[PATCH] powerpc/Makefile: fix build failure by disabling attribute-alias warning

[PATCH] powerpc/Makefile: fix build failure by disabling attribute-alias warning

[Christophe Leroy]

Latest GCC version emit many warnings similar to the following one.

As arch/powerpc code is built with -Werror, this breaks build with
GCC 8.1

This patch inhibits that warning

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
 arch/powerpc/Makefile | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index 26ccd0b91512..d6c557530ce8 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile
@@ -145,6 +145,8 @@ CFLAGS-$(CONFIG_PPC64)	+= $(call cc-option,-mno-pointers-to-nested-functions)
 CFLAGS-$(CONFIG_PPC32)	:= -ffixed-r2 $(MULTIPLEWORD)
 CFLAGS-$(CONFIG_PPC32)	+= $(call cc-option,-mno-readonly-in-sdata)
 
+CFLAGS-y += $(call cc-option,-Wno-attribute-alias)
+
 ifeq ($(CONFIG_PPC_BOOK3S_64),y)
 ifeq ($(CONFIG_CPU_LITTLE_ENDIAN),y)
 CFLAGS-$(CONFIG_GENERIC_CPU) += -mcpu=power8
-- 
2.13.3

Re: [PATCH] powerpc/Makefile: fix build failure by disabling attribute-alias warning

[Segher Boessenkool]

On Mon, May 28, 2018 at 02:17:49PM +0000, Christophe Leroy wrote:
> Latest GCC version emit many warnings similar to the following one.

You didn't actually show an example?

This warning should detect serious problems, so don't disable it without
first investigating please.

What do you call "latest version", btw?  Trunk, aka 9.0?  Or the most
advanced release, 8.1?  Or the latest release (which also is 8.1 :-) )


Segher

Re: [PATCH] powerpc/Makefile: fix build failure by disabling attribute-alias warning

[Christophe Leroy]

On 05/28/2018 02:17 PM, Christophe Leroy wrote:
> Latest GCC version emit many warnings similar to the following one.

Oops, forgot to include the failure text:

