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// SPDX-License-Identifier: GPL-2.0
/*
* Copyright (c) 2021, 2024, Oracle and/or its affiliates.
*/
#include <bpf_asm_helpers.h>
.text
/*
* void dt_strcmp_xor(char *s, const char *t, uint64_t len) {
* for (r6 = 0; r6 < len; r6++)
* s[r6] ^= t[r6];
* }
* where len is a positive multiple of 8.
*/
.align 4
.global dt_strcmp_xor
.type dt_strcmp_xor, @function
dt_strcmp_xor :
mov %r6, 0
.Lxor:
ldxdw %r4, [%r1+0]
ldxdw %r5, [%r2+0]
xor %r4, %r5
stxdw [%r1+0], %r4
add %r1, 8
add %r2, 8
add %r6, 8
jlt %r6, %r3, .Lxor
exit
.size dt_strcmp_xor, .-dt_strcmp_xor
/*
* void dt_strcmp_not(char *s, uint64_t len) {
* for (r6 = 0; r6 < len; r6++)
* s[r6] = ! s[r6]
* }
*/
.align 4
.global dt_strcmp_not
.type dt_strcmp_not, @function
dt_strcmp_not :
mov %r6, 0
.Lnot:
ldxb %r3, [%r1+0]
and %r3, 0xff
sub %r3, 1
rsh %r3, 63
stxb [%r1+0], %r3
add %r1, 1
add %r6, 1
jlt %r6, %r2, .Lnot
exit
.size dt_strcmp_not, .-dt_strcmp_not
/*
* int dt_strcmp(char *s, char *t, char *tmp1, char *tmp2, uint64_t flags) {
*
* [%fp-8]=s
* [%fp-16]=t
* [%fp-24]=tmp1
* [%fp-32]=tmp2
* r9=flags
*
* r8 = STRSZ
*
* // make temporary copies of strings
* r6 = bpf_probe_read_str(tmp1, STRSZ, s);
* r7 = bpf_probe_read_str(tmp2, STRSZ, t);
* tmp1[r6] = '\0';
* tmp2[r7] = '\0';
*
* // round r8 up to a multiple of 8
* r8 = (r8 + 7) & -8;
*
* // xor strings together, "not" bytes, and find first NULL
* // (this gives us the first byte that differs in the two strings)
* dt_strcmp_xor(tmp1, tmp2, r8);
* dt_strcmp_not(tmp1, r8);
* r0 = bpf_probe_read_str(tmp1, r8, tmp1);
* r0 -= 1;
*
* // based on this location, judge if the strings are >, <, or ==
* if (r0 > r6) goto Lsame;
* if (r0 > r7) goto Lsame;
*
* r7 = tmp2[r0];
*
* bpf_probe_read(tmp1, 1, &s[r0]);
* r6 = tmp1[0];
*
* // if all chars are the same, break tie on string length
* Lsame:
* if (r6 > r7) return +1
* if (r6 < r7) return -1
* return 0;
* }
*/
.align 4
.global dt_strcmp
.type dt_strcmp, @function
dt_strcmp :
stxdw [%fp+-8], %r1 /* Spill s */
stxdw [%fp+-16], %r2 /* Spill t */
stxdw [%fp+-24], %r3 /* Spill tmp1 */
stxdw [%fp+-32], %r4 /* Spill tmp2 */
mov %r9, %r5 /* flags */
lddw %r8, STRSZ /* r8 = STRSZ */
ldxdw %r1, [%fp+-24]
mov %r2, %r8
ldxdw %r3, [%fp+-8]
call BPF_FUNC_probe_read_str /* r6 = bpf_probe_read_str(tmp1, STRSZ, s) */
mov %r6, %r0
jle %r6, %r8, 1
mov %r6, %r8
ldxdw %r1, [%fp+-32]
mov %r2, %r8
ldxdw %r3, [%fp+-16]
call BPF_FUNC_probe_read_str /* r7 = bpf_probe_read_str(tmp2, STRSZ, t) */
mov %r7, %r0
jle %r7, %r8, 1
mov %r7, %r8
mov %r2, 0
ldxdw %r1, [%fp+-24]
add %r1, %r6
stxb [%r1+0], %r2 /* tmp1[r6] = '\0' */
ldxdw %r1, [%fp+-32]
add %r1, %r7
stxb [%r1+0], %r2 /* tmp2[r7] = '\0' */
add %r8, 7 /* round r8 up to a multiple of 8 */
and %r8, -8
ldxdw %r1, [%fp+-24]
ldxdw %r2, [%fp+-32]
mov %r3, %r8
call dt_strcmp_xor /* dt_strcmp_xor(tmp1, tmp2, r8) */
ldxdw %r1, [%fp+-24]
mov %r2, %r8
call dt_strcmp_not /* dt_strcmp_not(tmp1, r8) */
ldxdw %r1, [%fp+-24]
mov %r2, %r8
ldxdw %r3, [%fp+-24]
call BPF_FUNC_probe_read_str /* r0 = bpf_probe_read_str(tmp1, r8, tmp1) */
jsle %r0, 0, .L0 /* help the BPF verifier */
lddw %r8, STRSZ
jlt %r0, %r8, 1
mov %r0, %r8
sub %r0, 1 /* r0 -= 1 */
jgt %r0, %r6, .Lsame /* if (r0 > r6) goto Lsame */
jgt %r0, %r7, .Lsame /* if (r0 > r7) goto Lsame */
ldxdw %r7, [%fp+-32]
add %r7, %r0
ldxb %r7, [%r7+0]
and %r7, 0xff /* r7 = tmp2[r0] */
ldxdw %r1, [%fp+-24]
mov %r2, 1
ldxdw %r3, [%fp+-8]
add %r3, %r0
call BPF_FUNC_probe_read /* bpf_probe_read(tmp1, 1, &s[r0]) */
ldxdw %r6, [%fp+-24]
ldxb %r6, [%r6+0]
and %r6, 0xff /* r6 = tmp1[0] */
.Lsame:
jle %r6, %r7, 2 /* if (r6 > r7) return +1 */
mov %r0, 1
exit
jge %r6, %r7, 2 /* if (r6 < r7) return -1 */
mov %r0, -1
exit
.L0:
mov %r0, 0 /* return 0 */
exit
.size dt_strcmp, .-dt_strcmp
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