[PATCH] fixup libobjc usage of PCC_BITFIELD_TYPE_MATTERS

[PATCH] fixup libobjc usage of PCC_BITFIELD_TYPE_MATTERS

[tbsaunde+gcc]

From: Trevor Saunders <tbsaunde+gcc@tbsaunde.org>

Hi,

This adds a configure check to libobjc to find out if types of bitfields effect
their layout, and uses it to replace the rather broken usage of
PCC_BITFIELD_TYPE_MATTERS.

bootstrapped + regtested x86_64-linux-gnu, bootstrapped on ppc64le-linux-gnu
and ran check-objc there without failures, and checked the correct part of the
ifdef is used on a cross to m68k-linux-elf.  ok?  I'm sure I've gotten
something wrong since this is a bunch of auto tools ;-)

Trev

libobjc/ChangeLog:

2015-05-01  Trevor Saunders  <tbsaunde+gcc@tbsaunde.org>

	* acinclude.m4: Include bitfields.m4.
	* config.h.in: Regenerate.
	* configure: Likewise.
	* configure.ac: Invoke gt_BITFIELD_TYPE_MATTERS.
	* encoding.c: Check HAVE_BITFIELD_TYPE_MATTERS.

config/ChangeLog:

2015-05-01  Trevor Saunders  <tbsaunde+gcc@tbsaunde.org>

	* bitfields.m4: New file.
---
 config/bitfields.m4  | 26 ++++++++++++++++++++++++++
 libobjc/acinclude.m4 |  1 +
 libobjc/config.h.in  |  3 +++
 libobjc/configure    | 38 ++++++++++++++++++++++++++++++++++++++
 libobjc/configure.ac |  2 ++
 libobjc/encoding.c   |  3 ++-
 6 files changed, 72 insertions(+), 1 deletion(-)
 create mode 100644 config/bitfields.m4

diff --git a/config/bitfields.m4 b/config/bitfields.m4
new file mode 100644
index 0000000..ee8f3b5
--- /dev/null
+++ b/config/bitfields.m4
@@ -0,0 +1,26 @@
+dnl Copyright (C) 2015 Free Software Foundation, Inc.
+dnl This file is free software, distributed under the terms of the GNU
+dnl General Public License.  As a special exception to the GNU General
+dnl Public License, this file may be distributed as part of a program
+dnl that contains a configuration script generated by Autoconf, under
+dnl the same distribution terms as the rest of that program.
+
+# Define HAVE_BITFIELD_TYPE_MATTERS if the type of bitfields effects their
+# alignment.
+
+AC_DEFUN([gt_BITFIELD_TYPE_MATTERS],
+[
+  AC_CACHE_CHECK([if the type of bitfields matters], gt_cv_bitfield_type_matters,
+  [
+    AC_TRY_COMPILE(
+      [struct foo1 { char x; char :0; char y; };
+struct foo2 { char x; int :0; char y; };
+int foo1test[ sizeof (struct foo1) == 2 ? 1 : -1 ];
+int foo2test[ sizeof (struct foo2) == 5 ? 1 : -1]; ],
+      [], gt_cv_bitfield_type_matters=yes, gt_cv_bitfield_type_matters=no)
+  ])
+  if test $gt_cv_bitfield_type_matters = yes; then
+    AC_DEFINE(HAVE_BITFIELD_TYPE_MATTERS, 1,
+      [Define if the type of bitfields effects alignment.])
+  fi
+])
diff --git a/libobjc/acinclude.m4 b/libobjc/acinclude.m4
index bf78dbe..4193018 100644
--- a/libobjc/acinclude.m4
+++ b/libobjc/acinclude.m4
@@ -12,6 +12,7 @@ m4_include(../config/acx.m4)
 m4_include(../config/no-executables.m4)
 m4_include(../config/enable.m4)
 m4_include(../config/tls.m4)
+m4_include(../config/bitfields.m4)
 
 m4_include(../libtool.m4)
 dnl The lines below arrange for aclocal not to bring an installed
diff --git a/libobjc/config.h.in b/libobjc/config.h.in
index c055e7c..20d1fca 100644
--- a/libobjc/config.h.in
+++ b/libobjc/config.h.in
@@ -1,5 +1,8 @@
 /* config.h.in.  Generated from configure.ac by autoheader.  */
 
