arm64: cleanup {COMPAT_,}SET_PERSONALITY() macro

There is some work that should be done after setting the personality.
Currently it's done in the macro, which is not the best idea.

In this patch new arch_setup_new_exec() routine is introduced, and all
setup code is moved there, as suggested by Catalin:
https://lkml.org/lkml/2017/8/4/494

Cc: Pratyush Anand <panand@redhat.com>
Signed-off-by: Yury Norov <ynorov@caviumnetworks.com>
[catalin.marinas@arm.com: comments changed or removed]
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/include/asm/elf.h

@@ -139,7 +139,6 @@ typedef struct user_fpsimd_state elf_fpregset_t;
 
 #define SET_PERSONALITY(ex)						\
 ({									\
-	current->mm->context.flags = 0;					\
 	clear_thread_flag(TIF_32BIT);					\
 	current->personality &= ~READ_IMPLIES_EXEC;			\
 })
@@ -195,7 +194,6 @@ typedef compat_elf_greg_t		compat_elf_gregset_t[COMPAT_ELF_NGREG];
  */
 #define COMPAT_SET_PERSONALITY(ex)					\
 ({									\
-	current->mm->context.flags = MMCF_AARCH32;			\
 	set_thread_flag(TIF_32BIT);					\
  })
 #define COMPAT_ARCH_DLINFO

arch/arm64/include/asm/thread_info.h

@@ -60,6 +60,9 @@ struct thread_info {
 #define thread_saved_fp(tsk)	\
 	((unsigned long)(tsk->thread.cpu_context.fp))
 
+void arch_setup_new_exec(void);
+#define arch_setup_new_exec     arch_setup_new_exec
+
 #endif
 
 /*

arch/arm64/kernel/process.c

@@ -414,3 +414,11 @@ unsigned long arch_randomize_brk(struct mm_struct *mm)
 	else
 		return randomize_page(mm->brk, SZ_1G);
 }
+
+/*
+ * Called from setup_new_exec() after (COMPAT_)SET_PERSONALITY.
+ */
+void arch_setup_new_exec(void)
+{
+	current->mm->context.flags = is_compat_task() ? MMCF_AARCH32 : 0;
+}