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 --git a/libgcc/unwind-dw2-fde-dip.c b/libgcc/unwind-dw2-fde-dip.c
index 2f2ca35d549d528139caf588dff49bcbc626fefe..57d0c8812b13a2bfa8ff9b5e031347ad9afd7032 100644 (file)
--- 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)