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[PATCH, CFI] Fix EH for coldfire-uclinux


The following patch fixes a problem in EH on coldfire-uclinux. Due to peculiarities of ColdFire uClinux it is not possible to use PC-relative encoding for CFI. This problem was uncovered by recent switch of GCC to emit .cfi* directives by default.

To generate bFLT binaries for coldfire-uclinux elf2flt utility is used. Elf2flt does not honor PT_LOAD's from the executable. So, despite appearances of the ELF file, .text and .eh_frame sections will not end up in the same segment in bFLT file. Therefore PC-relative encoding cannot be used for CFI on coldfire-uclinux. Hence this patch defines CFI_DIFF_EXPR_OK to 0 for coldfire-uclinux.

However, there is one exception to the above -- encoding of LSDA. LSDA encoding is explicitly specified by the compiler and can be relied on. So the patch also adds CFI_DIFF_LSDA_OK macro to convince GAS to accept PC-relative encoding in this one case.

Tested on coldfire-uclinux and various other architectures where this patch is a no-op.

OK to check in?


Maxim Kuvyrkov
(650) 331-3385 x724

2009-11-01  Daniel Jacobowitz  <>
	    Maxim Kuvyrkov  <>

	* config/tc-m68k.h (CF_DIFF_EXPR_OK): Define to 0 for uClinux.
	(CFI_DIFF_LSDA_OK): Define.
	* config/te-uclinux.h: New file.
	* configure.tgt (m68k-uclinux): Define em.
	* dw2gencfi.c (CFI_DIFF_LSDA_OK): New macro.
	(dot_cfi_lsda, output_fde): Use instead of CFI_DIFF_EXPR_OK.
Index: gas/config/tc-m68k.h
--- gas/config/tc-m68k.h	(revision 267216)
+++ gas/config/tc-m68k.h	(working copy)
@@ -178,3 +178,13 @@ extern int tc_m68k_regname_to_dw2regnum 
 #define tc_cfi_frame_initial_instructions tc_m68k_frame_initial_instructions
 extern void tc_m68k_frame_initial_instructions (void);
+#ifdef TE_UCLINUX
+/* elf2flt does not honor PT_LOAD's from the executable.
+   .text and .eh_frame sections will not end up in the same segment and so
+   we cannot use PC-relative encoding for CFI.  */
+# define CFI_DIFF_EXPR_OK 0
+/* However, follow compiler's guidance when it specifies encoding for LSDA.  */
+# define CFI_DIFF_LSDA_OK 1
Index: gas/config/te-uclinux.h
--- gas/config/te-uclinux.h	(revision 0)
+++ gas/config/te-uclinux.h	(revision 0)
@@ -0,0 +1,22 @@
+/* Copyright 2009 Free Software Foundation, Inc.
+   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 3,
+   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
+   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, 51 Franklin Street - Fifth Floor, Boston, MA
+   02110-1301, USA.  */
+#define TE_UCLINUX
+#include "te-generic.h"
Index: gas/dw2gencfi.c
--- gas/dw2gencfi.c	(revision 267216)
+++ gas/dw2gencfi.c	(working copy)
@@ -36,6 +36,14 @@
 # endif
+# error "CFI_DIFF_EXPR_OK should imply CFI_DIFF_LSDA_OK"
 /* We re-use DWARF2_LINE_MIN_INSN_LENGTH for the code alignment field
    of the CIE.  Default to 1 if not otherwise specified.  */
@@ -758,7 +766,7 @@ dot_cfi_lsda (int ignored ATTRIBUTE_UNUS
   if ((encoding & 0xff) != encoding
       || ((encoding & 0x70) != 0
-#if CFI_DIFF_EXPR_OK || defined tc_cfi_emit_pcrel_expr
+#if CFI_DIFF_LSDA_OK || defined tc_cfi_emit_pcrel_expr
 	  && (encoding & 0x70) != DW_EH_PE_pcrel
@@ -1445,7 +1453,7 @@ output_fde (struct fde_entry *fde, struc
       exp = fde->lsda;
       if ((fde->lsda_encoding & 0x70) == DW_EH_PE_pcrel)
 	  exp.X_op = O_subtract;
 	  exp.X_op_symbol = symbol_temp_new_now ();
 	  emit_expr (&exp, augmentation_size);
Index: gas/configure.tgt
--- gas/configure.tgt	(revision 267216)
+++ gas/configure.tgt	(working copy)
@@ -267,7 +267,7 @@ case ${generic_target} in
   m68k-*-sysv4*)			fmt=elf em=svr4 ;;
   m68k-*-rtems*)			fmt=elf ;;
   m68k-*-linux-*)			fmt=elf em=linux ;;
-  m68k-*-uclinux*)			fmt=elf ;;
+  m68k-*-uclinux*)			fmt=elf em=uclinux ;;
   m68k-*-gnu*)				fmt=elf ;;
   m68k-*-netbsdelf*)			fmt=elf em=nbsd ;;
   m68k-*-netbsd*)			fmt=aout em=nbsd bfd_gas=yes ;;

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