[v7,5/6] powerpc/64: Make COMPAT user-selectable disabled on littleendian by default.
diff mbox series

Message ID c7c88e88408588fa6fcf858a5ae503b5e2f4ec0b.1567198492.git.msuchanek@suse.de
State New
Headers show
Series
  • Disable compat cruft on ppc64le v7
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Commit Message

Michal Suchánek Aug. 30, 2019, 9:03 p.m. UTC
On bigendian ppc64 it is common to have 32bit legacy binaries but much
less so on littleendian.

Signed-off-by: Michal Suchanek <msuchanek@suse.de>
Reviewed-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
v3: make configurable
---
 arch/powerpc/Kconfig | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

Comments

Michael Ellerman Sept. 2, 2019, 2:03 a.m. UTC | #1
Michal Suchanek <msuchanek@suse.de> writes:
> On bigendian ppc64 it is common to have 32bit legacy binaries but much
> less so on littleendian.

I think the toolchain people will tell you that there is no 32-bit
little endian ABI defined at all, if anything works it's by accident.

So I think we should not make this selectable, unless someone puts their
hand up to say they want it and are willing to test it and keep it
working.

cheers

> v3: make configurable
> ---
>  arch/powerpc/Kconfig | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 5bab0bb6b833..b0339e892329 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -264,8 +264,9 @@ config PANIC_TIMEOUT
>  	default 180
>  
>  config COMPAT
> -	bool
> -	default y if PPC64
> +	bool "Enable support for 32bit binaries"
> +	depends on PPC64
> +	default y if !CPU_LITTLE_ENDIAN
>  	select COMPAT_BINFMT_ELF
>  	select ARCH_WANT_OLD_COMPAT_IPC
>  	select COMPAT_OLD_SIGACTION
> -- 
> 2.22.0
Segher Boessenkool Sept. 2, 2019, 1 p.m. UTC | #2
On Mon, Sep 02, 2019 at 12:03:12PM +1000, Michael Ellerman wrote:
> Michal Suchanek <msuchanek@suse.de> writes:
> > On bigendian ppc64 it is common to have 32bit legacy binaries but much
> > less so on littleendian.
> 
> I think the toolchain people will tell you that there is no 32-bit
> little endian ABI defined at all, if anything works it's by accident.

There of course is a lot of powerpcle-* support.  The ABI used for it
on linux is the SYSV ABI, just like on BE 32-bit.

There also is specific powerpcle-linux support in GCC, and in binutils,
too.  Also, config.guess/config.sub supports it.  Half a year ago this
all built fine (no, I don't test it often either).

I don't think glibc supports it though, so I wonder if anyone builds an
actual system with it?  Maybe busybox or the like?

> So I think we should not make this selectable, unless someone puts their
> hand up to say they want it and are willing to test it and keep it
> working.

What about actual 32-bit LE systems?  Does anyone still use those?


Segher
Michael Ellerman Sept. 2, 2019, 11:53 p.m. UTC | #3
Segher Boessenkool <segher@kernel.crashing.org> writes:
> On Mon, Sep 02, 2019 at 12:03:12PM +1000, Michael Ellerman wrote:
>> Michal Suchanek <msuchanek@suse.de> writes:
>> > On bigendian ppc64 it is common to have 32bit legacy binaries but much
>> > less so on littleendian.
>> 
>> I think the toolchain people will tell you that there is no 32-bit
>> little endian ABI defined at all, if anything works it's by accident.
                ^
                v2

> There of course is a lot of powerpcle-* support.  The ABI used for it
> on linux is the SYSV ABI, just like on BE 32-bit.

I was talking about ELFv2, which is 64-bit only. But that was based on
me thinking we had a hard assumption in the kernel that ppc64le kernels
always expect ELFv2 userland. Looking at the code though I was wrong
about that, it looks like we will run little endian ELFv1 binaries,
though I don't think anyone is testing it.

> There also is specific powerpcle-linux support in GCC, and in binutils,
> too.  Also, config.guess/config.sub supports it.  Half a year ago this
> all built fine (no, I don't test it often either).
>
> I don't think glibc supports it though, so I wonder if anyone builds an
> actual system with it?  Maybe busybox or the like?
>
>> So I think we should not make this selectable, unless someone puts their
>> hand up to say they want it and are willing to test it and keep it
>> working.
>
> What about actual 32-bit LE systems?  Does anyone still use those?

Not that I've ever heard of.

cheers
Christophe Leroy Sept. 3, 2019, 5:21 a.m. UTC | #4
On 09/02/2019 11:53 PM, Michael Ellerman wrote:
> Segher Boessenkool <segher@kernel.crashing.org> writes:
>> On Mon, Sep 02, 2019 at 12:03:12PM +1000, Michael Ellerman wrote:
>>> Michal Suchanek <msuchanek@suse.de> writes:
>>>> On bigendian ppc64 it is common to have 32bit legacy binaries but much
>>>> less so on littleendian.
>>>
>>> I think the toolchain people will tell you that there is no 32-bit
>>> little endian ABI defined at all, if anything works it's by accident.
>                  ^
>                  v2
> 
>> There of course is a lot of powerpcle-* support.  The ABI used for it
>> on linux is the SYSV ABI, just like on BE 32-bit.
> 
> I was talking about ELFv2, which is 64-bit only. But that was based on
> me thinking we had a hard assumption in the kernel that ppc64le kernels
> always expect ELFv2 userland. Looking at the code though I was wrong
> about that, it looks like we will run little endian ELFv1 binaries,
> though I don't think anyone is testing it.
> 
>> There also is specific powerpcle-linux support in GCC, and in binutils,
>> too.  Also, config.guess/config.sub supports it.  Half a year ago this
>> all built fine (no, I don't test it often either).
>>
>> I don't think glibc supports it though, so I wonder if anyone builds an
>> actual system with it?  Maybe busybox or the like?
>>
>>> So I think we should not make this selectable, unless someone puts their
>>> hand up to say they want it and are willing to test it and keep it
>>> working.
>>
>> What about actual 32-bit LE systems?  Does anyone still use those?
> 
> Not that I've ever heard of.
> 

We dropped support from 32-bit LE at least with a1f3ae3fe8a1 
("powerpc/32: Use stmw/lmw for registers save/restore in asm").

Discussion about it can be found at 
https://patchwork.ozlabs.org/patch/899465/

Christophe

Patch
diff mbox series

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 5bab0bb6b833..b0339e892329 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -264,8 +264,9 @@  config PANIC_TIMEOUT
 	default 180
 
 config COMPAT
-	bool
-	default y if PPC64
+	bool "Enable support for 32bit binaries"
+	depends on PPC64
+	default y if !CPU_LITTLE_ENDIAN
 	select COMPAT_BINFMT_ELF
 	select ARCH_WANT_OLD_COMPAT_IPC
 	select COMPAT_OLD_SIGACTION