Confusion in usr/include/asm-generic/fcntl.h

usr/include/asm-generic/fcntl.h is giving 2 'make headers_check' warnings:
usr/include/asm-generic/fcntl.h:127: leaks CONFIG_64BIT to userspace where it is not valid usr/include/asm-generic/fcntl.h:149: leaks CONFIG_64BIT to userspace where it is not valid

usr/include/asm-generic/fcntl.h:

#ifndef CONFIG_64BIT will always be true for userspace. So what is the use of #ifndef CONFIG_64BIT ?

From: Jaswinder Singh Rajput <[email protected]>
Date: Wed, 21 Jan 2009 05:34:17 +0530

Quoted 5 lines

usr/include/asm-generic/fcntl.h is giving 2 'make headers_check' warnings:
usr/include/asm-generic/fcntl.h:127: leaks CONFIG_64BIT to userspace where it is not valid usr/include/asm-generic/fcntl.h:149: leaks CONFIG_64BIT to userspace where it is not valid

usr/include/asm-generic/fcntl.h:

...

Quoted 1 line

#ifndef CONFIG_64BIT will always be true for userspace. So what is the use of #ifndef CONFIG_64BIT ?

Good catch.

This file needs to test for 64-bit'ness using some non-CONFIG_* test. And the standard built-in CPP macros which can be used to check for that are different on every platform.

I think we should simply define a macro for use in the kernel, e.g. in <asm/types.h>. There already is a BITS_PER_LONG macro in there, maybe we can add an exported __BITS_PER_LONG there that checks for the right macro on each architecture.

On parisc, there is a major confusion in this area, at some point, all checks for __LP64__ got replaced with CONFIG_64BIT there. While I have not understood what the problem with __LP64__ was, the check for CONFIG_64BIT on parisc user space looks very wrong.

Quoted 4 lines

On parisc, there is a major confusion in this area, at some point, all checks for __LP64__ got replaced with CONFIG_64BIT there. While I have not understood what the problem with __LP64__ was, the check for CONFIG_64BIT on parisc user space looks very wrong.

From: Arnd Bergmann <[email protected]>

Quoted 4 lines

Quoted 4 lines

On parisc, there is a major confusion in this area, at some point, all checks for __LP64__ got replaced with CONFIG_64BIT there. While I have not understood what the problem with __LP64__ was, the check for CONFIG_64BIT on parisc user space looks very wrong.

I think the parisc mess is my fault. I once replaced the __LP64__ by CONFIG_64BIT and forgot that some files are exported to userspace. I'll clean that up and send patches.

Quoted 9 lines · Helge Deller

From: Arnd Bergmann <[email protected]>

Quoted 4 lines

Quoted 4 lines

On parisc, there is a major confusion in this area, at some point, all checks for __LP64__ got replaced with CONFIG_64BIT there. While I have not understood what the problem with __LP64__ was, the check for CONFIG_64BIT on parisc user space looks very wrong.

I think the parisc mess is my fault. I once replaced the __LP64__ by CONFIG_64BIT and forgot that some files are exported to userspace. I'll clean that up and send patches.

I have a patch set that introduces a lot more asm-generic headers where I also need a generic way to check for this. The approach I chose here was to check "#if __BITS_PER_LONG == 64" for anything that is exported to user space. Maybe you can #define this in asm/types.h and use this check in the parisc headers as well.

Could we add a new symbol for this?
We know we are going to use this in several places so a simpler varia=

would be more readable.
=20
Something like:
=20
#ifdef __64BIT
...
#endif
=20
When we define __64BIT we would use the =A0__BITS_PER_LONG =3D=3D 64 =

Quoted 2 lines · Sam Ravnborg

Could we add a new symbol for this?
We know we are going to use this in several places so a simpler var=

Quoted 9 lines

would be more readable.
=20
Something like:
=20
#ifdef __64BIT
...
#endif
=20
When we define __64BIT we would use the =A0__BITS_PER_LONG =3D=3D 6=

=20
I would prefer using the __BITS_PER_LONG =3D=3D 64 check directly, be=

it gives you a warning when __BITS_PER_LONG is undefined, whereas the #ifdef check gets easily fooled by include order problems. Note that this is not a problem in the kernel for CONFIG_* symbols which are always defined before the first #include.
=20

I would prefer using the __BITS_PER_LONG == 64 check directly, because it gives you a warning when __BITS_PER_LONG is undefined, whereas the #ifdef check gets easily fooled by include order problems. Note that this is not a problem in the kernel for CONFIG_* symbols which are always defined before the first #include.

Quoted 10 lines · Sam Ravnborg

Could we add a new symbol for this?
We know we are going to use this in several places so a simpler variant would be more readable.

Something like:

#ifdef __64BIT
...
#endif

Quoted 1 line

When we define __64BIT we would use the  __BITS_PER_LONG == 64 check.

I would prefer using the __BITS_PER_LONG == 64 check directly, because it gives you a warning when __BITS_PER_LONG is undefined, whereas the #ifdef check gets easily fooled by include order problems. Note that this is not a problem in the kernel for CONFIG_* symbols which are always defined before the first #include.

It gives the warning only if you add -Wundef which IIRC is not default with -Wall. And using the "__BITS_PER_LONG == 64" the risk of gitting the expression wrong is much higher than the simpler variant where you only write:

    __64BIT

But I have no strong feelings for it.