+/* Define if the type of bitfields effects alignment. */
+#undef HAVE_BITFIELD_TYPE_MATTERS
+
 /* Define to 1 if the target assembler supports thread-local storage. */
 #undef HAVE_CC_TLS
 
diff --git a/libobjc/configure b/libobjc/configure
index 642eb9c..0547f91 100755
--- a/libobjc/configure
+++ b/libobjc/configure
@@ -11530,6 +11530,44 @@ ac_compiler_gnu=$ac_cv_c_compiler_gnu
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_exception_model_name" >&5
 $as_echo "$ac_exception_model_name" >&6; }
 
+
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking if the type of bitfields matters" >&5
+$as_echo_n "checking if the type of bitfields matters... " >&6; }
+if test "${gt_cv_bitfield_type_matters+set}" = set; then :
+  $as_echo_n "(cached) " >&6
+else
+
+    cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+struct foo1 { char x; char :0; char y; };
+struct foo2 { char x; int :0; char y; };
+int foo1test[ sizeof (struct foo1) == 2 ? 1 : -1 ];
+int foo2test[ sizeof (struct foo2) == 5 ? 1 : -1];
+int
+main ()
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+  gt_cv_bitfield_type_matters=yes
+else
+  gt_cv_bitfield_type_matters=no
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $gt_cv_bitfield_type_matters" >&5
+$as_echo "$gt_cv_bitfield_type_matters" >&6; }
+  if test $gt_cv_bitfield_type_matters = yes; then
+
+$as_echo "#define HAVE_BITFIELD_TYPE_MATTERS 1" >>confdefs.h
+
+  fi
+
+
 # ------
 # Output
 # ------
diff --git a/libobjc/configure.ac b/libobjc/configure.ac
index c794a80..2d88519 100644
--- a/libobjc/configure.ac
+++ b/libobjc/configure.ac
@@ -266,6 +266,8 @@ fi
 AC_LANG_POP(C)
 AC_MSG_RESULT($ac_exception_model_name)
 
+gt_BITFIELD_TYPE_MATTERS
+
 # ------
 # Output
 # ------
diff --git a/libobjc/encoding.c b/libobjc/encoding.c
index 20ace46..abb6145 100644
--- a/libobjc/encoding.c
+++ b/libobjc/encoding.c
@@ -29,6 +29,7 @@ see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 /* FIXME: This file contains functions that will abort the entire
    program if they fail.  Is that really needed ?  */
 
+#include "config.h"
 #include "objc-private/common.h"
 #include "objc-private/error.h"
 #include "tconfig.h"
@@ -1167,7 +1168,7 @@ objc_layout_structure_next_member (struct objc_struct_layout *layout)
   /* Record must have at least as much alignment as any field.
      Otherwise, the alignment of the field within the record
      is meaningless.  */
-#if !PCC_BITFIELD_TYPE_MATTERS
+#ifndef HAVE_BITFIELD_TYPE_MATTERS
   layout->record_align = MAX (layout->record_align, desired_align);
 #else	/* PCC_BITFIELD_TYPE_MATTERS */
   if (*type == _C_BFLD)
-- 
2.3.0.80.g18d0fec.dirty

Re: [PATCH] fixup libobjc usage of PCC_BITFIELD_TYPE_MATTERS

[pinskia]

> On May 1, 2015, at 8:30 PM, tbsaunde+gcc@tbsaunde.org wrote:
> 
> From: Trevor Saunders <tbsaunde+gcc@tbsaunde.org>
> 
> Hi,
> 
> This adds a configure check to libobjc to find out if types of bitfields effect
> their layout, and uses it to replace the rather broken usage of
> PCC_BITFIELD_TYPE_MATTERS.
> 
> bootstrapped + regtested x86_64-linux-gnu, bootstrapped on ppc64le-linux-gnu
> and ran check-objc there without failures, and checked the correct part of the
> ifdef is used on a cross to m68k-linux-elf.  ok?  I'm sure I've gotten
> something wrong since this is a bunch of auto tools ;-)


This is ok.  I have been meaning to try to get rid of all uses of the target headers but never got around to finishing it. 

