Re: [PATCH 1/1] arch/powerpc: Rework local_paca to avoid LTO warnings
On Thu, 2019-03-14 at 10:54 +1100, Daniel Axtens wrote:
> "Alastair D'Silva" writes:
>
> > From: Alastair D'Silva
> >
> > When building an LTO kernel, the existing code generates warnings:
> > ./arch/powerpc/include/asm/paca.h:37:30: warning: register of
> > ‘local_paca’ used for multiple global register variables
> > register struct paca_struct *local_paca asm("r13");
> > ^
> > ./arch/powerpc/include/asm/paca.h:37:30: note: conflicts with
> > ‘local_paca’
> >
> > This patch reworks local_paca into an inline getter & setter
> > function,
> > which addresses the warning.
> >
> > Generated ASM from this patch is broadly similar (addresses have
> > changed and the compiler uses different GPRs in some places).
>
> Ditto to Christophe's comment; I'd love to know how to build this so
> I
> can actually see the differences. Perhaps you could bundle up all the
> required changes and send it as a patch series with a cover letter
> explaining this?
The differences are visible in a normal build, but if you want to play
with LTO, see my comments to Christophe.
>
> > +static inline struct paca_struct *get_paca_no_preempt_check(void)
> > +{
> > + register struct paca_struct *paca asm("r13");
> > + return paca;
> > +}
>
> Isn't the convention to have the { on the same line as the function,
> or
> am I horrible mis-remembering things?
>
You are :)
> Should these functions be __always_inline?
>
Yes, they should, I'll add that to V3.
--
Alastair D'Silva
Open Source Developer
Linux Technology Centre, IBM Australia
mob: 0423 762 819
Re: [PATCH 1/1] arch/powerpc: Rework local_paca to avoid LTO warnings
On Wed, 2019-03-13 at 10:06 +0100, Christophe Leroy wrote:
> Hello,
Thanks for reviewing :)
>
> Le 13/03/2019 à 04:42, Alastair D'Silva a écrit :
> > From: Alastair D'Silva
> >
> > When building an LTO kernel, the existing code generates warnings:
> > ./arch/powerpc/include/asm/paca.h:37:30: warning: register of
> > ‘local_paca’ used for multiple global register variables
> > register struct paca_struct *local_paca asm("r13");
> >^
> > ./arch/powerpc/include/asm/paca.h:37:30: note: conflicts with
> > ‘local_paca’
>
> How do you build a LTO kernel ?
I'm using Andi Kleen's LTO tree:
https://github.com/andikleen/linux-misc/tree/lto-420-1
with a few other patches:
https://github.com/andikleen/linux-misc/pull/27
You'll need to add the following to your .config:
CONFIG_LTO_MENU=y
CONFIG_LTO=y
>
> > This patch reworks local_paca into an inline getter & setter
> > function,
> > which addresses the warning.
>
> This patch adds sparse warnings, see
> https://patchwork.ozlabs.org/patch/1055875/
These warnings are bogus, they replace warnings that flagged against
spinlock.h.
> > Generated ASM from this patch is broadly similar (addresses have
> > changed and the compiler uses different GPRs in some places).
>
> Your text might be confusion. When I read it the first time I
> thought
> you were saying that the compiler was now using another GPR than r13.
>
I'll see if I can improve it.
> > Signed-off-by: Alastair D'Silva
>
> I guess the same has to be done for current, see
> arch/powerpc/include/asm/current.h :
>
> /*
> * We keep `current' in r2 for speed.
> */
> register struct task_struct *current asm ("r2");
Hmm, I didn't see problems on PPC64 as that already uses an inline
function. I'll address this in another patch for the PPC32 case.
