Re: File not found: /sys/kernel/debug/tracing/events/syscalls

[Naresh Kamboju]

Hi Masami San,

Thanks for the patch it solved the problem.

On Tue, 27 Nov 2018 at 21:41, Masami Hiramatsu
<masami.hiramatsu@xxxxxxxxxx> wrote:
>
> Hi,
>
> I found that the commit 4378a7d4be30 ("arm64: implement syscall
> wrappers") changed
> the syscall wrapper function names by adding __arm64_ prefix. So arm64
> kernel should
> have its own arch_syscall_match_sym_name().

arm64: ftrace: Fix to enable syscall events on arm64

From: Masami Hiramatsu <mhiramat@xxxxxxxxxx>

Since commit 4378a7d4be30 ("arm64: implement syscall wrappers")
introduced "__arm64_" prefix to all syscall wrapper symbols in
sys_call_table, syscall tracer can not find corresponding
metadata from syscall name. In the result, we have no syscall
ftrace events on arm64 kernel, and some bpf testcases are failed
on arm64.

To fix this issue, this introduces custom
arch_syscall_match_sym_name() which skips first 8 bytes when
comparing the syscall and symbol names.

Fixes: 4378a7d4be30 ("arm64: implement syscall wrappers")
Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Reported-by: Naresh Kamboju <naresh.kamboju@xxxxxxxxxx>
Tested-by: Naresh Kamboju <naresh.kamboju@xxxxxxxxxx>
---
 arch/arm64/include/asm/ftrace.h |    9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h
index caa955f10e19..a710f79db442 100644
--- a/arch/arm64/include/asm/ftrace.h
+++ b/arch/arm64/include/asm/ftrace.h
@@ -56,6 +56,15 @@ static inline bool
arch_trace_is_compat_syscall(struct pt_regs *regs)
 {
  return is_compat_task();
 }
+
+#define ARCH_HAS_SYSCALL_MATCH_SYM_NAME
+
+static inline bool arch_syscall_match_sym_name(const char *sym,
+       const char *name)
+{
+ /* Since all syscall functions have __arm64_ prefix, we must skip it */
+ return !strcmp(sym + 8, name);
+}
 #endif /* ifndef __ASSEMBLY__ */

 #endif /* __ASM_FTRACE_H */


>
> Thank you,
>
> 2018å11æ28æ(æ) 0:22 Naresh Kamboju <naresh.kamboju@xxxxxxxxxx>:
> >
> > While debugging the selftests/bpf: get_cgroup_id_user test failure on arm64
> > where the test is expecting trace file
> > /sys/kernel/debug/tracing/events/syscalls/sys_enter_nanosleep/id
> > but this path not enabled after enabling required kernel configuration also.
> > CONFIG_FTRACE_SYSCALLS=y
> >
> > strace output:
> > open(\"/sys/kernel/debug/tracing/events/syscalls/sys_enter_nanosleep/id\",
> > O_RDONLY) = -1 ENOENT (No such file or directory)
> >
> > This problem noticed on Linux mainline kernel version 4.20.0-rc3.
> >
> > Best regards
> > Naresh Kamboju
>
>
>
> --
> Masami Hiramatsu