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Re: [PATCH 01/12] Configury support for --enable-stack-protector.

On 20 Feb 2016, Andreas Schwab outgrape:

> Nix <> writes:
>> +AC_ARG_ENABLE([stack-protector],
>> +            AC_HELP_STRING([--enable-stack-protector=@<:@yes|no|all|strong@:>@],
>> +                           [Detect stack overflows in glibc functions with large string buffers, or in all glibc functions]),
> Please explain the meaning of the argument in the help string.

OK, so this is a bit long in the output:

                          Detect stack overflows in glibc functions, either
                          with local buffers (yes), or with those plus arrays
                          (strong), or all functions (all)

but it does what you asked for, I think.  Adjusted patch below.  (The
line in is rather long, but I don't think that line is
breakable easily.)

---------------- >8 ----------------
From: Nick Alcock <>
Date: Fri, 19 Feb 2016 17:25:05 +0000
Subject: [PATCH] Configury support for --enable-stack-protector.

This adds =all and =strong, with obvious semantics, and with a rather
arbitrarily-chosen default off, which we might well want to change to
something stronger once this patch has been tested by people other than

We don't validate the value of the option yet: that's in a later patch.
Nor do we use it for anything at this stage.

We differentiate between 'the compiler understands -fstack-protector'
and 'the user wanted -fstack-protector' so that we can pass
-fno-stack-protector in appropriate places even if the user didn't want
to turn on -fstack-protector for other parts.  (This helps us overcome
another existing limitation, that glibc doesn't work with GCC's hacked
to pass in -fstack-protector by default.)

We might want to add another configuration option to turn on
-fstack-protector for nscd and other network-facing operations by
default, but for now I've stuck with one option to control everything.
--- | 61 ++++++++++++++++++++++++++++++++++++++++--------------------
 1 file changed, 41 insertions(+), 20 deletions(-)

diff --git a/ b/
index 3c766b7..61bf882 100644
--- a/
+++ b/
@@ -232,6 +232,18 @@ AC_ARG_ENABLE([bind-now],
+dnl Build glibc with -fstack-protector, -fstack-protector-all, or
+dnl -fstack-protector-strong.
+            AC_HELP_STRING([--enable-stack-protector=@<:@yes|no|all|strong@:>@],
+                           [Detect stack overflows in glibc functions, either with local buffers (yes), or with those plus arrays (strong), or all functions (all)]),
+            [enable_stack_protector=$enableval],
+            [enable_stack_protector=no])
+case x"$enable_stack_protector" in
+    xall|xyes|xno|xstrong) ;;
+    *) AC_MSG_ERROR([Not a valid argument for --enable-stack-protector]);;
 dnl On some platforms we cannot use dynamic loading.  We must provide
 dnl static NSS modules.
@@ -602,6 +614,35 @@ fi
 test -n "$base_machine" || base_machine=$machine
+AC_CACHE_CHECK(for -fstack-protector, libc_cv_ssp, [dnl
+LIBC_TRY_CC_OPTION([$CFLAGS $CPPFLAGS -Werror -fstack-protector],
+		   [libc_cv_ssp=yes],
+		   [libc_cv_ssp=no])
+AC_CACHE_CHECK(for -fstack-protector-strong, libc_cv_ssp_strong, [dnl
+LIBC_TRY_CC_OPTION([$CFLAGS $CPPFLAGS -Werror -fstack-protector-strong],
+		   [libc_cv_ssp_strong=yes],
+		   [libc_cv_ssp_strong=no])
+AC_CACHE_CHECK(for -fstack-protector-all, libc_cv_ssp_all, [dnl
+LIBC_TRY_CC_OPTION([$CFLAGS $CPPFLAGS -Werror -fstack-protector-all],
+		   [libc_cv_ssp_all=yes],
+		   [libc_cv_ssp_all=no])
+if test x$enable_stack_protector = xyes && test $libc_cv_ssp = yes; then
+  stack_protector=-fstack-protector
+elif test x$enable_stack_protector = xall && test $libc_cv_ssp_all = yes; then
+  stack_protector=-fstack-protector-all
+elif test x$enable_stack_protector = xstrong && test $libc_cv_ssp_strong = yes; then
+  stack_protector=-fstack-protector-strong
 # For the multi-arch option we need support in the assembler & linker.
 AC_CACHE_CHECK([for assembler and linker STT_GNU_IFUNC support],
 	       libc_cv_ld_gnu_indirect_function, [dnl
@@ -1389,26 +1430,6 @@ else
-AC_CACHE_CHECK(for -fstack-protector, libc_cv_ssp, [dnl
-LIBC_TRY_CC_OPTION([$CFLAGS $CPPFLAGS -Werror -fstack-protector],
-		   [libc_cv_ssp=yes],
-		   [libc_cv_ssp=no])
-AC_CACHE_CHECK(for -fstack-protector-strong, libc_cv_ssp_strong, [dnl
-LIBC_TRY_CC_OPTION([$CFLAGS $CPPFLAGS -Werror -fstack-protector-strong],
-		   [libc_cv_ssp_strong=yes],
-		   [libc_cv_ssp_strong=no])
-if test "$libc_cv_ssp_strong" = "yes"; then
-  stack_protector="-fstack-protector-strong"
-elif test "$libc_cv_ssp" = "yes"; then
-  stack_protector="-fstack-protector"
 AC_CACHE_CHECK(whether cc puts quotes around section names,
 	       [cat > conftest.c <<EOF

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