> > ---
> > arch/powerpc/include/asm/paca.h | 44 +++-
> > -
> > arch/powerpc/kernel/paca.c | 2 +-
> > 2 files changed, 32 insertions(+), 14 deletions(-)
> >
> > diff --git a/arch/powerpc/include/asm/paca.h
> > b/arch/powerpc/include/asm/paca.h
> > index e843bc5d1a0f..9c9e2dea0f9b 100644
> > --- a/arch/powerpc/include/asm/paca.h
> > +++ b/arch/powerpc/include/asm/paca.h
> > @@ -34,19 +34,6 @@
> > #include
> > #include
> >
> > -register struct paca_struct *local_paca asm("r13");
> > -
> > -#if defined(CONFIG_DEBUG_PREEMPT) && defined(CONFIG_SMP)
> > -extern unsigned int debug_smp_processor_id(void); /* from
> > linux/smp.h */
> > -/*
> > - * Add standard checks that preemption cannot occur when using
> > get_paca():
> > - * otherwise the paca_struct it points to may be the wrong one
> > just after.
> > - */
> > -#define get_paca() ((void) debug_smp_processor_id(), local_paca)
> > -#else
> > -#define get_paca() local_paca
> > -#endif
> > -
> > #ifdef CONFIG_PPC_PSERIES
> > #define get_lppaca() (get_paca()->lppaca_ptr)
> > #endif
> > @@ -266,6 +253,37 @@ struct paca_struct {
> > #endif
> > } cacheline_aligned;
> >
> > +#if defined(CONFIG_DEBUG_PREEMPT) && defined(CONFIG_SMP)
> > +extern unsigned int debug_smp_processor_id(void); /* from
> > linux/smp.h */
> > +#endif
>
> Why moving this down, why not leaving at the same place as before ?
>
> If you really need to move it, you should remove the 'extern' at the
> same time to make checkpatch happy.
I moved it to keep it close to the usage of it.
I suppose the new implementation should be in the same place though.
> > +
> > +static inline struct paca_struct *get_paca_no_preempt_check(void)
> > +{
> > + register struct paca_struct *paca asm("r13");
>
> Should be a blank line there.
Whoops, I thought I ran checkpatch, but clearly, I forgot. I'll
resubmit.
> > + return paca;
> > +}
> > +
> > +static inline struct paca_struct *get_paca(void)
> > +{
> > +#if defined(CONFIG_DEBUG_PREEMPT) && defined(CONFIG_SMP)
> > + /*
> > +* Add standard checks that preemption cannot occur when using
> > get_paca():
> > +* otherwise the paca_struct it points to may be the wrong one
> > just after.
> > +*/
> > + debug_smp_processor_id();
> > +#endif
> > + return get_paca_no_preempt_check();
> > +}
> > +
> > +#define local_paca get_paca_no_preempt_check()
> > +
> > +static inline void set_paca(struct paca_struct *new)
> > +{
> > + register struct paca_struct *paca asm("r13");
>
> Blank line should be added here.
>
> > + paca = new;
> > +}
> > +
> > +
> > extern void copy_mm_to_paca(struct mm_struct *mm);
> > extern struct paca_struct **paca_ptrs;
> > extern void initialise_paca(struct paca_struct *new_paca, int
> > cpu);
> > diff --git a/arch/powerpc/kernel/paca.c
> > b/arch/powerpc/kernel/paca.c
> > index 913bfca09c4f..ae5c243f9d5a 100644
> > --- a/arch/powerpc/kernel/paca.c
> > +++ b/arch/powerpc/kernel/paca.c
> > @@ -172,7 +172,7 @@ void __init initialise_paca(struct paca_struct
> > *new_paca, int cpu)
> > void setup_paca(struct paca_struct *new_paca)
Re: [PATCH 1/1] arch/powerpc: Rework local_paca to avoid LTO warnings
On 14/3/19 10:54 am, Daniel Axtens wrote:
+static inline struct paca_struct *get_paca_no_preempt_check(void)
+{
+ register struct paca_struct *paca asm("r13");
+ return paca;
+}
Isn't the convention to have the { on the same line as the function, or
am I horrible mis-remembering things?
