Bug 23490 – DMD creating corrupted vtable

Created attachment 1862 reduced code for reproducing bug For certain module hierarchies, DMD is creating a corrupted vtable. Executable segfaults with the latest 2.101 release and LDC2 release 1.30. works fine with version 2.100 and with LDC2 1.29 releases. To replicate untar the attachment and: $ tar zxf code.tgz $ cd code $ rdmd test.d

Fascinating, deleting class Mu, which is a cousin to Frop, eliminates the segfault. And so does moving it below the definition of Frop! Definitely a regression introduced between .100 and .101 Traced to dmd commit b8cd91784e693b92eaf19034ab34c59a9836c98a to introduce the regression. Removing the code it added in expressionsem fixes the issue.

PR that has the offending commit: https://github.com/dlang/dmd/pull/14123

Confirmed. Function gets added to the vtable before the base vtbl has been copied across. Can add a internal ICE for this to ensure that the memcpy() doesn't override any existing entries. ``` --- a/compiler/src/dmd/dsymbolsem.d +++ b/compiler/src/dmd/dsymbolsem.d @@ -5153,6 +5153,7 @@ private extern(C++) final class DsymbolSemanticVisitor : Visitor } // Copy vtbl[] from base class + assert(cldec.vtbl.dim == 0); cldec.vtbl.setDim(cldec.baseClass.vtbl.dim); memcpy(cldec.vtbl.tdata(), cldec.baseClass.vtbl.tdata(), (void*).sizeof * cldec.vtbl.dim); ``` And running this test, we correctly hit the ICE. --- core.exception.AssertError@src/dmd/dsymbolsem.d(5156): Assertion failure ---------------- ??:? _d_assertp [0x557f420a04bc] src/dmd/dsymbolsem.d:5156 _ZN22DsymbolSemanticVisitor5visitEP16ClassDeclaration [0x557f41e16eff] src/dmd/dclass.d:1006 _ZN16ClassDeclaration6acceptEP7Visitor [0x557f41dc1565] src/dmd/dsymbolsem.d:130 _Z15dsymbolSemanticP7DsymbolP5Scope [0x557f41e07275] src/dmd/dmodule.d:1366 _ZN6Module19runDeferredSemanticEv [0x557f41de7ffc] src/dmd/dsymbolsem.d:2000 void dmd.dsymbolsem.DsymbolSemanticVisitor.visit(dmd.dmodule.Module).__lambda3!(dmd.dsymbol.Dsymbol).__lambda3(dmd.dsymbol.Dsymbol) [0x557f41e0d1e5] src/dmd/dsymbol.d:105 void dmd.dsymbol.foreachDsymbol(dmd.root.array.Array!(dmd.dsymbol.Dsymbol).Array*, void delegate(dmd.dsymbol.Dsymbol)) [0x557f41e008af] ---

With the ICE, it's easier to get a further reduction/consolidation of sources. frop.d --- import pop; class Mu: Pop { } class Frop : Pop { // final // does not fail if declared final void frolick() {} } --- pop.d --- import frop; import zoo: Zoo; class Pop { void poop(Frop ) { } void copy(Zoo ) { } } --- zoo.d --- import pop; import frop; class Foo(): Pop { override void poop(Frop frop) { frop.frolick; } } class Baz { Foo!() foo; Frop frop; } class Bar { static instance() { return new Baz; } auto ss = __traits(getAttributes, instance.frop); } class Zoo { } --- ICE triggered with: dmd -o- pop.d

@ibuclaw created dlang/dmd pull request #14661 "fix Issue 23490 - [REG 2.101] Class vtable being overwritten by class semantic ran out of order" fixing this issue: - fix Issue 23490 - [REG 2.101] Class vtable being overwritten by class semantic ran out of order https://github.com/dlang/dmd/pull/14661

dlang/dmd pull request #14661 "fix Issue 23490 - [REG 2.101] Class vtable being overwritten by class semantic ran out of order" was merged into stable: - 05ffb4e73629099faac07c50d5fa8f18bc2413a5 by Iain Buclaw: fix Issue 23490 - [REG 2.101] Class vtable being overwritten by class semantic ran out of order https://github.com/dlang/dmd/pull/14661

dlang/dmd pull request #14701 "merge stable" was merged into master: - 723ef3bc1d465c50d508cf75b2872c99a196f7df by Iain Buclaw: fix Issue 23490 - [REG 2.101] Class vtable being overwritten by class semantic ran out of order https://github.com/dlang/dmd/pull/14701