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[patch] aout+coff: Fix strict-aliasing rules error

From: Jan Kratochvil <jan dot kratochvil at redhat dot com>
To: binutils at sourceware dot org
Date: Tue, 8 Mar 2016 14:57:06 +0100
Subject: [patch] aout+coff: Fix strict-aliasing rules error
Authentication-results: sourceware.org; auth=none

Hi,

https://bugzilla.redhat.com/show_bug.cgi?id=1315191 by Dan Horak
gcc (GCC) 6.0.0 20160308 (experimental)
gcc-6.0.0-0.15.fc24
gcc-6.0.0-0.15.fc25
It did compile with:
gcc-6.0.0-0.14.fc24

aoutx.h:2504:7: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
       int type_code = aout_symbol (symbol)->type & 0xff;
       ^~~
coffcode.h:1817:3: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
   coffsymbol (section->symbol)->native = native;
   ^~~~~~~~~~

Full log attached.

This fix is probably wrong as it drops the type safety.  But ({ statements as
expressions }) are probably not allowed in GDB.


Jan

bfd/
2016-03-08  Jan Kratochvil  <jan.kratochvil@redhat.com>

	Fix strict-aliasing rules compilation error.
	* libaout.h (aout_symbol): Remove type safe indirection.
	* libcoff-in.h (coffsymbol): Likewise.
	* libcoff.h: Regenerate.

diff --git a/bfd/libaout.h b/bfd/libaout.h
index 8b70a9f..b60c40c 100644
--- a/bfd/libaout.h
+++ b/bfd/libaout.h
@@ -448,9 +448,7 @@ struct  aout_data_struct
 #define obj_aout_sym_hashes(bfd)           (adata (bfd).sym_hashes)
 #define obj_aout_dynamic_info(bfd)         (adata (bfd).dynamic_info)
 
-/* We take the address of the first element of an asymbol to ensure that the
-   macro is only ever applied to an asymbol.  */
-#define aout_symbol(asymbol) ((aout_symbol_type *)(&(asymbol)->the_bfd))
+#define aout_symbol(asymbol) ((aout_symbol_type *) (asymbol))
 
 /* Information we keep for each a.out section.  This is currently only
    used by the a.out backend linker.  */
diff --git a/bfd/libcoff-in.h b/bfd/libcoff-in.h
index 80f999d..fa1e9ac 100644
--- a/bfd/libcoff-in.h
+++ b/bfd/libcoff-in.h
@@ -188,9 +188,7 @@ struct xcoff_tdata
 
 #define xcoff_data(abfd) ((abfd)->tdata.xcoff_obj_data)
 
-/* We take the address of the first element of an asymbol to ensure that the
-   macro is only ever applied to an asymbol.  */
-#define coffsymbol(asymbol) ((coff_symbol_type *)(&((asymbol)->the_bfd)))
+#define coffsymbol(asymbol) ((coff_symbol_type *) (asymbol))
 
 /* Tdata for sections in XCOFF files.  This is used by the linker.  */
 
diff --git a/bfd/libcoff.h b/bfd/libcoff.h
index bbed3e0..8ce525b 100644
--- a/bfd/libcoff.h
+++ b/bfd/libcoff.h
@@ -192,9 +192,7 @@ struct xcoff_tdata
 
 #define xcoff_data(abfd) ((abfd)->tdata.xcoff_obj_data)
 
-/* We take the address of the first element of an asymbol to ensure that the
-   macro is only ever applied to an asymbol.  */
-#define coffsymbol(asymbol) ((coff_symbol_type *)(&((asymbol)->the_bfd)))
+#define coffsymbol(asymbol) ((coff_symbol_type *) (asymbol))
 