In file included from arch/powerpc/kernel/syscalls.c:24:
./include/linux/syscalls.h:233:18: warning: 'sys_mmap2' alias between 
functions of incompatible types 'long int(long unsigned int,  size_t, 
long unsigned int,  long unsigned int,  long unsigned int,  long 
unsigned int)' {aka 'long int(long unsigned int,  unsigned int,  long 
unsigned int,  long unsigned int,  long unsigned int,  long unsigned 
int)'} and 'long int(long int,  long int,  long int,  long int,  long 
int,  long int)' [-Wattribute-alias]
   asmlinkage long sys##name(__MAP(x,__SC_DECL,__VA_ARGS__)) \
                   ^~~
./include/linux/syscalls.h:222:2: note: in expansion of macro 
'__SYSCALL_DEFINEx'
   __SYSCALL_DEFINEx(x, sname, __VA_ARGS__)
   ^~~~~~~~~~~~~~~~~
./include/linux/syscalls.h:216:36: note: in expansion of macro 
'SYSCALL_DEFINEx'
  #define SYSCALL_DEFINE6(name, ...) SYSCALL_DEFINEx(6, _##name, 
__VA_ARGS__)
                                     ^~~~~~~~~~~~~~~
arch/powerpc/kernel/syscalls.c:65:1: note: in expansion of macro 
'SYSCALL_DEFINE6'
  SYSCALL_DEFINE6(mmap2, unsigned long, addr, size_t, len,
  ^~~~~~~~~~~~~~~
./include/linux/syscalls.h:238:18: note: aliased declaration here
   asmlinkage long __se_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__)) \
                   ^~~~~~~~
./include/linux/syscalls.h:222:2: note: in expansion of macro 
'__SYSCALL_DEFINEx'
   __SYSCALL_DEFINEx(x, sname, __VA_ARGS__)
   ^~~~~~~~~~~~~~~~~
./include/linux/syscalls.h:216:36: note: in expansion of macro 
'SYSCALL_DEFINEx'
  #define SYSCALL_DEFINE6(name, ...) SYSCALL_DEFINEx(6, _##name, 
__VA_ARGS__)
                                     ^~~~~~~~~~~~~~~
arch/powerpc/kernel/syscalls.c:65:1: note: in expansion of macro 
'SYSCALL_DEFINE6'
  SYSCALL_DEFINE6(mmap2, unsigned long, addr, size_t, len,
  ^~~~~~~~~~~~~~~
./include/linux/syscalls.h:233:18: warning: 'sys_mmap' alias between 
functions of incompatible types 'long int(long unsigned int,  size_t, 
long unsigned int,  long unsigned int,  long unsigned int,  off_t)' {aka 
'long int(long unsigned int,  unsigned int,  long unsigned int,  long 
unsigned int,  long unsigned int,  long int)'} and 'long int(long int, 
long int,  long int,  long int,  long int,  long int)' [-Wattribute-alias]
   asmlinkage long sys##name(__MAP(x,__SC_DECL,__VA_ARGS__)) \
                   ^~~
./include/linux/syscalls.h:222:2: note: in expansion of macro 
'__SYSCALL_DEFINEx'
   __SYSCALL_DEFINEx(x, sname, __VA_ARGS__)
   ^~~~~~~~~~~~~~~~~
./include/linux/syscalls.h:216:36: note: in expansion of macro 
'SYSCALL_DEFINEx'
  #define SYSCALL_DEFINE6(name, ...) SYSCALL_DEFINEx(6, _##name, 
__VA_ARGS__)
                                     ^~~~~~~~~~~~~~~
arch/powerpc/kernel/syscalls.c:72:1: note: in expansion of macro 
'SYSCALL_DEFINE6'
  SYSCALL_DEFINE6(mmap, unsigned long, addr, size_t, len,
  ^~~~~~~~~~~~~~~
./include/linux/syscalls.h:238:18: note: aliased declaration here
   asmlinkage long __se_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__)) \
                   ^~~~~~~~
./include/linux/syscalls.h:222:2: note: in expansion of macro 
'__SYSCALL_DEFINEx'
   __SYSCALL_DEFINEx(x, sname, __VA_ARGS__)
   ^~~~~~~~~~~~~~~~~
./include/linux/syscalls.h:216:36: note: in expansion of macro 
'SYSCALL_DEFINEx'
  #define SYSCALL_DEFINE6(name, ...) SYSCALL_DEFINEx(6, _##name, 
__VA_ARGS__)
                                     ^~~~~~~~~~~~~~~
arch/powerpc/kernel/syscalls.c:72:1: note: in expansion of macro 
'SYSCALL_DEFINE6'
  SYSCALL_DEFINE6(mmap, unsigned long, addr, size_t, len,
  ^~~~~~~~~~~~~~~
   CC      arch/powerpc/kernel/irq.o
   CC      arch/powerpc/kernel/align.o
   CC      arch/powerpc/kernel/signal_32.o
In file included from arch/powerpc/kernel/signal_32.c:29:
./include/linux/syscalls.h:233:18: warning: 'sys_swapcontext' alias 
between functions of incompatible types 'long int(struct ucontext *, 
struct ucontext *, long int)' and 'long int(long int,  long int,  long 
int)' [-Wattribute-alias]
   asmlinkage long sys##name(__MAP(x,__SC_DECL,__VA_ARGS__)) \
                   ^~~
./include/linux/syscalls.h:222:2: note: in expansion of macro 
'__SYSCALL_DEFINEx'
   __SYSCALL_DEFINEx(x, sname, __VA_ARGS__)
   ^~~~~~~~~~~~~~~~~
./include/linux/syscalls.h:213:36: note: in expansion of macro 
'SYSCALL_DEFINEx'
  #define SYSCALL_DEFINE3(name, ...) SYSCALL_DEFINEx(3, _##name, 
__VA_ARGS__)
                                     ^~~~~~~~~~~~~~~
arch/powerpc/kernel/signal_32.c:1044:1: note: in expansion of macro 
'SYSCALL_DEFINE3'
  SYSCALL_DEFINE3(swapcontext, struct ucontext __user *, old_ctx,
  ^~~~~~~~~~~~~~~
./include/linux/syscalls.h:238:18: note: aliased declaration here
   asmlinkage long __se_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__)) \
                   ^~~~~~~~
./include/linux/syscalls.h:222:2: note: in expansion of macro 
'__SYSCALL_DEFINEx'
   __SYSCALL_DEFINEx(x, sname, __VA_ARGS__)
   ^~~~~~~~~~~~~~~~~
./include/linux/syscalls.h:213:36: note: in expansion of macro 
'SYSCALL_DEFINEx'
  #define SYSCALL_DEFINE3(name, ...) SYSCALL_DEFINEx(3, _##name, 
__VA_ARGS__)
                                     ^~~~~~~~~~~~~~~
arch/powerpc/kernel/signal_32.c:1044:1: note: in expansion of macro 
'SYSCALL_DEFINE3'
  SYSCALL_DEFINE3(swapcontext, struct ucontext __user *, old_ctx,
  ^~~~~~~~~~~~~~~
./include/linux/syscalls.h:233:18: warning: 'sys_debug_setcontext' alias 
between functions of incompatible types 'long int(struct ucontext *, 
int,  struct sig_dbg_op *)' and 'long int(long int,  long int,  long 
int)' [-Wattribute-alias]
   asmlinkage long sys##name(__MAP(x,__SC_DECL,__VA_ARGS__)) \
                   ^~~
./include/linux/syscalls.h:222:2: note: in expansion of macro 
'__SYSCALL_DEFINEx'
   __SYSCALL_DEFINEx(x, sname, __VA_ARGS__)
   ^~~~~~~~~~~~~~~~~
./include/linux/syscalls.h:213:36: note: in expansion of macro 
'SYSCALL_DEFINEx'
  #define SYSCALL_DEFINE3(name, ...) SYSCALL_DEFINEx(3, _##name, 
__VA_ARGS__)
                                     ^~~~~~~~~~~~~~~
arch/powerpc/kernel/signal_32.c:1232:1: note: in expansion of macro 
'SYSCALL_DEFINE3'
  SYSCALL_DEFINE3(debug_setcontext, struct ucontext __user *, ctx,
  ^~~~~~~~~~~~~~~
./include/linux/syscalls.h:238:18: note: aliased declaration here
   asmlinkage long __se_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__)) \
                   ^~~~~~~~
./include/linux/syscalls.h:222:2: note: in expansion of macro 
'__SYSCALL_DEFINEx'
   __SYSCALL_DEFINEx(x, sname, __VA_ARGS__)
   ^~~~~~~~~~~~~~~~~
./include/linux/syscalls.h:213:36: note: in expansion of macro 
'SYSCALL_DEFINEx'
  #define SYSCALL_DEFINE3(name, ...) SYSCALL_DEFINEx(3, _##name, 
__VA_ARGS__)
                                     ^~~~~~~~~~~~~~~
arch/powerpc/kernel/signal_32.c:1232:1: note: in expansion of macro 
'SYSCALL_DEFINE3'
  SYSCALL_DEFINE3(debug_setcontext, struct ucontext __user *, ctx,
  ^~~~~~~~~~~~~~~


