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From: Siddhesh Poyarekar <siddhesh@gotplt.org>
To: Fangrui Song <maskray@google.com>, libc-alpha@sourceware.org
Subject: Re: [PATCH 0/3] Allow LLD 13.0.0 and improve compatibility with gold and clang
Date: Mon, 2 Aug 2021 09:32:55 +0530	[thread overview]
Message-ID: <a465b8a2-2f1b-cd6e-01ce-dd5936887265@gotplt.org> (raw)
In-Reply-To: <20210726035802.275992-1-maskray@google.com>

On 7/26/21 9:27 AM, Fangrui Song via Libc-alpha wrote:
> For malloc/tst-compathooks-on,
> 
>      malloc/tst-compathooks-on: Symbol `__free_hook' has different size in shared object, consider re-linking
> 
> the root cause is that lld's symbol versioning is different from GNU ld in an unusal case:
> 
>      __asm__ (".symver " "__free_hook" "," "__free_hook" "@" "GLIBC_2.2.5");
> 
> This leaves two symbols __free_hook and __free_hook@GLIBC_2.2.5.
> __free_hook is then attached a default version GLIBC_2.2.5.
> I think malloc/malloc-debug.c uses a fragile versioned symbol here.
> If the inline asm uses @@ the failure should go away.

The entire point of link time deprecation is to not emit a @@ symbol. 
If lld emits __free_hook@@GLIBC_2.2.5 in this case then this needs to be 
resolved.  How does one do symbol deprecation in lld?

> In summary, I think the failed tests touch some dark corners of the toolchain.
> These things do not really matter for real world applications.

Not having a default symbol version is a documented mechanism[1] to 
deprecate symbols, so this is not some obscure use case.  Symbol 
deprecation matters for real world applications.

Siddhesh

[1] See section 3.3 in https://www.akkadia.org/drepper/dsohowto.pdf:

"Every versioned DSO has at most one version
of every API which can be used at link-time. An API
(not ABI) can also vanish completely: this is a way to
deprecate APIs without affecting binary compatibility."

  parent reply	other threads:[~2021-08-02  4:03 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-26  3:57 [PATCH 0/3] Allow LLD 13.0.0 and improve compatibility with gold and clang Fangrui Song via Libc-alpha
2021-07-26  3:58 ` [PATCH 1/3] elf: Replace .tls_common with .tbss definition Fangrui Song via Libc-alpha
2021-07-29 14:26   ` H.J. Lu via Libc-alpha
2021-07-29 16:21     ` Fangrui Song via Libc-alpha
2021-07-26  3:58 ` [PATCH 2/3] elf: Skip tst-auditlogmod-* if the linker doesn't support --depaudit Fangrui Song via Libc-alpha
2021-07-29 14:23   ` H.J. Lu via Libc-alpha
2021-07-29 16:28     ` Fangrui Song via Libc-alpha
2021-07-26  3:58 ` [PATCH 3/3] configure: Allow LD to be LLD 13.0.0 or above Fangrui Song via Libc-alpha
2021-07-28 18:02 ` [PATCH 0/3] Allow LLD 13.0.0 and improve compatibility with gold and clang H.J. Lu via Libc-alpha
2021-07-28 21:52   ` Fangrui Song via Libc-alpha
2021-07-29 14:45     ` H.J. Lu via Libc-alpha
2021-07-30  7:57 ` Florian Weimer via Libc-alpha
2021-07-31  6:34   ` Fāng-ruì Sòng via Libc-alpha
2021-07-31  6:41     ` Florian Weimer via Libc-alpha
2021-08-02 20:55     ` Fāng-ruì Sòng via Libc-alpha
2021-08-02  4:02 ` Siddhesh Poyarekar [this message]
2021-08-02  4:23   ` Siddhesh Poyarekar
2021-08-08 16:50     ` Fāng-ruì Sòng via Libc-alpha
2021-08-08  2:54   ` Fāng-ruì Sòng via Libc-alpha
2021-08-08 16:45     ` Siddhesh Poyarekar

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