| Message ID | 20240503023209.80787-1-jhubbard@nvidia.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | selftests/resctrl: fix clang build warnings related to abs(), labs() calls | expand |
On Thu, 2 May 2024, John Hubbard wrote: > First of all, in order to build with clang at all, one must first apply > Valentin Obst's build fix for LLVM [1]. Furthermore, for this particular > resctrl directory, my pending fix [2] must also be applied. Once those > fixes are in place, then when building with clang, via: > > make LLVM=1 -C tools/testing/selftests > > ..two types of warnings occur: > > warning: absolute value function 'abs' given an argument of type > 'long' but has parameter of type 'int' which may cause truncation of > value > > warning: taking the absolute value of unsigned type 'unsigned long' > has no effect > > Fix these by: > > a) using labs() in place of abs(), when long integers are involved, and > > b) don't call labs() unnecessarily. > > [1] https://lore.kernel.org/all/20240329-selftests-libmk-llvm-rfc-v1-1-2f9ed7d1c49f@valentinobst.de/ > [2] https://lore.kernel.org/all/20240503021712.78601-1-jhubbard@nvidia.com/ > > Signed-off-by: John Hubbard <jhubbard@nvidia.com> > --- > tools/testing/selftests/resctrl/cmt_test.c | 4 ++-- > tools/testing/selftests/resctrl/mba_test.c | 2 +- > tools/testing/selftests/resctrl/mbm_test.c | 2 +- > 3 files changed, 4 insertions(+), 4 deletions(-) > > diff --git a/tools/testing/selftests/resctrl/cmt_test.c b/tools/testing/selftests/resctrl/cmt_test.c > index a81f91222a89..05a241519ae8 100644 > --- a/tools/testing/selftests/resctrl/cmt_test.c > +++ b/tools/testing/selftests/resctrl/cmt_test.c > @@ -40,11 +40,11 @@ static int show_results_info(unsigned long sum_llc_val, int no_of_bits, > int ret; > > avg_llc_val = sum_llc_val / num_of_runs; > - avg_diff = (long)abs(cache_span - avg_llc_val); > + avg_diff = (long)(cache_span - avg_llc_val); > diff_percent = ((float)cache_span - avg_llc_val) / cache_span * 100; > > ret = platform && abs((int)diff_percent) > max_diff_percent && > - abs(avg_diff) > max_diff; > + labs(avg_diff) > max_diff; > > ksft_print_msg("%s Check cache miss rate within %lu%%\n", > ret ? "Fail:" : "Pass:", max_diff_percent); This seems fine but... > diff --git a/tools/testing/selftests/resctrl/mba_test.c b/tools/testing/selftests/resctrl/mba_test.c > index 7946e32e85c8..673b2bb800f7 100644 > --- a/tools/testing/selftests/resctrl/mba_test.c > +++ b/tools/testing/selftests/resctrl/mba_test.c > @@ -77,7 +77,7 @@ static bool show_mba_info(unsigned long *bw_imc, unsigned long *bw_resc) > > avg_bw_imc = sum_bw_imc / (NUM_OF_RUNS - 1); > avg_bw_resc = sum_bw_resc / (NUM_OF_RUNS - 1); > - avg_diff = (float)labs(avg_bw_resc - avg_bw_imc) / avg_bw_imc; > + avg_diff = (float)(avg_bw_resc - avg_bw_imc) / avg_bw_imc; > avg_diff_per = (int)(avg_diff * 100); > > ksft_print_msg("%s Check MBA diff within %d%% for schemata %u\n", > diff --git a/tools/testing/selftests/resctrl/mbm_test.c b/tools/testing/selftests/resctrl/mbm_test.c > index d67ffa3ec63a..c873793d016d 100644 > --- a/tools/testing/selftests/resctrl/mbm_test.c > +++ b/tools/testing/selftests/resctrl/mbm_test.c > @@ -33,7 +33,7 @@ show_bw_info(unsigned long *bw_imc, unsigned long *bw_resc, size_t span) > > avg_bw_imc = sum_bw_imc / 4; > avg_bw_resc = sum_bw_resc / 4; > - avg_diff = (float)labs(avg_bw_resc - avg_bw_imc) / avg_bw_imc; > + avg_diff = (float)(avg_bw_resc - avg_bw_imc) / avg_bw_imc; > avg_diff_per = (int)(avg_diff * 100); > > ret = avg_diff_per > MAX_DIFF_PERCENT; But how are these two cases same after your change when you ended up removing taking the absolute value entirely?
