[PATCH 1/2] Used chunk needs to be removed from free_list

[Jeff Johnston]

Patch applied.  Thanks.

-- Jeff J.

On Tue, Aug 30, 2022 at 9:57 AM Torbjörn SVENSSON <
torbjorn.svensson@foss.st.com> wrote:

> When using nano malloc and the remaning heap space is not big enough to
> fullfill the allocation, malloc will attempt to merge the last chunk in
> the free list with a new allocation in order to create a bigger chunk.
> This is successful, but the chunk still remains in the free_list, so
> any later call to malloc can give out the same region without it first
> being freed.
>
> Possible sequence to verify:
>
> void *p1 = malloc(3000);
> void *p2 = malloc(4000);
> void *p3 = malloc(5000);
> void *p4 = malloc(6000);
> void *p5 = malloc(7000);
> free(p2);
> free(p4);
> void *p6 = malloc(35000);
> free(p6);
> void *p7 = malloc(42000);
> void *p8 = malloc(32000);
>
> Without the change, p7 and p8 points to the same address.
> Requirement, after malloc(35000), there is less than 42000 bytes
> available on the heap.
>
> Contributed by STMicroelectronics
>
> Signed-off-by: Torbjörn SVENSSON <torbjorn.svensson@foss.st.com>
> ---
>  newlib/libc/stdlib/nano-mallocr.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/newlib/libc/stdlib/nano-mallocr.c
> b/newlib/libc/stdlib/nano-mallocr.c
> index 99ad60dd0..43eb20e07 100644
> --- a/newlib/libc/stdlib/nano-mallocr.c
> +++ b/newlib/libc/stdlib/nano-mallocr.c
> @@ -336,6 +336,15 @@ void * nano_malloc(RARG malloc_size_t s)
>                 if (sbrk_aligned(RCALL alloc_size) != (void *)-1)
>                 {
>                     p->size += alloc_size;
> +
> +                   /* Remove chunk from free_list */
> +                   r = free_list;
> +                   while (r && p != r->next)
> +                   {
> +                     r = r->next;
> +                   }
> +                   r->next = NULL;
> +
>                     r = p;
>                 }
>                 else
> --
> 2.25.1
>
>