 /* Tdata for sections in XCOFF files.  This is used by the linker.  */

libtool: compile:  gcc -DHAVE_CONFIG_H -I. -I. -I. -I./../include -DHAVE_x86_64_elf64_vec -DHAVE_i386_elf32_vec -DHAVE_iamcu_elf32_vec -DHAVE_x86_64_elf32_vec -DHAVE_i386_aout_linux_vec -DHAVE_i386_pei_vec -DHAVE_x86_64_pei_vec -DHAVE_l1om_elf64_vec -DHAVE_k1om_elf64_vec -DHAVE_elf64_le_vec -DHAVE_elf64_be_vec -DHAVE_elf32_le_vec -DHAVE_elf32_be_vec -DHAVE_plugin_vec -DBINDIR=\"/usr/local/bin\" -W -Wall -Wstrict-prototypes -Wmissing-prototypes -Wshadow -Werror -I./../zlib -g -O2 -MT aout32.lo -MD -MP -MF .deps/aout32.Tpo -c aout32.c -o aout32.o
In file included from aout32.c:24:0:
aoutx.h: In function ‘aout_32_write_syms’:
aoutx.h:1871:4: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
    H_PUT_16 (abfd, aout_symbol (g)->desc,  nsp.e_desc);
    ^~~~~~~~
aoutx.h:1872:4: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
    H_PUT_8  (abfd, aout_symbol (g)->other, nsp.e_other);
    ^~~~~~~
aoutx.h:1873:4: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
    H_PUT_8  (abfd, aout_symbol (g)->type,  nsp.e_type);
    ^~~~~~~
aoutx.h: In function ‘aout_32_get_symbol_info’:
aoutx.h:2504:7: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
       int type_code = aout_symbol (symbol)->type & 0xff;
       ^~~
aoutx.h:2515:7: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
       ret->stab_other = (unsigned) (aout_symbol (symbol)->other & 0xff);
       ^~~
aoutx.h:2516:7: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
       ret->stab_desc = (unsigned) (aout_symbol (symbol)->desc & 0xffff);
       ^~~
aoutx.h: In function ‘aout_32_print_symbol’:
aoutx.h:2537:9: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
         (unsigned) (aout_symbol (symbol)->desc & 0xffff),
         ^
aoutx.h:2538:9: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
         (unsigned) (aout_symbol (symbol)->other & 0xff),
         ^
aoutx.h:2539:9: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
         (unsigned) (aout_symbol (symbol)->type));
         ^
aoutx.h:2549:4: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
    (unsigned) (aout_symbol (symbol)->desc & 0xffff),
    ^
aoutx.h:2550:4: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
    (unsigned) (aout_symbol (symbol)->other & 0xff),
    ^
aoutx.h:2551:4: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
    (unsigned) (aout_symbol (symbol)->type & 0xff));
    ^
cc1: all warnings being treated as errors
libtool: compile:  gcc -DHAVE_CONFIG_H -I. -I. -I. -I./../include -DHAVE_x86_64_elf64_vec -DHAVE_i386_elf32_vec -DHAVE_iamcu_elf32_vec -DHAVE_x86_64_elf32_vec -DHAVE_i386_aout_linux_vec -DHAVE_i386_pei_vec -DHAVE_x86_64_pei_vec -DHAVE_l1om_elf64_vec -DHAVE_k1om_elf64_vec -DHAVE_elf64_le_vec -DHAVE_elf64_be_vec -DHAVE_elf32_le_vec -DHAVE_elf32_be_vec -DHAVE_plugin_vec -DBINDIR=\"/usr/local/bin\" -W -Wall -Wstrict-prototypes -Wmissing-prototypes -Wshadow -Werror -I./../zlib -g -O2 -MT pei-i386.lo -MD -MP -MF .deps/pei-i386.Tpo -c pei-i386.c -o pei-i386.o
In file included from coff-i386.c:614:0,
                 from pei-i386.c:45:
coffcode.h: In function ‘coff_new_section_hook’:
coffcode.h:1817:3: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
   coffsymbol (section->symbol)->native = native;
   ^~~~~~~~~~
cc1: all warnings being treated as errors
