# HG changeset patch # User Paul Eggert # Date 1297553596 28800 # Node ID d9460671313ec98a060a186d280699137b0df2d3 # Parent 72901df54787e47c018f35f297965efc7e01425c stdlib: support non-GCC __attribute__ Fix a serious and tricky problem encountered when attempting to add the getloadavg module to Emacs. Emacs worked fine on RHEL 5.5, but it crashed due to memory corruption on Solaris 10 with Sun C 5.11. Emacs normally ORs 3-bit tags into their low-order bits that are otherwise zero. This tagging is optional inside Emacs but is preferred and is used when __attribute__ ((__aligned (8))) works, as it does with both recent-enough GCC and with Sun C 5.11. However, Sun C 5.11 is not GCC and does not #define __GNUC__ and __GNUC_MINOR__. When I added the getloadavg module to Emacs, it brought in stdlib.in.h, which contained this fragment: #ifndef __attribute__ # if __GNUC__ < 2 || (__GNUC__ == 2 && __GNUC_MINOR__ < 8) # define __attribute__(Spec) /* empty */ # endif #endif When files that include were compiled with Sun C 5.11, the above code disabled __attribute__ ((__aligned (8))), which caused variables to not be properly aligned, which eventually led to the pointer corruption mentioned above. (This was a bit hard to diagnose, unfortunately.) Several "#define __attribute__(X) /* empty */" code snippets need to be eradicated from Gnulib to work with non-GCC compilers that support __attribute__. The Autoconf way to do this is to test for each kind of attribute that we want support for, and selectively enable that in source code. Fix this problem just for stdlib.h, by adding a test for the __noreturn__ attribute, and change stdlib.in.h to use that test when needed. This technique can be easily generalized to the other *.in.h files and attributes, and a similar technique can be used for *.h and *.c files. This patch is enough to solve the problem for Emacs + getloadavg, and I thought I'd publish it for feedback before undertaking further, similar fixes in other modules. This patch does not arrange to #define HAVE_ATTRIBUTE_NORETURN because it's not needed for stdlib.h. It merely substitutes the value directly into stdlib.h. We may well need to #define it, or similar symbols, for other modules, but it's nice to also have an option to not #define it for applications like Emacs that do not need it. * lib/stdlib.in.h (__attribute__): Do not #define. (_GL_ATTRIBUTE_NORETURN): New macro, which in stdlib.h needs to be defined only if the _Exit module is also used. * m4/_Exit.m4 (gl_FUNC__EXIT): Require gl_ATTRIBUTE_NORETURN. * m4/stdlib_h.m4 (gl_STDLIB_H_DEFAULTS): Subst HAVE_ATTRIBUTE_NORETURN and default it to 1, its value on GNU platforms. * modules/_Exit (Files): Add m4/attribute.m4. * modules/stdlib (Makefile.am): Substitute HAVE_ATTRIBUTE_NORETURN. * m4/attribute.m4: New file. diff --git a/ChangeLog b/ChangeLog --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,65 @@ +2011-02-12 Paul Eggert + + stdlib: support non-GCC __attribute__ + + Fix a serious and tricky problem encountered when attempting to + add the getloadavg module to Emacs. Emacs worked fine on RHEL + 5.5, but it crashed due to memory corruption on Solaris 10 with + Sun C 5.11. Emacs normally ORs 3-bit tags into their low-order + bits that are