RISC-V: Report unresolved relocation error via linker's callback function.

Two patches from Nelson Chu.

It is better to use the linker's callback functions to handle the link time
error when relocating.  The unresolved relocation error can be regarded as
an unsupported relocation.  To make user easier to understand different errors,
we need to extend the current error message format of the callback function
since the format is fixed.

	bfd/
	* elfnn-riscv.c (riscv_elf_relocate_section): Use asprintf to extend
	the error message if needed, and then store the result into the
	`msg_buf`.  Finally, remember to free the unused `msg_buf`.  All error
	message for the dangerous relocation should be set before we call the
	callback function.  If we miss the error message since linker runs out
	of memory, we should set the default error message for the error.

	ld/
	* testsuite/ld-riscv-elf/lib-nopic-01a.s: Create the shared library
	lib-nopic-01a.so, it will be linked with lib-nopic-01b.s.
	* testsuite/ld-riscv-elf/lib-nopic-01b.s: Add new test for the
	unresolved relocation.  Link the non-pic code into a shared library
	may cause the error.
	* testsuite/ld-riscv-elf/lib-nopic-01b.d: Likewise.
	* testsuite/ld-riscv-elf/ld-riscv-elf.exp: Run the new test only when
	the shared library is supported.

R_RISCV_CALL, R_RISCV_JAL and R_RISCV_RVC_JUMP are pc-relative relocation.
For now, we do not allow the object with these relocation links into a shared
library since the referenced symbols may be loaded to the places that too far
from the pc.  We can improve the error message for these unsupported relocation
to notice user that they should recompile their code with `fPIC`.

	bfd/
	* elfnn-riscv.c (riscv_elf_relocate_section): Report the error message
	that user should recompile their code with `fPIC` when linking non-pic
	code into shared library.

	ld/
	* testsuite/ld-riscv-elf/lib-nopic-01b.d: Update the error message.

Change-Id: Ib3347a0a6fa1c2b20a9647c314d5bec2c322ff04

2 files changed, 59 insertions, 17 deletions

diff --git a/bfd/ChangeLog b/bfd/ChangeLog
index 74cdda4..b29b2ee 100644
--- a/bfd/ChangeLog
+++ b/bfd/ChangeLog
@@ -1,3 +1,16 @@
+2019-10-17  Nelson Chu  <nelson.chu@sifive.com>
+
+	* elfnn-riscv.c (riscv_elf_relocate_section): Report the error message
+	that user should recompile their code with `fPIC` when linking non-pic
+	code into shared library.
+
+	* elfnn-riscv.c (riscv_elf_relocate_section): Use asprintf to extend
+	the error message if needed, and then store the result into the
+	`msg_buf`.  Finally, remember to free the unused `msg_buf`.  All error
+	message for the dangerous relocation should be set before we call the
+	callback function.  If we miss the error message since linker runs out
+	of memory, we should set the default error message for the error.
+
 2019-10-16  Alan Modra  <amodra@gmail.com>
 
 	PR 13616
diff --git a/bfd/elfnn-riscv.c b/bfd/elfnn-riscv.c
index 4ffe6a3..6be209e 100644
--- a/bfd/elfnn-riscv.c
+++ b/bfd/elfnn-riscv.c
@@ -1787,6 +1787,7 @@ riscv_elf_relocate_section (bfd *output_bfd,
       int r_type = ELFNN_R_TYPE (rel->r_info), tls_type;
       reloc_howto_type *howto = riscv_elf_rtype_to_howto (input_bfd, r_type);
       const char *msg = NULL;
+      char *msg_buf = NULL;
       bfd_boolean resolved_to_zero;
 
       if (howto == NULL
@@ -2088,6 +2089,7 @@ riscv_elf_relocate_section (bfd *output_bfd,
 	       || (h != NULL && h->type == STT_SECTION))
 	      && rel->r_addend)
 	    {
+	      msg = _("%pcrel_lo section symbol with an addend");
 	      r = bfd_reloc_dangerous;
 	      break;
 	    }
@@ -2302,24 +2304,42 @@ riscv_elf_relocate_section (bfd *output_bfd,
 	  && _bfd_elf_section_offset (output_bfd, info, input_section,
 				      rel->r_offset) != (bfd_vma) -1)
 	{
-	  (*_bfd_error_handler)
-	    (_("%pB(%pA+%#" PRIx64 "): "
-	       "unresolvable %s relocation against symbol `%s'"),
-	     input_bfd,
-	     input_section,
-	     (uint64_t) rel->r_offset,
-	     howto->name,
-	     h->root.root.string);
-
-	  bfd_set_error (bfd_error_bad_value);
-	  ret = FALSE;
-	  goto out;
+	  switch (r_type)
+	    {
+	    case R_RISCV_CALL:
+	    case R_RISCV_JAL:
+	    case R_RISCV_RVC_JUMP:
+	      if (asprintf (&msg_buf,
+			    _("%%X%%P: relocation %s against `%s' can "
+			      "not be used when making a shared object; "
+			      "recompile with -fPIC\n"),
+			    howto->name,
+			    h->root.root.string) == -1)
+		msg_buf = NULL;
+	      break;
+
+	    default:
+	      if (asprintf (&msg_buf,
+			    _("%%X%%P: unresolvable %s relocation against "
+			      "symbol `%s'\n"),
+			    howto->name,
+			    h->root.root.string) == -1)
+		msg_buf = NULL;
+	      break;
+	    }
+
+	  msg = msg_buf;
+	  r = bfd_reloc_notsupported;
 	}
 
       if (r == bfd_reloc_ok)
 	r = perform_relocation (howto, rel, relocation, input_section,
 				input_bfd, contents);
 
+      /* We should have already detected the error and set message before.
+	 If the error message isn't set since the linker runs out of memory
+	 or we don't set it before, then we should set the default message
+	 with the "internal error" string here.  */
       switch (r)
 	{
 	case bfd_reloc_ok:
@@ -2338,17 +2358,21 @@ riscv_elf_relocate_section (bfd *output_bfd,
 	  break;
 
 	case bfd_reloc_outofrange:
-	  msg = _("%X%P: internal error: out of range error\n");
+	  if (msg == NULL)
+	    msg = _("%X%P: internal error: out of range error\n");
 	  break;
 
 	case bfd_reloc_notsupported:
-	  msg = _("%X%P: internal error: unsupported relocation error\n");
+	  if (msg == NULL)
+	    msg = _("%X%P: internal error: unsupported relocation error\n");
 	  break;
 
 	case bfd_reloc_dangerous:
+	  /* The error message should already be set.  */
+	  if (msg == NULL)
+	    msg = _("dangerous relocation error");
 	  info->callbacks->reloc_dangerous
-	    (info, "%pcrel_lo section symbol with an addend", input_bfd,
-	     input_section, rel->r_offset);
+	    (info, msg, input_bfd, input_section, rel->r_offset);
 	  break;
 
 	default:
@@ -2356,9 +2380,14 @@ riscv_elf_relocate_section (bfd *output_bfd,
 	  break;
 	}
 
-      if (msg)
+      /* Do not report error message for the dangerous relocation again.  */
+      if (msg && r != bfd_reloc_dangerous)
 	info->callbacks->einfo (msg);
 
+      /* Free the unused `msg_buf` if needed.  */
+      if (msg_buf)
+	free (msg_buf);
+
       /* We already reported the error via a callback, so don't try to report
 	 it again by returning false.  That leads to spurious errors.  */
       ret = TRUE;