| Message ID | 20211105163137.3324344-2-anders.roxell@linaro.org (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [1/2] selftests: timens: use 'llabs()' over 'abs()' | expand |
On Fri, Nov 5, 2021 at 9:31 AM Anders Roxell <anders.roxell@linaro.org> wrote: > > When building selftests/timens with clang, the compiler warn about the > function abs() see below: > > exec.c:33:8: error: absolute value function 'abs' given an argument of type 'long' but has parameter of type 'int' which may cause truncation of value [-Werror,-Wabsolute-value] > if (abs(tst.tv_sec - now.tv_sec) > 5) > ^ > exec.c:33:8: note: use function 'labs' instead > if (abs(tst.tv_sec - now.tv_sec) > 5) > ^~~ > labs Careful. Isn't the tv_sec member of `struct timespec` a `time_t` which is 32b on 32b hosts and 64b on 64b hosts? If I'm recalling that correctly, then this patch results in a harmless (though unnecessary) sign extension for 32b targets. That should be fine, but someone like Arnd should triple check if my concern is valid or not. So I'm in favor of this patch (dispatching to abs or labs based on 64b host) would hurt readability. > > The note indicates what to do, Rework to use the function 'labs()'. > > Signed-off-by: Anders Roxell <anders.roxell@linaro.org> > --- > tools/testing/selftests/timens/exec.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/tools/testing/selftests/timens/exec.c b/tools/testing/selftests/timens/exec.c > index e40dc5be2f66..d12ff955de0d 100644 > --- a/tools/testing/selftests/timens/exec.c > +++ b/tools/testing/selftests/timens/exec.c > @@ -30,7 +30,7 @@ int main(int argc, char *argv[]) > > for (i = 0; i < 2; i++) { > _gettime(CLOCK_MONOTONIC, &tst, i); > - if (abs(tst.tv_sec - now.tv_sec) > 5) > + if (labs(tst.tv_sec - now.tv_sec) > 5) > return pr_fail("%ld %ld\n", now.tv_sec, tst.tv_sec); > } > return 0; > @@ -50,7 +50,7 @@ int main(int argc, char *argv[]) > > for (i = 0; i < 2; i++) { > _gettime(CLOCK_MONOTONIC, &tst, i); > - if (abs(tst.tv_sec - now.tv_sec) > 5) > + if (labs(tst.tv_sec - now.tv_sec) > 5) > return pr_fail("%ld %ld\n", > now.tv_sec, tst.tv_sec); > } > @@ -70,7 +70,7 @@ int main(int argc, char *argv[]) > /* Check that a child process is in the new timens. */ > for (i = 0; i < 2; i++) { > _gettime(CLOCK_MONOTONIC, &tst, i); > - if (abs(tst.tv_sec - now.tv_sec - OFFSET) > 5) > + if (labs(tst.tv_sec - now.tv_sec - OFFSET) > 5) > return pr_fail("%ld %ld\n", > now.tv_sec + OFFSET, tst.tv_sec); > } > -- > 2.33.0 >
On Fri, Nov 5, 2021 at 9:35 PM Nick Desaulniers <ndesaulniers@google.com> wrote: > > On Fri, Nov 5, 2021 at 9:31 AM Anders Roxell <anders.roxell@linaro.org> wrote: > > > > When building selftests/timens with clang, the compiler warn about the > > function abs() see below: > > > > exec.c:33:8: error: absolute value function 'abs' given an argument of type 'long' but has parameter of type 'int' which may cause truncation of value [-Werror,-Wabsolute-value] > > if (abs(tst.tv_sec - now.tv_sec) > 5) > > ^ > > exec.c:33:8: note: use function 'labs' instead > > if (abs(tst.tv_sec - now.tv_sec) > 5) > > ^~~ > > labs > > Careful. > > Isn't the tv_sec member of `struct timespec` a `time_t` which is 32b > on 32b hosts and 64b on 64b hosts? If I'm recalling that correctly, > then this patch results in a harmless (though unnecessary) sign > extension for 32b targets. That should be fine, but someone like Arnd > should triple check if my concern is valid or not. It could actually be 'int', 'long' or 'long long' depending on the architecture and C library. Maybe we need a temporary variable of type 'long long' to hold the difference, and pass that to llabs()? Arnd
