[Bug libc/30095] New: Inhibit early libcalls before ifunc support is ready

["cmuellner at linux dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=30095

            Bug ID: 30095
           Summary: Inhibit early libcalls before ifunc support is ready
           Product: glibc
           Version: unspecified
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: libc
          Assignee: unassigned at sourceware dot org
          Reporter: cmuellner at linux dot com
                CC: drepper.fsp at gmail dot com
  Target Milestone: ---

When developing a first version of ifunc support for RISC-V, I encountered an
endless loop in the first few instructions of a statically linked RV64 binary.
When analyzing this issue, I observed that GCC has identified the loop in
_dl_aux_init() as memset-zero operation and replaced it with a libcall to
memset.

This turned out to be problematic because the ifunc support is not ready at
that time.

One solution is to set a function attribute to inhibit loop-to-libcall
transformations by the compiler ("-fno-tree-loop-distribute-patterns").
A corresponding patch has been sent as part of the RISC-V ifunc series:
  https://sourceware.org/pipermail/libc-alpha/2023-February/145350.html
 
https://patchwork.sourceware.org/project/glibc/patch/20230207001618.458947-2-christoph.muellner@vrull.eu/

The issue was triggered with GCC upstream/master and glibc upstream/master
cross-compiling glibc with "-O3" for RV64.

I believe this issue is not caused by a wrong implementation in the RISC-V
ifunc support, therefore, I decided the open this ticket (with the hope it can
get addressed independently of the ifunc series).

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