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1/*
2 * arch/alpha/lib/ev67-strlen_user.S
3 * 21264 version contributed by Rick Gorton <rick.gorton@api-networks.com>
4 *
5 * Return the length of the string including the NULL terminator
6 * (strlen+1) or zero if an error occurred.
7 *
8 * In places where it is critical to limit the processing time,
9 * and the data is not trusted, strnlen_user() should be used.
10 * It will return a value greater than its second argument if
11 * that limit would be exceeded. This implementation is allowed
12 * to access memory beyond the limit, but will not cross a page
13 * boundary when doing so.
14 *
15 * Much of the information about 21264 scheduling/coding comes from:
16 * Compiler Writer's Guide for the Alpha 21264
17 * abbreviated as 'CWG' in other comments here
18 * ftp.digital.com/pub/Digital/info/semiconductor/literature/dsc-library.html
19 * Scheduling notation:
20 * E - either cluster
21 * U - upper subcluster; U0 - subcluster U0; U1 - subcluster U1
22 * L - lower subcluster; L0 - subcluster L0; L1 - subcluster L1
23 * Try not to change the actual algorithm if possible for consistency.
24 */
25
26#include <asm/regdef.h>
27
28
29/* Allow an exception for an insn; exit if we get one. */
30#define EX(x,y...) \
31 99: x,##y; \
32 .section __ex_table,"a"; \
33 .long 99b - .; \
34 lda v0, $exception-99b(zero); \
35 .previous
36
37
38 .set noreorder
39 .set noat
40 .text
41
42 .globl __strlen_user
43 .ent __strlen_user
44 .frame sp, 0, ra
45
46 .align 4
47__strlen_user:
48 ldah a1, 32767(zero) # do not use plain strlen_user() for strings
49 # that might be almost 2 GB long; you should
50 # be using strnlen_user() instead
51 nop
52 nop
53 nop
54
55 .globl __strnlen_user
56
57 .align 4
58__strnlen_user:
59 .prologue 0
60 EX( ldq_u t0, 0(a0) ) # L : load first quadword (a0 may be misaligned)
61 lda t1, -1(zero) # E :
62
63 insqh t1, a0, t1 # U :
64 andnot a0, 7, v0 # E :
65 or t1, t0, t0 # E :
66 subq a0, 1, a0 # E : get our +1 for the return
67
68 cmpbge zero, t0, t1 # E : t1 <- bitmask: bit i == 1 <==> i-th byte == 0
69 subq a1, 7, t2 # E :
70 subq a0, v0, t0 # E :
71 bne t1, $found # U :
72
73 addq t2, t0, t2 # E :
74 addq a1, 1, a1 # E :
75 nop # E :
76 nop # E :
77
78 .align 4
79$loop: ble t2, $limit # U :
80 EX( ldq t0, 8(v0) ) # L :
81 nop # E :
82 nop # E :
83
84 cmpbge zero, t0, t1 # E :
85 subq t2, 8, t2 # E :
86 addq v0, 8, v0 # E : addr += 8
87 beq t1, $loop # U :
88
89$found: cttz t1, t2 # U0 :
90 addq v0, t2, v0 # E :
91 subq v0, a0, v0 # E :
92 ret # L0 :
93
94$exception:
95 nop
96 nop
97 nop
98 ret
99
100 .align 4 # currently redundant
101$limit:
102 nop
103 nop
104 subq a1, t2, v0
105 ret
106
107 .end __strlen_user