In Thumb2 mode, the stack register r13 is deprecated if the
destination register is the program counter (r15). Similar to
head.S, head-nommu.S uses r13 to store the return address used
after configuring the CPU's CP15 register. However, since we do
not enable a MMU, there will be no address switch and it is
possible to use branch with link instruction to call
__after_proc_init.
Avoid using r13 completely by using bl to call __after_proc_init
and get rid of __secondary_switched.
Beside removing unnecessary complexity, this also fixes a
compiler warning when compiling a !MMU kernel:
Warning: Use of r13 as a source register is deprecated when r15
is the destination register.
Suggested-by: Russell King <[email protected]>
Signed-off-by: Stefan Agner <[email protected]>
---
Changes in v2:
- Load r7 outside CONFIG_ARM_MPU since its used outside later on
arch/arm/kernel/head-nommu.S | 21 ++++++++-------------
1 file changed, 8 insertions(+), 13 deletions(-)
diff --git a/arch/arm/kernel/head-nommu.S b/arch/arm/kernel/head-nommu.S
index c966016..9b8c5a1 100644
--- a/arch/arm/kernel/head-nommu.S
+++ b/arch/arm/kernel/head-nommu.S
@@ -77,13 +77,13 @@ ENTRY(stext)
orr r6, r6, #(1 << MPU_RSR_EN) @ Set region enabled bit
bl __setup_mpu
#endif
- ldr r13, =__mmap_switched @ address to jump to after
- @ initialising sctlr
+
badr lr, 1f @ return (PIC) address
ldr r12, [r10, #PROCINFO_INITFUNC]
add r12, r12, r10
ret r12
- 1: b __after_proc_init
+1: bl __after_proc_init
+ b __mmap_switched
ENDPROC(stext)
#ifdef CONFIG_SMP
@@ -106,8 +106,7 @@ ENTRY(secondary_startup)
movs r10, r5 @ invalid processor?
beq __error_p @ yes, error 'p'
- adr r4, __secondary_data
- ldmia r4, {r7, r12}
+ ldr r7, __secondary_data
#ifdef CONFIG_ARM_MPU
/* Use MPU region info supplied by __cpu_up */
@@ -115,23 +114,19 @@ ENTRY(secondary_startup)
bl __setup_mpu @ Initialize the MPU
#endif
- badr lr, __after_proc_init @ return address
- mov r13, r12 @ __secondary_switched address
+ badr lr, 1f @ return (PIC) address
ldr r12, [r10, #PROCINFO_INITFUNC]
add r12, r12, r10
ret r12
-ENDPROC(secondary_startup)
-
-ENTRY(__secondary_switched)
+1: bl __after_proc_init
ldr sp, [r7, #12] @ set up the stack pointer
mov fp, #0
b secondary_start_kernel
-ENDPROC(__secondary_switched)
+ENDPROC(secondary_startup)
.type __secondary_data, %object
__secondary_data:
.long secondary_data
- .long __secondary_switched
#endif /* CONFIG_SMP */
/*
@@ -164,7 +159,7 @@ __after_proc_init:
#endif
mcr p15, 0, r0, c1, c0, 0 @ write control reg
#endif /* CONFIG_CPU_CP15 */
- ret r13
+ ret lr
ENDPROC(__after_proc_init)
.ltorg
--
2.4.1
Hi Stefan,
On 05/23/2015 01:25 AM, Stefan Agner wrote:
> In Thumb2 mode, the stack register r13 is deprecated if the
> destination register is the program counter (r15). Similar to
> head.S, head-nommu.S uses r13 to store the return address used
> after configuring the CPU's CP15 register. However, since we do
> not enable a MMU, there will be no address switch and it is
> possible to use branch with link instruction to call
> __after_proc_init.
>
> Avoid using r13 completely by using bl to call __after_proc_init
> and get rid of __secondary_switched.
>
> Beside removing unnecessary complexity, this also fixes a
> compiler warning when compiling a !MMU kernel:
> Warning: Use of r13 as a source register is deprecated when r15
> is the destination register.
>
> Suggested-by: Russell King <[email protected]>
> Signed-off-by: Stefan Agner <[email protected]>
> ---
> Changes in v2:
> - Load r7 outside CONFIG_ARM_MPU since its used outside later on
>
> arch/arm/kernel/head-nommu.S | 21 ++++++++-------------
> 1 file changed, 8 insertions(+), 13 deletions(-)
>
>
You can add my:
Tested-by: Maxime Coquelin <[email protected]>
Thanks!
Maxime
On 2015-05-23 01:25, Stefan Agner wrote:
> In Thumb2 mode, the stack register r13 is deprecated if the
> destination register is the program counter (r15). Similar to
> head.S, head-nommu.S uses r13 to store the return address used
> after configuring the CPU's CP15 register. However, since we do
> not enable a MMU, there will be no address switch and it is
> possible to use branch with link instruction to call
> __after_proc_init.
>
> Avoid using r13 completely by using bl to call __after_proc_init
> and get rid of __secondary_switched.
>
> Beside removing unnecessary complexity, this also fixes a
> compiler warning when compiling a !MMU kernel:
> Warning: Use of r13 as a source register is deprecated when r15
> is the destination register.
Submitted this patch to the patch tracking system, ID 8383/1.
--
Stefan