Re: [PATCH] S390: Enable static PIE

[Florian Weimer <fweimer@redhat.com>]

* Stefan Liebler via Libc-alpha:

> This commit enables static PIE on 64bit.  On 31bit, static PIE is
> not supported.
>
> - kernel (the mentioned links to the commits belong to 5.19 merge window):
>   - "s390/mmap: increase stack/mmap gap to 128MB"
>     https://git.kernel.org/pub/scm/linux/kernel/git/s390/linux.git/commit/?h=features&id=f2f47d0ef72c30622e62471903ea19446ea79ee2
>   - "s390/vdso: move vdso mapping to its own function"
>     https://git.kernel.org/pub/scm/linux/kernel/git/s390/linux.git/commit/?h=features&id=57761da4dc5cd60bed2c81ba0edb7495c3c740b8
>   - "s390/vdso: map vdso above stack"
>     https://git.kernel.org/pub/scm/linux/kernel/git/s390/linux.git/commit/?h=features&id=9e37a2e8546f9e48ea76c839116fa5174d14e033
>   - "s390/vdso: add vdso randomization"
>     https://git.kernel.org/pub/scm/linux/kernel/git/s390/linux.git/commit/?h=features&id=41cd81abafdc4e58a93fcb677712a76885e3ca25
>   (We can't test the kernel of the target system)
>   Otherwise if /proc/sys/kernel/randomize_va_space is turned off (0),
>   static PIE executables like ldconfig will crash.  While startup sbrk is
>   used to enlarge the HEAP.  Unfortunately the underlying brk syscall fails
>   as there is not enough space after the HEAP.  Then the address of the TLS
>   image is invalid and the following memcpy in __libc_setup_tls() leads
>   to a segfault.
>   If /proc/sys/kernel/randomize_va_space is activated (default: 2), there
>   is enough space after HEAP.

I'll work an early allocator that does not use the TCB and which should
avoid the sbrk crash.  Will that be sufficient to enable static PIE
binaries to run on unchanged kernels?

Otherwise I fear that we end up in a world of pain if we turn ldconfig
into a static PIE binary. 8-(

Thanks,
Florian