[libc] Control freelist malloc buffer size with a config (#96248)

Rather than propgating a compile define, add an explicit cmake flag for
controlling the size. The default for baremetal is 100KB and the default
for others is 1GB.

2 files changed, 4 insertions, 5 deletions

diff --git a/libc/src/stdlib/CMakeLists.txt b/libc/src/stdlib/CMakeLists.txt
index 3b1ca3a..51d53e0d 100644
--- a/libc/src/stdlib/CMakeLists.txt
+++ b/libc/src/stdlib/CMakeLists.txt
@@ -390,6 +390,8 @@ else()
         malloc.h
       DEPENDS
         libc.src.__support.freelist_heap
+      COMPILE_OPTIONS
+        -DLIBC_FREELIST_MALLOC_SIZE=${LIBC_CONF_FREELIST_MALLOC_BUFFER_SIZE}
     )
   else()
     add_entrypoint_external(
diff --git a/libc/src/stdlib/freelist_malloc.cpp b/libc/src/stdlib/freelist_malloc.cpp
index 0be7f34..4d3c42c 100644
--- a/libc/src/stdlib/freelist_malloc.cpp
+++ b/libc/src/stdlib/freelist_malloc.cpp
@@ -17,14 +17,11 @@
 namespace LIBC_NAMESPACE {
 
 namespace {
-// Users can define LIBC_FREELIST_MALLOC_SIZE for setting the default buffer
-// size used by freelist malloc.
 #ifdef LIBC_FREELIST_MALLOC_SIZE
+// This is set via the LIBC_CONF_FREELIST_MALLOC_BUFFER_SIZE configuration.
 constexpr size_t SIZE = LIBC_FREELIST_MALLOC_SIZE;
 #else
-// TODO: We should probably have something akin to what scudo/sanitizer
-// allocators do where each platform defines this.
-constexpr size_t SIZE = 0x40000000ULL; // 1GB
+#error "LIBC_FREELIST_MALLOC_SIZE was not defined for this build."
 #endif
 LIBC_CONSTINIT FreeListHeapBuffer<SIZE> freelist_heap_buffer;
 } // namespace