On Wed, Feb 8, 2023 at 4:11 PM Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> wrote: > > On Wed, Feb 8, 2023 at 2:01 PM John Stultz <jstultz@xxxxxxxxxx> wrote: > > > > On Sat, Nov 20, 2021 at 11:27:38AM +0000, Yafang Shao wrote: > > > As the sched:sched_switch tracepoint args are derived from the kernel, > > > we'd better make it same with the kernel. So the macro TASK_COMM_LEN is > > > converted to type enum, then all the BPF programs can get it through BTF. > > > > > > The BPF program which wants to use TASK_COMM_LEN should include the header > > > vmlinux.h. Regarding the test_stacktrace_map and test_tracepoint, as the > > > type defined in linux/bpf.h are also defined in vmlinux.h, so we don't > > > need to include linux/bpf.h again. > > > > > > Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx> > > > Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx> > > > Acked-by: David Hildenbrand <david@xxxxxxxxxx> > > > Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> > > > Cc: Arnaldo Carvalho de Melo <arnaldo.melo@xxxxxxxxx> > > > Cc: Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> > > > Cc: Michal Miroslaw <mirq-linux@xxxxxxxxxxxx> > > > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > > > Cc: Steven Rostedt <rostedt@xxxxxxxxxxx> > > > Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> > > > Cc: David Hildenbrand <david@xxxxxxxxxx> > > > Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> > > > Cc: Kees Cook <keescook@xxxxxxxxxxxx> > > > Cc: Petr Mladek <pmladek@xxxxxxxx> > > > --- > > > include/linux/sched.h | 9 +++++++-- > > > tools/testing/selftests/bpf/progs/test_stacktrace_map.c | 6 +++--- > > > tools/testing/selftests/bpf/progs/test_tracepoint.c | 6 +++--- > > > 3 files changed, 13 insertions(+), 8 deletions(-) > > > > Hey all, > > I know this is a little late, but I recently got a report that > > this change was causiing older versions of perfetto to stop > > working. > > > > Apparently newer versions of perfetto has worked around this > > via the following changes: > > https://android.googlesource.com/platform/external/perfetto/+/c717c93131b1b6e3705a11092a70ac47c78b731d%5E%21/ > > https://android.googlesource.com/platform/external/perfetto/+/160a504ad5c91a227e55f84d3e5d3fe22af7c2bb%5E%21/ > > > > But for older versions of perfetto, reverting upstream commit > > 3087c61ed2c4 ("tools/testing/selftests/bpf: replace open-coded 16 > > with TASK_COMM_LEN") is necessary to get it back to working. > > > > I haven't dug very far into the details, and obviously this doesn't > > break with the updated perfetto, but from a high level this does > > seem to be a breaking-userland regression. > > > > So I wanted to reach out to see if there was more context for this > > breakage? I don't want to raise a unnecessary stink if this was > > an unfortuante but forced situation. > > Let me understand what you're saying... > > The commit 3087c61ed2c4 did > > -/* Task command name length: */ > -#define TASK_COMM_LEN 16 > +/* > + * Define the task command name length as enum, then it can be visible to > + * BPF programs. > + */ > +enum { > + TASK_COMM_LEN = 16, > +}; > > > and that caused: > > cat /sys/kernel/debug/tracing/events/task/task_newtask/format > > to print > field:char comm[TASK_COMM_LEN]; offset:12; size:16; signed:0; > instead of > field:char comm[16]; offset:12; size:16; signed:0; > > so the ftrace parsing android tracing tool had to do: > > - if (Match(type_and_name.c_str(), R"(char [a-zA-Z_]+\[[0-9]+\])")) { > + if (Match(type_and_name.c_str(), > + R"(char [a-zA-Z_][a-zA-Z_0-9]*\[[a-zA-Z_0-9]+\])")) { > > to workaround this change. > Right? I believe so. > And what are you proposing? I'm not proposing anything. I was just wanting to understand more context around this, as it outwardly appears to be a user-breaking change, and that is usually not done, so I figured it was an issue worth raising. If the debug/tracing/*/format output is in the murky not-really-abi space, that's fine, but I wanted to know if this was understood as something that may require userland updates or if this was a unexpected side-effect. thanks -john
