Issue 21488 - Always compile dmd with -fPIC on POSIX targets

[ibuclaw]

Segmentation faults or linker errors occur on 32-bit PIE platforms if any object is not compiled with -fPIC.

[dlang-bot]

Thanks for your pull request, @ibuclaw!

Bugzilla references

Auto-close	Bugzilla	Severity	Description
✗	21488	normal	Bundled 32-bit dlang tools (ddemangle, dustmite, rdmd) segfault on startup

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "stable + dmd#12798"

[ibuclaw]

@WalterBright seems that there's something not right with string literals and -fPIC on 32-bit. Looks like a missing null terminator?

https://auto-tester.puremagic.com/show-run.ghtml?projectid=14&runid=4884149&isPull=true

[Geod24]

Looks like a missing null terminator?

Really ? What I see is:

 ... compilable/testheader2i.d      -o- -H -Hfgenerated/compilable/testheader2i.di -inline ()==============================
Test 'compilable/testheader2i.d' failed. The logged output:
Executing post-test script: tools/postscript.sh compilable/extra-files/header-postscript.sh compilable testheader2i generated/compilable/testheader2i.d.out0
+ source compilable/extra-files/header-postscript.sh
++ source tools/common_funcs.sh
++ grep -v 'D import file generated from' generated/compilable/testheader2i.di
++ test_name=header2i
++ diff -pu --strip-trailing-cr compilable/extra-files/header2i.di generated/compilable/testheader2i.di.2
--- compilable/extra-files/header2i.di	2021-07-01 19:51:26.072319059 -0700
+++ generated/compilable/testheader2i.di.2	2021-07-01 20:03:29.439094997 -0700
@@ -117,7 +117,7 @@ void test13275()
 	if (auto n = 1)
 	{
 	}
-	if (const n = 1)
+	if (const @trusted n = 1)
 	{
 	}
 	if (immutable n = 1)
@@ -126,7 +126,7 @@ void test13275()
 	if (shared n = 1)
 	{
 	}
-	if (const shared n = 1)
+	if (const shared @trusted n = 1)
 	{
 	}
 	if (int n = 1)
/home/braddr/sandbox/at-client/pull-4884281-Linux_32/dmd/generated/linux/release/32/dmd -conf= -m32 -Icompilable -o- -H -Hfgenerated/compilable/testheader2i.di -inline  -odgenerated/compilable -ofgenerated/compilable/testheader2i_0.o  -c compilable/testheader2i.d compilable/extra-files/header2.d 

==============================
Test 'compilable/testheader2i.d' failed: Expected rc == 0, but exited with rc == 1

Looks like the assignment ends up with an extra @trusted in its STC ? That would then be emitted here.

[ibuclaw]

Looks like a missing null terminator?

I shouldn't be attempting to triage at 3am in the morning, what I thought I saw was

+	if (const @trusted n = 1)
+	if (const @trusted shared n = 1)

Backend is still guilty until proven innocent.

[ibuclaw]

Both druntime and phobos are now built with shared (dlang/phobos#8154, dlang/druntime#3505), let's see if errors were caused by mixing PIC and non-PIC...

[Geod24]

I think you need a rebase

[ibuclaw]

I rebased against the wrong branch. :D

[WalterBright]

Backend is still guilty until proven innocent.

I need something more specific than that. If there's a code gen bug, please file a bug report.

[ibuclaw]

Backend is still guilty until proven innocent.

I need something more specific than that. If there's a code gen bug, please file a bug report.

There would be something more specific if it were reproducible in a i386/ubuntu:16.04 container.

[ibuclaw]

Also, bug from last year. https://issues.dlang.org/show_bug.cgi?id=21374

[WalterBright]

21374

Thank you. An assert fail in the code generator is clearly a codegen bug.

But there's nothing anyone can do about at one time, something went wrong somewhere.

[ibuclaw]

@WalterBright looks like the EBX has an address which is not pointing to GOT when calling into thunks.

Enabling this disabled code fixes the dll test on 32-bit here locally.
https://github.com/dlang/dmd/blob/master/src/dmd/backend/cod3.d#L4879-L4888

[ibuclaw]

@WalterBright looks like the EBX has an address which is not pointing to GOT when calling into thunks.

Enabling this disabled code fixes the dll test on 32-bit here locally.
https://github.com/dlang/dmd/blob/master/src/dmd/backend/cod3.d#L4879-L4888

Which means #2278 introduced a regression.

[ibuclaw]

Remaining issue in pipeline is due a PIC bug in the host compiler (2.079.0), fixed in 2.090 by #10696.

[ibuclaw]

This should really be pulled as soon as, because the longer it's left, the harder/longer it'll be to wean off ubuntu 14.04/16.04. DMD has already shot itself by not doing this 2-3 years ago with 64bit Linux.