Bug 5241 – dmd: ABI breakage/regression (TypeInfo.toString() returns partially corrupted string)

At some point, both dmd and Phobos1 added a new member to TypeInfo_Struct: m_flags. The way dmd handles this causes an ABI breakage: dmd will use the _calculated_ size of the struct to calculate the offset of the name string. After that, dmd _unconditionally_ writes the new m_flags field, and writes it at the same offset where the name string is supposed to start. As a result, TypeInfo names for structs are broken. The first 4 items of typeid(somestruct).toString() will contain garbage. I'm not really sure why after these 4 bytes, the expected string starts. Either I got it wrong, or the backend data segment writer does strange things? The problem doesn't appear if the object.d[i] contains the proper m_align. E.g. compare: http://www.dsource.org/projects/phobos/browser/branches/phobos-1.x/phobos/object.d#L141 http://www.dsource.org/projects/tango/browser/trunk/object.di#L163 (WARNING: BSD LICENSED CODE)

(In reply to comment #0) > At some point, both dmd and Phobos1 added a new member to TypeInfo_Struct: > m_flags. Damn, that should be m_align.

Lazy patch: diff --git a/idgen.c b/idgen.c index 023d8a9..c0cfc0b 100644 --- a/idgen.c +++ b/idgen.c @@ -232,6 +232,8 @@ Msgtable msgtable[] = // varargs implementation { "va_argsave_t", "__va_argsave_t" }, { "va_argsave", "__va_argsave" }, + + { "m_align" }, }; diff --git a/typinf.c b/typinf.c index 906795a..ab9d87b 100644 --- a/typinf.c +++ b/typinf.c @@ -593,8 +593,11 @@ void TypeInfoStructDeclaration::toDt(dt_t **pdt) // uint m_flags; dtdword(pdt, tc->hasPointers()); - // uint m_align; - dtdword(pdt, tc->alignsize()); + if (Type::typeinfostruct->search(NULL, Id::m_align, 0)) + { + // uint m_align; + dtdword(pdt, tc->alignsize()); + } #if DMDV2 // xgetMembers