On Fri, Nov 5, 2021 at 1:45 PM Arnd Bergmann <arnd@kernel.org> wrote: > > On Fri, Nov 5, 2021 at 9:35 PM Nick Desaulniers <ndesaulniers@google.com> wrote: > > > > On Fri, Nov 5, 2021 at 9:31 AM Anders Roxell <anders.roxell@linaro.org> wrote: > > > > > > When building selftests/timens with clang, the compiler warn about the > > > function abs() see below: > > > > > > exec.c:33:8: error: absolute value function 'abs' given an argument of type 'long' but has parameter of type 'int' which may cause truncation of value [-Werror,-Wabsolute-value] > > > if (abs(tst.tv_sec - now.tv_sec) > 5) > > > ^ > > > exec.c:33:8: note: use function 'labs' instead > > > if (abs(tst.tv_sec - now.tv_sec) > 5) > > > ^~~ > > > labs > > > > Careful. > > > > Isn't the tv_sec member of `struct timespec` a `time_t` which is 32b > > on 32b hosts and 64b on 64b hosts? If I'm recalling that correctly, > > then this patch results in a harmless (though unnecessary) sign > > extension for 32b targets. That should be fine, but someone like Arnd > > should triple check if my concern is valid or not. > > It could actually be 'int', 'long' or 'long long' depending on the architecture > and C library. Maybe we need a temporary variable of type 'long long' > to hold the difference, and pass that to llabs()? Yeah, that SGTM. Thanks for the review!
diff --git a/tools/testing/selftests/timens/exec.c b/tools/testing/selftests/timens/exec.c index e40dc5be2f66..d12ff955de0d 100644 --- a/tools/testing/selftests/timens/exec.c +++ b/tools/testing/selftests/timens/exec.c @@ -30,7 +30,7 @@ int main(int argc, char *argv[]) for (i = 0; i < 2; i++) { _gettime(CLOCK_MONOTONIC, &tst, i); - if (abs(tst.tv_sec - now.tv_sec) > 5) + if (labs(tst.tv_sec - now.tv_sec) > 5) return pr_fail("%ld %ld\n", now.tv_sec, tst.tv_sec); } return 0; @@ -50,7 +50,7 @@ int main(int argc, char *argv[]) for (i = 0; i < 2; i++) { _gettime(CLOCK_MONOTONIC, &tst, i); - if (abs(tst.tv_sec - now.tv_sec) > 5) + if (labs(tst.tv_sec - now.tv_sec) > 5) return pr_fail("%ld %ld\n", now.tv_sec, tst.tv_sec); } @@ -70,7 +70,7 @@ int main(int argc, char *argv[]) /* Check that a child process is in the new timens. */ for (i = 0; i < 2; i++) { _gettime(CLOCK_MONOTONIC, &tst, i); - if (abs(tst.tv_sec - now.tv_sec - OFFSET) > 5) + if (labs(tst.tv_sec - now.tv_sec - OFFSET) > 5) return pr_fail("%ld %ld\n", now.tv_sec + OFFSET, tst.tv_sec); }
When building selftests/timens with clang, the compiler warn about the function abs() see below: exec.c:33:8: error: absolute value function 'abs' given an argument of type 'long' but has parameter of type 'int' which may cause truncation of value [-Werror,-Wabsolute-value] if (abs(tst.tv_sec - now.tv_sec) > 5) ^ exec.c:33:8: note: use function 'labs' instead if (abs(tst.tv_sec - now.tv_sec) > 5) ^~~ labs The note indicates what to do, Rework to use the function 'labs()'. Signed-off-by: Anders Roxell <anders.roxell@linaro.org> --- tools/testing/selftests/timens/exec.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)