[Bug dynamic-link/27164] New: csu/libc-start.c should not call ARCH_APPLY_IREL in static pie mode

[Bug dynamic-link/27164] New: csu/libc-start.c should not call ARCH_APPLY_IREL in static pie mode

[i at maskray dot me]

https://sourceware.org/bugzilla/show_bug.cgi?id=27164

            Bug ID: 27164
           Summary: csu/libc-start.c should not call ARCH_APPLY_IREL in
                    static pie mode
           Product: glibc
           Version: unspecified
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: dynamic-link
          Assignee: unassigned at sourceware dot org
          Reporter: i at maskray dot me
  Target Milestone: ---

* In GNU ld, __rela_iplt_start is defined for -no-pie, but not for -pie.
* LLD defines __rela_iplt_start, regardless of -no-pie, -pie or -shared.

glibc csu/libc-start.c has undefined weak __rela_iplt_start/__rela_iplt_end and
currently requires the two to be equal in static pie mode.
Since there are unavoidable R_*_IRELATIVE relocations, this essentially
requires __rela_iplt_start and __rela_iplt_end to be 0, i.e.
the linker does not define the two symbols in -pie mode. However, this address
can be easily fixed on glibc side by differenciating static pie from static.

(Note GNU ld does not currently have -no-pie (its -no-pie is currently -n -o
"-pie"), but gold/LLD do have.)

binutils commit 3aa14d16c669ca75f9fa4e995a2e2d13069dff3f (2009-06-01) added
__rela_iplt_start to ld.
That was before glibc gained static pie support (2017;
http://sourceware.org/PR19574).
With static pie, I think the design of __rela_iplt_start should be revised.

diff -u =(ld.bfd --verbose) =(ld.bfd -pie --verbose) reveals two differences.
The image base (__executable_start) is an essential one but the other one
(whether __rela_iplt_start is defined) should not be their.


In
https://sourceware.org/git/?p=glibc.git;a=shortlog;h=refs/heads/google/grte/v5-2.27/master
,
I find "Make _dl_relocate_static_pie return an int indicating whether it
applied relocs." can address the exact glibc csu/libc-start.c issue.

I do see that GNU ld may not want a change (probably in a couple of years)
because it does not want to gratuitously break unpatched glibc `configure
--enable-static-pie`. But once glibc is fixed and the minimum required version
is bumped, the code can be removed from GNU ld. On glibc side, the explicit
guard before ARCH_APPLY_IREL also makes things more clear, not relying on
subtle zero address __rela_iplt_start.

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[Bug dynamic-link/27164] csu/libc-start.c should not call ARCH_APPLY_IREL in static pie mode

[carlos at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27164

Carlos O'Donell <carlos at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |Houdek.Ryan@fex-emu.org

--- Comment #1 from Carlos O'Donell <carlos at redhat dot com> ---
*** Bug 28066 has been marked as a duplicate of this bug. ***

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[Bug dynamic-link/27164] csu/libc-start.c should not call ARCH_APPLY_IREL in static pie mode

[hjl.tools at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27164

H.J. Lu <hjl.tools at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |hjl.tools at gmail dot com

--- Comment #2 from H.J. Lu <hjl.tools at gmail dot com> ---
Glibc uses DT_XXX to handle relocations, including IFUNC relocations.  Since
there is no need to relocate static executable and there is no DT_XXX in static
executable, I added __rela_iplt_start/__rela_iplt_end to handle IFUNC in static
executable which doesn't need relocation.  Since DT_XXX is used to handle
relocations, including IFUNC relocations, in static PIE, linker shouldn't
define __rela_iplt_start/__rela_iplt_end when DT_XXX is created.

Please fix the lld bug.

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[Bug dynamic-link/27164] csu/libc-start.c should not call ARCH_APPLY_IREL in static pie mode

[i at maskray dot me]

https://sourceware.org/bugzilla/show_bug.cgi?id=27164

--- Comment #3 from Fangrui Song <i at maskray dot me> ---
I worked around the glibc csu/libc-start.c ARCH_APPLY_IREL issue (unclear
semantics) and unneeded diff -u =(ld.bfd --verbose) =(ld.bfd -pie --verbose)
difference in ld.lld f8cb78e99aae9aa3f89f7bfe667db2c5b767f21f
([ELF] Don't define __rela_iplt_start for -pie/-shared)
(target: LLD 13.0.0)

but my complaint remains for glibc:
https://sourceware.org/pipermail/libc-alpha/2021-July/128981.html

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