From: Florian Weimer <fweimer@redhat.com>
To: "Arsen Arsenović" <arsen@gentoo.org>
Cc: libc-alpha@sourceware.org, Carlos O'Donell <carlos@redhat.com>,
Gentoo Toolchain <toolchain@gentoo.org>
Subject: Re: [PATCH] elf,nptl: Add -z lazy -z norelro to tests that need it
Date: Mon, 06 Mar 2023 10:15:45 +0100 [thread overview]
Message-ID: <87bkl6xmta.fsf@oldenburg.str.redhat.com> (raw)
In-Reply-To: <86fsakz5mr.fsf@gentoo.org> ("Arsen =?utf-8?Q?Arsenovi=C4=87?= =?utf-8?Q?=22's?= message of "Sat, 04 Mar 2023 18:46:50 +0100")
* Arsen Arsenović:
> Arsen Arsenović <arsen@gentoo.org> writes:
>
>> Hm. Something went awry while I was debugging this. I looked at a test
>> again just now and noticed that the symbols some of these tests were
>> crashing on came from libc (dlopen here) while loading constload2 (which
>> is dlopen'd from constload1). The backtrace contains a PLT trampoline
>> which then fixups dlopen inside the RELRO segment.
>>
>> I take it dlopen@got[plt] is not supposed to be in the RELRO range?
>>
>> I could have sworn this failed when fixing up bar (void) as a result of
>> constload2 dlopening constload3... but maybe that was a different
>> failure.
>>
>> Let's put this patch on hold while I investigate further.
>>
>> FWIW, this should be easy to reproduce by building with CC='gcc
>> -Wl,-z,relro,-z,now' or so, I think.
>
> Ah, I think I see the issue:
>
> ~/gnu/glibc/b2$ diff -u0 shlib.lds.-Wl,-z,{lazy,now},-z,relro
> --- shlib.lds.-Wl,-z,lazy,-z,relro 2023-03-04 19:54:42.977032934 +0100
> +++ shlib.lds.-Wl,-z,now,-z,relro 2023-03-04 18:57:03.195010040 +0100
> @@ -1 +1 @@
> -/* Script for -shared -z combreloc -z separate-code */
> +/* Script for -shared -z combreloc -z separate-code -z relro -z now */
> @@ -153,3 +153,2 @@
> - .got : { *(.got) *(.igot) }
> - . = DATA_SEGMENT_RELRO_END (SIZEOF (.got.plt) >= 24 ? 24 : 0, .);
> - .got.plt : { *(.got.plt) *(.igot.plt) }
> + .got : { *(.got.plt) *(.igot.plt) *(.got) *(.igot) }
> + . = DATA_SEGMENT_RELRO_END (0, .);
> ~/gnu/glibc/b2 1 $
>
> The builds system assumes that all the flags used while building glibc
> use the same linker script, and that this will be the same linker script
> as the one that's used initially to generate shlib.lds. This is not
> true when -z relro is set and -z {now,lazy} are being varied.
>
> This also explains why the problem only arose after we introduced
> -Wl,-z,now.
Interesting, thanks for looking into this.
Does the issue go away if you configure with --enable-bind-now?
That's what we are doing, and we don't see those test failures.
Florian
next prev parent reply other threads:[~2023-03-06 9:15 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-02 11:25 Arsen Arsenović
2023-03-03 11:51 ` Florian Weimer
2023-03-03 21:54 ` Arsen Arsenović
2023-03-04 17:46 ` Arsen Arsenović
2023-03-06 9:15 ` Florian Weimer [this message]
2023-03-06 14:17 ` Arsen Arsenović
2023-03-06 16:42 ` Arsen Arsenović
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