.word_copy_user:
cmp.gtu p9,p0=16,len1
(p9) br.cond.spnt 4f // if (16 > len1) skip 8-byte copy
;;
shr.u cnt=len1,3 // number of 64-bit words
;;
adds cnt=-1,cnt
;;
.pred.rel "mutex", p14, p15
(p14) sub src1=src1,t2
(p15) sub src1=src1,t1
//
// Now both src1 and dst1 point to an 8-byte aligned address. And
// we have more than 8 bytes to copy.
//
mov ar.lc=cnt
mov ar.ec=PIPE_DEPTH
mov pr.rot=1<<16 // p16=true all others are false
;;
3:
//
// The pipleline consists of 3 stages:
// 1 (p16): Load a word from src1
// 2 (EPI_1): Shift right pair, saving to tmp
// 3 (EPI): Store tmp to dst1
//
// To make it simple, use at least 2 (p16) loops to set up val1[n]
// because we need 2 back-to-back val1[] to get tmp.
// Note that this implies EPI_2 must be p18 or greater.
//
(pred) br.cond.spnt .copy_user_bit
.copy_user_bit
1: \
EX(.failure_out,(EPI) st8 [dst1]=tmp,8); \
(EPI_1) shrp tmp=val1[PIPE_DEPTH-2],val1[PIPE_DEPTH-1],rshift; \
EX(3f,(p16) ld8 val1[1]=[src1],8); \
(p16) mov val1[0]=r0; \
br.ctop.dptk 1b; \
;; \
br.cond.sptk.many .diff_align_do_tail; \
2: \
(EPI) st8 [dst1]=tmp,8; \
(EPI_1) shrp tmp=val1[PIPE_DEPTH-2],val1[PIPE_DEPTH-1],rshift; \
3: \
(p16) mov val1[1]=r0; \
(p16) mov val1[0]=r0; \
br.ctop.dptk 2b; \
;; \
br.cond.sptk.many .failure_in2
//
// Since the instruction 'shrp' requires a fixed 128-bit value
// specifying the bits to shift, we need to provide 7 cases
// below.
//
SWITCH(p6, 8)
SWITCH(p7, 16)
SWITCH(p8, 24)
SWITCH(p9, 32)
SWITCH(p10, 40)
SWITCH(p11, 48)
SWITCH(p12, 56)
;;
CASE(p6, 8)
CASE(p7, 16)
CASE(p8, 24)
CASE(p9, 32)
CASE(p10, 40)
CASE(p11, 48)
CASE(p12, 56)
;;
BODY(8)
BODY(16)
BODY(24)
BODY(32)
BODY(40)
BODY(48)
BODY(56)
;;
.diff_align_do_tail:
.pred.rel "mutex", p14, p15
(p14) sub src1=src1,t1
(p14) adds dst1=-8,dst1
(p15) sub dst1=dst1,t1
;;
4:
// Tail correction.
//
// The problem with this piplelined loop is that the last word is not
// loaded and thus parf of the last word written is not correct.
// To fix that, we simply copy the tail byte by byte.
sub len1=endsrc,src1,1
clrrrb
;;
mov ar.ec=PIPE_DEPTH
mov pr.rot=1<<16 // p16=true all others are false
mov ar.lc=len1
;;
5:
EX(.failure_in_pipe1,(p16) ld1 val1[0]=[src1],1)
EX(.failure_out,(EPI) st1 [dst1]=val1[PIPE_DEPTH-1],1)
br.ctop.dptk.few 5b
;;
mov ar.lc=saved_lc
mov pr=saved_pr,0xffffffffffff0000
mov ar.pfs=saved_pfs
br.ret.sptk.many rp
//
// Beginning of long mempcy (i.e. > 16 bytes)
//
.long_copy_user:
tbit.nz p6,p7=src1,0 // odd alignment
and tmp=7,tmp
;;
cmp.eq p10,p8=r0,tmp
mov len1=len // copy because of rotation
(p8) br.cond.dpnt .diff_align_copy_user
;;
// At this point we know we have more than 16 bytes to copy
// and also that both src and dest have the same alignment
// which may not be the one we want. So for now we must move
// forward slowly until we reach 16byte alignment: no need to
// worry about reaching the end of buffer.
//
EX(.failure_in1,(p6) ld1 val1[0]=[src1],1) // 1-byte aligned
(p6) adds len1=-1,len1;;
tbit.nz p7,p0=src1,1
;;
EX(.failure_in1,(p7) ld2 val1[1]=[src1],2) // 2-byte aligned
(p7) adds len1=-2,len1;;
tbit.nz p8,p0=src1,2
;;
//
// Stop bit not required after ld4 because if we fail on ld4
// we have never executed the ld1, therefore st1 is not executed.