On 5/3/2024 9:52 AM, John Hubbard wrote: > On 5/3/24 1:00 AM, Ilpo Järvinen wrote: >> On Thu, 2 May 2024, John Hubbard wrote: > ... >>> diff --git a/tools/testing/selftests/resctrl/mbm_test.c b/tools/testing/selftests/resctrl/mbm_test.c >>> index d67ffa3ec63a..c873793d016d 100644 >>> --- a/tools/testing/selftests/resctrl/mbm_test.c >>> +++ b/tools/testing/selftests/resctrl/mbm_test.c >>> @@ -33,7 +33,7 @@ show_bw_info(unsigned long *bw_imc, unsigned long *bw_resc, size_t span) >>> avg_bw_imc = sum_bw_imc / 4; >>> avg_bw_resc = sum_bw_resc / 4; >>> - avg_diff = (float)labs(avg_bw_resc - avg_bw_imc) / avg_bw_imc; >>> + avg_diff = (float)(avg_bw_resc - avg_bw_imc) / avg_bw_imc; >>> avg_diff_per = (int)(avg_diff * 100); >>> ret = avg_diff_per > MAX_DIFF_PERCENT; >> >> But how are these two cases same after your change when you ended up >> removing taking the absolute value entirely? > > All of the arguments are unsigned integers, so all arithmetic results > are interpreted as unsigned, so taking the absolute value of that is > always a no-op. It does not seem as though clang can see when values have been casted. I tried to do so explicitly with a: avg_diff = labs((long)avg_bw_resc - avg_bw_imc) / (float)avg_bw_imc; But that still triggers: warning: taking the absolute value of unsigned type 'unsigned long' has no effect [-Wabsolute-value] Looks like we may need to be more explicit types and not rely on casting so much to make the compiler happy. Reinette
On 5/3/24 11:37 AM, Reinette Chatre wrote: > On 5/3/2024 9:52 AM, John Hubbard wrote: >> On 5/3/24 1:00 AM, Ilpo Järvinen wrote: >>> On Thu, 2 May 2024, John Hubbard wrote: >> ... >>>> diff --git a/tools/testing/selftests/resctrl/mbm_test.c b/tools/testing/selftests/resctrl/mbm_test.c >>>> index d67ffa3ec63a..c873793d016d 100644 >>>> --- a/tools/testing/selftests/resctrl/mbm_test.c >>>> +++ b/tools/testing/selftests/resctrl/mbm_test.c >>>> @@ -33,7 +33,7 @@ show_bw_info(unsigned long *bw_imc, unsigned long *bw_resc, size_t span) >>>> avg_bw_imc = sum_bw_imc / 4; >>>> avg_bw_resc = sum_bw_resc / 4; >>>> - avg_diff = (float)labs(avg_bw_resc - avg_bw_imc) / avg_bw_imc; >>>> + avg_diff = (float)(avg_bw_resc - avg_bw_imc) / avg_bw_imc; >>>> avg_diff_per = (int)(avg_diff * 100); >>>> ret = avg_diff_per > MAX_DIFF_PERCENT; >>> >>> But how are these two cases same after your change when you ended up >>> removing taking the absolute value entirely? >> >> All of the arguments are unsigned integers, so all arithmetic results >> are interpreted as unsigned, so taking the absolute value of that is >> always a no-op. > > It does not seem as though clang can see when values have been casted. > I tried to do so explicitly with a: > avg_diff = labs((long)avg_bw_resc - avg_bw_imc) / (float)avg_bw_imc; The subtraction result will get promoted to an unsigned long, before being passed into labs(3). > > But that still triggers: > warning: taking the absolute value of unsigned type 'unsigned long' has no effect [-Wabsolute-value] As expected, yes. > > Looks like we may need to be more explicit types and not rely on casting so much > to make the compiler happy. > I assumed that this code did not expect to handle negative numbers, because it is using unsigned math throughout. If you do expect it to handle cases where, for example, this