[gcc r14-7165] libgcc, nios2: Fix exception handling on nios2 with -fpic

[Sandra Loosemore]

https://gcc.gnu.org/g:cc9cac9f073a9517f5b7fcffcb7c28b166339491

commit r14-7165-gcc9cac9f073a9517f5b7fcffcb7c28b166339491
Author: Sandra Loosemore <sandra@codesourcery.com>
Date:   Thu Jan 11 21:12:56 2024 +0000

    libgcc, nios2: Fix exception handling on nios2 with -fpic
    
    Exception handling on nios2-linux-gnu with -fpic has been broken since
    revision 790854ea7670f11c14d431c102a49181d2915965, "Use _dl_find_object
    in _Unwind_Find_FDE".  For whatever reason, this doesn't work on nios2.
    
    Nios2 uses the GOT address as the base for DW_EH_PE_datarel
    relocations in PIC; see my previous fix to make this work, revision
    2d33dcfe9f0494c9b56a8d704c3d27c5a4329ebc, "Support for GOT-relative
    DW_EH_PE_datarel encoding".  So this may be a horrible bug in the ABI
    or in my interpretation of it or just glibc's implementation of
    _dl_find_object for this target, but there's existing code out there
    that does things this way; and realistically, nobody is going to
    re-engineer this now that the vendor has EOL'ed the nios2
    architecture.  So, just skip over the code trying to use
    _dl_find_object on this target and fall back to the way that works.
    
    I plan to backport this patch to the GCC 12 and GCC 13 branches as well.
    
    libgcc/ChangeLog
            * unwind-dw2-fde-dip.c (_Unwind_Find_FDE): Do not try to use
            _dl_find_object on nios2; it doesn't work.

Diff:
---
 libgcc/unwind-dw2-fde-dip.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/libgcc/unwind-dw2-fde-dip.c b/libgcc/unwind-dw2-fde-dip.c
index 2f2ca35d549..57d0c8812b1 100644
--- a/libgcc/unwind-dw2-fde-dip.c
+++ b/libgcc/unwind-dw2-fde-dip.c
@@ -543,8 +543,9 @@ _Unwind_Find_FDE (void *pc, struct dwarf_eh_bases *bases)
     return ret;
 
   /* Use DLFO_STRUCT_HAS_EH_DBASE as a proxy for the existence of a glibc-style
-     _dl_find_object function.  */
-#ifdef DLFO_STRUCT_HAS_EH_DBASE
+     _dl_find_object function.  However, do not use _dl_find_object on nios2,
+     which uses the GOT address as the base for DW_EH_PE_datarel instead.  */
+#if defined(DLFO_STRUCT_HAS_EH_DBASE) && !defined(__nios2__)
   {
     struct dl_find_object dlfo;
     if (_dl_find_object (pc, &dlfo) == 0 && dlfo.dlfo_eh_frame != NULL)