PIC/PIE issue on Nios2

PIC/PIE issue on Nios2

[Romain Naour]

Hello,

The Buildroot project now generate Position-Independent Code (PIC) and link
Position-Independent Executables (PIE) by default.

This add -fPIE or -pie flag at compile/link time while building the toolchain
and the rootfs.

On Nios2 architecture this produce non working executable crashing the system
while starting the init process.

Run /init as init process
  with arguments:
    /init
  with environment:
    HOME=/
    TERM=linux
Failed to execute /init (error -12)

See: Buildroot build log and Qemu runtime test log in build artifacts:
https://gitlab.com/buildroot.org/buildroot/-/jobs/1285145889

Analyzing one of the binary with strace show that the problem occur
very early when starting the new process:

 # strace ./busybox
 execve("./busybox", ["./busybox"], 0x7f91ce90 /* 10 vars */) = -1 ENOMEM
(Cannot allocate memory)
 +++ killed by SIGSEGV +++

I tried with several binutils/glibc/gcc version without any success.

Is PIE is really supported for Nios2 architecture ?

Best regards,
Romain

Re: PIC/PIE issue on Nios2

[Florian Weimer]

* Romain Naour via Libc-alpha:

> Analyzing one of the binary with strace show that the problem occur
> very early when starting the new process:
>
>  # strace ./busybox
>  execve("./busybox", ["./busybox"], 0x7f91ce90 /* 10 vars */) = -1 ENOMEM
> (Cannot allocate memory)
>  +++ killed by SIGSEGV +++
>
> I tried with several binutils/glibc/gcc version without any success.
>
> Is PIE is really supported for Nios2 architecture ?

If the kernel cannot execve the executable at all, that looks more like
a linker problem.  It could also be a kernel bug, of course.  (Address
space layout is architecture-specific.)

There is PIE and statically linked PIE.  The latter should be supported
on all targets.  Statically linked PIE requires toolchain changes and a
little bit of architecture-specific code in glibc.

Thanks,
Florian

Re: PIC/PIE issue on Nios2

[Romain Naour]

Hello,

Le 28/05/2021 à 10:01, Florian Weimer a écrit :
> * Romain Naour via Libc-alpha:
> 
>> Analyzing one of the binary with strace show that the problem occur
>> very early when starting the new process:
>>
>>  # strace ./busybox
>>  execve("./busybox", ["./busybox"], 0x7f91ce90 /* 10 vars */) = -1 ENOMEM
>> (Cannot allocate memory)
>>  +++ killed by SIGSEGV +++
>>
>> I tried with several binutils/glibc/gcc version without any success.
>>
>> Is PIE is really supported for Nios2 architecture ?
> 
> If the kernel cannot execve the executable at all, that looks more like
> a linker problem.  It could also be a kernel bug, of course.  (Address
> space layout is architecture-specific.)
> 
> There is PIE and statically linked PIE.  The latter should be supported
> on all targets.  Statically linked PIE requires toolchain changes and a
> little bit of architecture-specific code in glibc.

I don't know about the status of required toolchain changes for statically
linked PIE for NiosII. The statically linked PIE option (--enable-static-pie) is
not used to build the toolchain so (as you said) it look like a linker problem
or kernel bug.

I tried with the latest kernel version without success.

For now, the PIC/PIE Buildroot option has been disabled for NiosII.

Best regards,
Romain


> 
> Thanks,
> Florian
>