happens: avg_bw_imc > avg_bw_resc ...then a proper solution is easy, and looks like this: diff --git a/tools/testing/selftests/resctrl/mbm_test.c b/tools/testing/selftests/resctrl/mbm_test.c index c873793d016d..b87f91a41494 100644 --- a/tools/testing/selftests/resctrl/mbm_test.c +++ b/tools/testing/selftests/resctrl/mbm_test.c @@ -17,8 +17,8 @@ static int show_bw_info(unsigned long *bw_imc, unsigned long *bw_resc, size_t span) { - unsigned long avg_bw_imc = 0, avg_bw_resc = 0; - unsigned long sum_bw_imc = 0, sum_bw_resc = 0; + long avg_bw_imc = 0, avg_bw_resc = 0; + long sum_bw_imc = 0, sum_bw_resc = 0; int runs, ret, avg_diff_per; float avg_diff = 0; Should I resend the patch with that approach? thanks,
On Fri, 3 May 2024, John Hubbard wrote: > On 5/3/24 11:37 AM, Reinette Chatre wrote: > > On 5/3/2024 9:52 AM, John Hubbard wrote: > > > On 5/3/24 1:00 AM, Ilpo Järvinen wrote: > > > > On Thu, 2 May 2024, John Hubbard wrote: > > > ... > > > > > diff --git a/tools/testing/selftests/resctrl/mbm_test.c > > > > > b/tools/testing/selftests/resctrl/mbm_test.c > > > > > index d67ffa3ec63a..c873793d016d 100644 > > > > > --- a/tools/testing/selftests/resctrl/mbm_test.c > > > > > +++ b/tools/testing/selftests/resctrl/mbm_test.c > > > > > @@ -33,7 +33,7 @@ show_bw_info(unsigned long *bw_imc, unsigned long > > > > > *bw_resc, size_t span) > > > > > avg_bw_imc = sum_bw_imc / 4; > > > > > avg_bw_resc = sum_bw_resc / 4; > > > > > - avg_diff = (float)labs(avg_bw_resc - avg_bw_imc) / avg_bw_imc; > > > > > + avg_diff = (float)(avg_bw_resc - avg_bw_imc) / avg_bw_imc; > > > > > avg_diff_per = (int)(avg_diff * 100); > > > > > ret = avg_diff_per > MAX_DIFF_PERCENT; > > > > > > > > But how are these two cases same after your change when you ended up > > > > removing taking the absolute value entirely? > > > > > > All of the arguments are unsigned integers, so all arithmetic results > > > are interpreted as unsigned, so taking the absolute value of that is > > > always a no-op. (I see there's a better patch posted already but since there are a few incorrect claims in this discussion, I'll do for the record type of reply.) This discussion now went to a tangent about the warning. My main point is that logic is not correct after removing labs(). I also disagree with the claim that using labs() on unsigned value is no-op because labs() takes long so unsigned is just forced into signed when calling which is why the warning triggers but it's very misleading warning (see below). > > It does not seem as though clang can see when values have been casted. > > I tried to do so explicitly with a: > > avg_diff = labs((long)avg_bw_resc - avg_bw_imc) / (float)avg_bw_imc; > > The subtraction result will get promoted to an unsigned long, before being > passed into labs(3). > > > But that still triggers: > > warning: taking the absolute value of unsigned type 'unsigned long' has no > > effect [-Wabsolute-value] > > As expected, yes. That error message isn't factually correct: unsigned long a = LONG_MAX; long b; a += 2; b = (long)a; printf("%llu %lli %lli\n", a, b, labs(a)); Prints (at least when built with gcc): 9223372036854775809 -9223372036854775807 9223372036854775807 labs(LONG_MAX + 1) won't work though since it's not positively presentable with long and the value is left untouched.