Thanks,
Andrew

> 
> Trev
> 
> libobjc/ChangeLog:
> 
> 2015-05-01  Trevor Saunders  <tbsaunde+gcc@tbsaunde.org>
> 
>    * acinclude.m4: Include bitfields.m4.
>    * config.h.in: Regenerate.
>    * configure: Likewise.
>    * configure.ac: Invoke gt_BITFIELD_TYPE_MATTERS.
>    * encoding.c: Check HAVE_BITFIELD_TYPE_MATTERS.
> 
> config/ChangeLog:
> 
> 2015-05-01  Trevor Saunders  <tbsaunde+gcc@tbsaunde.org>
> 
>    * bitfields.m4: New file.
> ---
> config/bitfields.m4  | 26 ++++++++++++++++++++++++++
> libobjc/acinclude.m4 |  1 +
> libobjc/config.h.in  |  3 +++
> libobjc/configure    | 38 ++++++++++++++++++++++++++++++++++++++
> libobjc/configure.ac |  2 ++
> libobjc/encoding.c   |  3 ++-
> 6 files changed, 72 insertions(+), 1 deletion(-)
> create mode 100644 config/bitfields.m4
> 
> diff --git a/config/bitfields.m4 b/config/bitfields.m4
> new file mode 100644
> index 0000000..ee8f3b5
> --- /dev/null
> +++ b/config/bitfields.m4
> @@ -0,0 +1,26 @@
> +dnl Copyright (C) 2015 Free Software Foundation, Inc.
> +dnl This file is free software, distributed under the terms of the GNU
> +dnl General Public License.  As a special exception to the GNU General
> +dnl Public License, this file may be distributed as part of a program
> +dnl that contains a configuration script generated by Autoconf, under
> +dnl the same distribution terms as the rest of that program.
> +
> +# Define HAVE_BITFIELD_TYPE_MATTERS if the type of bitfields effects their
> +# alignment.
> +
> +AC_DEFUN([gt_BITFIELD_TYPE_MATTERS],
> +[
> +  AC_CACHE_CHECK([if the type of bitfields matters], gt_cv_bitfield_type_matters,
> +  [
> +    AC_TRY_COMPILE(
> +      [struct foo1 { char x; char :0; char y; };
> +struct foo2 { char x; int :0; char y; };
> +int foo1test[ sizeof (struct foo1) == 2 ? 1 : -1 ];
> +int foo2test[ sizeof (struct foo2) == 5 ? 1 : -1]; ],
> +      [], gt_cv_bitfield_type_matters=yes, gt_cv_bitfield_type_matters=no)
> +  ])
> +  if test $gt_cv_bitfield_type_matters = yes; then
> +    AC_DEFINE(HAVE_BITFIELD_TYPE_MATTERS, 1,
> +      [Define if the type of bitfields effects alignment.])
> +  fi
> +])
> diff --git a/libobjc/acinclude.m4 b/libobjc/acinclude.m4
> index bf78dbe..4193018 100644
> --- a/libobjc/acinclude.m4
> +++ b/libobjc/acinclude.m4
> @@ -12,6 +12,7 @@ m4_include(../config/acx.m4)
> m4_include(../config/no-executables.m4)
> m4_include(../config/enable.m4)
> m4_include(../config/tls.m4)
> +m4_include(../config/bitfields.m4)
> 
> m4_include(../libtool.m4)
> dnl The lines below arrange for aclocal not to bring an installed
> diff --git a/libobjc/config.h.in b/libobjc/config.h.in
> index c055e7c..20d1fca 100644
> --- a/libobjc/config.h.in
> +++ b/libobjc/config.h.in
> @@ -1,5 +1,8 @@
> /* config.h.in.  Generated from configure.ac by autoheader.  */
> 
> +/* Define if the type of bitfields effects alignment. */
