glibc: support RHEL 6 -like kernels again

We lost the support with 2.25 -> 2.26

pkgs/development/libraries/glibc/allow-kernel-2.6.32.patch

@@ -0,0 +1,39 @@
+diff --git a/sysdeps/unix/sysv/linux/configure b/sysdeps/unix/sysv/linux/configure
+index cace758c01..38fe7fe0b0 100644
+--- a/sysdeps/unix/sysv/linux/configure
++++ b/sysdeps/unix/sysv/linux/configure
+@@ -69,7 +69,7 @@ fi
+ { $as_echo "$as_me:${as_lineno-$LINENO}: checking for kernel header at least $minimum_kernel" >&5
+ $as_echo_n "checking for kernel header at least $minimum_kernel... " >&6; }
+ decnum=`echo "$minimum_kernel.0.0.0" | sed 's/\([0-9]*\)\.\([0-9]*\)\.\([0-9]*\).*/(\1 * 65536 + \2 * 256 + \3)/'`;
+-abinum=`echo "$minimum_kernel.0.0.0" | sed 's/\([0-9]*\)\.\([0-9]*\)\.\([0-9]*\).*/\1,\2,\3/'`;
++abinum=`echo "2.6.32.0.0.0" | sed 's/\([0-9]*\)\.\([0-9]*\)\.\([0-9]*\).*/\1,\2,\3/'`;
+ cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+ /* end confdefs.h.  */
+ #include <linux/version.h>
+diff --git a/sysdeps/unix/sysv/linux/configure.ac b/sysdeps/unix/sysv/linux/configure.ac
+index 13abda0a51..6abc12eaed 100644
+--- a/sysdeps/unix/sysv/linux/configure.ac
++++ b/sysdeps/unix/sysv/linux/configure.ac
+@@ -50,7 +50,7 @@ fi
+ AC_MSG_CHECKING(for kernel header at least $minimum_kernel)
+ changequote(,)dnl
+ decnum=`echo "$minimum_kernel.0.0.0" | sed 's/\([0-9]*\)\.\([0-9]*\)\.\([0-9]*\).*/(\1 * 65536 + \2 * 256 + \3)/'`;
+-abinum=`echo "$minimum_kernel.0.0.0" | sed 's/\([0-9]*\)\.\([0-9]*\)\.\([0-9]*\).*/\1,\2,\3/'`;
++abinum=`echo "2.6.32.0.0.0" | sed 's/\([0-9]*\)\.\([0-9]*\)\.\([0-9]*\).*/\1,\2,\3/'`;
+ changequote([,])dnl
+ AC_TRY_COMPILE([#include <linux/version.h>
+ #if LINUX_VERSION_CODE < $decnum
+diff --git a/sysdeps/unix/sysv/linux/dl-osinfo.h b/sysdeps/unix/sysv/linux/dl-osinfo.h
+index 823cd8224d..482caaeeec 100644
+--- a/sysdeps/unix/sysv/linux/dl-osinfo.h
++++ b/sysdeps/unix/sysv/linux/dl-osinfo.h
+@@ -39,7 +39,7 @@
+ 	  GLRO(dl_osversion) = version;					      \
+ 									      \
+ 	/* Now we can test with the required version.  */		      \
+-	if (__LINUX_KERNEL_VERSION > 0 && version < __LINUX_KERNEL_VERSION)   \
++	if (__LINUX_KERNEL_VERSION > 0 && version < __LINUX_KERNEL_VERSION && version != 0x020620)   \
+ 	  /* Not sufficent.  */						      \
+ 	  FATAL ("FATAL: kernel too old\n");				      \
+       }									      \

pkgs/development/libraries/glibc/common.nix

@@ -65,6 +65,25 @@ stdenv.mkDerivation ({
          "/bin:/usr/bin", which is inappropriate on NixOS machines. This
          patch extends the search path by "/run/current-system/sw/bin". */
       ./fix_path_attribute_in_getconf.patch
+
+      /* Allow running with RHEL 6 -like kernels.  The patch adds an exception
+        for glibc to accept 2.6.32 and to tag the ELFs as 2.6.32-compatible
+        (otherwise the loader would refuse libc).
+        Note that glibc will fully work only on their heavily patched kernels
+        and we lose early mismatch detection on 2.6.32.
+
+        On major glibc updates we should check that the patched kernel supports
+        all the required features.  ATM it's verified up to glibc-2.26-115.
+        # HOWTO: check glibc sources for changes in kernel requirements
+        git log -p glibc-2.25.. sysdeps/unix/sysv/linux/x86_64/kernel-features.h sysdeps/unix/sysv/linux/kernel-features.h
+        # get kernel sources (update the URL)
+        mkdir tmp && cd tmp
+        curl http://vault.centos.org/6.9/os/Source/SPackages/kernel-2.6.32-696.el6.src.rpm | rpm2cpio - | cpio -idmv
+        tar xf linux-*.bz2
+        # check syscall presence, for example
+        less linux-*?/arch/x86/kernel/syscall_table_32.S
+       */
+      ./allow-kernel-2.6.32.patch
     ]
     ++ lib.optional stdenv.isx86_64 ./fix-x64-abi.patch;