[llvm-dev] Zero-sized globals in LLVM IR

[Shoaib Meenai via llvm-dev]

Slightly off-topic, but out of curiosity, what's the PE/COFF mechanism you're intending to use? The standard one I've seen is grouped sections, i.e. you have section$A containing your start symbol, section$C containing your end symbol, and then everything in between is placed in section$B, so the linker ensures it's sorted between the start and end symbols. The start and end symbols I've seen have always been sized the same as the other list entries, though I suppose you could make them zero-sized.

From: llvm-dev <llvm-dev-bounces at lists.llvm.org> on behalf of David Chisnall via llvm-dev <llvm-dev at lists.llvm.org>
Reply-To: David Chisnall <David.Chisnall at cl.cam.ac.uk>
Date: Tuesday, July 17, 2018 at 4:40 AM
To: Bruce Hoult <brucehoult at sifive.com>
Cc: Zhang via llvm-dev <llvm-dev at lists.llvm.org>
Subject: Re: [llvm-dev] Zero-sized globals in LLVM IR

On 17 Jul 2018, at 12:16, Bruce Hoult <brucehoult at sifive.com<mailto:brucehoult at sifive.com>> wrote:
I believe C says you can't have one. Every variable must have a distinct address. I don't know what LLVM IR says, but you could maybe insert an asm label.

I’m aware that C doesn’t permit this, but LLVM is intended to be a portable abstraction between source languages and target binary formats, and all supported object file formats do support it.  In PE/COFF, this is the standard way of implementing the equivalent of the GNU linker’s __start_ magic symbols, for example.

David

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