| Message ID | 1432337148-9894-1-git-send-email-stefan@agner.ch (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
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 <rmk+kernel@arm.linux.org.uk> > Signed-off-by: Stefan Agner <stefan@agner.ch> > --- > 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 <mcoquelin.stm32@gmail.com> 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
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
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 <rmk+kernel@arm.linux.org.uk> Signed-off-by: Stefan Agner <stefan@agner.ch> --- 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(-)