However, there is one special case, namely functions: they have the
opening brace at the beginning of the next line, thus:
int function(int x)
{
body of function
}
Heretic people all over the world have claimed that this inconsistency
is ... well ... inconsistent, but all right-thinking people know that
(a) K are **right** and (b) K are right. Besides, functions are
special anyway (you can't nest them in C).
--
Andrew Donnellan OzLabs, ADL Canberra
andrew.donnel...@au1.ibm.com IBM Australia Limited
Re: [PATCH 1/1] arch/powerpc: Rework local_paca to avoid LTO warnings
"Alastair D'Silva" writes:
> From: Alastair D'Silva
>
> When building an LTO kernel, the existing code generates warnings:
> ./arch/powerpc/include/asm/paca.h:37:30: warning: register of
> ‘local_paca’ used for multiple global register variables
> register struct paca_struct *local_paca asm("r13");
> ^
> ./arch/powerpc/include/asm/paca.h:37:30: note: conflicts with
> ‘local_paca’
>
> This patch reworks local_paca into an inline getter & setter function,
> which addresses the warning.
>
> Generated ASM from this patch is broadly similar (addresses have
> changed and the compiler uses different GPRs in some places).
Ditto to Christophe's comment; I'd love to know how to build this so I
can actually see the differences. Perhaps you could bundle up all the
required changes and send it as a patch series with a cover letter
explaining this?
> +static inline struct paca_struct *get_paca_no_preempt_check(void)
> +{
> + register struct paca_struct *paca asm("r13");
> + return paca;
> +}
Isn't the convention to have the { on the same line as the function, or
am I horrible mis-remembering things?
Should these functions be __always_inline?
Regards,
Daniel
> +
> +static inline struct paca_struct *get_paca(void)
> +{
> +#if defined(CONFIG_DEBUG_PREEMPT) && defined(CONFIG_SMP)
> + /*
> + * Add standard checks that preemption cannot occur when using
> get_paca():
> + * otherwise the paca_struct it points to may be the wrong one just
> after.
> + */
> + debug_smp_processor_id();
> +#endif
> + return get_paca_no_preempt_check();
> +}
> +
> +#define local_paca get_paca_no_preempt_check()
> +
> +static inline void set_paca(struct paca_struct *new)
> +{
> + register struct paca_struct *paca asm("r13");
> + paca = new;
> +}
> +
> +
> extern void copy_mm_to_paca(struct mm_struct *mm);
> extern struct paca_struct **paca_ptrs;
> extern void initialise_paca(struct paca_struct *new_paca, int cpu);
> diff --git a/arch/powerpc/kernel/paca.c b/arch/powerpc/kernel/paca.c
> index 913bfca09c4f..ae5c243f9d5a 100644
> --- a/arch/powerpc/kernel/paca.c
> +++ b/arch/powerpc/kernel/paca.c
> @@ -172,7 +172,7 @@ void __init initialise_paca(struct paca_struct *new_paca,
> int cpu)
> void setup_paca(struct paca_struct *new_paca)
> {
> /* Setup r13 */
> - local_paca = new_paca;
> + set_paca(new_paca);
>
> #ifdef CONFIG_PPC_BOOK3E
> /* On Book3E, initialize the TLB miss exception frames */
> --
> 2.20.1
Re: [PATCH 1/1] arch/powerpc: Rework local_paca to avoid LTO warnings
Hello,
Le 13/03/2019 à 04:42, Alastair D'Silva a écrit :
From: Alastair D'Silva
When building an LTO kernel, the existing code generates warnings:
./arch/powerpc/include/asm/paca.h:37:30: warning: register of
‘local_paca’ used for multiple global register variables
register struct paca_struct *local_paca asm("r13");
^
./arch/powerpc/include/asm/paca.h:37:30: note: conflicts with
‘local_paca’
How do you build a LTO kernel ?
