linux-kernel - [PATCH RFC v2 07/28] ARM: entry: Rewrite two asm calls in C

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Message-Id: <20241029-arm-generic-entry-v2-7-573519abef38@linaro.org>
Date: Tue, 29 Oct 2024 11:52:47 +0100
From: Linus Walleij <linus.walleij@...aro.org>
To: Oleg Nesterov <oleg@...hat.com>, Russell King <linux@...linux.org.uk>, 
 Kees Cook <kees@...nel.org>, Andy Lutomirski <luto@...capital.net>, 
 Will Drewry <wad@...omium.org>, Frederic Weisbecker <frederic@...nel.org>, 
 "Paul E. McKenney" <paulmck@...nel.org>, 
 Jinjie Ruan <ruanjinjie@...wei.com>, Arnd Bergmann <arnd@...db.de>, 
 Ard Biesheuvel <ardb@...nel.org>, Al Viro <viro@...iv.linux.org.uk>
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, 
 Linus Walleij <linus.walleij@...aro.org>
Subject: [PATCH RFC v2 07/28] ARM: entry: Rewrite two asm calls in C

The normal and trace entry code calls out to arm_syscall()
and sys_ni_syscall() from assembly, but these calls can
be moved over to the new C implementation.

Signed-off-by: Linus Walleij <linus.walleij@...aro.org>
---
 arch/arm/include/asm/traps.h   |  2 +-
 arch/arm/kernel/entry-common.S | 23 +++++------------------
 arch/arm/kernel/syscall.c      | 13 +++++++++++--
 arch/arm/kernel/traps.c        |  2 +-
 4 files changed, 18 insertions(+), 22 deletions(-)

diff --git a/arch/arm/include/asm/traps.h b/arch/arm/include/asm/traps.h
index 2621b9fb9b19..b888912c2450 100644
--- a/arch/arm/include/asm/traps.h
+++ b/arch/arm/include/asm/traps.h
@@ -40,7 +40,7 @@ asmlinkage void dump_backtrace_stm(u32 *stack, u32 instruction, const char *logl
 asmlinkage void do_undefinstr(struct pt_regs *regs);
 asmlinkage void handle_fiq_as_nmi(struct pt_regs *regs);
 asmlinkage void bad_mode(struct pt_regs *regs, int reason);
-asmlinkage int arm_syscall(int no, struct pt_regs *regs);
+int arm_syscall(int no, struct pt_regs *regs);
 asmlinkage void baddataabort(int code, unsigned long instr, struct pt_regs *regs);
 asmlinkage void __div0(void);
 asmlinkage void handle_bad_stack(struct pt_regs *regs);
diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index 57aa1084a047..77801d039b5f 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -264,18 +264,10 @@ ENTRY(vector_swi)
 	mov	r0, tbl
 	/* r1 already contains regs */
 	mov	r2, scno			@ syscall number from r7
-	badr	r3, __ret_fast_syscall
-	bl 	invoke_syscall
-
-	/* Restore regs into r1 and lr after C call */
+	/* We return here no matter what, also pass this as an argument */
 	badr	lr, __ret_fast_syscall
-	add	r1, sp, #S_OFF
-
-2:	cmp	scno, #(__ARM_NR_BASE - __NR_SYSCALL_BASE)
-	eor	r0, scno, #__NR_SYSCALL_BASE	@ put OS number back
-	bcs	arm_syscall
-	mov	why, #0				@ no longer a real syscall
-	b	sys_ni_syscall			@ not private func
+	mov	r3, lr
+	b 	invoke_syscall
 
 #if defined(CONFIG_OABI_COMPAT) || !defined(CONFIG_AEABI)
 	/*
@@ -308,13 +300,8 @@ __sys_trace:
 	mov	r0, tbl
 	badr	r3, __sys_trace_return
 	bl	invoke_syscall_trace
-
-	/* Restore regs into r1 and lr after C call */
-	add	r1, sp, #S_R0 + S_OFF		@ pointer to regs
-	badr	lr, __sys_trace_return
-
-	cmp	scno, #-1			@ skip the syscall?
-	bne	2b
+	cmp	r0, #-1
+	bne	__sys_trace_return
 	add	sp, sp, #S_OFF			@ restore stack
 
 __sys_trace_return_nosave:
diff --git a/arch/arm/kernel/syscall.c b/arch/arm/kernel/syscall.c
index be193266299f..d1259c6d2805 100644
--- a/arch/arm/kernel/syscall.c
+++ b/arch/arm/kernel/syscall.c
@@ -11,16 +11,25 @@ __visible int invoke_syscall(void *table, struct pt_regs *regs, int scno, void *
 		/* Doing this with return makes sure the stack gets pop:ed */
 		return invoke_syscall_asm(table, regs, scno, retp);
 
-	return 0;
+	if (scno >= __ARM_NR_BASE)
+		return arm_syscall(scno, regs);
+
+	return sys_ni_syscall();
 }
 
 int invoke_syscall_trace_asm(void *table, struct pt_regs *regs, int scno, void *retp);
 
 __visible int invoke_syscall_trace(void *table, struct pt_regs *regs, int scno, void *retp)
 {
+	if (scno == -1)
+		return -1;
+
 	if (scno < NR_syscalls)
 		/* Doing this with return makes sure the stack gets pop:ed */
 		return invoke_syscall_trace_asm(table, regs, scno, retp);
 
-	return 0;
+	if (scno >= __ARM_NR_BASE)
+		return arm_syscall(scno, regs);
+
+	return sys_ni_syscall();
 }
diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
index 480e307501bb..42f6bb593eb4 100644
--- a/arch/arm/kernel/traps.c
+++ b/arch/arm/kernel/traps.c
@@ -606,7 +606,7 @@ do_cache_op(unsigned long start, unsigned long end, int flags)
  *  0x9f0000 - 0x9fffff are some more esoteric system calls
  */
 #define NR(x) ((__ARM_NR_##x) - __ARM_NR_BASE)
-asmlinkage int arm_syscall(int no, struct pt_regs *regs)
+int arm_syscall(int no, struct pt_regs *regs)
 {
 	if ((no >> 16) != (__ARM_NR_BASE>> 16))
 		return bad_syscall(no, regs);

-- 
2.46.2