x86: honor absolute section when emitting code

Various provisions exist for insns to be placed in the absolute section,
yet actually trying to do so didn't work. While data emission (of non-
zero values) is not allowed by generic code, I think this functionality
is useful for the programmer to be able to determine the size of insns.
Therefore, rather than turning the silnet failure into a verbose one,
make things mostly work; the one class of insns not supported (yet) are
branches (JMP and Jcc) with dynamically determined displacement widths.
In this one case, an error now gets reported instead of silently
ignoring the code.

Also avoid recording ISA / feature usage for insns emitted to the
absolute section.

1 files changed, 76 insertions, 32 deletions

diff --git a/gas/config/tc-i386.c b/gas/config/tc-i386.c
index a9c79f1..5b0a014e 100644
--- a/gas/config/tc-i386.c
+++ b/gas/config/tc-i386.c
@@ -8426,6 +8426,15 @@ build_modrm_byte (void)
   return default_seg;
 }
 
+static INLINE void
+frag_opcode_byte (unsigned char byte)
+{
+  if (now_seg != absolute_section)
+    FRAG_APPEND_1_CHAR (byte);
+  else
+    ++abs_section_offset;
+}
+
 static unsigned int
 flip_code16 (unsigned int code16)
 {
@@ -8449,6 +8458,12 @@ output_branch (void)
   symbolS *sym;
   offsetT off;
 
+  if (now_seg == absolute_section)
+    {
+      as_bad (_("relaxable branches not supported in absolute section"));
+      return;
+    }
+
   code16 = flag_code == CODE_16BIT ? CODE16 : 0;
   size = i.disp_encoding == disp_encoding_32bit ? BIG : SMALL;
 
@@ -8578,14 +8593,14 @@ output_jump (void)
       size = 1;
       if (i.prefix[ADDR_PREFIX] != 0)
 	{
-	  FRAG_APPEND_1_CHAR (ADDR_PREFIX_OPCODE);
+	  frag_opcode_byte (ADDR_PREFIX_OPCODE);
 	  i.prefixes -= 1;
 	}
       /* Pentium4 branch hints.  */
       if (i.prefix[SEG_PREFIX] == CS_PREFIX_OPCODE /* not taken */
 	  || i.prefix[SEG_PREFIX] == DS_PREFIX_OPCODE /* taken */)
 	{
-	  FRAG_APPEND_1_CHAR (i.prefix[SEG_PREFIX]);
+	  frag_opcode_byte (i.prefix[SEG_PREFIX]);
 	  i.prefixes--;
 	}
     }
@@ -8599,7 +8614,7 @@ output_jump (void)
 
       if (i.prefix[DATA_PREFIX] != 0)
 	{
-	  FRAG_APPEND_1_CHAR (DATA_PREFIX_OPCODE);
+	  frag_opcode_byte (DATA_PREFIX_OPCODE);
 	  i.prefixes -= 1;
 	  code16 ^= flip_code16(code16);
 	}
@@ -8612,19 +8627,25 @@ output_jump (void)
   /* BND prefixed jump.  */
   if (i.prefix[BND_PREFIX] != 0)
     {
-      FRAG_APPEND_1_CHAR (i.prefix[BND_PREFIX]);
+      frag_opcode_byte (i.prefix[BND_PREFIX]);
       i.prefixes -= 1;
     }
 
   if (i.prefix[REX_PREFIX] != 0)
     {
-      FRAG_APPEND_1_CHAR (i.prefix[REX_PREFIX]);
+      frag_opcode_byte (i.prefix[REX_PREFIX]);
       i.prefixes -= 1;
     }
 
   if (i.prefixes != 0)
     as_warn (_("skipping prefixes on `%s'"), i.tm.name);
 
+  if (now_seg == absolute_section)
+    {
+      abs_section_offset += i.tm.opcode_length + size;
+      return;
+    }
+
   p = frag_more (i.tm.opcode_length + size);
   switch (i.tm.opcode_length)
     {
@@ -8686,6 +8707,12 @@ output_interseg_jump (void)
   if (i.prefixes != 0)
     as_warn (_("skipping prefixes on `%s'"), i.tm.name);
 
+  if (now_seg == absolute_section)
+    {
+      abs_section_offset += prefix + 1 + 2 + size;
+      return;
+    }
+
   /* 1 opcode; 2 segment; offset  */
   p = frag_more (prefix + 1 + 2 + size);
 
@@ -9098,7 +9125,7 @@ output_insn (void)
   enum mf_jcc_kind mf_jcc = mf_jcc_jo;
 
 #if defined (OBJ_ELF) || defined (OBJ_MAYBE_ELF)
-  if (IS_ELF && x86_used_note)
+  if (IS_ELF && x86_used_note && now_seg != absolute_section)
     {
       if (i.tm.cpu_flags.bitfield.cpucmov)
 	x86_isa_1_used |= GNU_PROPERTY_X86_ISA_1_CMOV;
@@ -9237,14 +9264,20 @@ output_insn (void)
 	  && (i.tm.base_opcode == 0xfaee8
 	      || i.tm.base_opcode == 0xfaef0
 	      || i.tm.base_opcode == 0xfaef8))
-        {
-          /* Encode lfence, mfence, and sfence as
-             f0 83 04 24 00   lock addl $0x0, (%{re}sp).  */
-          offsetT val = 0x240483f0ULL;
-          p = frag_more (5);
-          md_number_to_chars (p, val, 5);
-          return;
-        }
+	{
+	  /* Encode lfence, mfence, and sfence as
+	     f0 83 04 24 00   lock addl $0x0, (%{re}sp).  */
+	  if (now_seg != absolute_section)
+	    {
+	      offsetT val = 0x240483f0ULL;
+
+	      p = frag_more (5);
+	      md_number_to_chars (p, val, 5);
+	    }
+	  else
+	    abs_section_offset += 5;
+	  return;
+	}
 
