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Subject[PATCH] arm64: Minor refactoring of cpu_switch_to() to fix build breakage
Date
Commit 0c8c0f03e3a2 ("x86/fpu, sched: Dynamically allocate 'struct fpu'")
moved the thread_struct to the bottom of task_struct. As a result, the
offset is now too large to be used in an immediate add on arm64 with
some kernel configs:

arch/arm64/kernel/entry.S: Assembler messages:
arch/arm64/kernel/entry.S:588: Error: immediate out of range
arch/arm64/kernel/entry.S:597: Error: immediate out of range

There's really no reason for cpu_switch_to to take a task_struct pointer
in the first place, since all it does is access the thread.cpu_context
member. So, just pass that in directly.

Fixes: 0c8c0f03e3a2 ("x86/fpu, sched: Dynamically allocate 'struct fpu'")
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Olof Johansson <olof@lixom.net>
---
arch/arm64/include/asm/processor.h | 4 ++--
arch/arm64/kernel/asm-offsets.c | 2 --
arch/arm64/kernel/entry.S | 34 ++++++++++++++++------------------
arch/arm64/kernel/process.c | 3 ++-
4 files changed, 20 insertions(+), 23 deletions(-)

diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
index e4c893e..ba90764 100644
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h
@@ -152,8 +152,8 @@ static inline void cpu_relax(void)
#define cpu_relax_lowlatency() cpu_relax()

/* Thread switching */
-extern struct task_struct *cpu_switch_to(struct task_struct *prev,
- struct task_struct *next);
+extern struct task_struct *cpu_switch_to(struct cpu_context *prev,
+ struct cpu_context *next);

#define task_pt_regs(p) \
((struct pt_regs *)(THREAD_START_SP + task_stack_page(p)) - 1)
diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
index c99701a..c9e13f6 100644
--- a/arch/arm64/kernel/asm-offsets.c
+++ b/arch/arm64/kernel/asm-offsets.c
@@ -39,8 +39,6 @@ int main(void)
DEFINE(TI_TASK, offsetof(struct thread_info, task));
DEFINE(TI_CPU, offsetof(struct thread_info, cpu));
BLANK();
- DEFINE(THREAD_CPU_CONTEXT, offsetof(struct task_struct, thread.cpu_context));
- BLANK();
DEFINE(S_X0, offsetof(struct pt_regs, regs[0]));
DEFINE(S_X1, offsetof(struct pt_regs, regs[1]));
DEFINE(S_X2, offsetof(struct pt_regs, regs[2]));
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index f860bfd..2216326 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -579,29 +579,27 @@ ENDPROC(el0_irq)
/*
* Register switch for AArch64. The callee-saved registers need to be saved
* and restored. On entry:
- * x0 = previous task_struct (must be preserved across the switch)
- * x1 = next task_struct
+ * x0 = previous cpu_context (must be preserved across the switch)
+ * x1 = next cpu_context
* Previous and next are guaranteed not to be the same.
*
*/
ENTRY(cpu_switch_to)
- add x8, x0, #THREAD_CPU_CONTEXT
mov x9, sp
- stp x19, x20, [x8], #16 // store callee-saved registers
- stp x21, x22, [x8], #16
- stp x23, x24, [x8], #16
- stp x25, x26, [x8], #16
- stp x27, x28, [x8], #16
- stp x29, x9, [x8], #16
- str lr, [x8]
- add x8, x1, #THREAD_CPU_CONTEXT
- ldp x19, x20, [x8], #16 // restore callee-saved registers
- ldp x21, x22, [x8], #16
- ldp x23, x24, [x8], #16
- ldp x25, x26, [x8], #16
- ldp x27, x28, [x8], #16
- ldp x29, x9, [x8], #16
- ldr lr, [x8]
+ stp x19, x20, [x0], #16 // store callee-saved registers
+ stp x21, x22, [x0], #16
+ stp x23, x24, [x0], #16
+ stp x25, x26, [x0], #16
+ stp x27, x28, [x0], #16
+ stp x29, x9, [x0], #16
+ str lr, [x0]
+ ldp x19, x20, [x1], #16 // restore callee-saved registers
+ ldp x21, x22, [x1], #16
+ ldp x23, x24, [x1], #16
+ ldp x25, x26, [x1], #16
+ ldp x27, x28, [x1], #16
+ ldp x29, x9, [x1], #16
+ ldr lr, [x1]
mov sp, x9
ret
ENDPROC(cpu_switch_to)
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 223b093..6b9a09c 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -325,7 +325,8 @@ struct task_struct *__switch_to(struct task_struct *prev,
dsb(ish);

/* the actual thread switch */
- last = cpu_switch_to(prev, next);
+ last = cpu_switch_to(&prev->thread.cpu_context,
+ &next->thread.cpu_context);

return last;
}
--
1.7.10.4


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