[4/9] Sync scratch_buffer with gnulib
Commit Message
On 18/09/2017 03:09, Florian Weimer wrote:
> On 09/05/2017 10:25 PM, Adhemerval Zanella wrote:
>> - char __space[1024]
>> - __attribute__ ((aligned (__alignof__ (max_align_t))));
>> + max_align_t __space[(1023 + sizeof (max_align_t)) / sizeof (max_align_t)];
>
> This change needs a declaration from the GCC folks (probably from Richard Biener) that it does not break aliasing analysis. The old code uses a GCC extension (writing to a char array changes its dynamic type); it is not valid C. I don't know if the GCC extension also applies if the storage site is declared with a non-char type.
>
> Thanks,
> Florian
What about this below instead:
---
---
_Alignas/stdalign.h is supported since GCC 4.7 [1] (so it is safe to use
on glibc without configure support) and gnulib have its own version which
defines __alignas_is_defined depending on underlying compiler support.
[1] https://gcc.gnu.org/wiki/C11Status
Comments
On 09/18/2017 01:43 PM, Adhemerval Zanella wrote:
> +#if __alignas_is_defined
> + _Alignas (max_align_t) char __space[1024];
> +#else
> max_align_t __space[(1023 + sizeof (max_align_t)) / sizeof (max_align_t)];
> +#endif
This works for me on the glibc side.
By the way, do you have a rebased version of this patch?
Subject: [PATCH 05/18] posix: Rewrite to use struct scratch_buffer
instead of extend_alloca
Thanks,
Florian
On 18/09/2017 08:57, Florian Weimer wrote:
> On 09/18/2017 01:43 PM, Adhemerval Zanella wrote:
>> +#if __alignas_is_defined
>> + _Alignas (max_align_t) char __space[1024];
>> +#else
>> max_align_t __space[(1023 + sizeof (max_align_t)) / sizeof (max_align_t)];
>> +#endif
>
> This works for me on the glibc side.
Right, I will prepare a patch then.
>
> By the way, do you have a rebased version of this patch?
>
> Subject: [PATCH 05/18] posix: Rewrite to use struct scratch_buffer instead of extend_alloca
>
> Thanks,
> Florian
No, but I can send along with some more glob fixes I plan to.
@@ -60,13 +60,18 @@
#include <stdbool.h>
#include <stddef.h>
#include <stdlib.h>
+#include <stdalign.h>
/* Scratch buffer. Must be initialized with scratch_buffer_init
before its use. */
struct scratch_buffer {
void *data; /* Pointer to the beginning of the scratch area. */
size_t length; /* Allocated space at the data pointer, in bytes. */
+#if __alignas_is_defined
+ _Alignas (max_align_t) char __space[1024];
+#else
max_align_t __space[(1023 + sizeof (max_align_t)) / sizeof (max_align_t)];
+#endif
};
/* Initializes *BUFFER so that BUFFER->data points to BUFFER->__space