From 0e893757729dd68156b85c5bc9397e67d260db02 Mon Sep 17 00:00:00 2001 From: Mooffie Date: Wed, 16 Mar 2016 17:10:48 +0200 Subject: [PATCH] Ticket #3617: (mc_open): handle varargs mode_t promotion issue. On systems where 'mode_t' is smaller than 'int', doing 'va_arg (ap, mode_t)' is wrong because of C's "default argument promotions". GCC 4 creates crashing code in this case. The "va_arg" page of Gnulib's manual describes the problem and a simple solution: https://www.gnu.org/software/gnulib/manual/html_node/va_005farg.html However, since that solution reportedly (see thread at next link) still causes GCC to print warnings (for no good reason; perhaps this was fixed in newer GCCs), we pick a solution that defines a PROMOTED_MODE_T at the configuration stage: https://lists.gnu.org/archive/html/bug-gnulib/2009-05/msg00231.html (We take our 'mode_t.m4' from the most recent Gnulib source.) (If any of the URLs above no longer works, simply search the web for the mentioned words.) --- acinclude.m4 | 1 + configure.ac | 1 + lib/vfs/interface.c | 5 ++++- m4.include/mode_t.m4 | 26 ++++++++++++++++++++++++++ 4 files changed, 32 insertions(+), 1 deletion(-) create mode 100644 m4.include/mode_t.m4 diff --git a/acinclude.m4 b/acinclude.m4 index f228cd71f..861ca2261 100644 --- a/acinclude.m4 +++ b/acinclude.m4 @@ -3,6 +3,7 @@ m4_include([m4.include/ax_path_lib_pcre.m4]) m4_include([m4.include/dx_doxygen.m4]) m4_include([m4.include/mc-cflags.m4]) m4_include([m4.include/mc-check-search-type.m4]) +m4_include([m4.include/mode_t.m4]) m4_include([m4.include/ls-mntd-fs.m4]) m4_include([m4.include/fstypename.m4]) m4_include([m4.include/fsusage.m4]) diff --git a/configure.ac b/configure.ac index 4962f03ae..d0d8358cc 100644 --- a/configure.ac +++ b/configure.ac @@ -177,6 +177,7 @@ AC_CHECK_SIZEOF(uintmax_t) AC_TYPE_OFF_T AC_CHECK_SIZEOF(off_t) AC_TYPE_MODE_T +gl_PROMOTED_TYPE_MODE_T AC_TYPE_PID_T AC_TYPE_UID_T diff --git a/lib/vfs/interface.c b/lib/vfs/interface.c index 64acb9628..53934c035 100644 --- a/lib/vfs/interface.c +++ b/lib/vfs/interface.c @@ -200,7 +200,10 @@ mc_open (const vfs_path_t * vpath, int flags, ...) { va_list ap; va_start (ap, flags); - mode = va_arg (ap, mode_t); + /* We have to use PROMOTED_MODE_T instead of mode_t. Doing 'va_arg (ap, mode_t)' + * fails on systems where 'mode_t' is smaller than 'int' because of C's "default + * argument promotions". */ + mode = va_arg (ap, PROMOTED_MODE_T); va_end (ap); } diff --git a/m4.include/mode_t.m4 b/m4.include/mode_t.m4 new file mode 100644 index 000000000..0cd40dba4 --- /dev/null +++ b/m4.include/mode_t.m4 @@ -0,0 +1,26 @@ +# mode_t.m4 serial 2 +dnl Copyright (C) 2009-2016 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. + +# For using mode_t, it's sufficient to use AC_TYPE_MODE_T and +# include . + +# Define PROMOTED_MODE_T to the type that is the result of "default argument +# promotion" (ISO C 6.5.2.2.(6)) of the type mode_t. +AC_DEFUN([gl_PROMOTED_TYPE_MODE_T], +[ + AC_REQUIRE([AC_TYPE_MODE_T]) + AC_CACHE_CHECK([for promoted mode_t type], [gl_cv_promoted_mode_t], [ + dnl Assume mode_t promotes to 'int' if and only if it is smaller than 'int', + dnl and to itself otherwise. This assumption is not guaranteed by the ISO C + dnl standard, but we don't know of any real-world counterexamples. + AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include ]], + [[typedef int array[2 * (sizeof (mode_t) < sizeof (int)) - 1];]])], + [gl_cv_promoted_mode_t='int'], + [gl_cv_promoted_mode_t='mode_t']) + ]) + AC_DEFINE_UNQUOTED([PROMOTED_MODE_T], [$gl_cv_promoted_mode_t], + [Define to the type that is the result of default argument promotions of type mode_t.]) +])