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Date: Sun, 19 Jan 2020 12:31:34 +0100
From: Szabolcs Nagy <nsz@...t70.net>
To: musl@...ts.openwall.com
Subject: Re: Minor style patch to exit.c
* Markus Wichmann <nullplan@....net> [2020-01-19 12:07:43 +0100]:
> The previous version did have a maze of parentheses here. But the actual
> logic of the function is not to iterate over some numbers that happen to
> be convertible to pointers, but rather to iterate over an array of
> function pointers. So let us use pointer arithmetic correctly.
> ---
> src/exit/exit.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/src/exit/exit.c b/src/exit/exit.c
> index a6869b37..e02ba2be 100644
> --- a/src/exit/exit.c
> +++ b/src/exit/exit.c
> @@ -16,9 +16,9 @@ extern weak hidden void (*const __fini_array_start)(void), (*const __fini_array_
>
> static void libc_exit_fini(void)
> {
> - uintptr_t a = (uintptr_t)&__fini_array_end;
> - for (; a>(uintptr_t)&__fini_array_start; a-=sizeof(void(*)()))
> - (*(void (**)())(a-sizeof(void(*)())))();
> + void (*const *a)() = &__fini_array_end;
> + while (a > &__fini_array_start)
> + (*--a)();
this has undefined behaviour.
the original code was carefully written to avoid that.
you need to keep the uintptr_t cast since -- and > are
undefined for pointers that go out of bound or don't
point to the same object (and the _start, _end symbols
don't represent the same c language object, they are
independent).
> _fini();
> }
>
> --
> 2.17.1
>
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