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Subject[RFC PATCH v2 6/8] tools/nolibc/stdlib: Implement `malloc()`, `calloc()`, `realloc()` and `free()`
Date
Implement basic dynamic allocator functions. These functions are
currently only available on architectures that have nolibc mmap()
syscall implemented. These are not a super-fast memory allocator,
but at least they can satisfy basic needs for having heap without
libc.

Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org>
---

@@ Changelog:

Link: https://lore.kernel.org/lkml/20220320093750.159991-6-ammarfaizi2@gnuweeb.org
RFC v1 -> RFC v2:
- Move container_of() and offsetof() macro to types.h with a
separate patch (comment from Willy).
---
tools/include/nolibc/stdlib.h | 68 +++++++++++++++++++++++++++++++++++
1 file changed, 68 insertions(+)

diff --git a/tools/include/nolibc/stdlib.h b/tools/include/nolibc/stdlib.h
index aca8616335e3..a0ed75431e0a 100644
--- a/tools/include/nolibc/stdlib.h
+++ b/tools/include/nolibc/stdlib.h
@@ -11,7 +11,12 @@
#include "arch.h"
#include "types.h"
#include "sys.h"
+#include "string.h"

+struct nolibc_heap {
+ size_t len;
+ char user_p[] __attribute__((__aligned__));
+};

/* Buffer used to store int-to-ASCII conversions. Will only be implemented if
* any of the related functions is implemented. The area is large enough to
@@ -60,6 +65,18 @@ int atoi(const char *s)
return atol(s);
}

+static __attribute__((unused))
+void free(void *ptr)
+{
+ struct nolibc_heap *heap;
+
+ if (!ptr)
+ return;
+
+ heap = container_of(ptr, struct nolibc_heap, user_p);
+ munmap(heap, heap->len);
+}
+
/* Tries to find the environment variable named <name> in the environment array
* pointed to by global variable "environ" which must be declared as a char **,
* and must be terminated by a NULL (it is recommended to set this variable to
@@ -205,6 +222,57 @@ char *ltoa(long in)
return itoa_buffer;
}

+static __attribute__((unused))
+void *malloc(size_t len)
+{
+ struct nolibc_heap *heap;
+
+ heap = mmap(NULL, sizeof(*heap) + len, PROT_READ|PROT_WRITE,
+ MAP_ANONYMOUS|MAP_PRIVATE, -1, 0);
+ if (__builtin_expect(heap == MAP_FAILED, 0))
+ return NULL;
+
+ heap->len = sizeof(*heap) + len;
+ return heap->user_p;
+}
+
+static __attribute__((unused))
+void *calloc(size_t size, size_t nmemb)
+{
+ void *orig;
+ size_t res = 0;
+
+ if (__builtin_expect(__builtin_mul_overflow(nmemb, size, &res), 0)) {
+ SET_ERRNO(ENOMEM);
+ return NULL;
+ }
+
+ /*
+ * No need to zero the heap, the MAP_ANONYMOUS in malloc()
+ * already does it.
+ */
+ return malloc(res);
+}
+
+static __attribute__((unused))
+void *realloc(void *old_ptr, size_t new_size)
+{
+ struct nolibc_heap *heap;
+ void *ret;
+
+ ret = malloc(new_size);
+ if (__builtin_expect(!ret, 0))
+ return NULL;
+
+ if (!old_ptr)
+ return ret;
+
+ heap = container_of(old_ptr, struct nolibc_heap, user_p);
+ memcpy(ret, heap->user_p, heap->len);
+ munmap(heap, heap->len);
+ return ret;
+}
+
/* converts unsigned long integer <in> to a string using the static itoa_buffer
* and returns the pointer to that string.
*/
--
Ammar Faizi
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