[PATCH] elf/dl-deps.c: Make _dl_build_local_scope breadth first
Adhemerval Zanella
adhemerval.zanella@linaro.org
Tue Jan 11 19:26:18 GMT 2022
On 09/12/2021 20:53, Khem Raj via Libc-alpha wrote:
> From: Mark Hatle <mark.hatle@windriver.com>
>
> According to the ELF specification:
>
> When resolving symbolic references, the dynamic linker examines the symbol
> tables with a breadth-first search.
>
> This function was using a depth first search. By doing so the conflict
> resolution reported to the prelinker (when LD_TRACE_PRELINKING=1 is set)
> was incorrect. This caused problems when their were various circular
> dependencies between libraries. The problem usually manifested itself by
> the wrong IFUNC being executed.
>
> Similar issue has been reported here [1]
>
> [BZ# 20488]
>
> [1] https://sourceware.org/legacy-ml/libc-alpha/2016-05/msg00034.html
>
> Signed-off-by: Mark Hatle <mark.hatle@kernel.crashing.org>
> Signed-off-by: Khem Raj <raj.khem@gmail.com>
I am trying to understand why it this only an issue for LD_TRACE_PRELINKING=1,
do we have a testcase that stress it for a default usercase?
When you say the 'wrong IFUNC being executed' what exactly you mean here?
Could we use a testcase based on this?
> ---
> elf/dl-deps.c | 14 ++++++++++----
> 1 file changed, 10 insertions(+), 4 deletions(-)
>
> diff --git a/elf/dl-deps.c b/elf/dl-deps.c
> index 237d9636c5..e15f7f83d8 100644
> --- a/elf/dl-deps.c
> +++ b/elf/dl-deps.c
> @@ -73,13 +73,19 @@ _dl_build_local_scope (struct link_map **list, struct link_map *map)
> {
> struct link_map **p = list;
> struct link_map **q;
> + struct link_map **r;
>
> *p++ = map;
> map->l_reserved = 1;
> - if (map->l_initfini)
> - for (q = map->l_initfini + 1; *q; ++q)
> - if (! (*q)->l_reserved)
> - p += _dl_build_local_scope (p, *q);
> +
> + for (r = list; r < p; ++r)
> + if ((*r)->l_initfini)
> + for (q = (*r)->l_initfini + 1; *q; ++q)
> + if (! (*q)->l_reserved)
> + {
> + *p++ = *q;
> + (*q)->l_reserved = 1;
> + }
> return p - list;
> }
>
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