This patch reworks local_paca into an inline getter & setter function,
which addresses the warning.
This patch adds sparse warnings, see
https://patchwork.ozlabs.org/patch/1055875/
Generated ASM from this patch is broadly similar (addresses have
changed and the compiler uses different GPRs in some places).
Your text might be confusion. When I read it the first time I thought
you were saying that the compiler was now using another GPR than r13.
Signed-off-by: Alastair D'Silva
I guess the same has to be done for current, see
arch/powerpc/include/asm/current.h :
/*
* We keep `current' in r2 for speed.
*/
register struct task_struct *current asm ("r2");
---
arch/powerpc/include/asm/paca.h | 44 +++--
arch/powerpc/kernel/paca.c | 2 +-
2 files changed, 32 insertions(+), 14 deletions(-)
diff --git a/arch/powerpc/include/asm/paca.h b/arch/powerpc/include/asm/paca.h
index e843bc5d1a0f..9c9e2dea0f9b 100644
--- a/arch/powerpc/include/asm/paca.h
+++ b/arch/powerpc/include/asm/paca.h
@@ -34,19 +34,6 @@
#include
#include
-register struct paca_struct *local_paca asm("r13");
-
-#if defined(CONFIG_DEBUG_PREEMPT) && defined(CONFIG_SMP)
-extern unsigned int debug_smp_processor_id(void); /* from linux/smp.h */
-/*
- * Add standard checks that preemption cannot occur when using get_paca():
- * otherwise the paca_struct it points to may be the wrong one just after.
- */
-#define get_paca() ((void) debug_smp_processor_id(), local_paca)
-#else
-#define get_paca() local_paca
-#endif
-
#ifdef CONFIG_PPC_PSERIES
#define get_lppaca() (get_paca()->lppaca_ptr)
#endif
@@ -266,6 +253,37 @@ struct paca_struct {
#endif
} cacheline_aligned;
+#if defined(CONFIG_DEBUG_PREEMPT) && defined(CONFIG_SMP)
+extern unsigned int debug_smp_processor_id(void); /* from linux/smp.h */
+#endif
Why moving this down, why not leaving at the same place as before ?
If you really need to move it, you should remove the 'extern' at the
same time to make checkpatch happy.
+
+static inline struct paca_struct *get_paca_no_preempt_check(void)
+{
+ register struct paca_struct *paca asm("r13");
Should be a blank line there.
+ return paca;
+}
+
+static inline struct paca_struct *get_paca(void)
+{
+#if defined(CONFIG_DEBUG_PREEMPT) && defined(CONFIG_SMP)
+ /*
+* Add standard checks that preemption cannot occur when using
get_paca():
+* otherwise the paca_struct it points to may be the wrong one just
after.
+*/
+ debug_smp_processor_id();
+#endif
+ return get_paca_no_preempt_check();
+}
+
+#define local_paca get_paca_no_preempt_check()
+
+static inline void set_paca(struct paca_struct *new)
+{
+ register struct paca_struct *paca asm("r13");
Blank line should be added here.
+ paca = new;
+}
+
+
extern void copy_mm_to_paca(struct mm_struct *mm);
extern struct paca_struct **paca_ptrs;
extern void initialise_paca(struct paca_struct *new_paca, int cpu);
diff --git a/arch/powerpc/kernel/paca.c b/arch/powerpc/kernel/paca.c
index 913bfca09c4f..ae5c243f9d5a 100644
--- a/arch/powerpc/kernel/paca.c
+++ b/arch/powerpc/kernel/paca.c
@@ -172,7 +172,7 @@ void __init initialise_paca(struct paca_struct *new_paca,
int cpu)
void setup_paca(struct paca_struct *new_paca)
{
/* Setup r13 */
- local_paca = new_paca;
+ set_paca(new_paca);
#ifdef CONFIG_PPC_BOOK3E
/* On Book3E, initialize the TLB miss exception frames */
Christophe
