Initial revision

1 files changed, 469 insertions, 0 deletions

diff --git a/gas/ehopt.c b/gas/ehopt.c
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+++ b/gas/ehopt.c
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+/* ehopt.c--optimize gcc exception frame information.
+   Copyright (C) 1998 Free Software Foundation, Inc.
+   Written by Ian Lance Taylor <ian@cygnus.com>.
+
+This file is part of GAS, the GNU Assembler.
+
+GAS is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2, or (at your option)
+any later version.
+
+GAS is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with GAS; see the file COPYING.  If not, write to the Free
+Software Foundation, 59 Temple Place - Suite 330, Boston, MA
+02111-1307, USA. */
+
+#include "as.h"
+#include "subsegs.h"
+
+/* We include this ELF file, even though we may not be assembling for
+   ELF, since the exception frame information is always in a format
+   derived from DWARF.  */
+
+#include "elf/dwarf2.h"
+
+/* Try to optimize gcc 2.8 exception frame information.
+
+   Exception frame information is emitted for every function in the
+   .eh_frame section.  Simple information for a function with no
+   exceptions looks like this:
+
+__FRAME_BEGIN__:
+	.4byte	.LLCIE1	/ Length of Common Information Entry
+.LSCIE1:
+	.4byte	0x0	/ CIE Identifier Tag
+	.byte	0x1	/ CIE Version
+	.byte	0x0	/ CIE Augmentation (none)
+	.byte	0x1	/ ULEB128 0x1 (CIE Code Alignment Factor)
+	.byte	0x7c	/ SLEB128 -4 (CIE Data Alignment Factor)
+	.byte	0x8	/ CIE RA Column
+	.byte	0xc	/ DW_CFA_def_cfa
+	.byte	0x4	/ ULEB128 0x4
+	.byte	0x4	/ ULEB128 0x4
+	.byte	0x88	/ DW_CFA_offset, column 0x8
+	.byte	0x1	/ ULEB128 0x1
+	.align 4
+.LECIE1:
+	.set	.LLCIE1,.LECIE1-.LSCIE1	/ CIE Length Symbol
+	.4byte	.LLFDE1	/ FDE Length
+.LSFDE1:
+	.4byte	.LSFDE1-__FRAME_BEGIN__	/ FDE CIE offset
+	.4byte	.LFB1	/ FDE initial location
+	.4byte	.LFE1-.LFB1	/ FDE address range
+	.byte	0x4	/ DW_CFA_advance_loc4
+	.4byte	.LCFI0-.LFB1
+	.byte	0xe	/ DW_CFA_def_cfa_offset
+	.byte	0x8	/ ULEB128 0x8
+	.byte	0x85	/ DW_CFA_offset, column 0x5
+	.byte	0x2	/ ULEB128 0x2
+	.byte	0x4	/ DW_CFA_advance_loc4
+	.4byte	.LCFI1-.LCFI0
+	.byte	0xd	/ DW_CFA_def_cfa_register
+	.byte	0x5	/ ULEB128 0x5
+	.byte	0x4	/ DW_CFA_advance_loc4
+	.4byte	.LCFI2-.LCFI1
+	.byte	0x2e	/ DW_CFA_GNU_args_size
+	.byte	0x4	/ ULEB128 0x4
+	.byte	0x4	/ DW_CFA_advance_loc4
+	.4byte	.LCFI3-.LCFI2
+	.byte	0x2e	/ DW_CFA_GNU_args_size
+	.byte	0x0	/ ULEB128 0x0
+	.align 4
+.LEFDE1:
+	.set	.LLFDE1,.LEFDE1-.LSFDE1	/ FDE Length Symbol
+
+   The immediate issue we can address in the assembler is the
+   DW_CFA_advance_loc4 followed by a four byte value.  The value is
+   the difference of two addresses in the function.  Since gcc does
+   not know this value, it always uses four bytes.  We will know the
+   value at the end of assembly, so we can do better.  */
+
+static int eh_frame_code_alignment PARAMS ((void));
+
+/* Get the code alignment factor from the CIE.  */
+
+static int
+eh_frame_code_alignment ()
+{
+  static int code_alignment;
+  segT current_seg;
+  subsegT current_subseg;
+  fragS *f;
+  fixS *fix;
+  int offset;
+  char augmentation[10];
+  int iaug;
+
+  if (code_alignment != 0)
+    return code_alignment;