otherwise zero. This tagging is optional inside + Emacs but is preferred and is used when __attribute__ ((__aligned + (8))) works, as it does with both recent-enough GCC and with Sun C + 5.11. However, Sun C 5.11 is not GCC and does not #define + __GNUC__ and __GNUC_MINOR__. + + When I added the getloadavg module to Emacs, it brought in + stdlib.in.h, which contained this fragment: + + #ifndef __attribute__ + # if __GNUC__ < 2 || (__GNUC__ == 2 && __GNUC_MINOR__ < 8) + # define __attribute__(Spec) /* empty */ + # endif + #endif + + When files that include were compiled with Sun C 5.11, + the above code disabled __attribute__ ((__aligned (8))), which + caused variables to not be properly aligned, which eventually led + to the pointer corruption mentioned above. (This was a bit hard + to diagnose, unfortunately.) + + Several "#define __attribute__(X) /* empty */" code snippets need + to be eradicated from Gnulib to work with non-GCC compilers that + support __attribute__. The Autoconf way to do this is to test for + each kind of attribute that we want support for, and selectively + enable that in source code. + + Fix this problem just for stdlib.h, by adding a test for the + __noreturn__ attribute, and change stdlib.in.h to use that test + when needed. This technique can be easily generalized to the + other *.in.h files and attributes, and a similar technique can be + used for *.h and *.c files. This patch is enough to solve the + problem for Emacs + getloadavg, and I thought I'd publish it for + feedback before undertaking further, similar fixes in other + modules. + + This patch does not arrange to #define HAVE_ATTRIBUTE_NORETURN + because it's not needed for stdlib.h. It merely substitutes the + value directly into stdlib.h. We may well need to #define it, or + similar symbols, for other modules, but it's nice to also have an + option to not #define it for applications like Emacs that do not + need it. + + * lib/stdlib.in.h (__attribute__): Do not #define. + (_GL_ATTRIBUTE_NORETURN): New macro, which in stdlib.h needs to + be defined only if the _Exit module is also used. + * m4/_Exit.m4 (gl_FUNC__EXIT): Require gl_ATTRIBUTE_NORETURN. + * m4/stdlib_h.m4 (gl_STDLIB_H_DEFAULTS): Subst + HAVE_ATTRIBUTE_NORETURN and default it to 1, its value on GNU + platforms. + * modules/_Exit (Files): Add m4/attribute.m4. + * modules/stdlib (Makefile.am): Substitute HAVE_ATTRIBUTE_NORETURN. + * m4/attribute.m4: New file. + 2011-02-12 Bruno Haible wcsrtombs: Work around bug on native Windows. diff --git a/lib/stdlib.in.h b/lib/stdlib.in.h --- a/lib/stdlib.in.h +++ b/lib/stdlib.in.h @@ -88,12 +88,6 @@ # include #endif -#ifndef __attribute__ -# if __GNUC__ < 2 || (__GNUC__ == 2 && __GNUC_MINOR__ < 8) -# define __attribute__(Spec) /* empty */ -# endif -#endif - /* The definitions of _GL_FUNCDECL_RPL etc. are copied here. */ /* The definition of _GL_ARG_NONNULL is copied here. */ @@ -119,7 +113,12 @@ /* Terminate the current process with the given return code, without running the 'atexit' handlers. */ # if !