RFA: gas/cgen.[ch]: Make it easier to generate pc-relative relocations

[Joern Rennecke]

I find that it is currently too hard to get pc-relative relocations
right in a cgen-generated gas.  E.g. look at testsuite/ld-elf/merge* .

When the bfd_reloc_code_real_type of a fragment is selected, it is not
known if the fragment is pc-relative or not.
You could define tc_gen_reloc to your own function that parses the
expression to find out if it is pc-relative and do the right thing then,
but that would require a lot of duplicated code for each target,
and defeat the purpose of having gas_cgen_tc_gen_reloc.

With the appended patch, tc-<target>.h only has to do
#define GAS_CGEN_PCREL_R_TYPE(R_TYPE) gas_cgen_pcrel_r_type(R_TYPE)
to handle the vanilla pc-relative relocations.
If a few pc-relative relocations need different handling, that should
also be easily accomplished with a wrapper function.

2011-08-06  Joern Rennecke <address@hidden>

        * cgen.c (gas_cgen_pcrel_r_type): New function.
        (gas_cgen_tc_gen_reloc): Check for GAS_CGEN_PCREL_R_TYPE.
        * cgen.h (gas_cgen_pcrel_r_type): Declare.

Index: cgen.c
===================================================================
--- cgen.c      (revision 2024)
+++ cgen.c      (revision 2025)
@@ -1018,6 +1018,32 @@ gas_cgen_md_apply_fix (fixP, valP, seg)
   fixP->fx_addnumber = value;
 }
 
+bfd_reloc_code_real_type
+gas_cgen_pcrel_r_type (bfd_reloc_code_real_type r)
+{
+  switch (r)
+    {
+    case BFD_RELOC_8:
+      r = BFD_RELOC_8_PCREL;
+      break;
+    case BFD_RELOC_16:
+      r = BFD_RELOC_16_PCREL;
+      break;
+    case BFD_RELOC_24:
+      r = BFD_RELOC_24_PCREL;
+      break;
+    case BFD_RELOC_32:
+      r = BFD_RELOC_32_PCREL;
+      break;
+    case BFD_RELOC_64:
+      r = BFD_RELOC_64_PCREL;
+      break;
+    default:
+      break;
+    }
+  return r;
+}
+
 /* Translate internal representation of relocation info to BFD target format.
 
    FIXME: To what extent can we get all relevant targets to use this?  */
@@ -1027,10 +1053,16 @@ gas_cgen_tc_gen_reloc (section, fixP)
      asection * section ATTRIBUTE_UNUSED;
      fixS *     fixP;
 {
+  bfd_reloc_code_real_type r_type = fixP->fx_r_type;
   arelent *reloc;
+
   reloc = (arelent *) xmalloc (sizeof (arelent));
 
-  reloc->howto = bfd_reloc_type_lookup (stdoutput, fixP->fx_r_type);
+#ifdef GAS_CGEN_PCREL_R_TYPE
+  if (fixP->fx_pcrel)
+    r_type = GAS_CGEN_PCREL_R_TYPE (r_type);
+#endif
+  reloc->howto = bfd_reloc_type_lookup (stdoutput, r_type);
   if (reloc->howto == (reloc_howto_type *) NULL)
     {
       as_bad_where (fixP->fx_file, fixP->fx_line,
Index: cgen.h
===================================================================
--- cgen.h      (revision 2024)
+++ cgen.h      (revision 2025)
@@ -80,6 +80,8 @@ extern fixS * gas_cgen_record_fixup_exp 
                                         int, const CGEN_OPERAND *, int,
                                         expressionS *);
 
+extern bfd_reloc_code_real_type gas_cgen_pcrel_r_type 
(bfd_reloc_code_real_type);
+
 /* md_apply_fix handler */
 extern void gas_cgen_md_apply_fix (fixS *, valueT *, segT);