[PATCH] Fix handling of zero capacity regions in -Wanalyzer-allocation-size [PR106394]

[PATCH] Fix handling of zero capacity regions in -Wanalyzer-allocation-size [PR106394]

[Tim Lange]

This patch unifies the handling of zero capacity regions for structs
and other types in the allocation size checker.
Regression-tested on x86_64 Linux.

2022-07-22  Tim Lange  <mail@tim-lange.me>

gcc/analyzer/ChangeLog:

	PR analyzer/106394
	* region-model.cc (capacity_compatible_with_type): Always return true
	if alloc_size is zero.

gcc/testsuite/ChangeLog:

	PR analyzer/106394
	* gcc.dg/analyzer/pr106394.c: New test.

---
 gcc/analyzer/region-model.cc             |  2 +-
 gcc/testsuite/gcc.dg/analyzer/pr106394.c | 19 +++++++++++++++++++
 2 files changed, 20 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gcc.dg/analyzer/pr106394.c

diff --git a/gcc/analyzer/region-model.cc b/gcc/analyzer/region-model.cc
index 8b7b4e1f697..e01c30407c4 100644
--- a/gcc/analyzer/region-model.cc
+++ b/gcc/analyzer/region-model.cc
@@ -2956,7 +2956,7 @@ capacity_compatible_with_type (tree cst, tree pointee_size_tree,
   unsigned HOST_WIDE_INT alloc_size = TREE_INT_CST_LOW (cst);

   if (is_struct)
-    return alloc_size >= pointee_size;
+    return alloc_size == 0 || alloc_size >= pointee_size;
   return alloc_size % pointee_size == 0;
 }

diff --git a/gcc/testsuite/gcc.dg/analyzer/pr106394.c b/gcc/testsuite/gcc.dg/analyzer/pr106394.c
new file mode 100644
index 00000000000..96bb175fc14
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/analyzer/pr106394.c
@@ -0,0 +1,19 @@
+struct msm_gpu {
+  // [...snip...]
+  const struct msm_gpu_perfcntr *perfcntrs;
+  // [...snip...]
+};
+
+struct msm_gpu_perfcntr {
+  // [...snip...]
+  const char *name;
+};
+
+static const struct msm_gpu_perfcntr perfcntrs[] = {};
+
+struct msm_gpu *test(struct msm_gpu *gpu) {
+  // [...snip...]
+  gpu->perfcntrs = perfcntrs;
+  // [...snip...]
+  return gpu;
+}
--
2.36.1

Re: [PATCH] Fix handling of zero capacity regions in -Wanalyzer-allocation-size [PR106394]

[David Malcolm]

On Fri, 2022-07-22 at 16:27 +0200, Tim Lange wrote:
> This patch unifies the handling of zero capacity regions for structs
> and other types in the allocation size checker.
> Regression-tested on x86_64 Linux.

Thanks; looks good for trunk.

Dave