[PATCH 2/3] arm64: syscall.h: Add sign extension handling in syscall_get_return_value for compat

[He Zhe]

Add sign extension handling in syscall_get_return_value so that it can
handle 32-bit compatible case and can be used by for example audit, just
like what syscall_get_error does.

Signed-off-by: He Zhe <zhe.he@xxxxxxxxxxxxx>
---
 arch/arm64/include/asm/syscall.h | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/syscall.h b/arch/arm64/include/asm/syscall.h
index cfc0672013f6..cd7a22787aeb 100644
--- a/arch/arm64/include/asm/syscall.h
+++ b/arch/arm64/include/asm/syscall.h
@@ -44,7 +44,12 @@ static inline long syscall_get_error(struct task_struct *task,
 static inline long syscall_get_return_value(struct task_struct *task,
 					    struct pt_regs *regs)
 {
-	return regs->regs[0];
+	long val = regs->regs[0];
+
+	if (is_compat_thread(task_thread_info(task)))
+		val = sign_extend64(val, 31);
+
+	return val;
 }
 
 static inline void syscall_set_return_value(struct task_struct *task,
-- 
2.17.1