@HAVE__EXIT@ -_GL_FUNCDECL_SYS (_Exit, void, (int status) __attribute__ ((__noreturn__))); +# if @HAVE_ATTRIBUTE_NORETURN@ +# define _GL_ATTRIBUTE_NORETURN __attribute__ ((__noreturn__)) +# else +# define _GL_ATTRIBUTE_NORETURN +# endif +_GL_FUNCDECL_SYS (_Exit, void, (int status)) _GL_ATTRIBUTE_NORETURN; # endif _GL_CXXALIAS_SYS (_Exit, void, (int status)); _GL_CXXALIASWARN (_Exit); diff --git a/m4/_Exit.m4 b/m4/_Exit.m4 --- a/m4/_Exit.m4 +++ b/m4/_Exit.m4 @@ -1,4 +1,4 @@ -# _Exit.m4 serial 1 +# _Exit.m4 serial 2 dnl Copyright (C) 2010-2011 Free Software Foundation, Inc. dnl This file is free software; the Free Software Foundation dnl gives unlimited permission to copy and/or distribute it, @@ -7,6 +7,8 @@ AC_DEFUN([gl_FUNC__EXIT], [ AC_REQUIRE([gl_STDLIB_H_DEFAULTS]) + AC_REQUIRE([gl_ATTRIBUTE_NORETURN]) + AC_CHECK_FUNCS([_Exit]) if test $ac_cv_func__Exit = no; then HAVE__EXIT=0 diff --git a/m4/attribute.m4 b/m4/attribute.m4 new file mode 100644 --- /dev/null +++ b/m4/attribute.m4 @@ -0,0 +1,29 @@ +# Test for GCC-style __attribute__ support. + +dnl Copyright (C) 2011 Free Software Foundation, Inc. +dnl This file is free software; the Free Software Foundation +dnl gives unlimited permission to copy and/or distribute it, +dnl with or without modifications, as long as this notice is preserved. + +dnl from Paul Eggert + +# Currently only __attribute__ ((__noreturn__)) is done, +# but other macros can be added to this file as needed. + +# Test whether __attribute__ ((__noreturn__)) works. +AC_DEFUN([gl_ATTRIBUTE_NORETURN], [ + AC_CACHE_CHECK([for __attribute__ ((__noreturn__))], + [gl_cv_attribute_noreturn], + [gl_save_werror_flag=$ac_[]_AC_LANG_ABBREV[]_werror_flag + ac_[]_AC_LANG_ABBREV[]_werror_flag=yes + AC_COMPILE_IFELSE( + [AC_LANG_PROGRAM( + [[void never_come_back (int) __attribute__ ((__noreturn__));]])], + [gl_cv_attribute_noreturn=yes], + [gl_cv_attribute_noreturn=no]) + ac_[]_AC_LANG_ABBREV[]_werror_flag=$gl_save_werror_flag]) + if test $gl_cv_attribute_noreturn = no; then + HAVE_ATTRIBUTE_NORETURN=0 + fi + AC_SUBST([HAVE_ATTRIBUTE_NORETURN]) +]) diff --git a/m4/stdlib_h.m4 b/m4/stdlib_h.m4 --- a/m4/stdlib_h.m4 +++ b/m4/stdlib_h.m4 @@ -1,4 +1,4 @@ -# stdlib_h.m4 serial 36 +# stdlib_h.m4 serial 37 dnl Copyright (C) 2007-2011 Free Software Foundation, Inc. dnl This file is free software; the Free Software Foundation dnl gives unlimited permission to copy and/or distribute it, @@ -65,6 +65,7 @@ dnl Assume proper GNU behavior unless another module says otherwise. HAVE__EXIT=1; AC_SUBST([HAVE__EXIT]) HAVE_ATOLL=1; AC_SUBST([HAVE_ATOLL]) + HAVE_ATTRIBUTE_NORETURN=1; AC_SUBST([HAVE_ATTRIBUTE_NORETURN]) HAVE_CANONICALIZE_FILE_NAME=1; AC_SUBST([HAVE_CANONICALIZE_FILE_NAME]) HAVE_DECL_GETLOADAVG=1; AC_SUBST([HAVE_DECL_GETLOADAVG]) HAVE_GETSUBOPT=1; AC_SUBST([HAVE_GETSUBOPT]) diff --git a/modules/_Exit b/modules/_Exit --- a/modules/_Exit +++ b/modules/_Exit @@ -4,6 +4,7 @@ Files: lib/_Exit.c m4/_Exit.m4 +m4/attribute.m4 Depends-on: stdlib diff --git a/modules/stdlib b/modules/stdlib --- a/modules/stdlib +++ b/modules/stdlib @@ -57,6 +57,7 @@ < $(srcdir)/stdlib.in.h | \ sed -e 's|@''HAVE__EXIT''@|$(HAVE__EXIT)|g' \ -e 's|@''HAVE_ATOLL''@|$(HAVE_ATOLL)|g' \ + -e 's|@''HAVE_ATTRIBUTE_NORETURN''@|$(HAVE_ATTRIBUTE_NORETURN)|g' \ -e 's|@''HAVE_CANONICALIZE_FILE_NAME''@|$(HAVE_CANONICALIZE_FILE_NAME)|g' \ -e 's|@''HAVE_DECL_GETLOADAVG''@|$(HAVE_DECL_GETLOADAVG)|g' \ -e 's|@''HAVE_GETSUBOPT''@|$(HAVE_GETSUBOPT)|g' \