Re: Stop Gas from generating line info or address ranges

* doc/as.texi (.nop): Document optional size arg.
	* dwarf2dbg.c (dwarf2_gen_line_info_1): Only check SEC_ALLOC
	when ELF.  Warn whenever dwarf line number information is ignored.
	* frags.c (frag_offset_ignore_align_p): New function.
	* frags.h (frag_offset_ignore_align_p): Declare.
	* read.c (s_nop): Extend to support optional size arg.
	* testsuite/gas/elf/dwarf2-20.d: Expect warnings, and exact range.
	* testsuite/gas/elf/dwarf2-20.s: Emit 16 bytes worth of nops.
	* testsuite/gas/m68hc11/indexed12.d: Expect warnings.

gas/ChangeLog

@@ -1,3 +1,15 @@
+2020-11-18  Alan Modra  <amodra@gmail.com>
+
+	* doc/as.texi (.nop): Document optional size arg.
+	* dwarf2dbg.c (dwarf2_gen_line_info_1): Only check SEC_ALLOC
+	when ELF.  Warn whenever dwarf line number information is ignored.
+	* frags.c (frag_offset_ignore_align_p): New function.
+	* frags.h (frag_offset_ignore_align_p): Declare.
+	* read.c (s_nop): Extend to support optional size arg.
+	* testsuite/gas/elf/dwarf2-20.d: Expect warnings, and exact range.
+	* testsuite/gas/elf/dwarf2-20.s: Emit 16 bytes worth of nops.
+	* testsuite/gas/m68hc11/indexed12.d: Expect warnings.
+
 2020-11-18  Jozef Lawrynowicz  <jozef.l@mittosystems.com>
 	H.J. Lu  <hongjiu.lu@intel.com>
 

gas/doc/as.texi

@@ -6169,14 +6169,18 @@ counter, and @code{.nolist} decrements it.  Assembly listings are
 generated whenever the counter is greater than zero.
 
 @node Nop
-@section @code{.nop}
+@section @code{.nop [@var{size}]}
 
 @cindex @code{nop} directive
 @cindex filling memory with no-op instructions
-This directive emits a single no-op instruction.  It is provided on all
+This directive emits no-op instructions.  It is provided on all architectures,
-architectures, allowing the creation of architecture neutral tests involving
+allowing the creation of architecture neutral tests involving actual code.  The
-actual code.  The size of the generated instruction is target specific.  The
+size of the generated instruction is target specific, but if the optional
-instruction does affect the generation of DWARF debug line information.
+@var{size} argument is given and resolves to an absolute positive value at that
+point in assembly (no forward expressions allowed) then the fewest no-op
+instructions are emitted that equal or exceed a total @var{size} in bytes.
+@code{.nop} does affect the generation of DWARF debug line information.
+Some targets do not support using @code{.nop} with @var{size}.
 
 @node Nops
 @section @code{.nops @var{size}[, @var{control}]}

gas/dwarf2dbg.c

@@ -504,16 +504,18 @@ dwarf2_gen_line_info_1 (symbolS *label, struct dwarf2_line_info *loc)
 {
   struct line_subseg *lss;
   struct line_entry *e;
-  flagword need_flags = SEC_ALLOC | SEC_LOAD | SEC_CODE;
+  flagword need_flags = SEC_LOAD | SEC_CODE;
 
-  /* PR 26850: Do not record LOCs in non-executable, non-allocated,
+  /* PR 26850: Do not record LOCs in non-executable or non-loaded
-     or non-loaded sections.  */
+     sections.  SEC_ALLOC isn't tested for non-ELF because obj-coff.c
+     obj_coff_section is careless in setting SEC_ALLOC.  */
+  if (IS_ELF)
+    need_flags |= SEC_ALLOC;
   if ((now_seg->flags & need_flags) != need_flags)
     {
-      if (! SEG_NORMAL (now_seg))
+      /* FIXME: Add code to suppress multiple warnings ?  */
-	/* FIXME: Add code to suppress multiple warnings ?  */
+      as_warn ("dwarf line number information for %s ignored",
-	as_warn ("dwarf line number information for %s ignored",
+	       segment_name (now_seg));
-		 segment_name (now_seg));
       return;
     }
 

gas/frags.c

@@ -468,6 +468,48 @@ frag_offset_fixed_p (const fragS *frag1, const fragS *frag2, offsetT *offset)
   return FALSE;
 }
 
+/* Return TRUE if FRAG2 follows FRAG1 with a fixed relationship
+   between the two assuming alignment frags do nothing.  Set OFFSET to
+   the difference in address not already accounted for in the frag
+   FR_ADDRESS.  */
+
+bfd_boolean
+frag_offset_ignore_align_p (const fragS *frag1, const fragS *frag2,
+			    offsetT *offset)
+{
+  const fragS *frag;
+  offsetT off;
+
+  /* Start with offset initialised to difference between the two frags.
+     Prior to assigning frag addresses this will be zero.  */
+  off = frag1->fr_address - frag2->fr_address;
+  if (frag1 == frag2)
+    {
+      *offset = off;
+      return TRUE;
+    }
+
+  frag = frag1;
+  while (frag->fr_type == rs_fill
+	 || frag->fr_type == rs_align
+	 || frag->fr_type == rs_align_code
+	 || frag->fr_type == rs_align_test)
+    {
+      if (frag->fr_type == rs_fill)
+	off += frag->fr_fix + frag->fr_offset * frag->fr_var;
+      frag = frag->fr_next;
+      if (frag == NULL)
+	break;
+      if (frag == frag2)
+	{
+	  *offset = off;
+	  return TRUE;
+	}
+    }
+
+  return FALSE;
+}
+
 /* Return TRUE if we can determine whether FRAG2 OFF2 appears after
    (strict >, not >=) FRAG1 OFF1, assuming it is not before.  Set
    *OFFSET so that resolve_expression will resolve an O_gt operation

