[PATCH] s390: fix system call tracing

[Heiko Carstens]

When converting to autogenerated compat syscall wrappers all system
call entry points got a different symbol name: they all got a __s390x_
prefix.

This caused breakage with system call tracing, since an appropriate
arch_syscall_match_sym_name() was not provided. Add this function, and
while at it also add code to avoid compat system call tracing. s390
has different system call tables for native 64 bit system calls and
compat system calls. This isn't really supported in the common
code. However there are hardly any compat binaries left, therefore
just ignore compat system calls, like x86 and arm64 also do for the
same reason.

Fixes: aa0d6e70d3b3 ("s390: autogenerate compat syscall wrappers")
Signed-off-by: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
---
 arch/s390/include/asm/ftrace.h | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/arch/s390/include/asm/ftrace.h b/arch/s390/include/asm/ftrace.h
index 8ea270fdc7fb..1e14341201c5 100644
--- a/arch/s390/include/asm/ftrace.h
+++ b/arch/s390/include/asm/ftrace.h
@@ -81,5 +81,26 @@ static inline void ftrace_generate_call_insn(struct ftrace_insn *insn,
 #endif
 }
 
+/*
+ * Even though the system call numbers are identical for s390/s390x a
+ * different system call table is used for compat tasks. This may lead
+ * to e.g. incorrect or missing trace event sysfs files.
+ * Therefore simply do not trace compat system calls at all.
+ * See kernel/trace/trace_syscalls.c.
+ */
+#define ARCH_TRACE_IGNORE_COMPAT_SYSCALLS
+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)
+{
+	/* skip __s390x_ prefix */
+	return !strcmp(sym + 8, name);
+}
+
 #endif /* __ASSEMBLY__ */
 #endif /* _ASM_S390_FTRACE_H */
-- 
2.16.4