libtool: compile:  gcc -DHAVE_CONFIG_H -I. -I. -I. -I./../include -DHAVE_x86_64_elf64_vec -DHAVE_i386_elf32_vec -DHAVE_iamcu_elf32_vec -DHAVE_x86_64_elf32_vec -DHAVE_i386_aout_linux_vec -DHAVE_i386_pei_vec -DHAVE_x86_64_pei_vec -DHAVE_l1om_elf64_vec -DHAVE_k1om_elf64_vec -DHAVE_elf64_le_vec -DHAVE_elf64_be_vec -DHAVE_elf32_le_vec -DHAVE_elf32_be_vec -DHAVE_plugin_vec -DBINDIR=\"/usr/local/bin\" -W -Wall -Wstrict-prototypes -Wmissing-prototypes -Wshadow -Werror -I./../zlib -g -O2 -MT coffgen.lo -MD -MP -MF .deps/coffgen.Tpo -c coffgen.c -o coffgen.o
coffgen.c: In function ‘coff_get_lineno’:
coffgen.c:1510:3: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
   return coffsymbol (symbol)->lineno;
   ^~~~~~
coffgen.c: In function ‘coff_get_symbol_info’:
coffgen.c:2034:3: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
   if (coffsymbol (symbol)->native != NULL
   ^~
coffgen.c:2035:7: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
       && coffsymbol (symbol)->native->fix_value
       ^~
coffgen.c:2036:7: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
       && coffsymbol (symbol)->native->is_sym)
       ^~
coffgen.c:2037:5: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
     ret->value = coffsymbol (symbol)->native->u.syment.n_value -
     ^~~
coffgen.c: In function ‘coff_print_symbol’:
coffgen.c:2059:9: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
         coffsymbol (symbol)->native ? "n" : "g",
         ^~~~~~~~~~
coffgen.c:2060:9: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
         coffsymbol (symbol)->lineno ? "l" : " ");
         ^~~~~~~~~~
coffgen.c:2064:7: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
       if (coffsymbol (symbol)->native)
       ^~
coffgen.c:2068:4: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
    combined_entry_type *combined = coffsymbol (symbol)->native;
    ^~~~~~~~~~~~~~~~~~~
coffgen.c:2070:11: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
    struct lineno_cache_entry *l = coffsymbol (symbol)->lineno;
           ^~~~~~~~~~~~~~~~~~
coffgen.c:2191:6: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
      coffsymbol (symbol)->native ? "n" : "g",
      ^~~~~~~~~~
coffgen.c:2192:6: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
      coffsymbol (symbol)->lineno ? "l" : " ",
      ^~~~~~~~~~
cc1: all warnings being treated as errors
libtool: compile:  gcc -DHAVE_CONFIG_H -I. -I. -I. -I./../include -DHAVE_x86_64_elf64_vec -DHAVE_i386_elf32_vec -DHAVE_iamcu_elf32_vec -DHAVE_x86_64_elf32_vec -DHAVE_i386_aout_linux_vec -DHAVE_i386_pei_vec -DHAVE_x86_64_pei_vec -DHAVE_l1om_elf64_vec -DHAVE_k1om_elf64_vec -DHAVE_elf64_le_vec -DHAVE_elf64_be_vec -DHAVE_elf32_le_vec -DHAVE_elf32_be_vec -DHAVE_plugin_vec -DBINDIR=\"/usr/local/bin\" -W -Wall -Wstrict-prototypes -Wmissing-prototypes -Wshadow -Werror -I./../zlib -g -O2 -MT pei-x86_64.lo -MD -MP -MF .deps/pei-x86_64.Tpo -c pei-x86_64.c -o pei-x86_64.o
In file included from coff-x86_64.c:741:0,
                 from pei-x86_64.c:763:
coffcode.h: In function ‘coff_new_section_hook’:
coffcode.h:1817:3: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
   coffsymbol (section->symbol)->native = native;
   ^~~~~~~~~~
cc1: all warnings being treated as errors

Follow-Ups:
- Re: [patch] aout+coff: Fix strict-aliasing rules error
  - From: Pedro Alves
- Re: [patch] aout+coff: Fix strict-aliasing rules error
  - From: Alan Modra

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