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musl/src/time/clock_gettime.c

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initial check-in, version 0.5.0
15 years ago
#include <time.h>
some preliminaries for vdso clock support these changes also make it so clock_gettime(CLOCK_REALTIME, &ts) works even on pre-2.6 kernels, emulated via the gettimeofday syscall. there is no cost for the fallback check, as it falls under the error case that already must be checked for storing the error code in errno, but which would normally be hidden inside __syscall_ret.
15 years ago
#include <errno.h>
#include <stdint.h>
initial check-in, version 0.5.0
15 years ago
#include "syscall.h"
add working vdso clock_gettime support, including static linking the vdso symbol lookup code is based on the original 2011 patch by Nicholas J. Kain, with some streamlining, pointer arithmetic fixes, and one symbol version matching fix. on the consumer side (clock_gettime), per-arch macros for the particular symbol name and version to lookup are added in syscall_arch.h, and no vdso code is pulled in on archs which do not define these macros. at this time, vdso is enabled only on x86_64. the vdso support at the dynamic linker level is no longer useful to libc, but is left in place for the sake of debuggers (which may need the vdso in the link map to find its functions) and possibly use with dlsym.
12 years ago
#include "atomic.h"
initial check-in, version 0.5.0
15 years ago
improve clock_gettime and adapt it to support slightly-broken vdso these changes are motivated by a functionally similar patch by Hauke Mehrtens to address the needs of the new mips vdso clock_gettime, which wrongly fails with ENOSYS rather than falling back to making a syscall for clock ids it cannot handle from userspace. in the process of preparing to handle that case, it was noticed that the old clock_gettime use of the vdso was actually wrong with respect to error handling -- the tail call to the vdso function failed to set errno and instead returned an error code. since tail calls to vdso are no longer possible and since the plain syscall code is now needed as a fallback path anyway, it does not make sense to use a function pointer to call the plain syscall code path. instead, it's inlined at the end of the main clock_gettime function. the new code also avoids the need to test for initialization of the vdso function pointer by statically initializing it to a self-init function, and eliminates redundant loads from the volatile pointer object. finally, the use of a_cas_p on an object of type other than void *, which is not permitted aliasing, is replaced by using an object with the correct type and casting the value.
10 years ago
#ifdef VDSO_CGT_SYM
static void *volatile vdso_func;
clock_gettime: add support for 32-bit vdso with 64-bit time_t this fixes a major upcoming performance regression introduced by commit 72f50245d018af0c31b38dec83c557a4e5dd1ea8, whereby 32-bit archs would lose vdso clock_gettime after switching to 64-bit time_t, unless the kernel supports time64 and provides a time64 version of the vdso function. this would incur not just one but two syscalls: first, the failed time64 syscall, then the fallback time32 one. overflow of the 32-bit result is detected and triggers a revert to syscalls. normally, on a system that's not Y2038-ready, this would still overflow, but if the process has been migrated to a time64-capable kernel or if the kernel has been hot-patched to add time64 syscalls, it may conceivably work.
7 years ago
#ifdef VDSO_CGT32_SYM
static void *volatile vdso_func_32;
static int cgt_time32_wrap(clockid_t clk, struct timespec *ts)
{
long ts32[2];
int (*f)(clockid_t, long[2]) =
(int (*)(clockid_t, long[2]))vdso_func_32;
int r = f(clk, ts32);
if (!r) {
/* Fallback to syscalls if time32 overflowed. Maybe
* we lucked out and somehow migrated to a kernel with
* time64 syscalls available. */
if (ts32[0] < 0) {
a_cas_p(&vdso_func, (void *)cgt_time32_wrap, 0);
return -ENOSYS;
}
ts->tv_sec = ts32[0];
ts->tv_nsec = ts32[1];
}
return r;
}
#endif
improve clock_gettime and adapt it to support slightly-broken vdso these changes are motivated by a functionally similar patch by Hauke Mehrtens to address the needs of the new mips vdso clock_gettime, which wrongly fails with ENOSYS rather than falling back to making a syscall for clock ids it cannot handle from userspace. in the process of preparing to handle that case, it was noticed that the old clock_gettime use of the vdso was actually wrong with respect to error handling -- the tail call to the vdso function failed to set errno and instead returned an error code. since tail calls to vdso are no longer possible and since the plain syscall code is now needed as a fallback path anyway, it does not make sense to use a function pointer to call the plain syscall code path. instead, it's inlined at the end of the main clock_gettime function. the new code also avoids the need to test for initialization of the vdso function pointer by statically initializing it to a self-init function, and eliminates redundant loads from the volatile pointer object. finally, the use of a_cas_p on an object of type other than void *, which is not permitted aliasing, is replaced by using an object with the correct type and casting the value.
