[PATCH v3 07/11] arm64/tracing: fix compat syscall handling

On Wed, Oct 12, 2016 at 09:07:03AM +0200, Marcin Nowakowski wrote:

On 11.10.2016 15:36, Will Deacon wrote:

quoted

On Tue, Oct 11, 2016 at 12:42:52PM +0200, Marcin Nowakowski wrote:

quoted

diff --git a/arch/arm64/include/asm/unistd.h b/arch/arm64/include/asm/unistd.h
index e78ac26..276d049 100644
--- a/arch/arm64/include/asm/unistd.h
+++ b/arch/arm64/include/asm/unistd.h

@@ -45,6 +45,7 @@

#define __ARM_NR_compat_set_tls		(__ARM_NR_COMPAT_BASE+5)

#define __NR_compat_syscalls		394
+#define NR_compat_syscalls (__NR_compat_syscalls)

We may as well just define NR_compat_syscalls instead of
__NR_compat_syscalls and move the handful of users over.

I had tried to minimise the amount of arch-specific changes here -
especially those that are not directly related to the proposed syscall
handling change. But I agree having these 2 #defines is a bit unnecessary

There's only three users of __NR_compat_syscalls, so I think you can
move them over.

quoted

quoted

diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c
index 40ad08a..75d010f 100644
--- a/arch/arm64/kernel/ftrace.c
+++ b/arch/arm64/kernel/ftrace.c

@@ -176,4 +176,20 @@ int ftrace_disable_ftrace_graph_caller(void)

	return ftrace_modify_graph_caller(false);
}
#endif /* CONFIG_DYNAMIC_FTRACE */
+
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
+
+#if (defined CONFIG_FTRACE_SYSCALLS) && (defined CONFIG_COMPAT)
+
+extern const void *sys_call_table[];
+extern const void *compat_sys_call_table[];
+
+unsigned long __init arch_syscall_addr(int nr, bool compat)
+{
+	if (compat)
+		return (unsigned long)compat_sys_call_table[nr];
+
+	return (unsigned long)sys_call_table[nr];
+}

Do we care about the compat private syscalls (from base 0x0f0000)? We
need to make sure that we exhibit the same behaviour as a native
32-bit ARM machine.

Will

Tracing of such syscalls has been disabled for a long time (see
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=086ba77a6db0).
Apart from using non-contiguous numbers, they are not defined using standard
SYSCALL macros, so they do not have any metadata generated either.
My suggestion is that if you wanted those to be included in the trace then
it should be done separately from these changes.

Fine by me -- I just wanted to make sure our compat behaviour matched
the behaviour of native arch/arm/. It sounds like it does, so no need to
change anything here.

Acked-by: Will Deacon <redacted>

Will