On Wed, 6 Jun 2001, Gleb O. Raiko wrote: > It seems there is a bug in our memmove routine. The condition is rare > though, for example, memmove copies incorrectly, if src=5, dst=4, len=9. [...] > Two questions here. First, do we have a pattern that satisfies the > condition, i.e. is the bug showstopper? My guess, it's not. Second, does > somebody have ideas how to fix the bug? Well, I have, but want to hear > somebody else. Here is a quick fix I developed after reading your report. It fixes the case you described. Now memcpy() is invoked only if there is no overlap at all -- the approach is taken from the Alpha port. The copy loop begs for optimization (the original memmove() bits do as well), but at least it works correctly. The patch applies cleanly to 2.4.5 as of today. Ralf, I think it should get applied unless someone cooks up a better solution, i.e. optimizes it. I'll optimize it myself, eventually, if no one else does, but don't hold your breath. -- + Maciej W. Rozycki, Technical University of Gdansk, Poland + +--------------------------------------------------------------+ + e-mail: macro@ds2.pg.gda.pl, PGP key available + patch-mips-2.4.0-test12-20010110-memmove-1 diff -up --recursive --new-file linux-mips-2.4.0-test12-20010110.macro/arch/mips/lib/memcpy.S linux-mips-2.4.0-test12-20010110/arch/mips/lib/memcpy.S --- linux-mips-2.4.0-test12-20010110.macro/arch/mips/lib/memcpy.S Wed Dec 6 05:27:02 2000 +++ linux-mips-2.4.0-test12-20010110/arch/mips/lib/memcpy.S Sun Jun 10 17:50:55 2001 @@ -402,16 +402,20 @@ u_end_bytes: .align 5 LEAF(memmove) - sltu t0, a0, a1 # dst < src -> memcpy - bnez t0, memcpy - addu v0, a0, a2 - sltu t0, v0, a1 # dst + len < src -> non- - bnez t0, __memcpy # overlapping, can use memcpy + addu t0, a0, a2 + sltu t0, a1, t0 # dst + len <= src -> memcpy + addu t1, a1, a2 + sltu t1, a0, t1 # dst >= src + len -> memcpy + and t0, t1 + beqz t0, __memcpy move v0, a0 /* return value */ beqz a2, r_out END(memmove) LEAF(__rmemcpy) /* a0=dst a1=src a2=len */ + sltu t0, a1, a0 + beqz t0, r_end_bytes_up # src >= dst + nop addu a0, a2 # dst = dst + len addu a1, a2 # src = src + len @@ -563,6 +567,17 @@ r_end_bytes: subu a0, a0, 0x1 r_out: + jr ra + move a2, zero + +r_end_bytes_up: + lb t0, (a1) + subu a2, a2, 0x1 + sb t0, (a0) + addu a1, a1, 0x1 + bnez a2, r_end_bytes_up + addu a0, a0, 0x1 + jr ra move a2, zero
