MIPS16: Remove "extended" BREAK/SDBBP handling

Remove special casing for the `6' operand code used for the embedded
trap code of the BREAK and the SDBBP instructions to support supposedly
extended forms of these instructions.

According to all versions of the MIPS16 ASE specifications these
instructions are not extensible [1][2][3][4][5][7][8][10][11], and as
from revision 2.50 of the MIPS16e ASE specifications it has been further
clarified what was previously implied, that non-extesiable instructions
when preceded with an EXTEND prefix must cause a Reserved Instruction
exception [5][6][9][10].

Therefore supposedly extended BREAK and SDBBP instructions do not serve
their purpose anymore as they do not cause a Bp and a Debug exception
respectively and supporting these forms in disassembly only causes
confusion.

References:

[1] "Product Description, MIPS16 Application-Specific Extension",
    Version 1.3, MIPS Technologies, Inc., 970130, Table 3. "MIPS16
    Instruction Set Summary", p. 5

[2] same, Table 5 "RR Minor Opcodes (RR-type instructions)", p.10

[3] same, Table 18. "Extendable MIPS16 Instructions", p. 24

[4] "MIPS32 Architecture for Programmers, Volume IV-a: The MIPS16e
    Application-Specific Extension to the MIPS32 Architecture", MIPS
    Technologies, Inc., Document Number: MD00076, Revision 2.63, July
    16, 2013, Table 3.8 "MIPS16e Special Instructions", p. 38

[5] same, Section 3.11 "MIPS16e Extensible Instructions, p. 41

[6] same, Table 3.15 "MIPS16e Extensible Instructions", p. 41

[7] same, Table 3.24 "MIPS16e RR Encoding of the Funct Field", p. 49

[8] "MIPS64 Architecture for Programmers, Volume IV-a: The MIPS16e
    Application-Specific Extension to the MIPS64 Architecture", MIPS
    Technologies, Inc., Document Number: MD00077, Revision 2.60, June
    25, 2008, Table 1.8 "MIPS16e Special Instructions", p. 39

[9] same, Section 1.11 "MIPS16e Extensible Instructions", p. 42

[10] same, Table 1.15 "MIPS16e Extensible Instructions", pp. 42-43

[11] same, Table 1.24 "MIPS16e RR Encoding of the Funct Field", p. 50

	gas/
	* config/tc-mips.c (match_mips16_insn): Remove the `6' operand
	code special case and its associated comment.

	opcodes/
	* mips16-opc.c (decode_mips16_operand) <'6'>: Remove extended
	encoding support.

diff --git a/gas/ChangeLog b/gas/ChangeLog
index feac41ed7f98473790120ef275a72bd4c339fe68..f5dd23d6c326befc8e335728f36f2045674af2ac 100644 (file)
--- a/gas/ChangeLog
+++ b/gas/ChangeLog
@@ -1,3 +1,8 @@
+2016-12-23  Maciej W. Rozycki  <macro@imgtec.com>
+
+       * config/tc-mips.c (match_mips16_insn): Remove the `6' operand
+       code special case and its associated comment.
+
 2016-12-23  Maciej W. Rozycki  <macro@imgtec.com>
 
        * config/tc-mips.c (mips16_ip): Handle `.e' and `.t' instruction

diff --git a/gas/config/tc-mips.c b/gas/config/tc-mips.c
index 7536a5ba06742fdfcb040b56c7d35f62f28416f1..710560475623a26e531d6f6e91286069cab73579 100644 (file)
--- a/gas/config/tc-mips.c
+++ b/gas/config/tc-mips.c
@@ -8186,14 +8186,7 @@ match_mips16_insn (struct mips_cl_insn *insn, const struct mips_opcode *opcode,
       if (!operand)
        abort ();
 
-      /* '6' is a special case.  It is used for BREAK and SDBBP,
-        whose operands are only meaningful to the software that decodes
-        them.  This means that there is no architectural reason why
-        they cannot be prefixed by EXTEND, but in practice,
-        exception handlers will only look at the instruction
-        itself.  We therefore allow '6' to be extended when
-        disassembling but not when assembling.  */
-      if (operand->type != OP_PCREL && c != '6')
+      if (operand->type != OP_PCREL)
        {
          ext_operand = decode_mips16_operand (c, TRUE);
          if (operand != ext_operand)

diff --git a/opcodes/ChangeLog b/opcodes/ChangeLog
index 5166be4fa33d72049eb6601a66e372b12b1dd042..cb69f647c9c134731d8e8235ba70f246fb179ac5 100644 (file)
--- a/opcodes/ChangeLog
+++ b/opcodes/ChangeLog
@@ -1,3 +1,8 @@
+2016-12-23  Maciej W. Rozycki  <macro@imgtec.com>
+
+       * mips16-opc.c (decode_mips16_operand) <'6'>: Remove extended
+       encoding support.
+
 2016-12-23  Maciej W. Rozycki  <macro@imgtec.com>
 
        * mips16-opc.c (mips16_opcodes): Set NODS in `pinfo' for

diff --git a/opcodes/mips16-opc.c b/opcodes/mips16-opc.c
index 7d430dd1b972efed7e6465c06455c90aa79ad879..a6f6ad19075fca699eafe203e09f24a40c0a3c4b 100644 (file)
--- a/opcodes/mips16-opc.c
+++ b/opcodes/mips16-opc.c
@@ -50,6 +50,7 @@ decode_mips16_operand (char type, bfd_boolean extended_p)
   switch (type)
     {
     case '0': MAPPED_REG (0, 0, GP, reg_0_map);
+    case '6': UINT (6, 5);
 
     case 'L': SPECIAL (6, 5, ENTRY_EXIT_LIST);
     case 'M': SPECIAL (7, 0, SAVE_RESTORE_LIST);
@@ -81,7 +82,6 @@ decode_mips16_operand (char type, bfd_boolean extended_p)
 
       case '4': SINT (15, 0);
       case '5': SINT (16, 0);
-      case '6': SINT (16, 0);
       case '8': SINT (16, 0);
 
       case 'A': PCREL (16, 0, TRUE, 0, 2, FALSE, FALSE);
@@ -109,7 +109,6 @@ decode_mips16_operand (char type, bfd_boolean extended_p)
 
       case '4': SINT (4, 0);
       case '5': UINT (5, 0);
-      case '6': UINT (6, 5);
       case '8': UINT (8, 0);
 
       case 'A': PCREL (8, 0, FALSE, 2, 2, FALSE, FALSE);