Bug 20214 – GC: realloc can result in false pointers if address doesn't change

If GC.realloc doesn't change the address of the allocation (either by shrinking or extending in place), the non-allocated area can contain false pointers: import core.memory; import core.stdc.stdio; void main() { // allocate from large pool auto o = GC.malloc(10); auto p = (cast(void**)GC.malloc(4096 * (void*).sizeof))[0 .. 4096]; auto q = (cast(void**)GC.malloc(4096 * (void*).sizeof))[0 .. 4096]; if (p.ptr + p.length is q.ptr) { q[] = o; // fill with pointers // shrink, unused area cleared? auto nq = (cast(void**)GC.realloc(q.ptr, 4000 * (void*).sizeof))[0 .. 4000]; assert(q.ptr is nq.ptr); assert(q.ptr[4095] !is o); GC.free(q.ptr); // expected to extend in place auto np = (cast(void**)GC.realloc(p.ptr, 4200 * (void*).sizeof))[0 .. 4200]; assert(p.ptr is np.ptr); assert(q.ptr[4200] !is o); } else printf("unexpected pointers %p and %p\n", p.ptr, q.ptr); }

@rainers created dlang/druntime pull request #2798 "fix Issue 20214 - GC: realloc can result in false pointers if address…" fixing this issue: - fix Issue 20214 - GC: realloc can result in false pointers if address doesn't change clear additional memory also when shrinking or extending in place https://github.com/dlang/druntime/pull/2798

dlang/druntime pull request #2798 "fix Issue 20214 - GC: realloc can result in false pointers if address…" was merged into master: - 3223f9846701031f2945df702df453501aeb5a13 by Rainer Schuetze: fix Issue 20214 - GC: realloc can result in false pointers if address doesn't change clear additional memory also when shrinking or extending in place https://github.com/dlang/druntime/pull/2798