On 5/6/24 2:07 AM, Ilpo Järvinen wrote: > On Fri, 3 May 2024, John Hubbard wrote: > >> On 5/3/24 11:37 AM, Reinette Chatre wrote: >>> On 5/3/2024 9:52 AM, John Hubbard wrote: >>>> On 5/3/24 1:00 AM, Ilpo Järvinen wrote: >>>>> On Thu, 2 May 2024, John Hubbard wrote: >>>> ... >>>>>> diff --git a/tools/testing/selftests/resctrl/mbm_test.c >>>>>> b/tools/testing/selftests/resctrl/mbm_test.c >>>>>> index d67ffa3ec63a..c873793d016d 100644 >>>>>> --- a/tools/testing/selftests/resctrl/mbm_test.c >>>>>> +++ b/tools/testing/selftests/resctrl/mbm_test.c >>>>>> @@ -33,7 +33,7 @@ show_bw_info(unsigned long *bw_imc, unsigned long >>>>>> *bw_resc, size_t span) >>>>>> avg_bw_imc = sum_bw_imc / 4; >>>>>> avg_bw_resc = sum_bw_resc / 4; >>>>>> - avg_diff = (float)labs(avg_bw_resc - avg_bw_imc) / avg_bw_imc; >>>>>> + avg_diff = (float)(avg_bw_resc - avg_bw_imc) / avg_bw_imc; >>>>>> avg_diff_per = (int)(avg_diff * 100); >>>>>> ret = avg_diff_per > MAX_DIFF_PERCENT; >>>>> >>>>> But how are these two cases same after your change when you ended up >>>>> removing taking the absolute value entirely? >>>> >>>> All of the arguments are unsigned integers, so all arithmetic results >>>> are interpreted as unsigned, so taking the absolute value of that is >>>> always a no-op. > > (I see there's a better patch posted already but since there are a few > incorrect claims in this discussion, I'll do for the record type of > reply.) > > This discussion now went to a tangent about the warning. My main point is > that logic is not correct after removing labs(). > > I also disagree with the claim that using labs() on unsigned value is > no-op because labs() takes long so unsigned is just forced into signed > when calling which is why the warning triggers but it's very misleading > warning (see below). > Yes you are correct. >>> It does not seem as though clang can see when values have been casted. >>> I tried to do so explicitly with a: >>> avg_diff = labs((long)avg_bw_resc - avg_bw_imc) / (float)avg_bw_imc; >> >> The subtraction result will get promoted to an unsigned long, before being >> passed into labs(3). >> >>> But that still triggers: >>> warning: taking the absolute value of unsigned type 'unsigned long' has no >>> effect [-Wabsolute-value] >> >> As expected, yes. > > That error message isn't factually correct: > > unsigned long a = LONG_MAX; > long b; > > a += 2; > b = (long)a; > printf("%llu %lli %lli\n", a, b, labs(a)); > > Prints (at least when built with gcc): > > 9223372036854775809 -9223372036854775807 9223372036854775807 > > labs(LONG_MAX + 1) won't work though since it's not positively presentable > with long and the value is left untouched. > Thanks for setting the detailed record straight! :) thanks,
