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Date: Tue, 13 Feb 2024 17:25:40 +0100
To: cygwin AT cygwin DOT com
Subject: Re: Cygwin installer hangs when running post-install scripts
Message-ID: <ZcuYBL3D2rSjlhNu@calimero.vinschen.de>
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From: Corinna Vinschen via Cygwin <cygwin AT cygwin DOT com>
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Cc: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>,
        Kevin Ushey <kevinushey AT gmail DOT com>
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On Feb 13 11:09, Corinna Vinschen via Cygwin wrote:
> On Feb 12 14:38, Kevin Ushey via Cygwin wrote:
> > For reference, I first bumped into this when using Git Bash as bundled
> > with Git for Windows, but it sounds like the underlying issue may be
> > in Cygwin. See https://github.com/git-for-windows/git/issues/4808 for
> > more details.
> 
> There is, however, the stacktrace from your above issue report on
> github, which makes more sense, and, incidentally, occurs in code
> following cygwin_split_path in the .text segment:
> 
> (gdb) bt
> #0  0x00000002101eeaf3 in memmem () from [...]
> #1  0x0000000210095d91 in cwdstuff::override_win32_cwd(bool, unsigned int) ()
>    from [...]
> #2  0x000000021009642e in cwdstuff::set(path_conv*, char const*) () from [...]
> #3  0x0000000210047025 in dll_crt0_1(void*) () from [...]
> #4  [...]
> 
> This points to something going wrong during startup, while trying
> to evaluate the global pointer to the hidden ntdll.dll struct we
> called, for want of an official expression, FAST_CWD structure.
> 
> If we can rely on frame 1, a call to memmem crashes, that would
> mean the crash occurs in find_fast_cwd_pointer().
> 
> > Does any of this sound familiar? Is there anything else I can do to
> > get more information here; e.g. are there builds of Cygwin with debug
> > symbols published somewhere, or should I try producing my own debug
> > build?
> 
> Well, you could have mentioned that this is on AArch64.  Fortunately
> you did in the github case, but next time, please tell us here, too.
> 
> I assume you can't run any Cygwin binary, even from outside the
> installer?
> 
> Other than that, the only thing you really could do at this point is to
> check Cygwin's find_fast_cwd_pointer() function and go through this
> function step by step, diving into the assembler code this function
> inspects trying to find out which of the memmem calls fails and how to
> fix it.  And send a patch eventually.
> 
> However, there isn't much point there as long as this is an insider
> build.  In the past, the code often changed and was uncritical in the
> next official release.
> 
> One thing we can do is to skip the find_fast_cwd_pointer() code entirely
> when running on AArch64, but it's a bit annoying, given this wasn't
> necessary in previous AArch64 builds.

I've just pushed a (temporary?) patch to do just that.  This will be
in the test build cygwin-3.6.0-0.37.g4e77fa9b8bf4 which will be
installable via Cygwin's installer in an hour or two.

Please try if this works for you and report back.  You can use this
DLL as workaround for the time being then.


Corinna

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