> +#undef HAVE_BITFIELD_TYPE_MATTERS
> +
> /* Define to 1 if the target assembler supports thread-local storage. */
> #undef HAVE_CC_TLS
> 
> diff --git a/libobjc/configure b/libobjc/configure
> index 642eb9c..0547f91 100755
> --- a/libobjc/configure
> +++ b/libobjc/configure
> @@ -11530,6 +11530,44 @@ ac_compiler_gnu=$ac_cv_c_compiler_gnu
> { $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_exception_model_name" >&5
> $as_echo "$ac_exception_model_name" >&6; }
> 
> +
> +  { $as_echo "$as_me:${as_lineno-$LINENO}: checking if the type of bitfields matters" >&5
> +$as_echo_n "checking if the type of bitfields matters... " >&6; }
> +if test "${gt_cv_bitfield_type_matters+set}" = set; then :
> +  $as_echo_n "(cached) " >&6
> +else
> +
> +    cat confdefs.h - <<_ACEOF >conftest.$ac_ext
> +/* end confdefs.h.  */
> +struct foo1 { char x; char :0; char y; };
> +struct foo2 { char x; int :0; char y; };
> +int foo1test[ sizeof (struct foo1) == 2 ? 1 : -1 ];
> +int foo2test[ sizeof (struct foo2) == 5 ? 1 : -1];
> +int
> +main ()
> +{
> +
> +  ;
> +  return 0;
> +}
> +_ACEOF
> +if ac_fn_c_try_compile "$LINENO"; then :
> +  gt_cv_bitfield_type_matters=yes
> +else
> +  gt_cv_bitfield_type_matters=no
> +fi
> +rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
> +
> +fi
> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $gt_cv_bitfield_type_matters" >&5
> +$as_echo "$gt_cv_bitfield_type_matters" >&6; }
> +  if test $gt_cv_bitfield_type_matters = yes; then
> +
> +$as_echo "#define HAVE_BITFIELD_TYPE_MATTERS 1" >>confdefs.h
> +
> +  fi
> +
> +
> # ------
> # Output
> # ------
> diff --git a/libobjc/configure.ac b/libobjc/configure.ac
> index c794a80..2d88519 100644
> --- a/libobjc/configure.ac
> +++ b/libobjc/configure.ac
> @@ -266,6 +266,8 @@ fi
> AC_LANG_POP(C)
> AC_MSG_RESULT($ac_exception_model_name)
> 
> +gt_BITFIELD_TYPE_MATTERS
> +
> # ------
> # Output
> # ------
> diff --git a/libobjc/encoding.c b/libobjc/encoding.c
> index 20ace46..abb6145 100644
> --- a/libobjc/encoding.c
> +++ b/libobjc/encoding.c
> @@ -29,6 +29,7 @@ see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
> /* FIXME: This file contains functions that will abort the entire
>    program if they fail.  Is that really needed ?  */
> 
> +#include "config.h"
> #include "objc-private/common.h"
> #include "objc-private/error.h"
> #include "tconfig.h"
> @@ -1167,7 +1168,7 @@ objc_layout_structure_next_member (struct objc_struct_layout *layout)
>   /* Record must have at least as much alignment as any field.
>      Otherwise, the alignment of the field within the record
>      is meaningless.  */
> -#if !PCC_BITFIELD_TYPE_MATTERS
> +#ifndef HAVE_BITFIELD_TYPE_MATTERS
>   layout->record_align = MAX (layout->record_align, desired_align);
> #else    /* PCC_BITFIELD_TYPE_MATTERS */
>   if (*type == _C_BFLD)
> -- 
> 2.3.0.80.g18d0fec.dirty
> 