Christophe

> 
> As arch/powerpc code is built with -Werror, this breaks build with
> GCC 8.1
> 
> This patch inhibits that warning
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
> ---
>   arch/powerpc/Makefile | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
> index 26ccd0b91512..d6c557530ce8 100644
> --- a/arch/powerpc/Makefile
> +++ b/arch/powerpc/Makefile
> @@ -145,6 +145,8 @@ CFLAGS-$(CONFIG_PPC64)	+= $(call cc-option,-mno-pointers-to-nested-functions)
>   CFLAGS-$(CONFIG_PPC32)	:= -ffixed-r2 $(MULTIPLEWORD)
>   CFLAGS-$(CONFIG_PPC32)	+= $(call cc-option,-mno-readonly-in-sdata)
>   
> +CFLAGS-y += $(call cc-option,-Wno-attribute-alias)
> +
>   ifeq ($(CONFIG_PPC_BOOK3S_64),y)
>   ifeq ($(CONFIG_CPU_LITTLE_ENDIAN),y)
>   CFLAGS-$(CONFIG_GENERIC_CPU) += -mcpu=power8
> 

Re: [PATCH] powerpc/Makefile: fix build failure by disabling attribute-alias warning

[Christophe LEROY]

Le 28/05/2018 à 16:37, Segher Boessenkool a écrit :
> On Mon, May 28, 2018 at 02:17:49PM +0000, Christophe Leroy wrote:
>> Latest GCC version emit many warnings similar to the following one.
> 
> You didn't actually show an example?

Yes I forgot:

In file included from arch/powerpc/kernel/syscalls.c:24:
./include/linux/syscalls.h:233:18: warning: 'sys_mmap2' alias between 
functions of incompatible types 'long int(long unsigned int,  size_t, 
long unsigned int,  long unsigned int,  long unsigned int,  long 
unsigned int)' {aka 'long int(long unsigned int,  unsigned int,  long 
unsigned int,  long unsigned int,  long unsigned int,  long unsigned 
int)'} and 'long int(long int,  long int,  long int,  long int,  long 
int,  long int)' [-Wattribute-alias]
   asmlinkage long sys##name(__MAP(x,__SC_DECL,__VA_ARGS__)) \
                   ^~~
./include/linux/syscalls.h:222:2: note: in expansion of macro 
'__SYSCALL_DEFINEx'
   __SYSCALL_DEFINEx(x, sname, __VA_ARGS__)
   ^~~~~~~~~~~~~~~~~
./include/linux/syscalls.h:216:36: note: in expansion of macro 
'SYSCALL_DEFINEx'
  #define SYSCALL_DEFINE6(name, ...) SYSCALL_DEFINEx(6, _##name, 
__VA_ARGS__)
                                     ^~~~~~~~~~~~~~~
arch/powerpc/kernel/syscalls.c:65:1: note: in expansion of macro 
'SYSCALL_DEFINE6'
  SYSCALL_DEFINE6(mmap2, unsigned long, addr, size_t, len,
  ^~~~~~~~~~~~~~~
./include/linux/syscalls.h:238:18: note: aliased declaration here
   asmlinkage long __se_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__)) \
                   ^~~~~~~~
./include/linux/syscalls.h:222:2: note: in expansion of macro 
'__SYSCALL_DEFINEx'
   __SYSCALL_DEFINEx(x, sname, __VA_ARGS__)
   ^~~~~~~~~~~~~~~~~
./include/linux/syscalls.h:216:36: note: in expansion of macro 
'SYSCALL_DEFINEx'
  #define SYSCALL_DEFINE6(name, ...) SYSCALL_DEFINEx(6, _##name, 
__VA_ARGS__)
                                     ^~~~~~~~~~~~~~~
arch/powerpc/kernel/syscalls.c:65:1: note: in expansion of macro 
'SYSCALL_DEFINE6'
  SYSCALL_DEFINE6(mmap2, unsigned long, addr, size_t, len,
  ^~~~~~~~~~~~~~~

