Re: [PATCH] Properly align memory allocations and temporary buffers

> 
> "brian m. carlson" <sandals@crustytoothpaste.net> writes:
> 
>> I'm not opposed to a small amount of finagling for this case, but I am
>> very much opposed to defining your C ABI in an intentionally difficult
>> way.
> 
> I was looking at git_qsort_s() today and thought that its use of
> "char buf[1k]" on stack is something we would write for a system
> without alloca().
> 
> We already have xalloca() wrapper defined in the compat-util header.
> Perhaps it is a good idea to use it instead?
> 
> Both the true alloca() and xmalloc() we use as a fallback (when
> <alloca.h> is not available) are supposed to return a block of
> memory that is suitably aligned for any use, no?  

> compat/qsort_s.c | 20 +++++++++++---------
> 1 file changed, 11 insertions(+), 9 deletions(-)
> 
> diff --git c/compat/qsort_s.c w/compat/qsort_s.c
> index 52d1f0a73d..63660a4304 100644
> --- c/compat/qsort_s.c
> +++ w/compat/qsort_s.c
> @@ -49,21 +49,23 @@ int git_qsort_s(void *b, size_t n, size_t s,
> 		int (*cmp)(const void *, const void *, void *), void *ctx)
> {
> 	const size_t size = st_mult(n, s);
> -	char buf[1024];
> +	char *tmp;
> +	int use_alloca;
> 
> 	if (!n)
> 		return 0;
> 	if (!b || !cmp)
> 		return -1;
> 
> -	if (size < sizeof(buf)) {
> -		/* The temporary array fits on the small on-stack buffer. */
> -		msort_with_tmp(b, n, s, cmp, buf, ctx);
> -	} else {
> -		/* It's somewhat large, so malloc it.  */
> -		char *tmp = xmalloc(size);
> -		msort_with_tmp(b, n, s, cmp, tmp, ctx);
> +	use_alloca = (size < 1024);
> +
> +	tmp = use_alloca ? xalloca(size) : xmalloc(size);
> +
> +	msort_with_tmp(b, n, s, cmp, tmp, ctx);
> +
> +	if (use_alloca)
> +		xalloca_free(tmp);
> +	else
> 		free(tmp);
> -	}
> 	return 0;
> }