[PATCH] arm: always update thread_info->syscall

[Rafael David Tinoco]

Right now, only way for task->thread_info->syscall to be updated is if
if _TIF_SYSCALL_WORK is set in current's task thread_info->flags
(similar to what has_syscall_work() checks for arm64).

This means that "->syscall" will only be updated if we are tracing the
syscalls through ptrace, for example. This is NOT the same behavior as
arm64, when pt_regs->syscallno is updated in the beginning of svc0
handler for *every* syscall entry.

This patch fixes the issue since this behavior is needed for
/proc/<pid>/syscall 1st argument to be correctly updated.

Link: https://bugs.linaro.org/show_bug.cgi?id=3783
Cc: <stable@xxxxxxxxxxxxxxx> # v4.4 v4.9 v4.14 v4.19
Signed-off-by: Rafael David Tinoco <rafael.tinoco@xxxxxxxxxx>
---
 arch/arm/kernel/asm-offsets.c  | 1 +
 arch/arm/kernel/entry-common.S | 2 ++
 2 files changed, 3 insertions(+)

diff --git a/arch/arm/kernel/asm-offsets.c b/arch/arm/kernel/asm-offsets.c
index 3968d6c22455..bfe68a98e1c6 100644
--- a/arch/arm/kernel/asm-offsets.c
+++ b/arch/arm/kernel/asm-offsets.c
@@ -64,6 +64,7 @@ int main(void)
   DEFINE(TI_USED_CP,		offsetof(struct thread_info, used_cp));
   DEFINE(TI_TP_VALUE,		offsetof(struct thread_info, tp_value));
   DEFINE(TI_FPSTATE,		offsetof(struct thread_info, fpstate));
+  DEFINE(TI_SYSCALL,		offsetof(struct thread_info, syscall));
 #ifdef CONFIG_VFP
   DEFINE(TI_VFPSTATE,		offsetof(struct thread_info, vfpstate));
 #ifdef CONFIG_SMP
diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index 0465d65d23de..557e2add4e83 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -257,6 +257,8 @@ local_restart:
 	tst	r10, #_TIF_SYSCALL_WORK		@ are we tracing syscalls?
 	bne	__sys_trace
 
+	str	r7, [tsk, #TI_SYSCALL]		@ update thread_info->syscall
+
 	invoke_syscall tbl, scno, r10, __ret_fast_syscall
 
 	add	r1, sp, #S_OFF
-- 
2.20.0.rc1