Messages in this thread | | | Date | Tue, 22 Mar 2022 19:18:31 +0700 | From | Ammar Faizi <> | Subject | Re: [RFC PATCH v2 6/8] tools/nolibc/stdlib: Implement `malloc()`, `calloc()`, `realloc()` and `free()` |
| |
On 3/22/22 6:52 PM, David Laight wrote:
[...] >> +struct nolibc_heap { >> + size_t len; >> + char user_p[] __attribute__((__aligned__)); > > Doesn't that need (number) in the attribute?
The number is not mandatory.
Specifying no alignment argument implies the maximum alignment for the target, which is often, but by no means always, 8 or 16 bytes.
This has been discussed in the RFC v1, see the full message here:
https://lore.kernel.org/lkml/c7129520-5e9a-f9d1-cc12-5af9456c917f@gnuweeb.org/
>> +static __attribute__((unused)) >> +void *malloc(size_t len) >> +{ >> + struct nolibc_heap *heap; > > If you do (say): > len = ROUNDUP(len + sizeof *heap, 4096) > you can optimise a lot of the realloc() calls. > > I actually wonder if compiling a mini-libc.a > and then linking the programs against it might > be better than all these static functions? > -ffunction-sections can help a bit (where supported).
Rounding up is not useful here, because we don't have any free list to keep track the unused block of memory. I mean, even if it's rounded up, the extra space after rounded up cannot be utilized with this design. There is no book-keeping that tracks it.
Though, the kernel still allocates the size in multiple page size.
-- Ammar Faizi
| |