* Re: C11 low-hanging fruit
2012-08-26 1:42 C11 low-hanging fruit Gregor Richards
@ 2012-08-26 2:33 ` Gregor Richards
0 siblings, 0 replies; 2+ messages in thread
From: Gregor Richards @ 2012-08-26 2:33 UTC (permalink / raw)
To: musl
[-- Attachment #1: Type: text/plain, Size: 1722 bytes --]
New version of the patch, per chat on IRC:
* stdalign.h __GNUC__ test is simplified (since musl isn't going to
work well on GCC<3.1 anyway)
* feature test macros are simplified, aligned_alloc is unconditional
* aligned_alloc is now the fundamental implementation, with
posix_memalign in terms of it instead of the opposite
* the check for 'x' in fopen is simplified, as well as the check for '+'
With valediction,
- Gregor Richards
On 08/25/2012 09:42 PM, Gregor Richards wrote:
> Attached is a diff that adds the trivially-simple bits of C11. That
> is, those that require changes to the standard headers, but very
> little in the way of implementation. Included are:
> * stdalign.h , including backwards compatibility for GCC.
> * aligned_alloc
> * fopen(..., "...x")
> * conditional removal of gets
>
> Excluded are:
> * threads.h (waiting to see glibc's ABI)
> * stdatomic.h (complicated, probably has ABI implications too, not
> even fully supported by GCC yet)
> * uchar.h (this is MOSTLY trivial since musl's wchar is Unicode
> anyway, but char32_t makes it a bit more than some weak aliases)
> * at_quick_exit, quick_exit (I suspect that our benevolent dictator
> will have a lot to say in exactly what makes an exit "quick" or not,
> so I'm not touching this)
>
> I used __STDC_VERSION__ in the headers to control exposure of
> aligned_alloc and gets. aligned_alloc I additionally exposed with the
> non-standard feature test macro _ISOC11_SOURCE, for the simple reason
> that glibc does it; if you have a non-C11 compiler but C11 libc,
> -D_ISOC11_SOURCE is a much less gross way to get aligned_alloc than
> -D_GNU_SOURCE, anyway :)
>
> With valediction,
> - Gregor Richards
>
[-- Attachment #2: c11-easy.diff --]
[-- Type: text/x-diff, Size: 4597 bytes --]
diff --git a/include/stdalign.h b/include/stdalign.h
new file mode 100644
--- /dev/null
+++ b/include/stdalign.h
@@ -0,0 +1,23 @@
+#ifndef _STDALIGN_H
+#define _STDALIGN_H
+
+/* this whole header only works in C11 or with compiler extensions */
+#if __STDC_VERSION__ < 201112L
+
+#if __GNUC__
+#define _Alignas(t) __attribute__((__aligned__(t)))
+#define _Alignof(t) __alignof__(t)
+
+#else
+#error stdalign.h is only supported with C11 or GNU extensions
+
+#endif
+
+#endif
+
+#define alignas _Alignas
+#define alignof _Alignof
+#define __alignas_is_defined 1
+#define __alignof_is_defined 1
+
+#endif
diff --git a/include/stdio.h b/include/stdio.h
--- a/include/stdio.h
+++ b/include/stdio.h
@@ -90,7 +90,9 @@
int putchar(int);
char *fgets(char *, int, FILE *);
+#if __STDC_VERSION__ < 201112L
char *gets(char *);
+#endif
int fputs(const char *, FILE *);
int puts(const char *);
diff --git a/include/stdlib.h b/include/stdlib.h
--- a/include/stdlib.h
+++ b/include/stdlib.h
@@ -102,6 +102,8 @@
#endif
+void *aligned_alloc(size_t alignment, size_t size);
+
#if defined(_XOPEN_SOURCE) || defined(_GNU_SOURCE) \
|| defined(_BSD_SOURCE)
diff --git a/src/malloc/aligned_alloc.c b/src/malloc/aligned_alloc.c
new file mode 100644
--- /dev/null
+++ b/src/malloc/aligned_alloc.c
