From d6838ec44b4513280a3f43fcc402e246d543fb53 Mon Sep 17 00:00:00 2001 From: Namhyung Kim Date: Fri, 24 Jun 2022 16:13:08 -0700 Subject: [PATCH] perf offcpu: Fix build failure on old kernels Old kernels have a 'struct task_struct' which contains a "state" field and newer kernels have "__state" instead. While the get_task_state() in the BPF code handles that in some way, it assumed the current kernel has the new definition and it caused a build error on old kernels. We should not assume anything and access them carefully. Do not use 'task struct' directly access it instead using new and old definitions in a row. Fixes: edc41a1099c2d08c ("perf record: Enable off-cpu analysis with BPF") Reported-by: Ian Rogers Signed-off-by: Namhyung Kim Cc: Blake Jones Cc: Hao Luo Cc: Jiri Olsa Cc: Milian Wolff Cc: Peter Zijlstra Cc: Song Liu Cc: bpf@vger.kernel.org Link: http://lore.kernel.org/lkml/20220624231313.367909-2-namhyung@kernel.org Signed-off-by: Arnaldo Carvalho de Melo --- tools/perf/util/bpf_skel/off_cpu.bpf.c | 20 ++++++++++++++------ 1 file changed, 14 insertions(+), 6 deletions(-) diff --git a/tools/perf/util/bpf_skel/off_cpu.bpf.c b/tools/perf/util/bpf_skel/off_cpu.bpf.c index 792ae2847080..cc6d7fd55118 100644 --- a/tools/perf/util/bpf_skel/off_cpu.bpf.c +++ b/tools/perf/util/bpf_skel/off_cpu.bpf.c @@ -71,6 +71,11 @@ struct { __uint(max_entries, 1); } cgroup_filter SEC(".maps"); +/* new kernel task_struct definition */ +struct task_struct___new { + long __state; +} __attribute__((preserve_access_index)); + /* old kernel task_struct definition */ struct task_struct___old { long state; @@ -93,14 +98,17 @@ const volatile bool uses_cgroup_v1 = false; */ static inline int get_task_state(struct task_struct *t) { - if (bpf_core_field_exists(t->__state)) - return BPF_CORE_READ(t, __state); + /* recast pointer to capture new type for compiler */ + struct task_struct___new *t_new = (void *)t; - /* recast pointer to capture task_struct___old type for compiler */ - struct task_struct___old *t_old = (void *)t; + if (bpf_core_field_exists(t_new->__state)) { + return BPF_CORE_READ(t_new, __state); + } else { + /* recast pointer to capture old type for compiler */ + struct task_struct___old *t_old = (void *)t; - /* now use old "state" name of the field */ - return BPF_CORE_READ(t_old, state); + return BPF_CORE_READ(t_old, state); + } } static inline __u64 get_cgroup_id(struct task_struct *t)