A process spawned inside gem command running on latest ruby segfaults

[Jon Turney]

On 20/02/2025 15:33, Daisuke Fujimura via Cygwin wrote:
> Reproduction:
> - Use ruby-3.4.2-1 (test)
> - Install gem containing native libraries
> 
> ```
> $ uname -srvmpio
> CYGWIN_NT-10.0-22000 3.5.7-1.x86_64 2025-01-29 19:46 UTC x86_64
> unknown unknown Cygwin
> $ ruby -v
> ruby 3.4.2 (2025-02-15 revision d2930f8e7a) +PRISM [x86_64-cygwin]
> $ gem -v
> 3.5.11
> $ cd /tmp
> $ git clone https://cygwin.com/git/cygwin-packages/ruby-debug_inspector
> # Any gem that contains native libraries
> $ cd ruby-debug_inspector
> $ cygport ruby-debug_inspector.cygport fetch prep compile # preparation
> $ cygport ruby-debug_inspector.cygport install
> :
> ```
> 
> The process spawned inside `gem install` seems to raise SIGSEGV
> internally and exits.
> 
> ```
> $ gdb /usr/bin/ruby
> :
> (gdb) run /usr/bin/gem install -V --local --ignore-dependencies
> --document=rdoc,ri --build-root
> /tmp/ruby-debug_inspector/ruby-debug_inspector-1.1.0-1.x86_64/inst
> --install-dir /usr/share/gems --bindir /usr/bin
> debug_inspector-1.1.0.gem #
> https://github.com/cygwin/cygport/blob/0.36.9/cygclass/rubygem.cygclass#L134
> :
> :
> Building native extensions. This could take a while...
> current directory:
> /tmp/ruby-debug_inspector/ruby-debug_inspector-1.1.0-1.x86_64/inst/usr/share/gems/gems/debug_inspector-1.1.0/ext/debug_inspector
> ["/usr/bin/ruby.exe", "-I/usr/share/rubygems", "extconf.rb"]
> [New Thread 3600.0x23a0]
> [New Thread 3600.0x1278]
> [New Thread 3600.0x2794]
> creating Makefile
> 
> Thread 11 "ruby" received signal SIGSEGV, Segmentation fault.
> [Switching to Thread 3600.0x1278]
> 0x0000000000000000 in ?? ()
> 
[...]

> 
> SIGSEGV seems to occur inside the cygwin DLL.

You might get more useful backtrace information after the exception with 
the gdb setting 'set cygwin-exceptions on' (See [1]).

[1] https://cygwin.com/faq.html#faq.programming.debugging-cygwin

(It would be a nice project for someone to work on to see if is possible 
improve this gdb (mis)feature so it only ignores exceptions inside the 
cygwin DLL where exception::myfault() is on the SEH stack [which is used 
to implement things like "POSIX defines that this function returns 
EFAULT when you hand it an invalid pointer"], not all of them).

> This problem also occurs with ruby-3.3.2-3 (test).
> 
> We have confirmed that it also occurs in cygwin-3.6.