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

On 20 Feb 2016, Joseph Myers spake thusly:

> Any patch adding a new configure option should also document it in 
> install.texi and regenerate INSTALL.

Like this? (Assuming that using multiple @items in succession like that
is sensible. If there's a better way to delineate possible options in a
way that the reader can match up with the -fstack-protector options
described below, please susgest it.)

(I haven't included the INSTALL regeneration here, because when I try to
do it I end up with half of INSTALL getting re-word-wrapped, with
massive numbers of spurious changes that have nothing to do with the
stanza I've added. Is a particular version of texinfo required for this
to work?)

From: Nick Alcock <>

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 +++++++++++++++++++++++++++++++++++------------------
 manual/install.texi | 12 +++++++++++
 2 files changed, 53 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
diff --git a/manual/install.texi b/manual/install.texi
index b329950..cec2060 100644
--- a/manual/install.texi
+++ b/manual/install.texi
@@ -170,6 +170,18 @@ time.  Consult the @file{timezone} subdirectory for more details.
 @item --enable-lock-elision=yes
 Enable lock elision for pthread mutexes by default.
+@item --enable-stack-protector
+@item --enable-stack-protector=strong
+@item --enable-stack-protector=all
+Compile the C library and all other parts of the glibc package
+(including the threading and math libraries, NSS modules, and
+transliteration modules) using the GCC @option{-fstack-protector},
+@option{-fstack-protector-strong} or @option{-fstack-protector-all}
+options to detect stack overruns.  Only the dynamic linker and a small
+number of routines called directly from assembler are excluded from this
 @pindex pt_chown
 @findex grantpt
 @item --enable-pt_chown

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