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, 92 insertions, 0 deletions

diff --git a/src/allocators/failalloc.c b/src/allocators/failalloc.c
new file mode 100644
index 000000000..5257d1dec
--- /dev/null
+++ b/src/allocators/failalloc.c
@@ -0,0 +1,92 @@
+/*
+ * 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.
+ */
+
+#include "failalloc.h"
+
+void *git_failalloc_malloc(size_t len, const char *file, int line)
+{
+	GIT_UNUSED(len);
+	GIT_UNUSED(file);
+	GIT_UNUSED(line);
+
+	return NULL;
+}
+
+void *git_failalloc_calloc(size_t nelem, size_t elsize, const char *file, int line)
+{
+	GIT_UNUSED(nelem);
+	GIT_UNUSED(elsize);
+	GIT_UNUSED(file);
+	GIT_UNUSED(line);
+
+	return NULL;
+}
+
+char *git_failalloc_strdup(const char *str, const char *file, int line)
+{
+	GIT_UNUSED(str);
+	GIT_UNUSED(file);
+	GIT_UNUSED(line);
+
+	return NULL;
+}
+
+char *git_failalloc_strndup(const char *str, size_t n, const char *file, int line)
+{
+	GIT_UNUSED(str);
+	GIT_UNUSED(n);
+	GIT_UNUSED(file);
+	GIT_UNUSED(line);
+
+	return NULL;
+}
+
+char *git_failalloc_substrdup(const char *start, size_t n, const char *file, int line)
+{
+	GIT_UNUSED(start);
+	GIT_UNUSED(n);
+	GIT_UNUSED(file);
+	GIT_UNUSED(line);
+
+	return NULL;
+}
+
+void *git_failalloc_realloc(void *ptr, size_t size, const char *file, int line)
+{
+	GIT_UNUSED(ptr);
+	GIT_UNUSED(size);
+	GIT_UNUSED(file);
+	GIT_UNUSED(line);
+
+	return NULL;
+}
+
+void *git_failalloc_reallocarray(void *ptr, size_t nelem, size_t elsize, const char *file, int line)
+{
+	GIT_UNUSED(ptr);
+	GIT_UNUSED(nelem);
+	GIT_UNUSED(elsize);
+	GIT_UNUSED(file);
+	GIT_UNUSED(line);
+
+	return NULL;
+}
+
+void *git_failalloc_mallocarray(size_t nelem, size_t elsize, const char *file, int line)
+{
+	GIT_UNUSED(nelem);
+	GIT_UNUSED(elsize);
+	GIT_UNUSED(file);
+	GIT_UNUSED(line);
+
+	return NULL;
+}
+
+void git_failalloc_free(void *ptr)
+{
+	GIT_UNUSED(ptr);
+}