+
+  /* We should find the CIE at the start of the .eh_frame section.  */
+
+  current_seg = now_seg;
+  current_subseg = now_subseg;
+  subseg_new (".eh_frame", 0);
+#if defined (BFD_ASSEMBLER) || defined (MANY_SEGMENTS)
+  f = seg_info (now_seg)->frchainP->frch_root;
+#else
+  f = frchain_now->frch_root;
+#endif
+#ifdef BFD_ASSEMBLER
+  fix = seg_info (now_seg)->frchainP->fix_root;
+#else
+  fix = *seg_fix_rootP;
+#endif
+  subseg_set (current_seg, current_subseg);
+
+  /* Look through the frags of the section to find the code alignment.  */
+
+  /* First make sure that the CIE Identifier Tag is 0.  */
+
+  offset = 4;
+  while (f != NULL && offset >= f->fr_fix)
+    {
+      offset -= f->fr_fix;
+      f = f->fr_next;
+    }
+  if (f == NULL
+      || f->fr_fix - offset < 4
+      || f->fr_literal[offset] != 0
+      || f->fr_literal[offset + 1] != 0
+      || f->fr_literal[offset + 2] != 0
+      || f->fr_literal[offset + 3] != 0)
+    {
+      code_alignment = -1;
+      return -1;
+    }
+
+  /* Next make sure the CIE version number is 1.  */
+
+  offset += 4;
+  while (f != NULL && offset >= f->fr_fix)
+    {
+      offset -= f->fr_fix;
+      f = f->fr_next;
+    }
+  if (f == NULL
+      || f->fr_fix - offset < 1
+      || f->fr_literal[offset] != 1)
+    {
+      code_alignment = -1;
+      return -1;
+    }
+
+  /* Skip the augmentation (a null terminated string).  */
+
+  iaug = 0;
+  ++offset;
+  while (1)
+    {
+      while (f != NULL && offset >= f->fr_fix)
+	{
+	  offset -= f->fr_fix;
+	  f = f->fr_next;
+	}
+      if (f == NULL)
+	{
+	  code_alignment = -1;
+	  return -1;
+	}
+      while (offset < f->fr_fix && f->fr_literal[offset] != '\0')
+	{
+	  if ((size_t) iaug < (sizeof augmentation) - 1)
+	    {
+	      augmentation[iaug] = f->fr_literal[offset];
+	      ++iaug;
+	    }
+	  ++offset;
+	}
+      if (offset < f->fr_fix)
+	break;
+    }
+  ++offset;
+  while (f != NULL && offset >= f->fr_fix)
+    {
+      offset -= f->fr_fix;
+      f = f->fr_next;
+    }
+  if (f == NULL)
+    {
+      code_alignment = -1;
+      return -1;
+    }
+
+  augmentation[iaug] = '\0';
+  if (augmentation[0] == '\0')
+    {
+      /* No augmentation.  */
+    }
+  else if (strcmp (augmentation, "eh") == 0)
+    {
+      /* We have to skip a pointer.  Unfortunately, we don't know how
+	 large it is.  We find out by looking for a matching fixup.  */
+      while (fix != NULL
+	     && (fix->fx_frag != f || fix->fx_where != offset))
+	fix = fix->fx_next;
+      if (fix == NULL)
+	offset += 4;
+      else
+	offset += fix->fx_size;
+      while (f != NULL && offset >= f->fr_fix)
+	{
+	  offset -= f->fr_fix;
+	  f = f->fr_next;
+	}
+      if (f == NULL)
+	{
+	  code_alignment = -1;
+	  return -1;
+	}
+    }
+  else
+    {
+      code_alignment = -1;
+      return -1;
+    }
+
+  /* We're now at the code alignment factor, which is a ULEB128.  If
+     it isn't a single byte, forget it.  */
+
+  code_alignment = f->fr_literal[offset] & 0xff;
+  if ((code_alignment & 0x80) != 0 || code_alignment == 0)
+    {
+      code_alignment = -1;
+      return -1;
+    }
+
+  return code_alignment;
+}
+
+/* This function is called from emit_expr.  It looks for cases which
+   we can optimize.