10 years ago
static int cgt_init(clockid_t clk, struct timespec *ts)
initial check-in, version 0.5.0
15 years ago
{
improve clock_gettime and adapt it to support slightly-broken vdso these changes are motivated by a functionally similar patch by Hauke Mehrtens to address the needs of the new mips vdso clock_gettime, which wrongly fails with ENOSYS rather than falling back to making a syscall for clock ids it cannot handle from userspace. in the process of preparing to handle that case, it was noticed that the old clock_gettime use of the vdso was actually wrong with respect to error handling -- the tail call to the vdso function failed to set errno and instead returned an error code. since tail calls to vdso are no longer possible and since the plain syscall code is now needed as a fallback path anyway, it does not make sense to use a function pointer to call the plain syscall code path. instead, it's inlined at the end of the main clock_gettime function. the new code also avoids the need to test for initialization of the vdso function pointer by statically initializing it to a self-init function, and eliminates redundant loads from the volatile pointer object. finally, the use of a_cas_p on an object of type other than void *, which is not permitted aliasing, is replaced by using an object with the correct type and casting the value.
10 years ago
void *p = __vdsosym(VDSO_CGT_VER, VDSO_CGT_SYM);
clock_gettime: add support for 32-bit vdso with 64-bit time_t this fixes a major upcoming performance regression introduced by commit 72f50245d018af0c31b38dec83c557a4e5dd1ea8, whereby 32-bit archs would lose vdso clock_gettime after switching to 64-bit time_t, unless the kernel supports time64 and provides a time64 version of the vdso function. this would incur not just one but two syscalls: first, the failed time64 syscall, then the fallback time32 one. overflow of the 32-bit result is detected and triggers a revert to syscalls. normally, on a system that's not Y2038-ready, this would still overflow, but if the process has been migrated to a time64-capable kernel or if the kernel has been hot-patched to add time64 syscalls, it may conceivably work.
7 years ago
#ifdef VDSO_CGT32_SYM
if (!p) {
void *q = __vdsosym(VDSO_CGT32_VER, VDSO_CGT32_SYM);
if (q) {
a_cas_p(&vdso_func_32, 0, q);
p = cgt_time32_wrap;
}
}
#endif
improve clock_gettime and adapt it to support slightly-broken vdso these changes are motivated by a functionally similar patch by Hauke Mehrtens to address the needs of the new mips vdso clock_gettime, which wrongly fails with ENOSYS rather than falling back to making a syscall for clock ids it cannot handle from userspace. in the process of preparing to handle that case, it was noticed that the old clock_gettime use of the vdso was actually wrong with respect to error handling -- the tail call to the vdso function failed to set errno and instead returned an error code. since tail calls to vdso are no longer possible and since the plain syscall code is now needed as a fallback path anyway, it does not make sense to use a function pointer to call the plain syscall code path. instead, it's inlined at the end of the main clock_gettime function. the new code also avoids the need to test for initialization of the vdso function pointer by statically initializing it to a self-init function, and eliminates redundant loads from the volatile pointer object. finally, the use of a_cas_p on an object of type other than void *, which is not permitted aliasing, is replaced by using an object with the correct type and casting the value.