> 
> This warning should detect serious problems, so don't disable it without
> first investigating please.

It's been a discussion on this topic, ref 
https://lkml.org/lkml/2017/12/5/581

It says "The new warning seems reasonable in principle, but it doesn't
help us here, since we rely on the type mismatch to sanitize the
system call arguments. After I reported this as GCC PR82435, a new
-Wno-attribute-alias option was added that could be used to turn the
warning off globally on the command line, but I'd prefer to do it a
little more fine-grained"


> 
> What do you call "latest version", btw?  Trunk, aka 9.0?  Or the most
> advanced release, 8.1?  Or the latest release (which also is 8.1 :-) )

I encounter it with 8.1
According the refered discusion, it linked to GCC 8

Christophe

> 
> 
> Segher
> 

Re: [PATCH] powerpc/Makefile: fix build failure by disabling attribute-alias warning

[Segher Boessenkool]

On Mon, May 28, 2018 at 02:39:37PM +0000, Christophe Leroy wrote:
> In file included from arch/powerpc/kernel/syscalls.c:24:
> ./include/linux/syscalls.h:233:18: warning: 'sys_mmap2' alias between 
> functions of incompatible types 'long int(long unsigned int,  size_t, 
> long unsigned int,  long unsigned int,  long unsigned int,  long 
> unsigned int)' {aka 'long int(long unsigned int,  unsigned int,  long 
> unsigned int,  long unsigned int,  long unsigned int,  long unsigned 
> int)'} and 'long int(long int,  long int,  long int,  long int,  long 
> int,  long int)' [-Wattribute-alias]

So yes, these are actually different (int vs. long).

> In file included from arch/powerpc/kernel/signal_32.c:29:
> ./include/linux/syscalls.h:233:18: warning: 'sys_swapcontext' alias 
> between functions of incompatible types 'long int(struct ucontext *, 
> struct ucontext *, long int)' and 'long int(long int,  long int,  long 
> int)' [-Wattribute-alias]

And this one is quite spectacularly different.


Try putting this before the wacko aliases:

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wattribute-alias"

and this after:

#pragma GCC diagnostic pop

so that you will get this quite useful warning for all other code.


Segher

Re: [PATCH] powerpc/Makefile: fix build failure by disabling attribute-alias warning

[Mathieu Malaterre]

On Mon, May 28, 2018 at 5:07 PM, Segher Boessenkool
<segher@kernel.crashing.org> wrote:
> On Mon, May 28, 2018 at 02:39:37PM +0000, Christophe Leroy wrote:
>> In file included from arch/powerpc/kernel/syscalls.c:24:
>> ./include/linux/syscalls.h:233:18: warning: 'sys_mmap2' alias between
>> functions of incompatible types 'long int(long unsigned int,  size_t,
>> long unsigned int,  long unsigned int,  long unsigned int,  long
>> unsigned int)' {aka 'long int(long unsigned int,  unsigned int,  long
>> unsigned int,  long unsigned int,  long unsigned int,  long unsigned
>> int)'} and 'long int(long int,  long int,  long int,  long int,  long
>> int,  long int)' [-Wattribute-alias]
>
> So yes, these are actually different (int vs. long).
>
>> In file included from arch/powerpc/kernel/signal_32.c:29:
>> ./include/linux/syscalls.h:233:18: warning: 'sys_swapcontext' alias
>> between functions of incompatible types 'long int(struct ucontext *,
>> struct ucontext *, long int)' and 'long int(long int,  long int,  long
>> int)' [-Wattribute-alias]
>
> And this one is quite spectacularly different.

https://patchwork.kernel.org/patch/10375607/

>
> Try putting this before the wacko aliases:
>
> #pragma GCC diagnostic push
> #pragma GCC diagnostic ignored "-Wattribute-alias"
>
> and this after:
>
> #pragma GCC diagnostic pop
>
> so that you will get this quite useful warning for all other code.
>
>
> Segher