       /* Some processors fail on LOCK prefix. This options makes
 	 assembler ignore LOCK prefix and serves as a workaround.  */
@@ -9343,7 +9376,7 @@ output_insn (void)
 	  /* The prefix bytes.  */
 	  for (j = ARRAY_SIZE (i.prefix), q = i.prefix; j > 0; j--, q++)
 	    if (*q)
-	      FRAG_APPEND_1_CHAR (*q);
+	      frag_opcode_byte (*q);
 	}
       else
 	{
@@ -9353,7 +9386,7 @@ output_insn (void)
 		{
 		case SEG_PREFIX:
 		case ADDR_PREFIX:
-		  FRAG_APPEND_1_CHAR (*q);
+		  frag_opcode_byte (*q);
 		  break;
 		default:
 		  /* There should be no other prefixes for instructions
@@ -9367,13 +9400,20 @@ output_insn (void)
 	  if (i.vrex)
 	    abort ();
 	  /* Now the VEX prefix.  */
-	  p = frag_more (i.vex.length);
-	  for (j = 0; j < i.vex.length; j++)
-	    p[j] = i.vex.bytes[j];
+	  if (now_seg != absolute_section)
+	    {
+	      p = frag_more (i.vex.length);
+	      for (j = 0; j < i.vex.length; j++)
+		p[j] = i.vex.bytes[j];
+	    }
+	  else
+	    abs_section_offset += i.vex.length;
 	}
 
       /* Now the opcode; be careful about word order here!  */
-      if (i.tm.opcode_length == 1)
+      if (now_seg == absolute_section)
+	abs_section_offset += i.tm.opcode_length;
+      else if (i.tm.opcode_length == 1)
 	{
 	  FRAG_APPEND_1_CHAR (i.tm.base_opcode);
 	}
@@ -9406,9 +9446,9 @@ output_insn (void)
       /* Now the modrm byte and sib byte (if present).  */
       if (i.tm.opcode_modifier.modrm)
 	{
-	  FRAG_APPEND_1_CHAR ((i.rm.regmem << 0
-			       | i.rm.reg << 3
-			       | i.rm.mode << 6));
+	  frag_opcode_byte ((i.rm.regmem << 0)
+			     | (i.rm.reg << 3)
+			     | (i.rm.mode << 6));
 	  /* If i.rm.regmem == ESP (4)
 	     && i.rm.mode != (Register mode)
 	     && not 16 bit
@@ -9416,9 +9456,9 @@ output_insn (void)
 	  if (i.rm.regmem == ESCAPE_TO_TWO_BYTE_ADDRESSING
 	      && i.rm.mode != 3
 	      && !(i.base_reg && i.base_reg->reg_type.bitfield.word))
-	    FRAG_APPEND_1_CHAR ((i.sib.base << 0
-				 | i.sib.index << 3
-				 | i.sib.scale << 6));
+	    frag_opcode_byte ((i.sib.base << 0)
+			      | (i.sib.index << 3)
+			      | (i.sib.scale << 6));
 	}
 
       if (i.disp_operands)
@@ -9586,9 +9626,12 @@ output_disp (fragS *insn_start_frag, offsetT insn_start_off)
     {
       if (operand_type_check (i.types[n], disp))
 	{
-	  if (i.op[n].disps->X_op == O_constant)
+	  int size = disp_size (n);
+
+	  if (now_seg == absolute_section)
+	    abs_section_offset += size;
+	  else if (i.op[n].disps->X_op == O_constant)
 	    {
-	      int size = disp_size (n);
 	      offsetT val = i.op[n].disps->X_add_number;
 
 	      val = offset_in_range (val >> (size == 1 ? i.memshift : 0),
@@ -9599,7 +9642,6 @@ output_disp (fragS *insn_start_frag, offsetT insn_start_off)
 	  else
 	    {
 	      enum bfd_reloc_code_real reloc_type;
-	      int size = disp_size (n);
 	      int sign = i.types[n].bitfield.disp32s;
 	      int pcrel = (i.flags[n] & Operand_PCrel) != 0;
 	      fixS *fixP;
@@ -9732,9 +9774,12 @@ output_imm (fragS *insn_start_frag, offsetT insn_start_off)
 
       if (operand_type_check (i.types[n], imm))
 	{
-	  if (i.op[n].imms->X_op == O_constant)
+	  int size = imm_size (n);
+
+	  if (now_seg == absolute_section)
+	    abs_section_offset += size;
+	  else if (i.op[n].imms->X_op == O_constant)
 	    {
-	      int size = imm_size (n);
 	      offsetT val;
 
 	      val = offset_in_range (i.op[n].imms->X_add_number,
@@ -9749,7 +9794,6 @@ output_imm (fragS *insn_start_frag, offsetT insn_start_off)
 		 non-absolute imms).  Try to support other
 		 sizes ...  */
 	      enum bfd_reloc_code_real reloc_type;
-	      int size = imm_size (n);
 	      int sign;
 
 	      if (i.types[n].bitfield.imm32s