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exec: assert that RAMBlock size is non-zero

find_ram_offset() does not handle size=0 gracefully.  It hands out the
same RAMBlock offset multiple times, leading to obscure failures later

Add an assert to warn early if something is incorrectly allocating a
zero size RAMBlock.

Signed-off-by: Stefan Hajnoczi <>
Signed-off-by: Michael S. Tsirkin <>
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1 parent 8c7f3dd commit 49cd9ac6a1929467e2df5783a5183fc7708ec3ff Stefan Hajnoczi committed with mstsirkin Mar 11, 2013
Showing with 2 additions and 0 deletions.
  1. +2 −0 exec.c
2 exec.c
@@ -925,6 +925,8 @@ static ram_addr_t find_ram_offset(ram_addr_t size)
RAMBlock *block, *next_block;
ram_addr_t offset = RAM_ADDR_MAX, mingap = RAM_ADDR_MAX;
+ assert(size != 0); /* it would hand out same offset multiple times */
if (QTAILQ_EMPTY(&ram_list.blocks))
return 0;

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