alloc: set up an allocator that fails before library init

We require the library to be initialized with git_libgit2_init before it
is functional.  However, if a user tries to uses the library without
doing so - as they might when getting started with the library for the
first time - we will likely crash.

This commit introduces some guard rails - now instead of having _no_
allocator by default, we'll have an allocator that always fails, and
never tries to set an error message (since the thread-local state is
set up by git_libgit2_init).  We've modified the error retrieval
function to (try to) ensure that the library has been initialized before
getting the thread-local error message.

(Unfortunately, we cannot determine if the thread local storage has
actually been configured, this does require initialization by
git_libgit2_init.  But a naive attempt should be good enough for most
cases.)

1 files changed, 23 insertions, 0 deletions

diff --git a/src/allocators/failalloc.h b/src/allocators/failalloc.h
new file mode 100644
index 000000000..6115e51e7
--- /dev/null
+++ b/src/allocators/failalloc.h
@@ -0,0 +1,23 @@
+/*
+ * Copyright (C) the libgit2 contributors. All rights reserved.
+ *
+ * This file is part of libgit2, distributed under the GNU GPL v2 with
+ * a Linking Exception. For full terms see the included COPYING file.
+ */
+
+#ifndef INCLUDE_allocators_failalloc_h__
+#define INCLUDE_allocators_failalloc_h__
+
+#include "common.h"
+
+extern void *git_failalloc_malloc(size_t len, const char *file, int line);
+extern void *git_failalloc_calloc(size_t nelem, size_t elsize, const char *file, int line);
+extern char *git_failalloc_strdup(const char *str, const char *file, int line);
+extern char *git_failalloc_strndup(const char *str, size_t n, const char *file, int line);
+extern char *git_failalloc_substrdup(const char *start, size_t n, const char *file, int line);
+extern void *git_failalloc_realloc(void *ptr, size_t size, const char *file, int line);
+extern void *git_failalloc_reallocarray(void *ptr, size_t nelem, size_t elsize, const char *file, int line);
+extern void *git_failalloc_mallocarray(size_t nelem, size_t elsize, const char *file, int line);
+extern void git_failalloc_free(void *ptr);
+
+#endif