Re: RTLD_DEEPBIND question

On 19/04/2025 13:29, Konstantin Belousov wrote:
> On Sat, Apr 19, 2025 at 01:25:28PM +0300, Andriy Gapon wrote:
>> On 19/04/2025 12:39, Andriy Gapon wrote:
>>>   From a quick look at the code, should we try to resolve the symbol in
>>> refobj itself when it's marked with deepbind?
>> Oh, and it looks like objects loaded under the "deepbind" object (e.g.,
>> needed objects) may not be aware that they are in the deepbind sub-tree?
> 
> But should they?

That's a right question.

I have been reading about RTLD_DEEPBIND and Solaris flags like RTLD_GROUP, etc 
at the same time.  I guess that's why some things got "fused" in my mind.  So, I 
started believing that the concept of shared object dependency groups also 
applies to RTLD_DEEPBIND.

But that's not documented to be so, at least, in the documentation that I could 
find.  There are some in-depth documentation on Solaris run-time linker and its 
handling of various options.  But for Linux RTLD_DEEPBIND I could find only 
manual page references and they only say that deep-binding applies to to the 
object being dlopen-ed.

I am not sure if that's how the option actually works on Linux.
I allow for possibility that the manual pages omit (or, at least, do not spell 
out) some details for brevity.

In any case, I believe that the proposed patch is correct.
But I think that it would not help in my case.
I have: mdb -[dlopen]-> dtrace.so -[needs]-> libdtrace.so.
And it's a symbol in libdtrace.so that gets resolved to mdb instead of 
libdtrace.so itself.
The patch would affect how symbols in dtrace.so are resolved if I understand 
correctly.

> Lets start with some minimal intrusive change:
> 
> commit b4f4feb883a1be1d4ca3867f49baa20ce0c13d8d
> Author: Konstantin Belousov <kib@FreeBSD.org>
> Date:   Sat Apr 19 13:26:58 2025 +0300
> 
>      rtld: symbolic and deepbind are equivalent for the refobj
>      
>      Reported by:    avg
> 
> diff --git a/libexec/rtld-elf/rtld.c b/libexec/rtld-elf/rtld.c
> index 2346c6eae9f6..8ea6afb43752 100644
> --- a/libexec/rtld-elf/rtld.c
> +++ b/libexec/rtld-elf/rtld.c
> @@ -4679,12 +4679,13 @@ symlook_default(SymLook *req, const Obj_Entry *refobj)
>   	 */
>   	res = symlook_obj(&req1, refobj);
>   	if (res == 0 && (refobj->symbolic ||
> -	    ELF_ST_VISIBILITY(req1.sym_out->st_other) == STV_PROTECTED)) {
> +	    ELF_ST_VISIBILITY(req1.sym_out->st_other) == STV_PROTECTED ||
> +	    refobj->deepbind)) {
>   		req->sym_out = req1.sym_out;
>   		req->defobj_out = req1.defobj_out;
>   		assert(req->defobj_out != NULL);
>   	}
> -	if (refobj->symbolic || req->defobj_out != NULL)
> +	if (refobj->symbolic || req->defobj_out != NULL || refobj->deepbind)
>   		donelist_check(&donelist, refobj);
>   
>   	if (!refobj->deepbind)

-- 
Andriy Gapon