[ubsan] Support varlen arrays at end of struct as [1] or []

The --enable-ubsan configure feature complains when we index variable length arrays at the end of some structs because the arrays size is defined to be 1. Newer C compilers support declaring these as variable-sized using [] in the struct member type definition, which also quiets the UBSAN complaint. Test for this support in configure and use it if it is supported by the compiler. Signed-off-by: Coleman Kane <ckane@colemankane.org>
ckane · Aug 12, 2023 · f9a4a86 · f9a4a86
1 parent 8e20e0f
commit f9a4a86
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Showing 4 changed files with 34 additions and 4 deletions.
diff --git a/config/zfs-build.m4 b/config/zfs-build.m4
@@ -231,6 +231,7 @@ AC_DEFUN([ZFS_AC_CONFIG_ALWAYS], [
 	ZFS_AC_CONFIG_ALWAYS_CPPCHECK
 	ZFS_AC_CONFIG_ALWAYS_SHELLCHECK
 	ZFS_AC_CONFIG_ALWAYS_PARALLEL
+	ZFS_AC_CONFIG_ALWAYS_CC_VARSIZE_ARRAY_IN_STRUCT
 ])
 
 AC_DEFUN([ZFS_AC_CONFIG], [
@@ -630,3 +631,29 @@ AC_DEFUN([ZFS_AC_PACKAGE], [
 		ZFS_AC_ALIEN
 	])
 ])
+
+dnl #
+dnl # Test whether C compiler supports variable-length array at the
+dnl # end of a struct definition, and if it needs a constant or not
+dnl # declaring a size
+dnl #
+AC_DEFUN([ZFS_AC_CONFIG_ALWAYS_CC_VARSIZE_ARRAY_IN_STRUCT], [
+	AC_MSG_CHECKING(
+	    [if C compiler handles empty-index var-length array members])
+	AC_COMPILE_IFELSE([AC_LANG_SOURCE([
+		struct s {
+			int a;
+			int v[];
+		};
+
+		struct s test_array __attribute__((unused));
+	])], [
+		AC_MSG_RESULT([yes])
+		AC_DEFINE([VARLEN_ARRAY_IDX], [],
+		    [Index to use for variable-length array struct members])
+	], [
+		AC_MSG_RESULT([no])
+		AC_DEFINE([VARLEN_ARRAY_IDX], 1,
+		    [Index to use for variable-length array struct members])
+	])
+])
diff --git a/include/sys/sa_impl.h b/include/sys/sa_impl.h
@@ -177,8 +177,11 @@ typedef struct sa_hdr_phys {
 	 *
 	 */
 	uint16_t sa_layout_info;
-	uint16_t sa_lengths[1];	/* optional sizes for variable length attrs */
-	/* ... Data follows the lengths.  */
+	uint16_t sa_lengths[VARLEN_ARRAY_IDX];
+	/*
+	 * optional sizes for variable length attrs
+	 * ... Data follows the lengths.
+	 */
 } sa_hdr_phys_t;
 
 #define	SA_HDR_LAYOUT_NUM(hdr) BF32_GET(hdr->sa_layout_info, 0, 10)

diff --git a/include/sys/zap_impl.h b/include/sys/zap_impl.h
@@ -61,7 +61,7 @@ typedef struct mzap_phys {
 	uint64_t mz_salt;
 	uint64_t mz_normflags;
 	uint64_t mz_pad[5];
-	mzap_ent_phys_t mz_chunk[1];
+	mzap_ent_phys_t mz_chunk[VARLEN_ARRAY_IDX];
 	/* actually variable size depending on block size */
 } mzap_phys_t;
 

diff --git a/include/sys/zap_leaf.h b/include/sys/zap_leaf.h
@@ -132,7 +132,7 @@ typedef struct zap_leaf_phys {
 	 * with the ZAP_LEAF_CHUNK() macro.
 	 */
 
-	uint16_t l_hash[1];
+	uint16_t l_hash[VARLEN_ARRAY_IDX];
 } zap_leaf_phys_t;
 
 typedef union zap_leaf_chunk {