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

[Will Deacon <will.deacon@arm.com>]

On Tue, Oct 11, 2016 at 12:42:52PM +0200, Marcin Nowakowski wrote:
> Add arch_syscall_addr for arm64 and define NR_compat_syscalls, as the
> number of compat syscalls for arm64 exceeds the number defined by
> NR_syscalls.
> 
> Signed-off-by: Marcin Nowakowski <marcin.nowakowski@imgtec.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> Cc: linux-arm-kernel@lists.infradead.org
> ---
>  arch/arm64/include/asm/ftrace.h | 12 +-----------
>  arch/arm64/include/asm/unistd.h |  1 +
>  arch/arm64/kernel/Makefile      |  1 +
>  arch/arm64/kernel/ftrace.c      | 16 ++++++++++++++++
>  4 files changed, 19 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h
> index caa955f..b57ff7c 100644
> --- a/arch/arm64/include/asm/ftrace.h
> +++ b/arch/arm64/include/asm/ftrace.h
> @@ -41,17 +41,7 @@ static inline unsigned long ftrace_call_adjust(unsigned long addr)
>  
>  #define ftrace_return_address(n) return_address(n)
>  
> -/*
> - * Because AArch32 mode does not share the same syscall table with AArch64,
> - * tracing compat syscalls may result in reporting bogus syscalls or even
> - * hang-up, so just do not trace them.
> - * See kernel/trace/trace_syscalls.c
> - *
> - * x86 code says:
> - * If the user really wants these, then they should use the
> - * raw syscall tracepoints with filtering.
> - */
> -#define ARCH_TRACE_IGNORE_COMPAT_SYSCALLS
> +#define ARCH_COMPAT_SYSCALL_NUMBERS_OVERLAP 1
>  static inline bool arch_trace_is_compat_syscall(struct pt_regs *regs)
>  {
>  	return is_compat_task();
> 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.

> 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