[Issue 20132] New: segfault on fiber.call() in release mode

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20132

          Issue ID: 20132
           Summary: segfault on fiber.call() in release mode
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: zorael at gmail.com

dmd 2.078.1, Manjaro/Arch x86_64. dub 1.16.0, ldc 1.16.0.

When calling a specific Fiber in dub's release mode, the program segfaults. It
works in debug mode, and binaries compiled with ldc are not affected in either
mode. It does not happen on Windows, dmd 2.078.0.

> git clone https://github.com/zorael/tests -b fibersegfault
> cd tests
> dub build -b release-debug
> gdb --ex 'run' --ex 'bt' ./fibersegfault

I reduced it as much as I could, and the resulting source is a brittle mess.
Literally changing anything more in it, like removing or reordering function
calls, makes the segfault go away. It's only good for reproducing the segfault
and debugging, not for reasoning about.

> Program received signal SIGSEGV, Segmentation fault.
> 0x00005555555a355b in _D8kameloso7plugins4help13onCommandHelpFCQBnQBhQBc10HelpPluginSQCj3irc4defs8IRCEventZ2dgMFZv (__capture=0x0) at source/kameloso/plugins/help.d:15
> 15          void dg()
> #0  0x00005555555a355b in _D8kameloso7plugins4help13onCommandHelpFCQBnQBhQBc10HelpPluginSQCj3irc4defs8IRCEventZ2dgMFZv (__capture=0x0) at source/kameloso/plugins/help.d:15
> #1  0x00007ffff7d7936c in core.thread.Fiber.run() () from /usr/lib/libphobos2.so.0.87
> #2  0x00007ffff7d78733 in fiber_entryPoint () from /usr/lib/libphobos2.so.0.87
> #3  0x0000000000000000 in ?? ()
> Backtrace stopped: Cannot access memory at address 0x7ffff7fce000

__capture=0x0?

--