Re: [PATCH] fixup libobjc usage of PCC_BITFIELD_TYPE_MATTERS

[Jakub Jelinek]

On Fri, May 01, 2015 at 11:30:53PM -0400, tbsaunde+gcc@tbsaunde.org wrote:
> +    AC_TRY_COMPILE(
> +      [struct foo1 { char x; char :0; char y; };
> +struct foo2 { char x; int :0; char y; };
> +int foo1test[ sizeof (struct foo1) == 2 ? 1 : -1 ];
> +int foo2test[ sizeof (struct foo2) == 5 ? 1 : -1]; ],

Shouldn't the 5 be sizeof (int) + 1?  I mean, we have targets with 16-bit
ints.  I hope no target sizeof (int) == 1, that would break this test too
(perhaps you could use long long  :0; instead?).
Also, the anon bitfield changes alignment only on a subset of targets:
targetm.align_anon_bitfield ()
says if it makes a difference.
So, wouldn't it be better to test instead if
struct C { char a; char b : 1; char c; };
struct D { char a; long long b : 1; char c; };
int footest[sizeof (struct C) < sizeof (struct D)] ? 1 : -1];
?  Tested that it works with powerpc compiler with -mbit-align vs.
-mno-bit-align.

	Jakub

Re: [PATCH] fixup libobjc usage of PCC_BITFIELD_TYPE_MATTERS

[Trevor Saunders]

On Sat, May 02, 2015 at 10:03:13AM +0200, Jakub Jelinek wrote:
> On Fri, May 01, 2015 at 11:30:53PM -0400, tbsaunde+gcc@tbsaunde.org wrote:
> > +    AC_TRY_COMPILE(
> > +      [struct foo1 { char x; char :0; char y; };
> > +struct foo2 { char x; int :0; char y; };
> > +int foo1test[ sizeof (struct foo1) == 2 ? 1 : -1 ];
> > +int foo2test[ sizeof (struct foo2) == 5 ? 1 : -1]; ],
> 
> Shouldn't the 5 be sizeof (int) + 1?  I mean, we have targets with 16-bit
> ints.  I hope no target sizeof (int) == 1, that would break this test too
> (perhaps you could use long long  :0; instead?).

yeah, I just mindlessly ported the test program in tm.texi.  I'm dubious
anyone tries to use objective C on machines with 16 bit int, and doing
it on a machine with 8 bit int sounds insane, but who knows, and maybe
something else will need this test some day?

> Also, the anon bitfield changes alignment only on a subset of targets:
> targetm.align_anon_bitfield ()
> says if it makes a difference.

 the use of anon bitfields with width 0 seemed dubious to me without knowing
 about this.

> So, wouldn't it be better to test instead if
> struct C { char a; char b : 1; char c; };
> struct D { char a; long long b : 1; char c; };
> int footest[sizeof (struct C) < sizeof (struct D)] ? 1 : -1];
> ?  Tested that it works with powerpc compiler with -mbit-align vs.
> -mno-bit-align.

seems reasonable to me.

fwiw I committed the original patch last night since Andrew ok'd it, but
obviously we can improve it.  We should probably update the test in
tm.texi at the same time, or I guess better yet just refer to the m4
test there.

Trev

> 
> 	Jakub

Re: [PATCH] fixup libobjc usage of PCC_BITFIELD_TYPE_MATTERS

[Jakub Jelinek]

On Sat, May 02, 2015 at 09:08:21AM -0400, Trevor Saunders wrote:
> > > +    AC_TRY_COMPILE(
> > > +      [struct foo1 { char x; char :0; char y; };
> > > +struct foo2 { char x; int :0; char y; };
> > > +int foo1test[ sizeof (struct foo1) == 2 ? 1 : -1 ];
> > > +int foo2test[ sizeof (struct foo2) == 5 ? 1 : -1]; ],
> > 
> > Shouldn't the 5 be sizeof (int) + 1?  I mean, we have targets with 16-bit
> > ints.  I hope no target sizeof (int) == 1, that would break this test too
> > (perhaps you could use long long  :0; instead?).
> 
> yeah, I just mindlessly ported the test program in tm.texi.  I'm dubious
> anyone tries to use objective C on machines with 16 bit int, and doing
> it on a machine with 8 bit int sounds insane, but who knows, and maybe
> something else will need this test some day?

8-bit int isn't C compliant, generally, char has to be at least 8-bit,
short and int at least 16-bit, long at least 32-bit and long long at least
64-bit (this comes from the C requirements of minimum value for
U{CHAR,SHRT,INT,LONG,LLONG}_MAX).  sizeof (int) == 1 was for the case
where e.g. char would be 16-bit and int as well, or 32-bit char and
32-bit int, etc.

