[PATCH] tcg: Remove null pointer arithmetic in tcg_malloc()

[Ilya Leoshkevich <iii@linux.ibm.com>]

Clang 20.1.6 (Fedora 20.1.6-1.fc42)'s UBSAN complains:

    qemu/include/tcg/tcg.h:715:19: runtime error: applying non-zero offset 64 to null pointer

The code uses NULL as pool's initial start and end, with the intention
that `pool_cur + size > pool_end` should trigger the allocation.
Unfortunately C prohibits adding non-zero to NULL, even if the result
is not dereferenced.

Fix by using a dummy pool.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
 tcg/tcg.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tcg/tcg.c b/tcg/tcg.c
index d714ae2889c..afcc7ec8849 100644
--- a/tcg/tcg.c
+++ b/tcg/tcg.c
@@ -1358,13 +1358,14 @@ void *tcg_malloc_internal(TCGContext *s, int size)
 
 void tcg_pool_reset(TCGContext *s)
 {
+    static uint8_t dummy_pool;
     TCGPool *p, *t;
     for (p = s->pool_first_large; p; p = t) {
         t = p->next;
         g_free(p);
     }
     s->pool_first_large = NULL;
-    s->pool_cur = s->pool_end = NULL;
+    s->pool_cur = s->pool_end = &dummy_pool;
     s->pool_current = NULL;
 }
 
-- 
2.49.0