[10/12] Work even with compilers hacked to enable -fstack-protector by default.
Commit Message
From: Nick Alcock <nick.alcock@oracle.com>
With all the machinery we just added, we can easily arrange to work even
when the compiler passes in -fstack-protector automatically: all the
necessary bits of glibc are always compiled with -fno-stack-protector
now.
So tear out the check in configure, and add appropriate calls to
-fno-stack-protector and/or -lssp in tests that need them (largely
those that use -nostdlib).
---
aclocal.m4 | 6 ++---
configure.ac | 76 ++++++++++++++++++++----------------------------------------
2 files changed, 28 insertions(+), 54 deletions(-)
Comments
On Sat, 20 Feb 2016, Nix wrote:
> From: Nick Alcock <nick.alcock@oracle.com>
>
> With all the machinery we just added, we can easily arrange to work even
> when the compiler passes in -fstack-protector automatically: all the
> necessary bits of glibc are always compiled with -fno-stack-protector
> now.
>
> So tear out the check in configure, and add appropriate calls to
> -fno-stack-protector and/or -lssp in tests that need them (largely
> those that use -nostdlib).
You should avoid ever linking with -lssp. Tests should return the same
results when built with a minimal static-only bootstrap compiler (which
likely has libssp disabled) as with a full compiler (indeed, a full
compiler may well have libssp disabled as well), so that such a bootstrap
compiler can produce glibc binaries identical to those produced by an
alternating sequence of GCC and glibc builds.
@@ -141,7 +141,7 @@ int _start (void) { return 0; }
int __start (void) { return 0; }
$1
EOF
-AS_IF([AC_TRY_COMMAND([${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS -o conftest
+AS_IF([AC_TRY_COMMAND([${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp -o conftest
conftest.c -static -nostartfiles -nostdlib
1>&AS_MESSAGE_LOG_FD])],
[$2], [$3])
@@ -226,7 +226,7 @@ if test x"$gnu_ld" = x"yes"; then
cat > conftest.c <<EOF
int _start (void) { return 42; }
EOF
- if AC_TRY_COMMAND([${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS
+ if AC_TRY_COMMAND([${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $libssp
$2 -nostdlib -nostartfiles
-fPIC -shared -o conftest.so conftest.c
1>&AS_MESSAGE_LOG_FD])
@@ -268,7 +268,7 @@ libc_compiler_builtin_inlined=no
cat > conftest.c <<EOF
int _start (void) { $2 return 0; }
EOF
-if ! AC_TRY_COMMAND([${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS
+if ! AC_TRY_COMMAND([${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
$3 -nostdlib -nostartfiles
-S conftest.c -o - | fgrep "$1"
1>&AS_MESSAGE_LOG_FD])
@@ -643,6 +643,20 @@ fi
AC_SUBST(libc_cv_ssp)
AC_SUBST(stack_protector)
+if test -n "$stack_protector"; then
+ dnl While most tests can be conducted with stack protection on, a few are
+ dnl incompatible with it.
+ no_ssp=-fno-stack-protector
+ libssp="-lssp_nonshared -lssp"
+else
+ no_ssp=
+ libssp=
+
+ if test x"$enable_stack_protector" != xno; then
+ AC_MSG_ERROR([--enable-stack-protector=$enable_stack_protector specified, but specified level of stack protection is not supported by the compiler.])
+ fi
+fi
+
# For the multi-arch option we need support in the assembler & linker.
AC_CACHE_CHECK([for assembler and linker STT_GNU_IFUNC support],
libc_cv_ld_gnu_indirect_function, [dnl
@@ -662,7 +676,7 @@ __start:
