Re: [PATCH] csu: Skip ARCH_SETUP_IREL if _dl_relocate_static_pie applied IRELATIVE relocations [BZ #27164]

["Fāng-ruì Sòng via Libc-alpha" <libc-alpha@sourceware.org>]

On Tue, Jul 13, 2021 at 4:21 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Tue, Jul 13, 2021 at 4:07 PM Fangrui Song via Libc-alpha
> <libc-alpha@sourceware.org> wrote:
> >
> > On 2021-07-13, Siddhesh Poyarekar wrote:
> > >On 7/13/21 1:36 PM, Fangrui Song via Libc-alpha wrote:
> > >>A toolchain project can do some workaround for a libc if this choice
> > >>makes a large community happy. However, I think it is important not to
> > >>take it granted. It is inadequate to just dismiss toolchain developers'
> > >>reasonable complaints. The libc should actively fix the issues so that
> > >>the toolchain will not need to bear unneeded code in the future.
> > >>
> > >>I actually have contributed quite a few lld/ELF patches to work around
> > >>glibc. For this one I just feel it is not right to just patch lld/ELF
> > >>without fixing glibc.
> > >
> > >What's the utility of having the __rela_iplt{_start,_end} symbols in
> > >all binaries other than, maybe, simplifying the static linker
> > >implementation?  How does it improve things for the generated
> > >application code in the end?  AFAICT it is doing the opposite by
> > >requiring application startup to add a conditional to work around the
> > >presence of a redundant symbol.
> > >
> > >Siddhesh
> >
> > Please see the sentence from the first message
> > "In addition, this enables a future simplification to GNU ld: we can
> > drop a linker script difference between -no-pie and -pie."
>
> Did you mean non-PIE static and PIE static?  Neither PIE nor PDE
> define __rela_iplt{_start,_end}.
>
> > This is the only difference other than image base difference.
>
> There are many differences between non-PIE static and PIE static.
> Non-PIE static doesn't have DT_XXX sections.

% diff -U1 =(ld.bfd --verbose) =(ld.bfd -pie --verbose)
--- /tmp/zshEtZMxJ      2021-07-13 16:30:50.228732445 -0700
+++ /tmp/zshNM1wJL      2021-07-13 16:30:50.232732450 -0700
@@ -12,3 +12,3 @@
 ==================================================
-/* Script for -z combreloc -z separate-code */
+/* Script for -pie -z combreloc -z separate-code */
 /* Copyright (C) 2014-2020 Free Software Foundation, Inc.
@@ -24,3 +24,3 @@
 {
-  PROVIDE (__executable_start = SEGMENT_START("text-segment",
0x400000)); . = SEGMENT_START("text-segment", 0x400000) +
SIZEOF_HEADERS;
+  PROVIDE (__executable_start = SEGMENT_START("text-segment", 0)); .
= SEGMENT_START("text-segment", 0) + SIZEOF_HEADERS;
   .interp         : { *(.interp) }
@@ -55,5 +55,3 @@
       *(.rela.plt)
-      PROVIDE_HIDDEN (__rela_iplt_start = .);
       *(.rela.iplt)
-      PROVIDE_HIDDEN (__rela_iplt_end = .);
     }