10 years ago
int (*f)(clockid_t, struct timespec *) =
(int (*)(clockid_t, struct timespec *))p;
a_cas_p(&vdso_func, (void *)cgt_init, p);
return f ? f(clk, ts) : -ENOSYS;
initial check-in, version 0.5.0
15 years ago
}
some preliminaries for vdso clock support these changes also make it so clock_gettime(CLOCK_REALTIME, &ts) works even on pre-2.6 kernels, emulated via the gettimeofday syscall. there is no cost for the fallback check, as it falls under the error case that already must be checked for storing the error code in errno, but which would normally be hidden inside __syscall_ret.
15 years ago
improve clock_gettime and adapt it to support slightly-broken vdso these changes are motivated by a functionally similar patch by Hauke Mehrtens to address the needs of the new mips vdso clock_gettime, which wrongly fails with ENOSYS rather than falling back to making a syscall for clock ids it cannot handle from userspace. in the process of preparing to handle that case, it was noticed that the old clock_gettime use of the vdso was actually wrong with respect to error handling -- the tail call to the vdso function failed to set errno and instead returned an error code. since tail calls to vdso are no longer possible and since the plain syscall code is now needed as a fallback path anyway, it does not make sense to use a function pointer to call the plain syscall code path. instead, it's inlined at the end of the main clock_gettime function. the new code also avoids the need to test for initialization of the vdso function pointer by statically initializing it to a self-init function, and eliminates redundant loads from the volatile pointer object. finally, the use of a_cas_p on an object of type other than void *, which is not permitted aliasing, is replaced by using an object with the correct type and casting the value.
10 years ago
static void *volatile vdso_func = (void *)cgt_init;
#endif
use weak aliase rather than weak reference for vdso clock_gettime this works around pcc's lack of working support for weak references, and in principle is nice because it gets us back to the stage where the only weak symbol feature we use is weak aliases, nothing else. having fewer dependencies on fancy linker features is a good thing.
15 years ago
int __clock_gettime(clockid_t clk, struct timespec *ts)
{
improve clock_gettime and adapt it to support slightly-broken vdso these changes are motivated by a functionally similar patch by Hauke Mehrtens to address the needs of the new mips vdso clock_gettime, which wrongly fails with ENOSYS rather than falling back to making a syscall for clock ids it cannot handle from userspace. in the process of preparing to handle that case, it was noticed that the old clock_gettime use of the vdso was actually wrong with respect to error handling -- the tail call to the vdso function failed to set errno and instead returned an error code. since tail calls to vdso are no longer possible and since the plain syscall code is now needed as a fallback path anyway, it does not make sense to use a function pointer to call the plain syscall code path. instead, it's inlined at the end of the main clock_gettime function. the new code also avoids the need to test for initialization of the vdso function pointer by statically initializing it to a self-init function, and eliminates redundant loads from the volatile pointer object. finally, the use of a_cas_p on an object of type other than void *, which is not permitted aliasing, is replaced by using an object with the correct type and casting the value.
10 years ago
int r;
add working vdso clock_gettime support, including static linking the vdso symbol lookup code is based on the original 2011 patch by Nicholas J. Kain, with some streamlining, pointer arithmetic fixes, and one symbol version matching fix. on the consumer side (clock_gettime), per-arch macros for the particular symbol name and version to lookup are added in syscall_arch.h, and no vdso code is pulled in on archs which do not define these macros. at this time, vdso is enabled only on x86_64. the vdso support at the dynamic linker level is no longer useful to libc, but is left in place for the sake of debuggers (which may need the vdso in the link map to find its functions) and possibly use with dlsym.
12 years ago
#ifdef VDSO_CGT_SYM
improve clock_gettime and adapt it to support slightly-broken vdso these changes are motivated by a functionally similar patch by Hauke Mehrtens to address the needs of the new mips vdso clock_gettime, which wrongly fails with ENOSYS rather than falling back to making a syscall for clock ids it cannot handle from userspace. in the process of preparing to handle that case, it was noticed that the old clock_gettime use of the vdso was actually wrong with respect to error handling -- the tail call to the vdso function failed to set errno and instead returned an error code. since tail calls to vdso are no longer possible and since the plain syscall code is now needed as a fallback path anyway, it does not make sense to use a function pointer to call the plain syscall code path. instead, it's inlined at the end of the main clock_gettime function. the new code also avoids the need to test for initialization of the vdso function pointer by statically initializing it to a self-init function, and eliminates redundant loads from the volatile pointer object. finally, the use of a_cas_p on an object of type other than void *, which is not permitted aliasing, is replaced by using an object with the correct type and casting the value.