gas/frags.h

@@ -154,6 +154,8 @@ char *frag_var (relax_stateT type,
 		char *opcode);
 
 bfd_boolean frag_offset_fixed_p (const fragS *, const fragS *, offsetT *);
+bfd_boolean frag_offset_ignore_align_p (const fragS *, const fragS *,
+					offsetT *);
 bfd_boolean frag_gtoffset_p (valueT, const fragS *, valueT, const fragS *,
 			     offsetT *);
 

gas/read.c

@@ -3506,6 +3506,11 @@ s_space (int mult)
 void
 s_nop (int ignore ATTRIBUTE_UNUSED)
 {
+  expressionS exp;
+  fragS *start;
+  addressT start_off;
+  offsetT frag_off;
+
 #ifdef md_flush_pending_output
   md_flush_pending_output ();
 #endif
@@ -3515,29 +3520,42 @@ s_nop (int ignore ATTRIBUTE_UNUSED)
 #endif
 
   SKIP_WHITESPACE ();
+  expression (&exp);
   demand_empty_rest_of_line ();
 
+  start = frag_now;
+  start_off = frag_now_fix ();
+  do
+    {
 #ifdef md_emit_single_noop
-  md_emit_single_noop;
+      md_emit_single_noop;
 #else
-  char * nop;
+      char *nop;
 
 #ifndef md_single_noop_insn
 #define md_single_noop_insn "nop"
 #endif
-  /* md_assemble might modify its argument, so
+      /* md_assemble might modify its argument, so
-     we must pass it a string that is writeable.  */
+	 we must pass it a string that is writable.  */
-  if (asprintf (&nop, "%s", md_single_noop_insn) < 0)
+      if (asprintf (&nop, "%s", md_single_noop_insn) < 0)
-    as_fatal ("%s", xstrerror (errno));
+	as_fatal ("%s", xstrerror (errno));
 
-  /* Some targets assume that they can update input_line_pointer inside
+      /* Some targets assume that they can update input_line_pointer
-     md_assemble, and, worse, that they can leave it assigned to the string
+	 inside md_assemble, and, worse, that they can leave it
-     pointer that was provided as an argument.  So preserve ilp here.  */
+	 assigned to the string pointer that was provided as an
-  char * saved_ilp = input_line_pointer;
+	 argument.  So preserve ilp here.  */
-  md_assemble (nop);
+      char *saved_ilp = input_line_pointer;
-  input_line_pointer = saved_ilp;
+      md_assemble (nop);
-  free (nop);
+      input_line_pointer = saved_ilp;
+      free (nop);
 #endif
+#ifdef md_flush_pending_output
+      md_flush_pending_output ();
+#endif
+    } while (exp.X_op == O_constant
+	     && exp.X_add_number > 0
+	     && frag_offset_ignore_align_p (start, frag_now, &frag_off)
+	     && frag_off + frag_now_fix () < start_off + exp.X_add_number);
 }
 
 void

gas/testsuite/gas/elf/dwarf2-20.d

@@ -3,6 +3,12 @@
 #name: DWARF2_20: debug ranges ignore non-code sections
 # The mn10200 target has a pointer size of 3, but it does not use segment selectors.  This confuses DWARF and readelf will complain.
 #xfail: mn102*-*
+# score-elf, tic6x-elf and xtensa-elf need special handling to support .nop 16
+#xfail: score-* tic6x-* xtensa-*
+#warning: .* \.alloc0 ignored
+#warning: .* \.alloc1 ignored
+#warning: .* \.nonalloc ignored
+#warning: .* \.nonallocexec ignored
 
 Contents of the .debug_aranges section:
 
@@ -13,6 +19,6 @@ Contents of the .debug_aranges section:
 [ 	]+Segment Size:[ 	]+0
 
 [ 	]+Address[ 	]+Length
-[ 	]+0+000 0+00. 
+[ 	]+0+000 0+010 
 [ 	]+0+000 0+000 
 #pass

gas/testsuite/gas/elf/dwarf2-20.s

@@ -1,10 +1,10 @@
 	.section .alloc0,"a"
-	.nop
+	.nop 16
 	.section .alloc1,"a"
-	.nop
+	.nop 16
 	.section .nonalloc,""
-	.nop
+	.nop 16
 	.section .allocexec,"ax"
-	.nop
+	.nop 16
 	.section .nonallocexec,"x"
-	.nop
+	.nop 16

gas/testsuite/gas/m68hc11/indexed12.d

@@ -2,6 +2,10 @@
 #as: -m68hc12 -gdwarf2
 #name: 68HC12 indexed addressing mode with 5, 9 and 16-bit offsets (indexed12)
 #source: indexed12.s
+#warning: .* line number information for \.data ignored
+#warning: .* line number information for \.data ignored
+#warning: .* line number information for \.data ignored
+#warning: .* line number information for \.data ignored
 
 .*: +file format elf32\-m68hc12