Bug in DMD? (page 2)

March 03, 2023

Re: Bug in DMD?

Posted by ryuukk_
in reply to Vladimir Panteleev

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ryuukk_

Posted in reply to Vladimir Panteleev

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On Friday, 3 March 2023 at 01:11:06 UTC, Vladimir Panteleev wrote:

On Friday, 3 March 2023 at 01:07:07 UTC, ryuukk_ wrote:

I couldn't figure out dustmite, so i started from 0 and managed to hit something:

https://github.com/ryuukk/dmd_bug

Assertion failed: array index out of bounds, file game\app.d, line 5

Wich indicates probably TLS problem?

Yeah... rt.a.stuffs is a TLS variable. The D runtime manages TLS. extern(C) main bypasses D runtime initialization.

I have some questions:

why does it work with LDC?
why does it work with DMD when build/link in 2 step?
why it doesn't work when DMD is invoked once for build/link
is this a bug in DMD or my code is wrong?
if it's wrong, then why does it compile/no error?

#!/usr/bin/env bash

set -e

build_dmd() {
	echo "build dmd"
	dmd \
	-debug -g \
	-m64 -vcolumns -betterC -w -i -i=-std -i=-core \
	-Igame \
	-Istuff/ \
	stuff/rt/object.d \
	game/app.d \
	-of=game.exe
}

build_ldc() {
	echo "build ldc"
	ldc2 \
	-d-debug -g \
	-m64 -vcolumns -betterC -w -i -i=-std -i=-core \
	-Igame \
	-Istuff/ \
	stuff/rt/object.d \
	game/app.d \
	-of=game.exe
}

build_dmd_and_link() {
	echo "build dmd and link (2step)"
	dmd \
	-debug -g -c \
	-m64 -vcolumns -betterC -w -i -i=-std -i=-core \
	-Igame \
	-Istuff/ \
	stuff/rt/object.d \
	game/app.d \
	-of=game.obj

	dmd \
	-debug -g  \
	-m64 -vcolumns -betterC -w -i -i=-std -i=-core \
	-Igame \
	-Istuff/ \
	game.obj \
	-of=game.exe
}


build_ldc
./game.exe
rm game.obj game.exe

build_dmd_and_link
./game.exe
rm game.obj game.exe

build_dmd
./game.exe
rm game.obj game.exe

This works: ```d extern(C) void main() { Stuff[5] temp = [ Stuff(), Stuff(), Stuff(), Stuff(), Stuff(), ]; stuffs = temp[]; stuffs[0].do_something(); } ``` ```d Stuff[] stuffs; ``` The problem here is dmd isn't initializing TLS with a value, but TLS itself is working.

On Friday, 3 March 2023 at 01:24:42 UTC, Richard (Rikki) Andrew Cattermole wrote: > This works: > > ```d > extern(C) void main() > { > Stuff[5] temp = [ > Stuff(), > Stuff(), > Stuff(), > Stuff(), > Stuff(), > ]; > stuffs = temp[]; > stuffs[0].do_something(); > } > ``` > > ```d > Stuff[] stuffs; > ``` > > The problem here is dmd isn't initializing TLS with a value, but TLS itself is working. So it is a DMD bug?

On Friday, 3 March 2023 at 01:37:42 UTC, Richard (Rikki) Andrew Cattermole wrote: > On 03/03/2023 2:33 PM, ryuukk_ wrote: >> So it is a DMD bug? > > Yes and thanks to you I can now say that we can absolutely get rid of DllMain requirement for DLLs! glad the outcome is positive, and i apologies about earlier comments, i may have sounded a little bit rude

On Friday, 3 March 2023 at 01:21:52 UTC, ryuukk_ wrote:

I have some questions:

why does it work with LDC?
why does it work with DMD when build/link in 2 step?
why it doesn't work when DMD is invoked once for build/link

I think these are probably coincidences and the answer can be summarized as "that's what ends up happening due to the details of the implementation".

is this a bug in DMD or my code is wrong?

I would say the code is wrong in principle, though as you've noted it can still work in some specific circumstances.

if it's wrong, then why does it compile/no error?

extern(C) main is a low-level feature, because it effectively turns off parts of the language. However, the rest of the program doesn't know that this is the case - currently the compiler simply assumes you know what you're doing. Maybe it's not OK that it's easy to use it by accident.

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