//
EX(.failure_in1,(p8) ld4 val2[0]=[src1],4) // 4-byte aligned
;;
EX(.failure_out,(p6) st1 [dst1]=val1[0],1)
tbit.nz p9,p0=src1,3
;;
//
// Stop bit not required after ld8 because if we fail on ld8
// we have never executed the ld2, therefore st2 is not executed.
//
EX(.failure_in1,(p9) ld8 val2[1]=[src1],8) // 8-byte aligned
EX(.failure_out,(p7) st2 [dst1]=val1[1],2)
(p8) adds len1=-4,len1
;;
EX(.failure_out, (p8) st4 [dst1]=val2[0],4)
(p9) adds len1=-8,len1;;
shr.u cnt=len1,4 // number of 128-bit (2x64bit) words
;;
EX(.failure_out, (p9) st8 [dst1]=val2[1],8)
tbit.nz p6,p0=len1,3
cmp.eq p7,p0=r0,cnt
adds tmp=-1,cnt // br.ctop is repeat/until
(p7) br.cond.dpnt .dotail // we have less than 16 bytes left
;;
adds src2=8,src1
adds dst2=8,dst1
mov ar.lc=tmp
;;
//
// 16bytes/iteration
//
2:
EX(.failure_in3,(p16) ld8 val1[0]=[src1],16)
(p16) ld8 val2[0]=[src2],16
EX(.failure_out, (EPI) st8 [dst1]=val1[PIPE_DEPTH-1],16)
(EPI) st8 [dst2]=val2[PIPE_DEPTH-1],16
br.ctop.dptk 2b
;; // RAW on src1 when fall through from loop
//
// Tail correction based on len only
//
// No matter where we come from (loop or test) the src1 pointer
// is 16 byte aligned AND we have less than 16 bytes to copy.
//
.dotail:
EX(.failure_in1,(p6) ld8 val1[0]=[src1],8) // at least 8 bytes
tbit.nz p7,p0=len1,2
;;
EX(.failure_in1,(p7) ld4 val1[1]=[src1],4) // at least 4 bytes
tbit.nz p8,p0=len1,1
;;
EX(.failure_in1,(p8) ld2 val2[0]=[src1],2) // at least 2 bytes
tbit.nz p9,p0=len1,0
;;
EX(.failure_out, (p6) st8 [dst1]=val1[0],8)
;;
EX(.failure_in1,(p9) ld1 val2[1]=[src1]) // only 1 byte left
mov ar.lc=saved_lc
;;
EX(.failure_out,(p7) st4 [dst1]=val1[1],4)
mov pr=saved_pr,0xffffffffffff0000
;;
EX(.failure_out, (p8) st2 [dst1]=val2[0],2)
mov ar.pfs=saved_pfs
;;
EX(.failure_out, (p9) st1 [dst1]=val2[1])
br.ret.sptk.many rp
//
// Here we handle the case where the byte by byte copy fails
// on the load.
// Several factors make the zeroing of the rest of the buffer kind of
// tricky:
// - the pipeline: loads/stores are not in sync (pipeline)
//
// In the same loop iteration, the dst1 pointer does not directly
// reflect where the faulty load was.
//
// - pipeline effect
// When you get a fault on load, you may have valid data from
// previous loads not yet store in transit. Such data must be
// store normally before moving onto zeroing the rest.
//
// - single/multi dispersal independence.
//
// solution:
// - we don't disrupt the pipeline, i.e. data in transit in
// the software pipeline will be eventually move to memory.
// We simply replace the load with a simple mov and keep the
// pipeline going. We can't really do this inline because
// p16 is always reset to 1 when lc > 0.
//
.failure_in_pipe1:
sub ret0=endsrc,src1 // number of bytes to zero, i.e. not copied
1:
(p16) mov val1[0]=r0
(EPI) st1 [dst1]=val1[PIPE_DEPTH-1],1
br.ctop.dptk 1b
;;
mov pr=saved_pr,0xffffffffffff0000
mov ar.lc=saved_lc
mov ar.pfs=saved_pfs
br.ret.sptk.many rp
//
// This is the case where the byte by byte copy fails on the load
// when we copy the head. We need to finish the pipeline and copy
// zeros for the rest of the destination. Since this happens
// at the top we still need to fill the body and tail.
.failure_in_pipe2:
sub ret0=endsrc,src1 // number of bytes to zero, i.e. not copied
2:
(p16) mov val1[0]=r0
(EPI) st1 [dst1]=val1[PIPE_DEPTH-1],1
br.ctop.dptk 2b
;;
sub len=enddst,dst1,1 // precompute len
br.cond.dptk.many .failure_in1bis
;;
//
// Here we handle the head & tail part when we check for alignment.
