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[Qemu-arm] [PATCH v2] target/arm: Stop using variable length array in dc

From: Peter Maydell
Subject: [Qemu-arm] [PATCH v2] target/arm: Stop using variable length array in dc_zva
Date: Fri, 3 May 2019 13:04:48 +0100

Currently the dc_zva helper function uses a variable length
array. In fact we know (as the comment above remarks) that
the length of this array is bounded because the architecture
limits the block size and QEMU limits the target page size.
Use a fixed array size and assert that we don't run off it.

Signed-off-by: Peter Maydell <address@hidden>
Changes v1->v2:
 * use ARRAY_SIZE() instead of sizeof()
 * add a comment to make it a bit clearer that the
   expected size of hostaddr[] is only 2 entries
 target/arm/helper.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/target/arm/helper.c b/target/arm/helper.c
index 81a92ab4911..10444d12b18 100644
--- a/target/arm/helper.c
+++ b/target/arm/helper.c
@@ -1,4 +1,5 @@
 #include "qemu/osdep.h"
+#include "qemu/units.h"
 #include "target/arm/idau.h"
 #include "trace.h"
 #include "cpu.h"
@@ -13099,14 +13100,17 @@ void HELPER(dc_zva)(CPUARMState *env, uint64_t 
          * We know that in fact for any v8 CPU the page size is at least 4K
          * and the block size must be 2K or less, but TARGET_PAGE_SIZE is only
          * 1K as an artefact of legacy v5 subpage support being present in the
-         * same QEMU executable.
+         * same QEMU executable. So in practice the hostaddr[] array has
+         * two entries, given the current setting of TARGET_PAGE_BITS_MIN.
         int maxidx = DIV_ROUND_UP(blocklen, TARGET_PAGE_SIZE);
-        void *hostaddr[maxidx];
+        void *hostaddr[DIV_ROUND_UP(2 * KiB, 1 << TARGET_PAGE_BITS_MIN)];
         int try, i;
         unsigned mmu_idx = cpu_mmu_index(env, false);
         TCGMemOpIdx oi = make_memop_idx(MO_UB, mmu_idx);
+        assert(maxidx <= ARRAY_SIZE(hostaddr));
         for (try = 0; try < 2; try++) {
             for (i = 0; i < maxidx; i++) {

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