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build-sys: Check behavior of -Werror=shadow before deciding to use it

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gcc versions 4.6 and earlier used to complain when a local variable
shadows a global function, 4.7 and above only complain if a local
variable shadows a global variable.

Fix this by checking whether gcc 4.7+ behavior is in place before
deciding to use -Werror=shadow in $(CFLAGS), by using a custom test
program source that shadows a global function with a local variable and
confirming that -Werror=shadow does not make the compile to break.

Tested:
- On gcc 4.7 and 4.8, confirmed nothing changed (other than the order of
  the -Werror=shadow argument, going to the end of CFLAGS.)
- On gcc 4.6, confirmed by looking at the config.log output that the
  check for -Werror=shadow failed and it was not included in CFLAGS.
- Ran `make V=1` to confirm -Werror=shadow was still in use, introduced
  a bogus shadowing issue and confirmed it was caught when building with
  a recent gcc.
This commit is contained in:
Filipe Brandenburger 2015-09-05 16:52:51 -07:00
parent 6a937f0645
commit a01a4517e1
2 changed files with 19 additions and 6 deletions
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12
configure.ac
View File

@ -171,7 +171,6 @@ CC_CHECK_FLAGS_APPEND([with_cflags], [CFLAGS], [\
-Werror=implicit-function-declaration \
-Werror=missing-declarations \
-Werror=return-type \
-Werror=shadow \
-Wstrict-prototypes \
-Wredundant-decls \
-Wmissing-noreturn \
@ -196,6 +195,17 @@ CC_CHECK_FLAGS_APPEND([with_cflags], [CFLAGS], [\
-fPIE \
--param=ssp-buffer-size=4])
CC_CHECK_FLAG_APPEND([with_cflags], [CFLAGS], [-Werror=shadow], [
#include <time.h>
#include <inttypes.h>
typedef uint64_t usec_t;
usec_t now(clockid_t clock);
int main(void) {
struct timespec now;
return 0;
}
])
AS_CASE([$CC], [*clang*],
[CC_CHECK_FLAGS_APPEND([with_cppflags], [CPPFLAGS], [\
-Wno-typedef-redefinition \

13
m4/attributes.m4
View File

@ -35,15 +35,18 @@ dnl well.
dnl Check if FLAG in ENV-VAR is supported by compiler and append it
dnl to WHERE-TO-APPEND variable. Note that we invert -Wno-* checks to
dnl -W* as gcc cannot test for negated warnings.
dnl CC_CHECK_FLAG_APPEND([WHERE-TO-APPEND], [ENV-VAR], [FLAG])
dnl -W* as gcc cannot test for negated warnings. If a C snippet is passed,
dnl use it, otherwise use a simple main() definition that just returns 0.
dnl CC_CHECK_FLAG_APPEND([WHERE-TO-APPEND], [ENV-VAR], [FLAG], [C-SNIPPET])
AC_DEFUN([CC_CHECK_FLAG_APPEND], [
AC_CACHE_CHECK([if $CC supports flag $3 in envvar $2],
AS_TR_SH([cc_cv_$2_$3]),
[eval "AS_TR_SH([cc_save_$2])='${$2}'"
eval "AS_TR_SH([$2])='-Werror `echo "$3" | sed 's/^-Wno-/-W/'`'"
AC_LINK_IFELSE([AC_LANG_SOURCE([int main(void) { return 0; } ])],
AC_LINK_IFELSE([AC_LANG_SOURCE(ifelse([$4], [],
[int main(void) { return 0; } ],
[$4]))],
[eval "AS_TR_SH([cc_cv_$2_$3])='yes'"],
[eval "AS_TR_SH([cc_cv_$2_$3])='no'"])
eval "AS_TR_SH([$2])='$cc_save_$2'"])
@ -52,10 +55,10 @@ AC_DEFUN([CC_CHECK_FLAG_APPEND], [
[eval "$1='${$1} $3'"])
])
dnl CC_CHECK_FLAGS_APPEND([WHERE-TO-APPEND], [ENV-VAR], [FLAG1 FLAG2])
dnl CC_CHECK_FLAGS_APPEND([WHERE-TO-APPEND], [ENV-VAR], [FLAG1 FLAG2], [C-SNIPPET])
AC_DEFUN([CC_CHECK_FLAGS_APPEND], [
for flag in [$3]; do
CC_CHECK_FLAG_APPEND([$1], [$2], $flag)
CC_CHECK_FLAG_APPEND([$1], [$2], $flag, [$4])
done
])