GC issue? List.pool overwritten by allocated object

[Denis Feklushkin]

On Tuesday, 13 May 2025 at 10:21:12 UTC, Denis Feklushkin wrote:

I added simple `debug(PRINTF)` section exactly after druntime 
allocator. It throws error if newly allocated memory intersects 
with already allocated internal bucket List structures. I hope I 
didn't make a mistake in this code?

```d
auto p = runLocked!(mallocNoSync, mallocTime, numMallocs)(size, 
bits, localAllocSize, ti);

debug(PRINTF)
{
     outer:
     foreach(List* firstList; gcx.bucket)
     {
         List* curr = firstList;
         while(curr !is null)
         {
             void* p_end = cast(ubyte*) p + localAllocSize;
             void* curr_end = cast(ubyte*) curr + List.sizeof;

             const bool notIntersects = ((p < curr && p_end < 
curr) || (p > curr_end && p_end > curr_end));

             if(!notIntersects)
             {
                 printf("%p - allocated into bucket List value, 
located on %p: firstList.pool=%p curr.pool=%p\n",
                     p, curr, firstList.pool, curr.pool);

                 assert(false);
                 break outer;
             }

             curr = curr.next;
         }
     }
}
```

Druntime was built as debug version with enabled INVARIANT, 
MEMSTOMP and PRINTF

Then this snippet was used with compiled druntime (do not forget 
to replace path to new druntime in ldc2.conf):
```d
/+ dub.sdl:
	name "issue"
+/
// How to run: dub run --single app.d

class C {}

void main()
{
     new C;
}
```

```
> dub run --single app.d --compiler=ldc2
     Starting Performing "debug" build using ldc2 for x86_64.
     Building issue ~master: building configuration [application]
      Linking issue
      Running issue
_d_newclass(ci = 0x56496398c350, app.C)
0x5649a1312c90.Gcx::addRange(0x564963985940, 0x564963994718)
GC::malloc(gcx = 0x5649a1312c90, size = 16 bits = 2, ti = app.C)
   => p = 0x7fa30e5cb000
0x7fa30e5cb000 - allocated into bucket List value, located on 
0x7fa30e5cb010: firstList.pool=0x5649a1313fa0 
curr.pool=0x5649a1313fa0
core.exception.AssertError at core/internal/gc/impl/conservative/gc.d(505): Assertion failure
----------------
core/runtime.d:831 [0x564963942d45]
core/lifetime.d:126 [0x56496394234c]
core/runtime.d:753 [0x564963942d0e]
core/runtime.d:773 [0x564963942640]
rt/dmain2.d:241 [0x564963920f30]
rt/deh.d:47 [0x564963949b9e]
rt/dwarfeh.d:347 [0x564963921ac2]
core/exception.d:569 [0x564963936a05]
core/exception.d:808 [0x564963936444]
core/internal/gc/impl/conservative/gc.d:505 [0x5649639502f3]
core/internal/gc/proxy.d:156 [0x56496393cf70]
core/internal/gc/impl/proto/gc.d:101 [0x5649639604fb]
core/internal/gc/proxy.d:156 [0x56496393cf70]
rt/lifetime.d:130 [0x5649639235fe]
app.d:10 [0x56496391a7af]
rt/dmain2.d:520 [0x56496392169c]
rt/dmain2.d:474 [0x5649639214b2]
rt/dmain2.d:520 [0x5649639215ba]
rt/dmain2.d:474 [0x5649639214b2]
rt/dmain2.d:545 [0x564963921372]
rt/dmain2.d:333 [0x564963921040]
/home/denizzz/ldc2_standalone/bin/../import/core/internal/entrypoint.d:42 [0x56496391a7f1]
??:? [0x7fa30e6f6ca7]
??:? __libc_start_main [0x7fa30e6f6d64]
??:? [0x56496391a6d0]
GC.fullCollect()
processing GC Marks, (nil)
rt_finalize2(p = 0x5649a1312c20)
Error Program exited with code 1
```

Am I making an obvious mistake somewhere?