1 | /* Get the frequency of the time base. |
2 | Copyright (C) 2012-2022 Free Software Foundation, Inc. |
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 |
17 | <https://www.gnu.org/licenses/>. */ |
18 | |
19 | #include <stdint.h> |
20 | #include <string.h> |
21 | |
22 | #include <libc-internal.h> |
23 | #include <not-cancel.h> |
24 | #include <sysdep-vdso.h> |
25 | |
26 | static uint64_t |
27 | get_timebase_freq_fallback (void) |
28 | { |
29 | hp_timing_t result = 0L; |
30 | |
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); |
36 | if (__glibc_unlikely (fd == -1)) |
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 | } |
96 | |
97 | return result; |
98 | } |
99 | |
100 | uint64_t |
101 | __get_timebase_freq (void) |
102 | { |
103 | /* The vDSO does not have a fallback mechanism (such calling a syscall). */ |
104 | uint64_t (*vdsop)(void) = GLRO(dl_vdso_get_tbfreq); |
105 | if (vdsop == NULL) |
106 | return get_timebase_freq_fallback (); |
107 | |
108 | return INTERNAL_VSYSCALL_CALL_TYPE (vdsop, uint64_t, 0); |
109 | } |
110 | weak_alias (__get_timebase_freq, __ppc_get_timebase_freq) |
111 | |