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Message-ID: <20150720073647.GA10504@gmail.com>
Date: Mon, 20 Jul 2015 09:36:47 +0200
From: Ingo Molnar <mingo@...nel.org>
To: Olof Johansson <olof@...om.net>
Cc: will.deacon@....com, catalin.marinas@....com,
linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH] arm64: Minor refactoring of cpu_switch_to() to fix build
breakage
* Olof Johansson <olof@...om.net> wrote:
> 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@...ux.intel.com>
> Signed-off-by: Olof Johansson <olof@...om.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(-)
So why not pass in 'thread_struct' as the patch below does - it looks much simpler
to me. This way the assembly doesn't have to be changed at all.
Thanks,
Ingo
=====================================>
* Guenter <linux@...ck-us.net> wrote:
> On Sat, Jul 18, 2015 at 04:27:17PM -0700, Guenter wrote:
> > Hi,
> >
> > Commit 0c8c0f03e3a2 ("x86/fpu, sched: Dynamically allocate 'struct fpu'")
> > causes s390 builds in mainline to fail as follows.
> >
> > arch/s390/kernel/traps.c: Assembler messages:
> > arch/s390/kernel/traps.c:262: Error: operand out of range
> > (0x00000000000023e8 is not between 0x0000000000000000 and 0x0000000000000fff)
> > arch/s390/kernel/traps.c:300: Error: operand out of range
> > (0x00000000000023e8 is not between 0x0000000000000000 and 0x0000000000000fff)
> >
>
> Also:
>
> arm64:allmodconfig:
>
> 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
> make[1]: *** [arch/arm64/kernel/entry.o] Error 1
>
> I didn't bisect that one, but it looks like the cause is the same.
Hm, it looks like the new, increased offset of 'thread_struct' within
'task_struct' goes over a limit that these instructions are able to support on
arm64:
arch/arm64/kernel/asm-offsets.c: DEFINE(THREAD_CPU_CONTEXT, offsetof(struct task_struct, thread.cpu_context));
arch/arm64/kernel/entry.S: add x8, x0, #THREAD_CPU_CONTEXT
arch/arm64/kernel/entry.S: add x8, x1, #THREAD_CPU_CONTEXT
If there's no instruction that can support such offset sizes then I suspect the
straightforward fix would be to pass in thread_struct instead - like the patch
below. That's a tiny bit cleaner for type encapsulation anyway.
Warning: it's not even build tested, but in case it works:
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Thanks,
Ingo
================
arch/arm64/include/asm/processor.h | 4 ++--
arch/arm64/kernel/asm-offsets.c | 2 +-
arch/arm64/kernel/process.c | 2 +-
3 files changed, 4 insertions(+), 4 deletions(-)
diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
index e4c893e54f01..890f84bb3b8c 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 thread_struct *prev,
+ struct thread_struct *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 c99701a34d7b..3785373c2369 100644
--- a/arch/arm64/kernel/asm-offsets.c
+++ b/arch/arm64/kernel/asm-offsets.c
@@ -39,7 +39,7 @@ 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));
+ DEFINE(THREAD_CPU_CONTEXT, offsetof(struct thread_struct, cpu_context));
BLANK();
DEFINE(S_X0, offsetof(struct pt_regs, regs[0]));
DEFINE(S_X1, offsetof(struct pt_regs, regs[1]));
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 223b093c9440..436e95bda1b2 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -325,7 +325,7 @@ 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, &next.thread);
return last;
}
--
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