| Message ID | 20210214170940.32358-1-hauke@hauke-m.de (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | testptp: Fix compile with musl libc | expand |
Hi Hauke, On Sun, Feb 14, 2021 at 06:09:40PM +0100, Hauke Mehrtens wrote: > Musl libc does not define the glibc specific macro __GLIBC_PREREQ(), but > it has the clock_adjtime() function. Assume that a libc implementation > which does not define __GLIBC_PREREQ at all still implements > clock_adjtime(). > > This fixes a build problem with musl libc because the __GLIBC_PREREQ() > macro is missing. > > Fixes: 42e1358e103d ("ptp: In the testptp utility, use clock_adjtime from glibc when available") > Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de> > --- > tools/testing/selftests/ptp/testptp.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/tools/testing/selftests/ptp/testptp.c b/tools/testing/selftests/ptp/testptp.c > index f7911aaeb007..ecffe2c78543 100644 > --- a/tools/testing/selftests/ptp/testptp.c > +++ b/tools/testing/selftests/ptp/testptp.c > @@ -38,6 +38,7 @@ > #define NSEC_PER_SEC 1000000000LL > > /* clock_adjtime is not available in GLIBC < 2.14 */ > +#ifdef __GLIBC_PREREQ > #if !__GLIBC_PREREQ(2, 14) > #include <sys/syscall.h> > static int clock_adjtime(clockid_t id, struct timex *tx) > @@ -45,6 +46,7 @@ static int clock_adjtime(clockid_t id, struct timex *tx) > return syscall(__NR_clock_adjtime, id, tx); > } > #endif > +#endif /* __GLIBC_PREREQ */ I guess this works, but as you say, there is still an assumption to be made there, which is that all other C libraries provide the clock_adjtime syscall definition. So it is likely that this set of #if's and #ifdef's will be revisited again and again and ... Maybe this is a matter of personal preference, but I wonder if it's not actually preferable to do something like this? #include <sys/syscall.h> static int compat_clock_adjtime(clockid_t id, struct timex *tx) { return syscall(__NR_clock_adjtime, id, tx); } #define clock_adjtime compat_clock_adjtime This way, everybody uses the same definition of clock_adjtime, and we bypass the definition provided by libc if there is one, and we provide our own if there is none.
On 2/14/21 6:37 PM, Vladimir Oltean wrote: > Hi Hauke, > > On Sun, Feb 14, 2021 at 06:09:40PM +0100, Hauke Mehrtens wrote: >> Musl libc does not define the glibc specific macro __GLIBC_PREREQ(), but >> it has the clock_adjtime() function. Assume that a libc implementation >> which does not define __GLIBC_PREREQ at all still implements >> clock_adjtime(). >> >> This fixes a build problem with musl libc because the __GLIBC_PREREQ() >> macro is missing. >> >> Fixes: 42e1358e103d ("ptp: In the testptp utility, use clock_adjtime from glibc when available") >> Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de> >> --- >> tools/testing/selftests/ptp/testptp.c | 2 ++ >> 1 file changed, 2 insertions(+) >> >> diff --git a/tools/testing/selftests/ptp/testptp.c b/tools/testing/selftests/ptp/testptp.c >> index f7911aaeb007..ecffe2c78543 100644 >> --- a/tools/testing/selftests/ptp/testptp.c >> +++ b/tools/testing/selftests/ptp/testptp.c >> @@ -38,6 +38,7 @@ >> #define NSEC_PER_SEC 1000000000LL >> >> /* clock_adjtime is not available in GLIBC < 2.14 */ >> +#ifdef __GLIBC_PREREQ >> #if !__GLIBC_PREREQ(2, 14) >> #include <sys/syscall.h> >> static int clock_adjtime(clockid_t id, struct timex *tx) >> @@ -45,6 +46,7 @@ static int clock_adjtime(clockid_t id, struct timex *tx) >> return syscall(__NR_clock_adjtime, id, tx); >> } >> #endif >> +#endif /* __GLIBC_PREREQ */ > > I guess this works, but as you say, there is still an assumption to be > made there, which is that all other C libraries provide the clock_adjtime > syscall definition. So it is likely that this set of #if's and #ifdef's > will be revisited again and again and ... > > Maybe this is a matter of personal preference, but I wonder if it's not > actually preferable to do something like this? > > #include <sys/syscall.h> > > static int compat_clock_adjtime(clockid_t id, struct timex *tx) > { > return syscall(__NR_clock_adjtime, id, tx); > } > > #define clock_adjtime compat_clock_adjtime > > This way, everybody uses the same definition of clock_adjtime, and we > bypass the definition provided by libc if there is one, and we provide > our own if there is none. > Hi, glibc 2.14 was released 1. June 2011 and musl libc also supports this function since version v0.9.7 28. October 2012. I would just assume that the libc has this function. musl also does some special handling, probably for the 64 bit time handling, in this function: https://git.musl-libc.org/cgit/musl/tree/src/linux/clock_adjtime.c#n37 I am not sure if this will also work fine with the compat function. Hauke
On Sun, Feb 14, 2021 at 07:00:39PM +0100, Hauke Mehrtens wrote: > glibc 2.14 was released 1. June 2011 and musl libc also supports this > function since version v0.9.7 28. October 2012. I would just assume that the > libc has this function. Considering that somebody wanted it to work with a GNU libc prior to 2011, why would we not assume that somebody will eventually want it to work with a musl libc prior to 2012? > musl also does some special handling, probably for the 64 bit time handling, > in this function: > https://git.musl-libc.org/cgit/musl/tree/src/linux/clock_adjtime.c#n37 > I am not sure if this will also work fine with the compat function. I've stared at commit https://git.musl-libc.org/cgit/musl/commit/src/linux/clock_adjtime.c?id=2b4fd6f75b4fa66d28cddcf165ad48e8fda486d1 which added the conversion logic between struct ktimex64/struct ktimex and struct timex, and sadly I don't understand what is the point of wrapping the clock_adjtime function around the SYS_clock_adjtime64 syscall, when the struct timex::time member will still not be Y2038 safe on 32-bit systems... That being said, I didn't know that musl libc provides any wrappers around these syscalls.
diff --git a/tools/testing/selftests/ptp/testptp.c b/tools/testing/selftests/ptp/testptp.c index f7911aaeb007..ecffe2c78543 100644 --- a/tools/testing/selftests/ptp/testptp.c +++ b/tools/testing/selftests/ptp/testptp.c @@ -38,6 +38,7 @@ #define NSEC_PER_SEC 1000000000LL /* clock_adjtime is not available in GLIBC < 2.14 */ +#ifdef __GLIBC_PREREQ #if !__GLIBC_PREREQ(2, 14) #include <sys/syscall.h> static int clock_adjtime(clockid_t id, struct timex *tx) @@ -45,6 +46,7 @@ static int clock_adjtime(clockid_t id, struct timex *tx) return syscall(__NR_clock_adjtime, id, tx); } #endif +#endif /* __GLIBC_PREREQ */ static void show_flag_test(int rq_index, unsigned int flags, int err) {
Musl libc does not define the glibc specific macro __GLIBC_PREREQ(), but it has the clock_adjtime() function. Assume that a libc implementation which does not define __GLIBC_PREREQ at all still implements clock_adjtime(). This fixes a build problem with musl libc because the __GLIBC_PREREQ() macro is missing. Fixes: 42e1358e103d ("ptp: In the testptp utility, use clock_adjtime from glibc when available") Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de> --- tools/testing/selftests/ptp/testptp.c | 2 ++ 1 file changed, 2 insertions(+)