EOF
libc_cv_ld_gnu_indirect_function=no
if ${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS \
- -nostartfiles -nostdlib \
+ -nostartfiles -nostdlib $no_ssp \
-o conftest conftest.S 1>&AS_MESSAGE_LOG_FD 2>&AS_MESSAGE_LOG_FD; then
# Do a link to see if the backend supports IFUNC relocs.
$READELF -r conftest 1>&AS_MESSAGE_LOG_FD
@@ -1131,8 +1145,8 @@ extern int glibc_conftest_frobozz;
void _start() { glibc_conftest_frobozz = 1; }
EOF
if ${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS \
- -nostartfiles -nostdlib \
- -o conftest conftest.s conftest1.c 1>&AS_MESSAGE_LOG_FD 2>&AS_MESSAGE_LOG_FD; then
+ -nostartfiles -nostdlib $no_ssp \
+ -o conftest conftest.s conftest1.c $libssp 1>&AS_MESSAGE_LOG_FD 2>&AS_MESSAGE_LOG_FD; then
libc_cv_asm_set_directive=yes
else
libc_cv_asm_set_directive=no
@@ -1148,12 +1162,12 @@ AC_CACHE_CHECK(linker support for protected data symbol,
int bar __attribute__ ((visibility ("protected"))) = 1;
EOF
libc_cv_protected_data=no
- if AC_TRY_COMMAND(${CC-cc} -nostdlib -nostartfiles -fPIC -shared conftest.c -o conftest.so); then
+ if AC_TRY_COMMAND(${CC-cc} -nostdlib -nostartfiles -fPIC -shared conftest.c -o conftest.so $libssp); then
cat > conftest.c <<EOF
extern int bar;
int main (void) { return bar; }
EOF
- if AC_TRY_COMMAND(${CC-cc} -nostdlib -nostartfiles conftest.c -o conftest conftest.so); then
+ if AC_TRY_COMMAND(${CC-cc} -nostdlib -nostartfiles conftest.c -o conftest conftest.so $libssp); then
libc_cv_protected_data=yes
fi
fi
@@ -1277,7 +1291,7 @@ EOF
if AC_TRY_COMMAND([${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS
-fPIC -shared -o conftest.so conftest.c
-nostdlib -nostartfiles
- -Wl,-z,combreloc 1>&AS_MESSAGE_LOG_FD])
+ -Wl,-z,combreloc $libssp 1>&AS_MESSAGE_LOG_FD])
then
dnl The following test is a bit weak. We must use a tool which can test
dnl cross-platform since the gcc used can be a cross compiler. Without
@@ -1313,9 +1327,9 @@ AC_CACHE_CHECK(for --hash-style option,
cat > conftest.c <<EOF
int _start (void) { return 42; }
EOF
-if AC_TRY_COMMAND([${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS
+if AC_TRY_COMMAND([${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
-fPIC -shared -o conftest.so conftest.c
- -Wl,--hash-style=both -nostdlib 1>&AS_MESSAGE_LOG_FD])
+ -Wl,--hash-style=both -nostdlib $libssp 1>&AS_MESSAGE_LOG_FD])
then
libc_cv_hashstyle=yes
else
@@ -1385,7 +1399,7 @@ int foo (void) { return mumble; }
EOF
if AC_TRY_COMMAND([${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS
-fPIC -shared -o conftest.so conftest.c
- -nostdlib -nostartfiles
+ -nostdlib -nostartfiles $libssp
1>&AS_MESSAGE_LOG_FD])
then
dnl look for GLOB_DAT relocation.
@@ -1402,7 +1416,7 @@ AC_SUBST(libc_cv_has_glob_dat)
AC_CACHE_CHECK(linker output format, libc_cv_output_format, [dnl
if libc_cv_output_format=`
-${CC-cc} -nostartfiles -nostdlib -Wl,--print-output-format 2>&AS_MESSAGE_LOG_FD`
+${CC-cc} -nostartfiles -nostdlib $no_ssp -Wl,--print-output-format 2>&AS_MESSAGE_LOG_FD`
then
:
else
@@ -1601,46 +1615,6 @@ if test $libc_cv_predef_fortify_source = yes; then
fi
AC_SUBST(CPPUNDEFS)
-dnl Check for silly hacked compilers inserting -fstack-protector.
-dnl This breaks badly for the early startup code we compile, since
-dnl the compiled code can refer to a magic machine-dependent location
-dnl for the canary value before we have sufficient setup for that to
-dnl work. It's also questionable to build all of libc with this flag
-dnl even when you're doing that for most applications you build, since
-dnl libc's code is so heavily-used and performance-sensitive. If we
-dnl ever really want to make that work, it should be enabled explicitly
-dnl in the libc build, not inherited from implicit compiler settings.
-AC_CACHE_CHECK([whether $CC implicitly enables -fstack-protector],
- libc_cv_predef_stack_protector, [
-AC_TRY_COMPILE([extern void foobar (char *);],
- [char large_array[2048]; foobar (large_array);], [
-libc_undefs=`$NM -u conftest.o |
- LC_ALL=C $AWK '$1 == "U" { print $2 | "sort -u"; next } { exit(1) }' \
- 2>&AS_MESSAGE_LOG_FD` || {
- AC_MSG_ERROR([confusing output from $NM -u])
-}
-echo >&AS_MESSAGE_LOG_FD "libc_undefs='$libc_undefs'"
-# On some architectures, there are architecture-specific undefined
-# symbols (resolved by the linker), so filter out unknown symbols.
-# This will fail to produce the correct result if the compiler
-# defaults to -fstack-protector but this produces an undefined symbol
-# other than __stack_chk_fail. However, compilers like that have not
-# been encountered in practice.
-libc_undefs=`echo "$libc_undefs" | egrep '^(foobar|__stack_chk_fail)$'`
-case "$libc_undefs" in
-foobar) libc_cv_predef_stack_protector=no ;;
-'__stack_chk_fail
-foobar') libc_cv_predef_stack_protector=yes ;;
-*) AC_MSG_ERROR([unexpected symbols in test: $libc_undefs]) ;;
-esac],
- [AC_MSG_ERROR([test compilation failed])])
-])
-libc_extra_cflags=
-if test $libc_cv_predef_stack_protector = yes; then
- libc_extra_cflags="$libc_extra_cflags -fno-stack-protector"
-fi
-libc_extra_cppflags=
-
# Some linkers on some architectures support __ehdr_start but with
# bugs. Make sure usage of it does not create relocations in the
# output (as the linker should resolve them all for us).
@@ -1651,7 +1625,7 @@ old_LDFLAGS="$LDFLAGS"
old_LIBS="$LIBS"
CFLAGS="$CFLAGS -fPIC"
LDFLAGS="$LDFLAGS -nostdlib -nostartfiles -shared"
-LIBS=
+LIBS=$libssp
AC_LINK_IFELSE([AC_LANG_SOURCE([
typedef struct {
char foo;