10 years ago
int (*f)(clockid_t, struct timespec *) =
(int (*)(clockid_t, struct timespec *))vdso_func;
if (f) {
r = f(clk, ts);
if (!r) return r;
if (r == -EINVAL) return __syscall_ret(r);
/* Fall through on errors other than EINVAL. Some buggy
* vdso implementations return ENOSYS for clocks they
* can't handle, rather than making the syscall. This
* also handles the case where cgt_init fails to find
* a vdso function to use. */
add working vdso clock_gettime support, including static linking the vdso symbol lookup code is based on the original 2011 patch by Nicholas J. Kain, with some streamlining, pointer arithmetic fixes, and one symbol version matching fix. on the consumer side (clock_gettime), per-arch macros for the particular symbol name and version to lookup are added in syscall_arch.h, and no vdso code is pulled in on archs which do not define these macros. at this time, vdso is enabled only on x86_64. the vdso support at the dynamic linker level is no longer useful to libc, but is left in place for the sake of debuggers (which may need the vdso in the link map to find its functions) and possibly use with dlsym.
12 years ago
}
#endif
improve clock_gettime and adapt it to support slightly-broken vdso these changes are motivated by a functionally similar patch by Hauke Mehrtens to address the needs of the new mips vdso clock_gettime, which wrongly fails with ENOSYS rather than falling back to making a syscall for clock ids it cannot handle from userspace. in the process of preparing to handle that case, it was noticed that the old clock_gettime use of the vdso was actually wrong with respect to error handling -- the tail call to the vdso function failed to set errno and instead returned an error code. since tail calls to vdso are no longer possible and since the plain syscall code is now needed as a fallback path anyway, it does not make sense to use a function pointer to call the plain syscall code path. instead, it's inlined at the end of the main clock_gettime function. the new code also avoids the need to test for initialization of the vdso function pointer by statically initializing it to a self-init function, and eliminates redundant loads from the volatile pointer object. finally, the use of a_cas_p on an object of type other than void *, which is not permitted aliasing, is replaced by using an object with the correct type and casting the value.
10 years ago
clock_gettime: add time64 syscall support, decouple 32-bit time_t the time64 syscall has to be used if time_t is 64-bit, since there's no way of knowing before making a syscall whether the result will fit in 32 bits, and the 32-bit syscalls do not report overflow as an error. on 64-bit archs, there is no change to the code after preprocessing. on current 32-bit archs, the result is now read from the kernel through long[2] array, then copied into the timespec, to remove the assumption that time_t is the same as long. vdso clock_gettime is still used in place of a syscall if available. 32-bit archs with 64-bit time_t must use the time64 version of the vdso function; if it's not available, performance will significantly suffer. support for both vdso functions could be added, but would break the ability to move a long-lived process from a pre-time64 kernel to one that can outlast Y2038 with checkpoint/resume, at least without added hacks to identify that the 32-bit function is no longer usable and stop using it (e.g. by seeing negative tv_sec). this possibility may be explored in future work on the function.
7 years ago
#ifdef SYS_clock_gettime64
fix regression in clock_gettime on 32-bit archs without vdso commit 72f50245d018af0c31b38dec83c557a4e5dd1ea8 broke this by creating a code path where r is uninitialized.
7 years ago
r = -ENOSYS;
clock_gettime: add time64 syscall support, decouple 32-bit time_t the time64 syscall has to be used if time_t is 64-bit, since there's no way of knowing before making a syscall whether the result will fit in 32 bits, and the 32-bit syscalls do not report overflow as an error. on 64-bit archs, there is no change to the code after preprocessing. on current 32-bit archs, the result is now read from the kernel through long[2] array, then copied into the timespec, to remove the assumption that time_t is the same as long. vdso clock_gettime is still used in place of a syscall if available. 32-bit archs with 64-bit time_t must use the time64 version of the vdso function; if it's not available, performance will significantly suffer. support for both vdso functions could be added, but would break the ability to move a long-lived process from a pre-time64 kernel to one that can outlast Y2038 with checkpoint/resume, at least without added hacks to identify that the 32-bit function is no longer usable and stop using it (e.g. by seeing negative tv_sec). this possibility may be explored in future work on the function.
