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8ad11b9a | 1 | /* Get the frequency of the time base. |
2b778ceb | 2 | Copyright (C) 2012-2021 Free Software Foundation, Inc. |
8ad11b9a TMQMF |
3 | This file is part of the GNU C Library. |
4 | ||
5 | The GNU C Library is free software; you can redistribute it and/or | |
6 | modify it under the terms of the GNU Lesser General Public | |
7 | License as published by the Free Software Foundation; either | |
8 | version 2.1 of the License, or (at your option) any later version. | |
9 | ||
10 | The GNU C Library is distributed in the hope that it will be useful, | |
11 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
13 | Lesser General Public License for more details. | |
14 | ||
15 | You should have received a copy of the GNU Lesser General Public | |
16 | License along with the GNU C Library; if not, see | |
5a82c748 | 17 | <https://www.gnu.org/licenses/>. */ |
8ad11b9a | 18 | |
1ab29350 | 19 | #include <stdint.h> |
6e8ba7fd AZ |
20 | #include <string.h> |
21 | ||
8ad11b9a | 22 | #include <libc-internal.h> |
6e8ba7fd | 23 | #include <not-cancel.h> |
1bdda52f | 24 | #include <sysdep-vdso.h> |
8ad11b9a | 25 | |
986a5064 AZ |
26 | static uint64_t |
27 | get_timebase_freq_fallback (void) | |
8ad11b9a | 28 | { |
6e8ba7fd AZ |
29 | hp_timing_t result = 0L; |
30 | ||
6e8ba7fd AZ |
31 | /* We read the information from the /proc filesystem. /proc/cpuinfo |
32 | contains at least one line like: | |
33 | timebase : 33333333 | |
34 | We search for this line and convert the number into an integer. */ | |
35 | int fd = __open_nocancel ("/proc/cpuinfo", O_RDONLY); | |
335c1007 | 36 | if (__glibc_unlikely (fd == -1)) |
6e8ba7fd AZ |
37 | return result; |
38 | ||
39 | /* The timebase will be in the 1st 1024 bytes for systems with up | |
40 | to 8 processors. If the first read returns less then 1024 | |
41 | bytes read, we have the whole cpuinfo and can start the scan. | |
42 | Otherwise we will have to read more to insure we have the | |
43 | timebase value in the scan. */ | |
44 | char buf[1024]; | |
45 | ssize_t n; | |
46 | ||
47 | n = __read_nocancel (fd, buf, sizeof (buf)); | |
48 | if (n == sizeof (buf)) | |
49 | { | |
50 | /* We are here because the 1st read returned exactly sizeof | |
51 | (buf) bytes. This implies that we are not at EOF and may | |
52 | not have read the timebase value yet. So we need to read | |
53 | more bytes until we know we have EOF. We copy the lower | |
54 | half of buf to the upper half and read sizeof (buf)/2 | |
55 | bytes into the lower half of buf and repeat until we | |
56 | reach EOF. We can assume that the timebase will be in | |
57 | the last 512 bytes of cpuinfo, so two 512 byte half_bufs | |
58 | will be sufficient to contain the timebase and will | |
59 | handle the case where the timebase spans the half_buf | |
60 | boundry. */ | |
61 | const ssize_t half_buf = sizeof (buf) / 2; | |
62 | while (n >= half_buf) | |
63 | { | |
64 | memcpy (buf, buf + half_buf, half_buf); | |
65 | n = __read_nocancel (fd, buf + half_buf, half_buf); | |
66 | } | |
67 | if (n >= 0) | |
68 | n += half_buf; | |
69 | } | |
70 | __close_nocancel (fd); | |
71 | ||
72 | if (__glibc_likely (n > 0)) | |
73 | { | |
74 | char *mhz = memmem (buf, n, "timebase", 7); | |
75 | ||
76 | if (__glibc_likely (mhz != NULL)) | |
77 | { | |
78 | char *endp = buf + n; | |
79 | ||
80 | /* Search for the beginning of the string. */ | |
81 | while (mhz < endp && (*mhz < '0' || *mhz > '9') && *mhz != '\n') | |
82 | ++mhz; | |
83 | ||
84 | while (mhz < endp && *mhz != '\n') | |
85 | { | |
86 | if (*mhz >= '0' && *mhz <= '9') | |
87 | { | |
88 | result *= 10; | |
89 | result += *mhz - '0'; | |
90 | } | |
91 | ||
92 | ++mhz; | |
93 | } | |
94 | } | |
95 | } | |
6e8ba7fd AZ |
96 | |
97 | return result; | |
8ad11b9a | 98 | } |
986a5064 AZ |
99 | |
100 | uint64_t | |
101 | __get_timebase_freq (void) | |
102 | { | |
103 | /* The vDSO does not have a fallback mechanism (such calling a syscall). */ | |
1bdda52f | 104 | uint64_t (*vdsop)(void) = GLRO(dl_vdso_get_tbfreq); |
986a5064 AZ |
105 | if (vdsop == NULL) |
106 | return get_timebase_freq_fallback (); | |
107 | ||
bc2eb932 | 108 | return INTERNAL_VSYSCALL_CALL_TYPE (vdsop, uint64_t, 0); |
986a5064 | 109 | } |
8ad11b9a | 110 | weak_alias (__get_timebase_freq, __ppc_get_timebase_freq) |