Avoid variable length arrays and remove declarations within code

MSVC doesn't support C99, and building as C++ to be able to use them is
dangerous, as C++ and C99 are incompatible.

Introduce a VARIABLE_ARRAY macro that either uses VLA when supported,
or alloca() otherwise. Note that using alloca() inside loops doesn't
quite work like VLAs, thus the use of VARIABLE_ARRAY there is discouraged.
It might be worth investigating ways to check whether VARIABLE_ARRAY is
used in such context at runtime in debug builds and bail out if that
happens.

4 files changed, 15 insertions, 13 deletions

diff --git a/src/arena.c b/src/arena.c
index f13b5e1..7fac361 100644
--- a/src/arena.c
+++ b/src/arena.c
@@ -640,14 +640,14 @@ arena_chunk_purge(arena_t *arena, arena_chunk_t *chunk)
 			if (mapelm->bits & CHUNK_MAP_LARGE)
 				pageind += mapelm->bits >> LG_PAGE;
 			else {
+				size_t binind;
+				arena_bin_info_t *bin_info;
 				arena_run_t *run = (arena_run_t *)((uintptr_t)
 				    chunk + (uintptr_t)(pageind << LG_PAGE));
 
 				assert((mapelm->bits >> LG_PAGE) == 0);
-				size_t binind = arena_bin_index(arena,
-				    run->bin);
-				arena_bin_info_t *bin_info =
-				    &arena_bin_info[binind];
+				binind = arena_bin_index(arena, run->bin);
+				bin_info = &arena_bin_info[binind];
 				pageind += bin_info->run_size >> LG_PAGE;
 			}
 		}
@@ -1056,11 +1056,12 @@ arena_bin_runs_first(arena_bin_t *bin)
 	if (mapelm != NULL) {
 		arena_chunk_t *chunk;
 		size_t pageind;
+		arena_run_t *run;
 
 		chunk = (arena_chunk_t *)CHUNK_ADDR2BASE(mapelm);
 		pageind = ((((uintptr_t)mapelm - (uintptr_t)chunk->map) /
 		    sizeof(arena_chunk_map_t))) + map_bias;
-		arena_run_t *run = (arena_run_t *)((uintptr_t)chunk +
+		run = (arena_run_t *)((uintptr_t)chunk +
 		    (uintptr_t)((pageind - (mapelm->bits >> LG_PAGE)) <<
 		    LG_PAGE));
 		return (run);
@@ -1596,14 +1597,15 @@ arena_dalloc_bin(arena_t *arena, arena_chunk_t *chunk, void *ptr,
 	size_t pageind;
 	arena_run_t *run;
 	arena_bin_t *bin;
-	size_t size;
+	arena_bin_info_t *bin_info;
+	size_t size, binind;
 
 	pageind = ((uintptr_t)ptr - (uintptr_t)chunk) >> LG_PAGE;
 	run = (arena_run_t *)((uintptr_t)chunk + (uintptr_t)((pageind -
 	    (mapelm->bits >> LG_PAGE)) << LG_PAGE));
 	bin = run->bin;
-	size_t binind = arena_bin_index(arena, bin);
-	arena_bin_info_t *bin_info = &arena_bin_info[binind];
+	binind = arena_bin_index(arena, bin);
+	bin_info = &arena_bin_info[binind];
 	if (config_fill || config_stats)
 		size = bin_info->reg_size;
 
diff --git a/src/ctl.c b/src/ctl.c
index 4b41d1d..2734604 100644
--- a/src/ctl.c
+++ b/src/ctl.c
@@ -520,7 +520,7 @@ static void
 ctl_refresh(void)
 {
 	unsigned i;
-	arena_t *tarenas[narenas];
+	VARIABLE_ARRAY(arena_t *, tarenas, narenas);
 
 	if (config_stats) {
 		malloc_mutex_lock(&chunks_mtx);
@@ -1232,7 +1232,7 @@ arenas_purge_ctl(const size_t *mib, size_t miblen, void *oldp, size_t *oldlenp,
 		ret = EFAULT;
 		goto label_return;
 	} else {
-		arena_t *tarenas[narenas];
+		VARIABLE_ARRAY(arena_t *, tarenas, narenas);
 
 		malloc_mutex_lock(&arenas_lock);
 		memcpy(tarenas, arenas, sizeof(arena_t *) * narenas);
diff --git a/src/stats.c b/src/stats.c
index 08f7098..2854b30 100644
--- a/src/stats.c
+++ b/src/stats.c
@@ -498,7 +498,7 @@ stats_print(void (*write_cb)(void *, const char *), void *cbopaque,
 
 			CTL_GET("arenas.narenas", &narenas, unsigned);
 			{
-				bool initialized[narenas];
+				VARIABLE_ARRAY(bool, initialized, narenas);
 				size_t isz;
 				unsigned i, ninitialized;
 
@@ -527,7 +527,7 @@ stats_print(void (*write_cb)(void *, const char *), void *cbopaque,
 
 			CTL_GET("arenas.narenas", &narenas, unsigned);
 			{
-				bool initialized[narenas];
+				VARIABLE_ARRAY(bool, initialized, narenas);
 				size_t isz;
 				unsigned i;
 
diff --git a/src/tsd.c b/src/tsd.c
index 09f06e8..d7714b0 100644
--- a/src/tsd.c
+++ b/src/tsd.c
@@ -36,7 +36,7 @@ JEMALLOC_ATTR(visibility("default"))
 void
 _malloc_thread_cleanup(void)
 {
-	bool pending[ncleanups], again;
+	bool pending[MALLOC_TSD_CLEANUPS_MAX], again;
 	unsigned i;
 
 	for (i = 0; i < ncleanups; i++)