From: Florian Weimer <fweimer@redhat.com>
To: Patrick Palka <ppalka@redhat.com>
Cc: Patrick Palka via Gcc-patches <gcc-patches@gcc.gnu.org>,
libstdc++@gcc.gnu.org
Subject: Re: [PATCH 2/2] libstdc++: Move stream initialization into compiled library [PR44952]
Date: Fri, 04 Nov 2022 19:16:56 +0100 [thread overview]
Message-ID: <87o7tmy487.fsf@oldenburg.str.redhat.com> (raw)
In-Reply-To: <d9d95eb6-54b1-9a3b-98c2-27ee978fa32b@idea> (Patrick Palka's message of "Fri, 4 Nov 2022 13:47:10 -0400 (EDT)")
* Patrick Palka:
> On Fri, 4 Nov 2022, Florian Weimer wrote:
>
>> * Patrick Palka via Gcc-patches:
>>
>> > This patch moves the global object for constructing the standard streams
>> > out from <iostream> and into the compiled library on targets that support
>> > the init_priority attribute. This means that <iostream> no longer
>> > introduces a separate global constructor in each TU that includes it.
>> >
>> > We can do this only if the init_priority attribute is supported because
>> > we need to force that the stream initialization runs first before any
>> > user-defined global initializer in programs that that use a static
>> > libstdc++.a.
>>
>> I think this breaks initialization of iostreams of shared objects that
>> are preloaded with LD_PRELOAD. With the constructor, they initialize
>> iostreams once they are loaded via their own ELF constructors (even
>> before libstdc++'s ELF constructors run). Without the constructor in
>> <iostream>, that no longer happens.
>
> IIUC wouldn't that shared object depend on libstdc++.so and hence
> libstdc++'s constructors would still run before the shared object's?
Hmm, right, we only reorder the symbol binding order, not the
initialization order. The preloaded object will not participate in a
cycle with libstdc++, so I think this should indeed be a safe change.
Thanks,
Florian
next prev parent reply other threads:[~2022-11-04 18:17 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-04 15:05 [PATCH 1/2] c++: correct __has_attribute(init_priority) Patrick Palka
2022-11-04 15:05 ` [PATCH 2/2] libstdc++: Move stream initialization into compiled library [PR44952] Patrick Palka
2022-11-04 15:24 ` Jonathan Wakely
2022-11-04 16:31 ` Patrick Palka
2022-11-04 16:42 ` Jonathan Wakely
2022-11-04 16:57 ` Florian Weimer
2022-11-04 17:47 ` Patrick Palka
2022-11-04 18:16 ` Florian Weimer [this message]
2022-11-15 16:10 ` Hans-Peter Nilsson
2022-11-04 15:55 ` [PATCH 1/2] c++: correct __has_attribute(init_priority) Jason Merrill
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