+
+   Rather than try to parse all this information as we read it, we
+   look for a single byte DW_CFA_advance_loc4 followed by a 4 byte
+   difference.  We turn that into a rs_cfa_advance frag, and handle
+   those frags at the end of the assembly.  If the gcc output changes
+   somewhat, this optimization may stop working.
+
+   This function returns non-zero if it handled the expression and
+   emit_expr should not do anything, or zero otherwise.  It can also
+   change *EXP and *PNBYTES.  */
+
+int
+check_eh_frame (exp, pnbytes)
+     expressionS *exp;
+     unsigned int *pnbytes;
+{
+  static int saw_size;
+  static symbolS *size_end_sym;
+  static int saw_advance_loc4;
+  static fragS *loc4_frag;
+  static int loc4_fix;
+
+  if (saw_size
+      && S_IS_DEFINED (size_end_sym))
+    {
+      /* We have come to the end of the CIE or FDE.  See below where
+         we set saw_size.  We must check this first because we may now
+         be looking at the next size.  */
+      saw_size = 0;
+      saw_advance_loc4 = 0;
+    }
+
+  if (flag_traditional_format)
+    {
+      /* Don't optimize.  */
+    }
+  else if (strcmp (segment_name (now_seg), ".eh_frame") != 0)
+    {
+      saw_size = 0;
+      saw_advance_loc4 = 0;
+    }
+  else if (! saw_size
+	   && *pnbytes == 4)
+    {
+      /* This might be the size of the CIE or FDE.  We want to know
+         the size so that we don't accidentally optimize across an FDE
+         boundary.  We recognize the size in one of two forms: a
+         symbol which will later be defined as a difference, or a
+         subtraction of two symbols.  Either way, we can tell when we
+         are at the end of the FDE because the symbol becomes defined
+         (in the case of a subtraction, the end symbol, from which the
+         start symbol is being subtracted).  Other ways of describing
+         the size will not be optimized.  */
+      if ((exp->X_op == O_symbol || exp->X_op == O_subtract)
+	  && ! S_IS_DEFINED (exp->X_add_symbol))
+	{
+	  saw_size = 1;
+	  size_end_sym = exp->X_add_symbol;
+	}
+    }
+  else if (saw_size
+	   && *pnbytes == 1
+	   && exp->X_op == O_constant
+	   && exp->X_add_number == DW_CFA_advance_loc4)
+    {
+      /* This might be a DW_CFA_advance_loc4.  Record the frag and the
+         position within the frag, so that we can change it later.  */
+      saw_advance_loc4 = 1;
+      frag_grow (1);
+      loc4_frag = frag_now;
+      loc4_fix = frag_now_fix ();
+    }
+  else if (saw_advance_loc4
+	   && *pnbytes == 4
+	   && exp->X_op == O_constant)
+    {
+      int ca;
+
+      /* This is a case which we can optimize.  The two symbols being
+         subtracted were in the same frag and the expression was
+         reduced to a constant.  We can do the optimization entirely
+         in this function.  */
+
+      saw_advance_loc4 = 0;
+
+      ca = eh_frame_code_alignment ();
+      if (ca < 0)
+	{
+	  /* Don't optimize.  */
+	}
+      else if (exp->X_add_number % ca == 0
+	       && exp->X_add_number / ca < 0x40)
+	{
+	  loc4_frag->fr_literal[loc4_fix]
+	    = DW_CFA_advance_loc | (exp->X_add_number / ca);
