RISC-V: PR31179, The SET/ADD/SUB fix breaks ABI compatibility with 2.41 objects

[thirdparty/binutils-gdb.git] / bfd / elfnn-riscv.c

diff --git a/bfd/elfnn-riscv.c b/bfd/elfnn-riscv.c
index 042266e791b453e7ef9b91153e29cc88e3f83a3f..509d61e50170885b0d9272ab6d760fe90b4d05b2 100644 (file)
--- a/bfd/elfnn-riscv.c
+++ b/bfd/elfnn-riscv.c
@@ -1735,19 +1735,9 @@ perform_relocation (const reloc_howto_type *howto,
   if (howto->pc_relative)
     value -= sec_addr (input_section) + rel->r_offset;
 
-  switch (ELFNN_R_TYPE (rel->r_info))
-    {
-    case R_RISCV_SUB6:
-    case R_RISCV_SUB8:
-    case R_RISCV_SUB16:
-    case R_RISCV_SUB32:
-    case R_RISCV_SUB64:
-    case R_RISCV_SUB_ULEB128:
-      value -= rel->r_addend;
-      break;
-    default:
-      value += rel->r_addend;
-    }
+  /* PR31179, ignore the non-zero addend of R_RISCV_SUB_ULEB128.  */
+  if (ELFNN_R_TYPE (rel->r_info) != R_RISCV_SUB_ULEB128)
+    value += rel->r_addend;
 
   switch (ELFNN_R_TYPE (rel->r_info))
     {
@@ -2530,9 +2520,35 @@ riscv_elf_relocate_section (bfd *output_bfd,
          if (uleb128_set_rel != NULL
              && uleb128_set_rel->r_offset == rel->r_offset)
            {
-             relocation = uleb128_set_vma - relocation + uleb128_set_rel->r_addend;
+             relocation = uleb128_set_vma - relocation
+                          + uleb128_set_rel->r_addend;
              uleb128_set_vma = 0;
              uleb128_set_rel = NULL;
+
+             /* PR31179, the addend of SUB_ULEB128 should be zero if using
+                .uleb128, but we make it non-zero by accident in assembler,
+                so just ignore it in perform_relocation, and make assembler
+                continue doing the right thing.  Don't reset the addend of
+                SUB_ULEB128 to zero here since it will break the --emit-reloc,
+                even though the non-zero addend is unexpected.
+
+                We encourage people to rebuild their stuff to get the
+                non-zero addend of SUB_ULEB128, but that might need some
+                times, so report warnings to inform people need to rebuild
+                if --check-uleb128 is enabled.  However, since the failed
+                .reloc cases for ADD/SET/SUB/ULEB128 are rarely to use, it
+                may acceptable that stop supproting them until people rebuld
+                their stuff, maybe half-year or one year later.  I believe
+                this might be the least harmful option that we should go.
+
+                Or maybe we should teach people that don't write the
+                .reloc R_RISCV_SUB* with non-zero constant, and report
+                warnings/errors in assembler.  */
+             if (htab->params->check_uleb128
+                 && rel->r_addend != 0)
+               _bfd_error_handler (_("%pB: warning: R_RISCV_SUB_ULEB128 with"
+                                     " non-zero addend, please rebuild by"
+                                     " binutils 2.42 or up"), input_bfd);
            }
          else
            {