[PATCH] Cygwin: cygheap: fix fork error after heap has grown

[David McFarland]

2f9b8ff0 introduced a problem where forks would sometimes fail with:

child_copy: cygheap read copy failed, 0x0..0x80044C750, done 0, windows pid 14032, Win32 error 299

When cygheap_max was > CYGHEAP_STORAGE_INITIAL, commit_size would be set to
allocsize(cygheap_max), which is an address, not a size.  VirtualAlloc would be
called to commit commit_size bytes, which would fail, and then child_copy would
be called with zero as the base address.

Fixes: 2f9b8ff00cce ("Cygwin: decouple cygheap from Cygwin DLL")
Signed-off-by: David McFarland <corngood@gmail.com>
---
 winsup/cygwin/mm/cygheap.cc | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/winsup/cygwin/mm/cygheap.cc b/winsup/cygwin/mm/cygheap.cc
index 6a20c159a..a20ee5972 100644
--- a/winsup/cygwin/mm/cygheap.cc
+++ b/winsup/cygwin/mm/cygheap.cc
@@ -87,7 +87,8 @@ cygheap_fixup_in_child (bool execed)
   SIZE_T commit_size = CYGHEAP_STORAGE_INITIAL - CYGHEAP_STORAGE_LOW;
 
   if (child_proc_info->cygheap_max > (void *) CYGHEAP_STORAGE_INITIAL)
-    commit_size = allocsize (child_proc_info->cygheap_max);
+    commit_size = allocsize ((char *) child_proc_info->cygheap_max
+                   - CYGHEAP_STORAGE_LOW);
   cygheap = (init_cygheap *) VirtualAlloc ((LPVOID) CYGHEAP_STORAGE_LOW,
 					   CYGHEAP_STORAGE_HIGH
 					   - CYGHEAP_STORAGE_LOW,
-- 
2.39.0.windows.2.1.gf04e877035