> I would suggest the following patch for kernel 2036 (stable) -->
> --- kernel/memmgr.old 2006-08-18 10:22:33.000000000 +0200
> +++ kernel/memmgr.c 2006-08-18 10:22:33.000000000 +0200
> @@ -66,7 +66,12 @@
> /* join both MCBs */
> p->m_type = q->m_type; /* possibly the next MCB is the last one
> */
> p->m_size += q->m_size + 1; /* one for q's MCB itself */
> +#if 0 /* this disturbs QB 4.x double-free... */
> q->m_type = 'K'; /* Invalidate the magic number */
> +#else
+ q->>m_type = MCB_NORMAL; /* make QB 4.x happy... */
+ q->>m_psp = FREE_PSP; /* leave MCB as "valid but free" */
> +#endif
> }
q->>m_type = MCB_NORMAL; /* make QB 4.x happy... */
is not a good idea (could also be MCB_LAST). just leave it as it is
q->>m_psp = FREE_PSP; /* leave MCB as "valid but free" */
is necessary (it's already free)
leaving
p->m_size += q->m_size + 1; /* one for q's MCB itself */
+#if 0 /* this disturbs QB 4.x double-free... */
q->m_type = 'K'; /* Invalidate the magic number */
+#endif
as the patch I'd recommend
OTOH, now imagine a program
memptr = dos_alloc(100);
dos_free(memptr);
mem2 = dosalloc(10);
dos_resize(memptr,200); /* which will ALSO take ownership of THIS
block !! */
...
you can crash the DOS MCB-list in amazing interesting ways, just by
dos_resize() and dos_free() with freed MCBs
with
q->m_type = 'K'; /* Invalidate the magic number */
you have a good chance to catch this (all bad calls fail)
so IMHO in general your patch is not a good idea to do.
but of course you could have a kernel_config option
sys config BRUN40_COMPATIBLE=1
Tom
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