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From: Florian Weimer <fweimer@redhat.com>
To: Rich Felker <dalias@libc.org>
Cc: musl@lists.openwall.com
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	<20230405122044.GG4163@brightrain.aerifal.cx>
Date: Wed, 05 Apr 2023 14:25:20 +0200
In-Reply-To: <20230405122044.GG4163@brightrain.aerifal.cx> (Rich Felker's
	message of "Wed, 5 Apr 2023 08:20:44 -0400")
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Subject: Re: [musl] Re: [PATCH v9 0/13] implement dlmem() function (fwd)

* Rich Felker:

> On Wed, Apr 05, 2023 at 02:13:16PM +0200, Florian Weimer wrote:
>> * Rich Felker:
>> 
>> > Well this is disturbing. We probably need to fix gcc here (and a lot
>> > of code in the wild may be broken) because musl has no such locking
>> > where it doesn't belong.
>> 
>> We have a helper function in glibc (_dl_find_object) that replaces all
>> the previous object traversal logic and caching in libgcc, so it's no
>> longer an issue with current gcc and glibc.
>
> Does gcc automatically detect and use this if available? What gcc
> versions does that cover? We could certainly add it, but I suspect
> coverage will be incomplete... :/

It's using a macro from <dlfcn.h> as a proxy to indicate libc support:

+  /* Use DLFO_STRUCT_HAS_EH_DBASE as a proxy for the existence of a glibc-style
+     _dl_find_object function.  */
+#ifdef DLFO_STRUCT_HAS_EH_DBASE

It's not dependent upon __GLIBC__.

>> Unfortunately that means that the generic dl_iterate_phdr code will
>> be fixed by adding its own locking.
>
> Not sure why that's unfortunate; it's what it should have been doing
> all along.

I missed a negation.  I meant that It's unlikely that it's going to be
fixed, unless you write a patch yourself. 8->

Thanks,
Florian