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To: cygwin AT jdrake DOT com
Subject: Re: fork error when trying to call VirtualAlloc with size==0
Date: Fri, 23 May 2025 09:59:48 +0800
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From: Yuyi Wang via Cygwin <cygwin AT cygwin DOT com>
Reply-To: Yuyi Wang <Strawberry_Str AT hotmail DOT com>
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On Wed, 22 May 2025, Jeremy Drake wrote:
> Ultimately, playing whack-a-mole in a 64-bit address space hoping that the
> DLL will load in the same place as the parent is an exercise in futility,
> especially in only 6 attempts.

Outside cygwin, rustc also try 5 times to load the proc macro DLL, so there are
30 attempts. Could this issue be solved by running rebaseall on binaries in
`/usr/bin`? Should we introduce `rebase` to rustc?

Another idea: is it possible to provide an API to disable reload-on-fork of a
specific DLL? Although it might be unsafe, I think it's OK here, because rustc
just wants to execute the linker, and in this case the proc macro DLLs won't be
used in the new process.

In rust-lang/rust#141276, Jeremy Drake wrote:
> It seems like in most cases it'd probably use posix_spawn

If I were right, posix_spawn also uses fork + exec. That's why I don't think
switching to `Command::spawn` would solve this problem. However, the non-POSIX
spawn* APIs don't use fork. I'm not sure if it worth a try. As it seems that the
linker is executed by LLVM, I think it may be better to patch LLVM.

--
Yuyi Wang

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