	Jakub

Re: [PATCH] fixup libobjc usage of PCC_BITFIELD_TYPE_MATTERS

[Andreas Schwab]

tbsaunde+gcc@tbsaunde.org writes:

> +AC_DEFUN([gt_BITFIELD_TYPE_MATTERS],
> +[
> +  AC_CACHE_CHECK([if the type of bitfields matters], gt_cv_bitfield_type_matters,
> +  [
> +    AC_TRY_COMPILE(
> +      [struct foo1 { char x; char :0; char y; };
> +struct foo2 { char x; int :0; char y; };
> +int foo1test[ sizeof (struct foo1) == 2 ? 1 : -1 ];
> +int foo2test[ sizeof (struct foo2) == 5 ? 1 : -1]; ],
> +      [], gt_cv_bitfield_type_matters=yes, gt_cv_bitfield_type_matters=no)
> +  ])
> +  if test $gt_cv_bitfield_type_matters = yes; then
> +    AC_DEFINE(HAVE_BITFIELD_TYPE_MATTERS, 1,
> +      [Define if the type of bitfields effects alignment.])
> +  fi
> +])

gcc/config/aarch64/aarch64.h:#define PCC_BITFIELD_TYPE_MATTERS  1

configure:11554: /opt/gcc/gcc-20150503/Build/./gcc/xgcc -B/opt/gcc/gcc-20150503/Build/./gcc/ -B/usr/aarch64-suse-linux/bin/ -B/usr/aarch64-suse-linux/lib/ -isystem /usr/aarch64-suse-linux/include -isystem /usr/aarch64-suse-linux/sys-include    -c -O2 -g  conftest.c >&5
conftest.c:27:5: error: size of array 'foo2test' is negative
 int foo2test[ sizeof (struct foo2) == 5 ? 1 : -1];
     ^
configure:11554: $? = 1

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

Re: [PATCH] fixup libobjc usage of PCC_BITFIELD_TYPE_MATTERS

[Trevor Saunders]

On Sun, May 03, 2015 at 10:59:46AM +0200, Andreas Schwab wrote:
> tbsaunde+gcc@tbsaunde.org writes:
> 
> > +AC_DEFUN([gt_BITFIELD_TYPE_MATTERS],
> > +[
> > +  AC_CACHE_CHECK([if the type of bitfields matters], gt_cv_bitfield_type_matters,
> > +  [
> > +    AC_TRY_COMPILE(
> > +      [struct foo1 { char x; char :0; char y; };
> > +struct foo2 { char x; int :0; char y; };
> > +int foo1test[ sizeof (struct foo1) == 2 ? 1 : -1 ];
> > +int foo2test[ sizeof (struct foo2) == 5 ? 1 : -1]; ],
> > +      [], gt_cv_bitfield_type_matters=yes, gt_cv_bitfield_type_matters=no)
> > +  ])
> > +  if test $gt_cv_bitfield_type_matters = yes; then
> > +    AC_DEFINE(HAVE_BITFIELD_TYPE_MATTERS, 1,
> > +      [Define if the type of bitfields effects alignment.])
> > +  fi
> > +])
> 
> gcc/config/aarch64/aarch64.h:#define PCC_BITFIELD_TYPE_MATTERS  1
> 
> configure:11554: /opt/gcc/gcc-20150503/Build/./gcc/xgcc -B/opt/gcc/gcc-20150503/Build/./gcc/ -B/usr/aarch64-suse-linux/bin/ -B/usr/aarch64-suse-linux/lib/ -isystem /usr/aarch64-suse-linux/include -isystem /usr/aarch64-suse-linux/sys-include    -c -O2 -g  conftest.c >&5
> conftest.c:27:5: error: size of array 'foo2test' is negative
>  int foo2test[ sizeof (struct foo2) == 5 ? 1 : -1];
>      ^
> configure:11554: $? = 1

ok, a quick test seems to show Jakub's version of the test works in this
case so lets try that.

Trev

> 
> Andreas.
> 
> -- 
> Andreas Schwab, schwab@linux-m68k.org
> GPG Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
> "And now for something completely different."

