db26984a36
Perf's BPF prologue generator unconditionally fetches 8 bytes for function parameters, which causes problems on big endian machines. Thomas gives a detailed analysis for this problem: http://lkml.kernel.org/r/968ebda5-abe4-8830-8d69-49f62529d151@linux.vnet.ibm.com ---- 8< ---- I investigated perf test BPF for s390x and have a question regarding the 38.3 subtest (bpf-prologue test) which fails on s390x. When I turn on trace_printk in tests/bpf-script-test-prologue.c I see this output in /sys/kernel/debug/tracing/trace: [root@s8360047 perf]# cat /sys/kernel/debug/tracing/trace perf-30229 [000] d..2 170161.535791: : f_mode 2001d00000000 offset:0 orig:0 perf-30229 [000] d..2 170161.535809: : f_mode 6001f00000000 offset:0 orig:0 perf-30229 [000] d..2 170161.535815: : f_mode 6001f00000000 offset:1 orig:0 perf-30229 [000] d..2 170161.535819: : f_mode 2001d00000000 offset:1 orig:0 perf-30229 [000] d..2 170161.535822: : f_mode 2001d00000000 offset:2 orig:1 perf-30229 [000] d..2 170161.535825: : f_mode 6001f00000000 offset:2 orig:1 perf-30229 [000] d..2 170161.535828: : f_mode 6001f00000000 offset:3 orig:1 perf-30229 [000] d..2 170161.535832: : f_mode 2001d00000000 offset:3 orig:1 perf-30229 [000] d..2 170161.535835: : f_mode 2001d00000000 offset:4 orig:0 perf-30229 [000] d..2 170161.535841: : f_mode 6001f00000000 offset:4 orig:0 [...] There are 3 parameters the eBPF program tests/bpf-script-test-prologue.c accesses: f_mode (member of struct file at offset 140) offset and orig. They are parameters of the lseek() system call triggered in this test case in function llseek_loop(). What is really strange is the value of f_mode. It is an 8 byte value, whereas in the probe event it is defined as a 4 byte value. The lower 4 bytes are all zero and do not belong to member f_mode. The correct value should be 2001d for read-only and 6001f for read-write open mode. Here is the output of the 'perf test -vv bpf' trace: Try to find probe point from debuginfo. Matched function: null_lseek [2d9310d] Probe point found: null_lseek+0 Searching 'file' variable in context. Converting variable file into trace event. converting f_mode in file f_mode type is unsigned int. Opening /sys/kernel/debug/tracing//README write=0 Searching 'offset' variable in context. Converting variable offset into trace event. offset type is long long int. Searching 'orig' variable in context. Converting variable orig into trace event. orig type is int. Found 1 probe_trace_events. Opening /sys/kernel/debug/tracing//kprobe_events write=1 Writing event: p:perf_bpf_probe/func _text+8794224 f_mode=+140(%r2):x32 ---- 8< ---- This patch parses the type of each argument and converts data from memory to expected type. Now the test runs successfully on 4.13.0-rc5: [root@s8360046 perf]# ./perf test bpf 38: BPF filter : 38.1: Basic BPF filtering : Ok 38.2: BPF pinning : Ok 38.3: BPF prologue generation : Ok 38.4: BPF relocation checker : Ok [root@s8360046 perf]# Signed-off-by: Wang Nan <wangnan0@huawei.com> Cc: Hendrik Brueckner <brueckner@linux.vnet.ibm.com> Link: http://lkml.kernel.org/r/20170815092159.31912-1-tmricht@linux.vnet.ibm.com Signed-off-by: Thomas-Mich Richter <tmricht@linux.vnet.ibm.com> Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com> |
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README
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.