@@ -0,0 +1,51 @@
+#include <stdlib.h>
+#include <stdint.h>
+#include <errno.h>
+
+/* This function should work with most dlmalloc-like chunk bookkeeping
+ * systems, but it's only guaranteed to work with the native implementation
+ * used in this library. */
+
+void *aligned_alloc(size_t align, size_t len)
+{
+ unsigned char *mem, *new, *end;
+ size_t header, footer;
+
+ if ((align & -align & -sizeof(void *)) != align) {
+ errno = EINVAL;
+ return NULL;
+ }
+
+ if (len > SIZE_MAX - align) {
+ errno = ENOMEM;
+ return NULL;
+ }
+
+ if (align <= 4*sizeof(size_t)) {
+ if (!(mem = malloc(len)))
+ return NULL;
+ return mem;
+ }
+
+ if (!(mem = malloc(len + align-1)))
+ return NULL;
+
+ header = ((size_t *)mem)[-1];
+ end = mem + (header & -8);
+ footer = ((size_t *)end)[-2];
+ new = (void *)((uintptr_t)mem + align-1 & -align);
+
+ if (!(header & 7)) {
+ ((size_t *)new)[-2] = ((size_t *)mem)[-2] + (new-mem);
+ ((size_t *)new)[-1] = ((size_t *)mem)[-1] - (new-mem);
+ return new;
+ }
+
+ ((size_t *)mem)[-1] = header&7 | new-mem;
+ ((size_t *)new)[-2] = footer&7 | new-mem;
+ ((size_t *)new)[-1] = header&7 | end-new;
+ ((size_t *)end)[-2] = footer&7 | end-new;
+
+ if (new != mem) free(mem);
+ return new;
+}
diff --git a/src/malloc/posix_memalign.c b/src/malloc/posix_memalign.c
--- a/src/malloc/posix_memalign.c
+++ b/src/malloc/posix_memalign.c
@@ -1,47 +1,12 @@
#include <stdlib.h>
-#include <stdint.h>
-#include <errno.h>
-
-/* This function should work with most dlmalloc-like chunk bookkeeping
- * systems, but it's only guaranteed to work with the native implementation
- * used in this library. */
int posix_memalign(void **res, size_t align, size_t len)
{
- unsigned char *mem, *new, *end;
- size_t header, footer;
-
- if ((align & -align & -sizeof(void *)) != align) return EINVAL;
- if (len > SIZE_MAX - align) return ENOMEM;
-
- if (align <= 4*sizeof(size_t)) {
- if (!(mem = malloc(len)))
- return errno;
+ void *mem = allocate_aligned(align, len);
+ if (mem) {
*res = mem;
return 0;
+ } else {
+ return errno;
}
-
- if (!(mem = malloc(len + align-1)))
- return errno;
-
- header = ((size_t *)mem)[-1];
- end = mem + (header & -8);
- footer = ((size_t *)end)[-2];
- new = (void *)((uintptr_t)mem + align-1 & -align);
-
- if (!(header & 7)) {
- ((size_t *)new)[-2] = ((size_t *)mem)[-2] + (new-mem);
- ((size_t *)new)[-1] = ((size_t *)mem)[-1] - (new-mem);
- *res = new;
- return 0;
- }
-
- ((size_t *)mem)[-1] = header&7 | new-mem;
- ((size_t *)new)[-2] = footer&7 | new-mem;
- ((size_t *)new)[-1] = header&7 | end-new;
- ((size_t *)end)[-2] = footer&7 | end-new;
-
- if (new != mem) free(mem);
- *res = new;
- return 0;
}
diff --git a/src/stdio/fopen.c b/src/stdio/fopen.c
--- a/src/stdio/fopen.c
+++ b/src/stdio/fopen.c
@@ -5,7 +5,6 @@
FILE *f;
int fd;
int flags;
- int plus = !!strchr(mode, '+');
/* Check for valid initial mode character */
if (!strchr("rwa", *mode)) {
@@ -14,9 +13,10 @@
}
/* Compute the flags to pass to open() */
- if (plus) flags = O_RDWR;
+ if (strchr(mode, '+')) flags = O_RDWR;
else if (*mode == 'r') flags = O_RDONLY;
else flags = O_WRONLY;
+ if (strchr(mode, 'x')) flags |= O_EXCL;
if (*mode != 'r') flags |= O_CREAT;
if (*mode == 'w') flags |= O_TRUNC;
if (*mode == 'a') flags |= O_APPEND;
^ permalink raw reply [flat|nested] 2+ messages in thread