diff --git a/tools/testing/selftests/resctrl/cmt_test.c b/tools/testing/selftests/resctrl/cmt_test.c index a81f91222a89..05a241519ae8 100644 --- a/tools/testing/selftests/resctrl/cmt_test.c +++ b/tools/testing/selftests/resctrl/cmt_test.c @@ -40,11 +40,11 @@ static int show_results_info(unsigned long sum_llc_val, int no_of_bits, int ret; avg_llc_val = sum_llc_val / num_of_runs; - avg_diff = (long)abs(cache_span - avg_llc_val); + avg_diff = (long)(cache_span - avg_llc_val); diff_percent = ((float)cache_span - avg_llc_val) / cache_span * 100; ret = platform && abs((int)diff_percent) > max_diff_percent && - abs(avg_diff) > max_diff; + labs(avg_diff) > max_diff; ksft_print_msg("%s Check cache miss rate within %lu%%\n", ret ? "Fail:" : "Pass:", max_diff_percent); diff --git a/tools/testing/selftests/resctrl/mba_test.c b/tools/testing/selftests/resctrl/mba_test.c index 7946e32e85c8..673b2bb800f7 100644 --- a/tools/testing/selftests/resctrl/mba_test.c +++ b/tools/testing/selftests/resctrl/mba_test.c @@ -77,7 +77,7 @@ static bool show_mba_info(unsigned long *bw_imc, unsigned long *bw_resc) avg_bw_imc = sum_bw_imc / (NUM_OF_RUNS - 1); avg_bw_resc = sum_bw_resc / (NUM_OF_RUNS - 1); - avg_diff = (float)labs(avg_bw_resc - avg_bw_imc) / avg_bw_imc; + avg_diff = (float)(avg_bw_resc - avg_bw_imc) / avg_bw_imc; avg_diff_per = (int)(avg_diff * 100); ksft_print_msg("%s Check MBA diff within %d%% for schemata %u\n", diff --git a/tools/testing/selftests/resctrl/mbm_test.c b/tools/testing/selftests/resctrl/mbm_test.c index d67ffa3ec63a..c873793d016d 100644 --- a/tools/testing/selftests/resctrl/mbm_test.c +++ b/tools/testing/selftests/resctrl/mbm_test.c @@ -33,7 +33,7 @@ show_bw_info(unsigned long *bw_imc, unsigned long *bw_resc, size_t span) avg_bw_imc = sum_bw_imc / 4; avg_bw_resc = sum_bw_resc / 4; - avg_diff = (float)labs(avg_bw_resc - avg_bw_imc) / avg_bw_imc; + avg_diff = (float)(avg_bw_resc - avg_bw_imc) / avg_bw_imc; avg_diff_per = (int)(avg_diff * 100); ret = avg_diff_per > MAX_DIFF_PERCENT;
First of all, in order to build with clang at all, one must first apply Valentin Obst's build fix for LLVM [1]. Furthermore, for this particular resctrl directory, my pending fix [2] must also be applied. Once those fixes are in place, then when building with clang, via: make LLVM=1 -C tools/testing/selftests ...two types of warnings occur: warning: absolute value function 'abs' given an argument of type 'long' but has parameter of type 'int' which may cause truncation of value warning: taking the absolute value of unsigned type 'unsigned long' has no effect Fix these by: a) using labs() in place of abs(), when long integers are involved, and b) don't call labs() unnecessarily. [1] https://lore.kernel.org/all/20240329-selftests-libmk-llvm-rfc-v1-1-2f9ed7d1c49f@valentinobst.de/ [2] https://lore.kernel.org/all/20240503021712.78601-1-jhubbard@nvidia.com/ Signed-off-by: John Hubbard <jhubbard@nvidia.com> --- tools/testing/selftests/resctrl/cmt_test.c | 4 ++-- tools/testing/selftests/resctrl/mba_test.c | 2 +- tools/testing/selftests/resctrl/mbm_test.c | 2 +- 3 files changed, 4 insertions(+), 4 deletions(-) base-commit: f03359bca01bf4372cf2c118cd9a987a5951b1c8 prerequisite-patch-id: b901ece2a5b78503e2fb5480f20e304d36a0ea27 prerequisite-patch-id: 8d96c4b8c3ed6d9ea2588ef7f594ae0f9f83c279