// The following code handles only the load failures. The
// main diffculty comes from the fact that loads/stores are
// scheduled. So when you fail on a load, the stores corresponding
// to previous successful loads must be executed.
//
// However some simplifications are possible given the way
// things work.
//
// 1) HEAD
// Theory of operation:
//
// Page A | Page B
// ---------|-----
// 1|8 x
// 1 2|8 x
// 4|8 x
// 1 4|8 x
// 2 4|8 x
// 1 2 4|8 x
// |1
// |2 x
// |4 x
//
// page_size >= 4k (2^12). (x means 4, 2, 1)
// Here we suppose Page A exists and Page B does not.
//
// As we move towards eight byte alignment we may encounter faults.
// The numbers on each page show the size of the load (current alignment).
//
// Key point:
// - if you fail on 1, 2, 4 then you have never executed any smaller
// size loads, e.g. failing ld4 means no ld1 nor ld2 executed
// before.
//
// This allows us to simplify the cleanup code, because basically you
// only have to worry about "pending" stores in the case of a failing
// ld8(). Given the way the code is written today, this means only
// worry about st2, st4. There we can use the information encapsulated
// into the predicates.
//
// Other key point:
// - if you fail on the ld8 in the head, it means you went straight
// to it, i.e. 8byte alignment within an unexisting page.
// Again this comes from the fact that if you crossed just for the ld8 then
// you are 8byte aligned but also 16byte align, therefore you would
// either go for the 16byte copy loop OR the ld8 in the tail part.
// The combination ld1, ld2, ld4, ld8 where you fail on ld8 is impossible
// because it would mean you had 15bytes to copy in which case you
// would have defaulted to the byte by byte copy.
//
//
// 2) TAIL
// Here we now we have less than 16 bytes AND we are either 8 or 16 byte
// aligned.
//
// Key point:
// This means that we either:
// - are right on a page boundary
// OR
// - are at more than 16 bytes from a page boundary with
// at most 15 bytes to copy: no chance of crossing.
//
// This allows us to assume that if we fail on a load we haven't possibly
// executed any of the previous (tail) ones, so we don't need to do
// any stores. For instance, if we fail on ld2, this means we had
// 2 or 3 bytes left to copy and we did not execute the ld8 nor ld4.
//
// This means that we are in a situation similar the a fault in the
// head part. That's nice!
//
.failure_in1:
sub ret0=endsrc,src1 // number of bytes to zero, i.e. not copied
sub len=endsrc,src1,1
//
// we know that ret0 can never be zero at this point
// because we failed why trying to do a load, i.e. there is still
// some work to do.
// The failure_in1bis and length problem is taken care of at the
// calling side.
//
;;
.failure_in1bis: // from (.failure_in3)
mov ar.lc=len // Continue with a stupid byte store.
;;
5:
st1 [dst1]=r0,1
br.cloop.dptk 5b
;;
mov pr=saved_pr,0xffffffffffff0000
mov ar.lc=saved_lc
mov ar.pfs=saved_pfs
br.ret.sptk.many rp
//
// Here we simply restart the loop but instead
// of doing loads we fill the pipeline with zeroes
// We can't simply store r0 because we may have valid
// data in transit in the pipeline.
// ar.lc and ar.ec are setup correctly at this point
//
// we MUST use src1/endsrc here and not dst1/enddst because
// of the pipeline effect.
//
.failure_in3:
sub ret0=endsrc,src1 // number of bytes to zero, i.e. not copied
;;
2:
(p16) mov val1[0]=r0
(p16) mov val2[0]=r0
(EPI) st8 [dst1]=val1[PIPE_DEPTH-1],16
(EPI) st8 [dst2]=val2[PIPE_DEPTH-1],16
br.ctop.dptk 2b
;;
cmp.ne p6,p0=dst1,enddst // Do we need to finish the tail ?
sub len=enddst,dst1,1 // precompute len
(p6) br.cond.dptk .failure_in1bis
;;
mov pr=saved_pr,0xffffffffffff0000
mov ar.lc=saved_lc
mov ar.pfs=saved_pfs
br.ret.sptk.many rp
.failure_in2:
sub ret0=endsrc,src1
cmp.ne p6,p0=dst1,enddst // Do we need to finish the tail ?
sub len=enddst,dst1,1 // precompute len
(p6) br.cond.dptk .failure_in1bis
;;
mov pr=saved_pr,0xffffffffffff0000
mov ar.lc=saved_lc
mov ar.pfs=saved_pfs
br.ret.sptk.many rp
//
// handling of failures on stores: that's the easy part
//
.failure_out:
sub ret0=enddst,dst1
mov pr=saved_pr,0xffffffffffff0000
mov ar.lc=saved_lc
mov ar.pfs=saved_pfs
br.ret.sptk.many rp
END(__copy_user)
