From: lion@...
Date: 2018-07-02T19:21:56+00:00
Subject: [ruby-core:87756] [Ruby trunk Bug#14883] Ruby 2.5 Fails to Build on	PowerPC 32-bit (BE)

Issue #14883 has been updated by lion (Daming Yang).


Bingo. It is also an issue for the systemd-nspawn container indeed.

systemd-nspawn have used a libseccomp whitelist instead of a blacklist by default since last year.
`rt_sigprocmask()` & `sigprocmask()` are on the whitelist, but `swapcontext()` is not.

Addressed the container issue at https://github.com/systemd/systemd/issues/9485

**You may add `--system-call-filter=swapcontext` on your systemd-nspawn command line as a workaround.**

I hope Ruby will have an enhancement for reporting the error of `getcontext()`.

lion (Daming Yang) wrote:
> contd.
> 
> When it comes to a glibc function `getcontext()`, 'the root issue' of the bug, we can check it in this way:
> 
> ~~~c
> // cat lion_getcontext.c
> #include <ucontext.h>
> #include <errno.h>
> int main() {
>     ucontext_t c;
>     if (getcontext(&c) < 0)
>         return errno;
>     return 0;
> }
> // gcc lion_getcontext.c && ./a.out; echo $?
> ~~~
> 
> Note that the 'host' Bai has, is 32-bit (PPC32) userspace container(systemd-nspawn) on a 64-bit (PPC64) kernel.
> 
> Although the container is a kind of virtualisation, I think it does matter when it comes to glibc and syscall.
> 
> After running the test program, I got
> - 0 on my amd64 laptop,
> - 0 on Bai's PPC64 machine,
> - 1(EPERM) on the PPC32-over-PPC64 container. This is why Ruby SEGV'ed on here.
> 
> Use `strace ./a.out` to trace syscalls. Interesting, the underlying syscalls are different.
> ~~~
> AMD64: rt_sigprocmask(SIG_BLOCK, NULL, [], 8)  = 0
> PPC64: rt_sigprocmask(SIG_BLOCK, NULL, [], 8)  = 0
> PPC32-over-PPC64: swapcontext(0xfffa8dc8, 0) = -1 EPERM (Operation not permitted)
> ~~~
> 
> But it was weird.
> It seems that neither https://github.com/torvalds/linux/blob/v4.8/arch/powerpc/kernel/signal_64.c#L588
> nor https://github.com/torvalds/linux/blob/v4.8/arch/powerpc/kernel/signal_32.c#L1121
> has `return -EPERM;` or does likewise.
> 
> Why was the errno `EPERM`? SELinux is disabled.
> Is it a Linux *capability* issue only if programs run in a systemd-nspawn container?


----------------------------------------
Bug #14883: Ruby 2.5 Fails to Build on PowerPC 32-bit (BE)
https://bugs.ruby-lang.org/issues/14883#change-72780

* Author: mingcongbai (Mingcong Bai)
* Status: Feedback
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: 2.5.1
* Backport: 2.3: UNKNOWN, 2.4: UNKNOWN, 2.5: UNKNOWN
----------------------------------------
When building Ruby 2.5.1 on a PowerPC 32-bit (Big Endian) host, the build fails as it generates rdoc - segmentation fault. The build log is as follows:

https://pastebin.aosc.io/paste/jJWjWPadcmJeLEkvpgnMqQ

Configure parameters...

... \
    --enable-shared \
    --disable-rpath \
    --with-dbm-type=gdbm_compat

On the same host with the same build environment, Ruby 2.4 builds just fine. The current Git master exhibits the same issue.



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