Re: [PATCH] fixup libobjc usage of PCC_BITFIELD_TYPE_MATTERS

[Jeff Law]

On 05/01/2015 09:30 PM, tbsaunde+gcc@tbsaunde.org wrote:
> From: Trevor Saunders <tbsaunde+gcc@tbsaunde.org>
>
> Hi,
>
> This adds a configure check to libobjc to find out if types of bitfields effect
> their layout, and uses it to replace the rather broken usage of
> PCC_BITFIELD_TYPE_MATTERS.
>
> bootstrapped + regtested x86_64-linux-gnu, bootstrapped on ppc64le-linux-gnu
> and ran check-objc there without failures, and checked the correct part of the
> ifdef is used on a cross to m68k-linux-elf.  ok?  I'm sure I've gotten
> something wrong since this is a bunch of auto tools ;-)
>
> Trev
>
> libobjc/ChangeLog:
>
> 2015-05-01  Trevor Saunders  <tbsaunde+gcc@tbsaunde.org>
>
> 	* acinclude.m4: Include bitfields.m4.
> 	* config.h.in: Regenerate.
> 	* configure: Likewise.
> 	* configure.ac: Invoke gt_BITFIELD_TYPE_MATTERS.
> 	* encoding.c: Check HAVE_BITFIELD_TYPE_MATTERS.
OK with the general direction here.  If Jakub's test is better, then go 
with it as a follow-up.

jeff

[PATCH] Improve the test in bitfields.m4

[tbsaunde+gcc]

From: Trevor Saunders <tbsaunde+gcc@tbsaunde.org>

Hi,

here's what I committed.  bootstrapped + regtested x86_64-linux-gnu.

Trev

Using a named bitfield with a width more than 0 means we won't hit
weirdness caused by the bitfield not really needing to exist.  Changing
int to long long means we won't have trouble with some arch where size
of int is 1 or 2.

libobjc/ChangeLog:

2015-05-04  Trevor Saunders  <tbsaunde+gcc@tbsaunde.org>

	* configure: Regenerate.

config/ChangeLog:

2015-05-04  Trevor Saunders  <tbsaunde+gcc@tbsaunde.org>

	* bitfields.m4: Change int to long long, and use bitfields of
	width 1 instead of 0.
---
 config/bitfields.m4 | 7 +++----
 libobjc/configure   | 7 +++----
 2 files changed, 6 insertions(+), 8 deletions(-)

diff --git a/config/bitfields.m4 b/config/bitfields.m4
index ee8f3b5..8185cd3 100644
--- a/config/bitfields.m4
+++ b/config/bitfields.m4
@@ -13,10 +13,9 @@ AC_DEFUN([gt_BITFIELD_TYPE_MATTERS],
   AC_CACHE_CHECK([if the type of bitfields matters], gt_cv_bitfield_type_matters,
   [
     AC_TRY_COMPILE(
-      [struct foo1 { char x; char :0; char y; };
-struct foo2 { char x; int :0; char y; };
-int foo1test[ sizeof (struct foo1) == 2 ? 1 : -1 ];
-int foo2test[ sizeof (struct foo2) == 5 ? 1 : -1]; ],
+      [struct foo1 { char x; char y:1; char z; };
+struct foo2 { char x; long long int y:1; char z; };
+int foo1test[ sizeof (struct foo1) < sizeof (struct foo2) ? 1 : -1 ]; ],
       [], gt_cv_bitfield_type_matters=yes, gt_cv_bitfield_type_matters=no)
   ])
   if test $gt_cv_bitfield_type_matters = yes; then
diff --git a/libobjc/configure b/libobjc/configure
index 0547f91..2f71735 100755
--- a/libobjc/configure
+++ b/libobjc/configure
@@ -11539,10 +11539,9 @@ else
 
     cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
-struct foo1 { char x; char :0; char y; };
-struct foo2 { char x; int :0; char y; };
-int foo1test[ sizeof (struct foo1) == 2 ? 1 : -1 ];
-int foo2test[ sizeof (struct foo2) == 5 ? 1 : -1];
+struct foo1 { char x; char y:1; char z; };
+struct foo2 { char x; long long int y:1; char z; };
+int foo1test[ sizeof (struct foo1) < sizeof (struct foo2) ? 1 : -1 ];
 int
 main ()
 {
-- 
2.4.0