7 years ago
if (sizeof(time_t) > 4)
r = __syscall(SYS_clock_gettime64, clk, ts);
if (SYS_clock_gettime == SYS_clock_gettime64 || r!=-ENOSYS)
return __syscall_ret(r);
long ts32[2];
r = __syscall(SYS_clock_gettime, clk, ts32);
if (r==-ENOSYS && clk==CLOCK_REALTIME) {
r = __syscall(SYS_gettimeofday, ts32, 0);
ts32[1] *= 1000;
}
if (!r) {
ts->tv_sec = ts32[0];
ts->tv_nsec = ts32[1];
return r;
}
return __syscall_ret(r);
#else
improve clock_gettime and adapt it to support slightly-broken vdso these changes are motivated by a functionally similar patch by Hauke Mehrtens to address the needs of the new mips vdso clock_gettime, which wrongly fails with ENOSYS rather than falling back to making a syscall for clock ids it cannot handle from userspace. in the process of preparing to handle that case, it was noticed that the old clock_gettime use of the vdso was actually wrong with respect to error handling -- the tail call to the vdso function failed to set errno and instead returned an error code. since tail calls to vdso are no longer possible and since the plain syscall code is now needed as a fallback path anyway, it does not make sense to use a function pointer to call the plain syscall code path. instead, it's inlined at the end of the main clock_gettime function. the new code also avoids the need to test for initialization of the vdso function pointer by statically initializing it to a self-init function, and eliminates redundant loads from the volatile pointer object. finally, the use of a_cas_p on an object of type other than void *, which is not permitted aliasing, is replaced by using an object with the correct type and casting the value.
10 years ago
r = __syscall(SYS_clock_gettime, clk, ts);
if (r == -ENOSYS) {
if (clk == CLOCK_REALTIME) {
__syscall(SYS_gettimeofday, ts, 0);
ts->tv_nsec = (int)ts->tv_nsec * 1000;
return 0;
}
r = -EINVAL;
}
return __syscall_ret(r);
clock_gettime: add time64 syscall support, decouple 32-bit time_t the time64 syscall has to be used if time_t is 64-bit, since there's no way of knowing before making a syscall whether the result will fit in 32 bits, and the 32-bit syscalls do not report overflow as an error. on 64-bit archs, there is no change to the code after preprocessing. on current 32-bit archs, the result is now read from the kernel through long[2] array, then copied into the timespec, to remove the assumption that time_t is the same as long. vdso clock_gettime is still used in place of a syscall if available. 32-bit archs with 64-bit time_t must use the time64 version of the vdso function; if it's not available, performance will significantly suffer. support for both vdso functions could be added, but would break the ability to move a long-lived process from a pre-time64 kernel to one that can outlast Y2038 with checkpoint/resume, at least without added hacks to identify that the 32-bit function is no longer usable and stop using it (e.g. by seeing negative tv_sec). this possibility may be explored in future work on the function.
7 years ago
#endif
use weak aliase rather than weak reference for vdso clock_gettime this works around pcc's lack of working support for weak references, and in principle is nice because it gets us back to the stage where the only weak symbol feature we use is weak aliases, nothing else. having fewer dependencies on fancy linker features is a good thing.
15 years ago
}
some preliminaries for vdso clock support these changes also make it so clock_gettime(CLOCK_REALTIME, &ts) works even on pre-2.6 kernels, emulated via the gettimeofday syscall. there is no cost for the fallback check, as it falls under the error case that already must be checked for storing the error code in errno, but which would normally be hidden inside __syscall_ret.
15 years ago
weak_alias(__clock_gettime, clock_gettime);