From: "Fāng-ruì Sòng" <maskray@google.com>
To: Florian Weimer <fweimer@redhat.com>
Cc: "H.J. Lu" <hjl.tools@gmail.com>,
GNU C Library <libc-alpha@sourceware.org>,
"Carlos O'Donell" <carlos@redhat.com>,
Adhemerval Zanella <adhemerval.zanella@linaro.org>,
Joseph Myers <joseph@codesourcery.com>
Subject: Re: [PATCH v2] elf: Avoid nested functions in the loader (all ports) [BZ #27220]
Date: Thu, 23 Sep 2021 10:34:09 -0700 [thread overview]
Message-ID: <CAFP8O3KztG2z+Gw3-fBZngZveD9=U+bW7u-JgJH4MMpn3Wz3NA@mail.gmail.com> (raw)
In-Reply-To: <87v92rnrkg.fsf@oldenburg.str.redhat.com>
On Thu, Sep 23, 2021 at 10:13 AM Florian Weimer <fweimer@redhat.com> wrote:
>
> * Fāng-ruì Sòng:
>
> > For elf/dl-reloc.os on x86-64, I think the nested function version can
> > use *(rbp - offset) to get some arguments.
> > The new version needs more instructions but the cost is small compared
> > with the expensive _dl_lookup_symbol_x.
>
> I have a patch that reduces the number of _dl_lookup_symbol_x calls for
> the self-relocation (bootstrap or not):
>
> [v3,3/3] elf: Rework exception handling in the dynamic loader [BZ #25486]
> <https://patchwork.sourceware.org/project/glibc/patch/05e1b5b43416eba58f2bab968320fa3d38e33479.1607085588.git.fweimer@redhat.com/>
>
> It needs rebase on the current tree.
>
> We recently lost the internal _r_debug reference, which is probably a
> bug. Other architectures have some other crud in ld.so. But I think we
> can get the number of symbols used in self-relocation down to zero on
> all architectures fairly easily.
>
> Once we do that, how much of the bootstrap relocation goo is really
> left?
>
> Thanks,
> Florian
>
If self-relocations means relocations used in rtld.c and
elf/dl-reloc-static-pie.o:
The new version doesn't cause differences near _dl_lookup_symbol_x call sites.
I think the relocation code sequence doesn't change.
@@ -5757,7 +5789,7 @@
push 0
push 1
call <L509>
- 0000000000004ec7: R_X86_64_PLT32 _dl_lookup_symbol_x-0x4
+ 0000000000004f27: R_X86_64_PLT32 _dl_lookup_symbol_x-0x4
<L509>:
pop r8
pop r9
The new rtld.os is slightly larger, but I guess that it is just
because GCC inlines one more place.
next prev parent reply other threads:[~2021-09-23 17:34 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-23 7:17 Fangrui Song
2021-09-23 8:07 ` Andreas Schwab
2021-09-23 8:17 ` Fangrui Song
2021-09-23 8:39 ` Andreas Schwab
2021-09-23 13:08 ` Zack Weinberg
2021-09-23 16:11 ` Fangrui Song
2021-09-23 16:19 ` H.J. Lu
2021-09-23 16:58 ` Fāng-ruì Sòng
2021-09-23 17:13 ` Florian Weimer
2021-09-23 17:34 ` Fāng-ruì Sòng [this message]
2021-09-23 17:40 ` Florian Weimer
2021-09-23 19:05 ` Fangrui Song
2021-09-23 21:48 ` Florian Weimer
2021-09-23 22:41 ` Fāng-ruì Sòng
2021-09-24 5:58 ` Florian Weimer
2021-09-24 7:23 ` Florian Weimer
2021-09-24 7:32 ` Fāng-ruì Sòng
2021-09-24 8:27 ` Florian Weimer
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