+	  /* No more bytes needed.  */
+	  return 1;
+	}
+      else if (exp->X_add_number < 0x100)
+	{
+	  loc4_frag->fr_literal[loc4_fix] = DW_CFA_advance_loc1;
+	  *pnbytes = 1;
+	}
+      else if (exp->X_add_number < 0x10000)
+	{
+	  loc4_frag->fr_literal[loc4_fix] = DW_CFA_advance_loc2;
+	  *pnbytes = 2;
+	}
+    }
+  else if (saw_advance_loc4
+	   && *pnbytes == 4
+	   && exp->X_op == O_subtract)
+    {
+
+      /* This is a case we can optimize.  The expression was not
+         reduced, so we can not finish the optimization until the end
+         of the assembly.  We set up a variant frag which we handle
+         later.  */
+
+      saw_advance_loc4 = 0;
+
+      frag_var (rs_cfa, 4, 0, 0, make_expr_symbol (exp),
+		loc4_fix, (char *) loc4_frag);
+
+      return 1;
+    }
+  else
+    saw_advance_loc4 = 0;
+
+  return 0;
+}
+
+/* The function estimates the size of a rs_cfa variant frag based on
+   the current values of the symbols.  It is called before the
+   relaxation loop.  We set fr_subtype to the expected length.  */
+
+int
+eh_frame_estimate_size_before_relax (frag)
+     fragS *frag;
+{
+  int ca;
+  offsetT diff;
+  int ret;
+
+  ca = eh_frame_code_alignment ();
+  diff = resolve_symbol_value (frag->fr_symbol, 0);
+
+  if (ca < 0)
+    ret = 4;
+  else if (diff % ca == 0 && diff / ca < 0x40)
+    ret = 0;
+  else if (diff < 0x100)
+    ret = 1;
+  else if (diff < 0x10000)
+    ret = 2;
+  else
+    ret = 4;
+
+  frag->fr_subtype = ret;
+
+  return ret;
+}
+
+/* This function relaxes a rs_cfa variant frag based on the current
+   values of the symbols.  fr_subtype is the current length of the
+   frag.  This returns the change in frag length.  */
+
+int
+eh_frame_relax_frag (frag)
+     fragS *frag;
+{
+  int oldsize, newsize;
+
+  oldsize = frag->fr_subtype;
+  newsize = eh_frame_estimate_size_before_relax (frag);
+  return newsize - oldsize;
+}
+
+/* This function converts a rs_cfa variant frag into a normal fill
+   frag.  This is called after all relaxation has been done.
+   fr_subtype will be the desired length of the frag.  */
+
+void
+eh_frame_convert_frag (frag)
+     fragS *frag;
+{
+  offsetT diff;
+  fragS *loc4_frag;
+  int loc4_fix;
+
+  loc4_frag = (fragS *) frag->fr_opcode;
+  loc4_fix = (int) frag->fr_offset;
+
+  diff = resolve_symbol_value (frag->fr_symbol, 1);
+
+  if (frag->fr_subtype == 0)
+    {
+      int ca;
+
+      ca = eh_frame_code_alignment ();
+      assert (ca > 0 && diff % ca == 0 && diff / ca < 0x40);
+      loc4_frag->fr_literal[loc4_fix] = DW_CFA_advance_loc | (diff / ca);
+    }
+  else if (frag->fr_subtype == 1)
+    {
+      assert (diff < 0x100);
+      loc4_frag->fr_literal[loc4_fix] = DW_CFA_advance_loc1;
+      frag->fr_literal[frag->fr_fix] = diff;
+    }
+  else if (frag->fr_subtype == 2)
+    {
+      assert (diff < 0x10000);
+      loc4_frag->fr_literal[loc4_fix] = DW_CFA_advance_loc2;
+      md_number_to_chars (frag->fr_literal + frag->fr_fix, diff, 2);
+    }
+  else
+    md_number_to_chars (frag->fr_literal + frag->fr_fix, diff, 4);
+
+  frag->fr_fix += frag->fr_subtype;
+  frag->fr_type = rs_fill;
+  frag->fr_offset = 0;
+}