Messages in this thread | | | From | Ian Rogers <> | Date | Thu, 14 May 2020 12:06:48 -0700 | Subject | Re: [PATCH perf/core] perf intel-pt: Fix clang build failure in intel_pt_synth_pebs_sample |
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On Thu, May 14, 2020 at 8:01 AM Gustavo A. R. Silva <gustavoars@kernel.org> wrote: > > On Thu, May 14, 2020 at 10:10:30AM -0300, Arnaldo Carvalho de Melo wrote: > > Em Wed, May 13, 2020 at 06:47:38PM -0500, Gustavo A. R. Silva escreveu: > > > Fix the following build failure generated with command > > > $ make CC=clang HOSTCC=clang -C tools/ perf: > > > > > > util/intel-pt.c:1802:24: error: field 'br_stack' with variable sized type 'struct branch_stack' not at the end of a struct or class is a GNU extension [-Werror,-Wgnu-variable-sized-type-not-at-end] > > > struct branch_stack br_stack; > > > ^ > > > 1 error generated. > > > > > > Fix this by reordering the members of struct br. > > > > Yeah, I noticed that as far back as with ubuntu 16.04's clang: > > > > clang version 3.8.0-2ubuntu4 (tags/RELEASE_380/final) > > > > util/intel-pt.c:1802:24: error: field 'br_stack' with variable sized type 'struct branch_stack' not at the end of a struct or class is a GNU > > extension [-Werror,-Wgnu-variable-sized-type-not-at-end] > > struct branch_stack br_stack; > > ^ > > 1 error generated. > > > > > > Will fold this with the bug introducing the problem to avoid bisection > > problems. > > > > I agree. Also, the commit hash of the "Fixes" tag only applies to the > perf/core branch and, I guess that might create confusion.
So while this fixes the warning I believe it breaks the intent of the code.
tools/perf/util/branch.h: struct branch_stack { u64 nr; u64 hw_idx; struct branch_entry entries[]; };
tools/perf/util/intel-pt.c: struct { struct branch_stack br_stack; struct branch_entry entries[LBRS_MAX]; } br;
The array in br is trying to extend branch_stack's entries array. You might have to do something like:
alignas(alignof(branch_stack)) char storage[sizeof(branch_stack) + sizeof(branch_entry) * LBRS_MAX]; struct branch_stack *br = &storage;
malloc/free may be nicer on the eyeballs.
Thanks, Ian
> Thanks > -- > Gustavo
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