Quoted 8 lines · Helge Deller

From: Arnd Bergmann <[email protected]>

Quoted 4 lines

Quoted 4 lines

On parisc, there is a major confusion in this area, at some point, all checks for __LP64__ got replaced with CONFIG_64BIT there. While I have not understood what the problem with __LP64__ was, the check for CONFIG_64BIT on parisc user space looks very wrong.

I think the parisc mess is my fault. I once replaced the __LP64__ by CONFIG_64BIT and forgot that some files are exported to userspace. I'll clean that up and send patches.

I have a patch set that introduces a lot more asm-generic headers where I also need a generic way to check for this. The approach I chose here was to check "#if __BITS_PER_LONG == 64" for anything that is exported to user space. Maybe you can #define this in asm/types.h and use this check in the parisc headers as well.

Quoted 3 lines

This file needs to test for 64-bit'ness using some non-CONFIG_* test. And the standard built-in CPP macros which can be used to check for that are different on every platform.

I think we should simply define a macro for use in the kernel, e.g. in <asm/types.h>. There already is a BITS_PER_LONG macro in there, maybe we can add an exported __BITS_PER_LONG there that checks for the right macro on each architecture.

On parisc, there is a major confusion in this area, at some point, all checks for __LP64__ got replaced with CONFIG_64BIT there. While I have not understood what the problem with __LP64__ was,

the check for
CONFIG_64BIT on parisc user space looks very wrong.

Quoted 1 line

CONFIG_64BIT on parisc user space looks very wrong.

This shouldn't be exported to user space. Is that what you meant?

Quoted 2 lines

Quoted 1 line

CONFIG_64BIT on parisc user space looks very wrong.

This shouldn't be exported to user space. Is that what you meant?

This does get exported to user space as applications sometimes need to know whether they are running under a 32 or 64-bit kernel. See config.guess. However, it certainly would be wrong to use this to make decisions about user space.

CONFIG_* macros are not (or at least should not) be exported to userspace! Userspace should not make compile-time decisions based on kernel configuration -- a runtime property!

Unfortunately, this decision was made years ago...

dave@mx3210:~$ uname -m
parisc64
dave@hiauly6:~/gnu/gcc-4.4/gcc$ uname -m
parisc

The only significant difference between the above two machines is that mx3210 is running a 64-bit kernel and hiauly6 is running a 32-bit kernel. Both are PA 2.0 machines. Some PA 2.0 machines can only run 64-bit kernels. The workstations can typically run both.

The issue for user space is that 64-bit kernels can support both 32 and 64-bit applications. This affects build scripts and make files. The default machine selected by config.guess for parisc64 is hppa64. Separate applications provide 32-bit and 64-bit support in binutils, cc and gdb. hppa64 selects 64-bit support when build these applications. So, if you want a 32-bit compiler, you need to explicitly override the default chosen by config.guess.

From: Jaswinder Singh Rajput <[email protected]>
Date: Wed, 21 Jan 2009 05:34:17 +0530

Quoted 5 lines

usr/include/asm-generic/fcntl.h is giving 2 'make headers_check' warnings:
usr/include/asm-generic/fcntl.h:127: leaks CONFIG_64BIT to userspace where it is not valid usr/include/asm-generic/fcntl.h:149: leaks CONFIG_64BIT to userspace where it is not valid

usr/include/asm-generic/fcntl.h:

...

Quoted 1 line

#ifndef CONFIG_64BIT will always be true for userspace. So what is the use of #ifndef CONFIG_64BIT ?

Good catch.

This file needs to test for 64-bit'ness using some non-CONFIG_* test. And the standard built-in CPP macros which can be used to check for that are different on every platform.

We can, of course, also do our own thing as DaveM suggested

Quoted 13 lines · David Miller

From: Jaswinder Singh Rajput <[email protected]>
Date: Wed, 21 Jan 2009 05:34:17 +0530

Quoted 5 lines

usr/include/asm-generic/fcntl.h is giving 2 'make headers_check' warnings:
usr/include/asm-generic/fcntl.h:127: leaks CONFIG_64BIT to userspace where it is not valid usr/include/asm-generic/fcntl.h:149: leaks CONFIG_64BIT to userspace where it is not valid

usr/include/asm-generic/fcntl.h:

...

Quoted 1 line

#ifndef CONFIG_64BIT will always be true for userspace. So what is the use of #ifndef CONFIG_64BIT ?

Good catch.

Quoted 4 lines

This file needs to test for 64-bit'ness using some non-CONFIG_* test. And the standard built-in CPP macros which can be used to check for that are different on every platform.

There are a few ways to check for 64-bitness that are platform-independent, unfortunately each of them have drawbacks.

So who wins the race for CONFIG_64BIT and will be right candidate for usr/include/asm-generic/fcntl.h:

1. #if BITS_PER_LONG == 64

OR

2. #if __BITS_PER_LONG == 64

OR

3. #ifdef __LP64__

OR

4. #if __SIZEOF_POINTER__ == 8

OR

5. #if LONG_MAX > 2147483647L

OR

6. #ifdef __64BIT

Quoted 2 lines

2. #if __BITS_PER_LONG == 64

my suggestion, looks good