Enable glibc to include support for kernel versions different than the version from the kernel headers.

Thanks to Nate CASE <ncase@xes-inc.com> for suggesting this use-case, and providing the patch.

 /trunk/scripts/build/libc_glibc.sh        |    4     2     2     0 +-
 /trunk/scripts/build/libc_eglibc.sh       |    2     1     1     0 +-
 /trunk/config/libc/glibc-eglibc-common.in |   44    44     0     0 +++++++++++++++++++++++++++++++++++++
 3 files changed, 47 insertions(+), 3 deletions(-)

config/libc/glibc-eglibc-common.in

@@ -67,3 +67,47 @@ config LIBC_ADDONS_LIST
       earlier.
 
       Eg.: crypt        (for very old libces)
+
+config LIBC_GLIBC_USE_HEADERS_MIN_KERNEL
+    bool
+    prompt "Use headers version for minimum kernel version supported"
+    default y
+    help
+      If enabled, crosstool-ng will use the chosen version of kernel
+      headers for the glibc minimum kernel version supported, which is
+      what gets passed to "--enable-kernel=" when configuring glibc.
+
+      Enabling this will ensure that no legacy compatibility code for
+      older kernels is built into your C libraries, but it will
+      be unable to run on kernel versions older than whichever kernel
+      headers version you've built the toolchain for.
+
+      If you know for sure that your toolchain will never need to build
+      applications that will run under a kernel version older than your
+      chosen kernel headers version (CT_KERNEL_VERSION), you can choose
+      "y" here.
+
+config LIBC_GLIBC_MIN_KERNEL_CHOSEN
+    string
+    prompt "Minimum kernel version supported"
+    default "2.6.9"
+    depends on ! LIBC_GLIBC_USE_HEADERS_MIN_KERNEL
+    help
+      Specify the earliest Linux kernel version you want glibc to
+      include support for.  This does not have to match the kernel
+      headers version used for your toolchain.  This controls what is
+      passed to the "--enable-kernel=" option to the glibc configure
+      script.
+
+      If you want to be able to statically link programs with your
+      toolchain's C library, make sure this kernel version is lower than
+      all kernels you wish to support to avoid "FATAL: kernel too old"
+      errors.  The higher the version you specify, the less legacy code
+      will be built into libc.
+
+      Most people can leave this at the default value of "2.6.9".
+
+config LIBC_GLIBC_MIN_KERNEL
+    string
+    default KERNEL_VERSION if LIBC_GLIBC_USE_HEADERS_MIN_KERNEL
+    default LIBC_GLIBC_MIN_KERNEL_CHOSEN if ! LIBC_GLIBC_USE_HEADERS_MIN_KERNEL

scripts/build/libc_eglibc.sh

@@ -198,7 +198,7 @@ do_libc() {
     # We don't need to be conditional on wether the user did set different
     # values, as they CT_LIBC_GLIBC_EXTRA_CONFIG is passed after extra_config
 
-    extra_config="--enable-kernel=$(echo ${CT_KERNEL_VERSION} |sed -r -e 's/^([^.]+\.[^.]+\.[^.]+)(|\.[^.]+)$/\1/;')"
+    extra_config="--enable-kernel=$(echo ${CT_LIBC_GLIBC_MIN_KERNEL} |sed -r -e 's/^([^.]+\.[^.]+\.[^.]+)(|\.[^.]+)$/\1/;')"
 
     case "${CT_THREADS}" in
         nptl)           extra_config="${extra_config} --with-__thread --with-tls";;

scripts/build/libc_glibc.sh

@@ -211,7 +211,7 @@ do_libc_start_files() {
     extra_config=""
     case "${CT_LIBC_GLIBC_EXTRA_CONFIG}" in
         *enable-kernel*) ;;
-        *) extra_config="${extra_config} --enable-kernel=$(echo ${CT_KERNEL_VERSION} |sed -r -e 's/^([^.]+\.[^.]+\.[^.]+)(|\.[^.]+)$/\1/;')"
+        *) extra_config="${extra_config} --enable-kernel=$(echo ${CT_LIBC_GLIBC_MIN_KERNEL} |sed -r -e 's/^([^.]+\.[^.]+\.[^.]+)(|\.[^.]+)$/\1/;')"
     esac
     case "${CT_LIBC_GLIBC_EXTRA_CONFIG}" in
         *-tls*) ;;
@@ -314,7 +314,7 @@ do_libc() {
     # We don't need to be conditional on wether the user did set different
     # values, as they CT_LIBC_GLIBC_EXTRA_CONFIG is passed after extra_config
 
-    extra_config="--enable-kernel=$(echo ${CT_KERNEL_VERSION} |sed -r -e 's/^([^.]+\.[^.]+\.[^.]+)(|\.[^.]+)$/\1/;')"
+    extra_config="--enable-kernel=$(echo ${CT_LIBC_GLIBC_MIN_KERNEL} |sed -r -e 's/^([^.]+\.[^.]+\.[^.]+)(|\.[^.]+)$/\1/;')"
 
     case "${CT_THREADS}" in
         nptl)           extra_config="${extra_config} --with-__thread --with-tls";;