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Subject[PATCH v2 7/9] 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.

Cc: David Laight <David.Laight@ACULAB.COM>
Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org>
===

@@ Changelog:

Link v1: https://lore.gnuweeb.org/gwml/20220324073039.140946-10-ammarfaizi2@gnuweeb.org
v1 -> v2:
* No changes *

Link v2: https://lore.kernel.org/lkml/20220322102115.186179-7-ammarfaizi2@gnuweeb.org
RFC v2 -> v1:
- Round up the malloc() allocation to 4096 (comment from David).
- Don't realloc() if we still have enough memory to contain the
requested new size (comment from David).
- Fix conflict with getenv() fix (after rebase).

Link v1: 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 | 81 +++++++++++++++++++++++++++++++++++
1 file changed, 81 insertions(+)

diff --git a/tools/include/nolibc/stdlib.h b/tools/include/nolibc/stdlib.h
index 8a07e263f0d0..8fd32eaf8037 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);
+}
+
/* getenv() 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
@@ -91,6 +108,70 @@ char *getenv(const char *name)
return _getenv(name, environ);
}

+static __attribute__((unused))
+void *malloc(size_t len)
+{
+ struct nolibc_heap *heap;
+
+ /* Always allocate memory with size multiple of 4096. */
+ len = sizeof(*heap) + len;
+ len = (len + 4095UL) & -4096UL;
+ heap = mmap(NULL, len, PROT_READ|PROT_WRITE, MAP_ANONYMOUS|MAP_PRIVATE,
+ -1, 0);
+ if (__builtin_expect(heap == MAP_FAILED, 0))
+ return NULL;
+
+ heap->len = 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;
+ size_t user_p_len;
+ void *ret;
+
+ if (!old_ptr)
+ return malloc(new_size);
+
+ heap = container_of(old_ptr, struct nolibc_heap, user_p);
+ user_p_len = heap->len - sizeof(*heap);
+ /*
+ * Don't realloc() if @user_p_len >= @new_size, this block of
+ * memory is still enough to handle the @new_size. Just return
+ * the same pointer.
+ */
+ if (user_p_len >= new_size)
+ return old_ptr;
+
+ ret = malloc(new_size);
+ if (__builtin_expect(!ret, 0))
+ return NULL;
+
+ memcpy(ret, heap->user_p, heap->len);
+ munmap(heap, heap->len);
+ return ret;
+}
+
/* Converts the unsigned long integer <in> to its hex representation into
* buffer <buffer>, which must be long enough to store the number and the
* trailing zero (17 bytes for "ffffffffffffffff" or 9 for "ffffffff"). The
--
Ammar Faizi
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