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.

include/jemalloc/internal/jemalloc_internal.h.in

@@ -319,6 +319,20 @@ static const bool config_ivsalloc =
 #define	ALIGNMENT_CEILING(s, alignment)					\
 	(((s) + (alignment - 1)) & (-(alignment)))
 
+/* Declare a variable length array */
+#if __STDC_VERSION__ < 199901L
+#  ifdef _MSC_VER
+#    include <malloc.h>
+#    define alloca _alloca
+#  else
+#    include <alloca.h>
+#  endif
+#  define VARIABLE_ARRAY(type, name, count) \
+	type *name = alloca(sizeof(type) * count)
+#else
+#  define VARIABLE_ARRAY(type, name, count) type name[count]
+#endif
+
 #ifdef JEMALLOC_VALGRIND
 /*
  * The JEMALLOC_VALGRIND_*() macros must be macros rather than functions

include/jemalloc/internal/prof.h

@@ -542,8 +542,9 @@ prof_free(const void *ptr, size_t size)
 	cassert(config_prof);
 
 	if ((uintptr_t)ctx > (uintptr_t)1) {
+		prof_thr_cnt_t *tcnt;
 		assert(size == isalloc(ptr, true));
-		prof_thr_cnt_t *tcnt = prof_lookup(ctx->bt);
+		tcnt = prof_lookup(ctx->bt);
 
 		if (tcnt != NULL) {
 			tcnt->epoch++;

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;
 

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);

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;
 

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++)

test/bitmap.c

@@ -30,11 +30,13 @@ test_bitmap_init(void)
 		bitmap_info_init(&binfo, i);
 		{
 			size_t j;
-			bitmap_t bitmap[bitmap_info_ngroups(&binfo)];
+			bitmap_t *bitmap = malloc(sizeof(bitmap_t) *
+				bitmap_info_ngroups(&binfo));
 			bitmap_init(bitmap, &binfo);
 
 			for (j = 0; j < i; j++)
 				assert(bitmap_get(bitmap, &binfo, j) == false);
+			free(bitmap);
 
 		}
 	}
@@ -50,12 +52,14 @@ test_bitmap_set(void)
 		bitmap_info_init(&binfo, i);
 		{
 			size_t j;
-			bitmap_t bitmap[bitmap_info_ngroups(&binfo)];
+			bitmap_t *bitmap = malloc(sizeof(bitmap_t) *
+				bitmap_info_ngroups(&binfo));
 			bitmap_init(bitmap, &binfo);
 
 			for (j = 0; j < i; j++)
 				bitmap_set(bitmap, &binfo, j);
 			assert(bitmap_full(bitmap, &binfo));
+			free(bitmap);
 		}
 	}
 }
@@ -70,7 +74,8 @@ test_bitmap_unset(void)
 		bitmap_info_init(&binfo, i);
 		{
 			size_t j;
-			bitmap_t bitmap[bitmap_info_ngroups(&binfo)];
+			bitmap_t *bitmap = malloc(sizeof(bitmap_t) *
+				bitmap_info_ngroups(&binfo));
 			bitmap_init(bitmap, &binfo);
 
 			for (j = 0; j < i; j++)
@@ -81,6 +86,7 @@ test_bitmap_unset(void)
 			for (j = 0; j < i; j++)
 				bitmap_set(bitmap, &binfo, j);
 			assert(bitmap_full(bitmap, &binfo));
+			free(bitmap);
 		}
 	}
 }
@@ -95,7 +101,8 @@ test_bitmap_sfu(void)
 		bitmap_info_init(&binfo, i);
 		{
 			ssize_t j;
-			bitmap_t bitmap[bitmap_info_ngroups(&binfo)];
+			bitmap_t *bitmap = malloc(sizeof(bitmap_t) *
+				bitmap_info_ngroups(&binfo));
 			bitmap_init(bitmap, &binfo);
 
 			/* Iteratively set bits starting at the beginning. */
@@ -125,6 +132,7 @@ test_bitmap_sfu(void)
 			}
 			assert(bitmap_sfu(bitmap, &binfo) == i - 1);
 			assert(bitmap_full(bitmap, &binfo));
+			free(bitmap);
 		}
 	}
 }