[PATCH v2 1/7] bfd:pru: Fix LDI32 relocation to conform to TI ABI

[Dimitar Dimitrov <dimitar at dinux dot eu>]

My original implementation for LDI32 pseudo does not conform to
the TI ABI.  I wrongly documented my TI PRU ELF inspection, which
got propagated into the binutils implementation.

Issue was exposed when running the GCC ABI testsuite against TI toolchain.
According to TI ABI, LDI32 must use first LDI instruction to load
the MSB 16bits, and second LDI instruction for the LSB 16bits.

This patch will break binary compatibility with previously released
binutils versions for PRU. Still, I think it is better to fix
binutils to conform to the chip vendor ABI.

When an old object file link is attempted, the new LD will refuse to
link it with the following error:
   ld: error: x.o: old incompatible object file detected

Patch version 2: Added checks for old unsupported object files.

2018-05-02  Dimitar Dimitrov  <dimitar@dinux.eu>

        * elf32-pru.c (pru_elf32_do_ldi32_relocate): Make LDI32 relocation
          conformant to TI ABI.
        (pru_elf32_relax_section): Ditto.
        (pru_elf_relax_delete_bytes): Fix offsets for new LDI32 code.

Signed-off-by: Dimitar Dimitrov <dimitar@dinux.eu>
---
 bfd/elf32-pru.c | 49 +++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 41 insertions(+), 8 deletions(-)

diff --git a/bfd/elf32-pru.c b/bfd/elf32-pru.c
index a3c431ba7e..99ac8ade0c 100644
--- a/bfd/elf32-pru.c
+++ b/bfd/elf32-pru.c
@@ -565,17 +565,28 @@ pru_elf32_do_ldi32_relocate (bfd *abfd, reloc_howto_type *howto,
   in2 = bfd_get_32 (abfd, location + 4);
 
   /* Extract the addend - should be zero per my understanding.  */
-  num = GET_INSN_FIELD (IMM16, in1) | (GET_INSN_FIELD (IMM16, in2) << 16);
+  num = (GET_INSN_FIELD (IMM16, in1) << 16) | GET_INSN_FIELD (IMM16, in2);
   BFD_ASSERT (!num);
 
   relocation += num;
 
-  SET_INSN_FIELD (IMM16, in1, relocation & 0xffff);
-  SET_INSN_FIELD (IMM16, in2, relocation >> 16);
+  SET_INSN_FIELD (IMM16, in1, relocation >> 16);
+  SET_INSN_FIELD (IMM16, in2, relocation & 0xffff);
 
   bfd_put_32 (abfd, in1, location);
   bfd_put_32 (abfd, in2, location + 4);
 
+  /* Old GAS and LD versions have a bug, where the two
+     LDI instructions are swapped.  Detect such object
+     files and bail.  */
+  if (GET_INSN_FIELD (RDSEL, in1) != RSEL_31_16)
+    {
+      /* xgettext:c-format */
+      _bfd_error_handler (_("error: %pB: old incompatible object file detected"),
+			  abfd);
+      return bfd_reloc_notsupported;
+    }
+
   return bfd_reloc_ok;
 }
 
@@ -1094,7 +1105,7 @@ pru_elf_relax_delete_bytes (bfd *abfd,
 	 continue;
 
        shrinked_insn_address = (sec->output_section->vma
-				+ sec->output_offset + addr - count);
+				+ sec->output_offset + addr);
 
        irel = elf_section_data (isec)->relocs;
        /* PR 12161: Read in the relocs for this section if necessary.  */
@@ -1354,17 +1365,39 @@ pru_elf32_relax_section (bfd * abfd, asection * sec,
 
 	  if ((long) value >> 16 == 0)
 	    {
+	      unsigned long insn;
+
 	      /* Note that we've changed the relocs, section contents.  */
 	      elf_section_data (sec)->relocs = internal_relocs;
 	      elf_section_data (sec)->this_hdr.contents = contents;
 	      symtab_hdr->contents = (unsigned char *) isymbuf;
 
-	      /* Delete bytes.  */
-	      if (!pru_elf_relax_delete_bytes (abfd, sec, irel->r_offset + 4, 4))
+	      /* Make the second instruction load the 16-bit constant
+		 into the full 32-bit register.  */
+	      insn = bfd_get_32 (abfd, contents + irel->r_offset + 4);
+
+	      /* Old GAS and LD versions have a bug, where the two
+		 LDI instructions are swapped.  Detect such object
+		 files and bail.  */
+	      if (GET_INSN_FIELD (RDSEL, insn) != RSEL_15_0)
+		{
+		  /* xgettext:c-format */
+		  _bfd_error_handler (_("error: %pB: old incompatible object file detected"),
+				      abfd);
+		  goto error_return;
+		}
+
+	      SET_INSN_FIELD (RDSEL, insn, RSEL_31_0);
+	      bfd_put_32 (abfd, insn, contents + irel->r_offset + 4);
+
+	      /* Delete the first LDI instruction.  Note that there should
+		 be no relocations or symbols pointing to the second LDI
+		 instruction.  */
+	      if (!pru_elf_relax_delete_bytes (abfd, sec, irel->r_offset, 4))
 		goto error_return;
 
-	      /* We're done with deletion of the second instruction.
-		 Set a regular LDI relocation for the first instruction
+	      /* We're done with deletion of the first instruction.
+		 Set a regular LDI relocation for the second instruction
 		 we left to load the 16-bit value into the 32-bit
 		 register.  */
 	      irel->r_info = ELF32_R_INFO (ELF32_R_SYM (irel->r_info),
-- 
2.11.0