b9b6a2ea2b
We shouldn't hardcode the size of the tracepoint common_ fields, use the
offset of the 'id'/'__syscallnr' field in the sys_enter event instead.
This caused the augmented syscalls code to fail on a particular build of a
PREEMPT_RT_FULL kernel where these extra 'common_migrate_disable' and
'common_padding' fields were before the syscall id one:
# cat /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/format
name: sys_enter
ID: 22
format:
field:unsigned short common_type; offset:0; size:2; signed:0;
field:unsigned char common_flags; offset:2; size:1; signed:0;
field:unsigned char common_preempt_count; offset:3; size:1; signed:0;
field:int common_pid; offset:4; size:4; signed:1;
field:unsigned short common_migrate_disable; offset:8; size:2; signed:0;
field:unsigned short common_padding; offset:10; size:2; signed:0;
field:long id; offset:16; size:8; signed:1;
field:unsigned long args[6]; offset:24; size:48; signed:0;
print fmt: "NR %ld (%lx, %lx, %lx, %lx, %lx, %lx)", REC->id, REC->args[0], REC->args[1], REC->args[2], REC->args[3], REC->args[4], REC->args[5]
#
All those 'common_' prefixed fields are zeroed when they hit a BPF tracepoint
hook, we better just discard those, i.e. somehow pass an offset to the
BPF program from the start of the ctx and make adjustments in the 'perf trace'
handlers to adjust the offset of the syscall arg offsets obtained from tracefs.
Till then, fix it the quick way and add this to the augmented_raw_syscalls.c to
bet it to work in such kernels:
diff --git a/tools/perf/examples/bpf/augmented_raw_syscalls.c b/tools/perf/examples/bpf/augmented_raw_syscalls.c
index 53c233370fae..1f746f931e13 100644
--- a/tools/perf/examples/bpf/augmented_raw_syscalls.c
+++ b/tools/perf/examples/bpf/augmented_raw_syscalls.c
@@ -38,12 +38,14 @@ struct bpf_map SEC("maps") syscalls = {
struct syscall_enter_args {
unsigned long long common_tp_fields;
+ long rt_common_tp_fields;
long syscall_nr;
unsigned long args[6];
};
struct syscall_exit_args {
unsigned long long common_tp_fields;
+ long rt_common_tp_fields;
long syscall_nr;
long ret;
};
Just to check that this was the case. Fix it properly later, for now remove the
hardcoding of the offset in the 'perf trace' side and document the situation
with this patch.
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Luis Cláudio Gonçalves <lclaudio@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/n/tip-2pqavrktqkliu5b9nzouio21@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
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README
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.