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Message-ID: <1cc26358-5ebd-4fe4-a16c-280829508692@foss.arm.com>
Date: Thu, 20 Nov 2025 21:08:40 -0600
From: Bill Roberts <bill.roberts@...s.arm.com>
To: Rich Felker <dalias@...c.org>
Cc: musl@...ts.openwall.com, Szabolcs Nagy <nsz@...t70.net>
Subject: Re: questions on src/ldso/aarch64/dlsym.s
On 11/20/25 9:00 PM, Rich Felker wrote:
> On Thu, Nov 20, 2025 at 08:49:07PM -0600, Bill Roberts wrote:
>> Howdy folks,
>>
>> I was hoping you could shed some light on src/ldso/aarch64/dlsym.s? As it's
>> not apparent to me how this stub gets executed. I have tried a few things to
>> no avail. I don't get how there is C symbols defined with the same name and
>> then these defined in asm, what am I missing, it seems obvious...
>>
>> ```asm
>> .global dlsym
>> .hidden __dlsym
>> .type dlsym,%function
>> dlsym:
>> mov x2,x30
>> b __dlsym
>> ```
>>
>> Thanks,
>> Bill
>
> In the make rules, presence of src/xxx/$ARCH/yyy.[csS] files replaces
> the corresponding src/xxx/yyy.c file and prevents the latter from
> being built at all. The above isn't a stub, it's the definition for
> the public dlsym symbol, and it calls the hidden __dlsym symbol.
>
> __dlsym in turn has an always-failing weak definition in
> src/ldso/__dlsym.c that's superseded by the actually-functional
> definition of __dlsym in ldso/dynlink.c for dynamic libc.
>
> Rich
Thanks, Rich, that makes a lot more sense now. So is there a huge
benefit in using the generic c implementation (I'm assuming its a
generic implementation) versus an arch specific stub?
I ask this on the crusade to ditching .s and .S for .c and inline
assembly. So when I went to a .c file, it was clashing from the
aforementioned Make logic. Perhaps this is better just in a .S (capital)
file, then we can use an ifdef on bti c, or perhaps as Szabolcs
mentioned in the past, just leave the bti c in there unconditionally as
its backwards compat?
Bill
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