[PATCH v5] Mips support for PT_GNU_STACK

[Dragan Mladjenovic <dmladjenovic at wavecomp dot com>]

From: "Dragan Mladjenovic" <dmladjenovic@wavecomp.com>

Hello everyone,

This is updated v4 version of the patch as per suggestion in [1].

Best regards,

Dragan

[1] https://sourceware.org/ml/libc-alpha/2019-08/msg00508.html

2019-08-21  Dragan Mladjenovic  <dmladjenovic@wavecomp.com>

	* sysdeps/unix/sysv/linux/mips/Makefile (test-xfail-check-execstack):
	Move under mips-has-gnustack != yes.
	(CFLAGS-.o*, ASFLAGS-.o*): New rules.
	Apply -Wa,-execstack if mips-force-execstack == yes.
	* sysdeps/unix/sysv/linux/mips/configure: Regenerated.
	* sysdeps/unix/sysv/linux/mips/configure.ac (mips-force-execstack):
	New var. Set to yes for hard-float builds with minimum_kernel < 4.8.0
	or minimum_kernel not set at all.
	(mips-has-gnustack): New var.
	Use value of libc_cv_as_noexecstack if mips-force-execstack != yes,
	otherwise set to no.
---
 sysdeps/unix/sysv/linux/mips/Makefile     | 21 +++++++++++++++-----
 sysdeps/unix/sysv/linux/mips/configure.ac | 32 +++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+), 5 deletions(-)

diff --git a/sysdeps/unix/sysv/linux/mips/Makefile b/sysdeps/unix/sysv/linux/mips/Makefile
index 8217f42..03044e7 100644
--- a/sysdeps/unix/sysv/linux/mips/Makefile
+++ b/sysdeps/unix/sysv/linux/mips/Makefile
@@ -63,14 +63,25 @@ sysdep-dl-routines += dl-static
 
 sysdep_routines += dl-vdso
 endif
-
-# Supporting non-executable stacks on MIPS requires changes to both
-# the Linux kernel and glibc.  See
-# <https://sourceware.org/ml/libc-alpha/2016-01/msg00567.html> and
-# <https://sourceware.org/ml/libc-alpha/2016-01/msg00719.html>.
+# If the compiler doesn't use GNU.stack note,
+# this test is expected to fail.
+ifneq ($(mips-has-gnustack),yes)
 test-xfail-check-execstack = yes
 endif
+endif
 
 ifeq ($(subdir),stdlib)
 gen-as-const-headers += ucontext_i.sym
 endif
+
+ifeq ($(mips-force-execstack),yes)
+CFLAGS-.o += -Wa,-execstack
+CFLAGS-.os += -Wa,-execstack
+CFLAGS-.op += -Wa,-execstack
+CFLAGS-.oS += -Wa,-execstack
+
+ASFLAGS-.o += -Wa,-execstack
+ASFLAGS-.os += -Wa,-execstack
+ASFLAGS-.op += -Wa,-execstack
+ASFLAGS-.oS += -Wa,-execstack
+endif
diff --git a/sysdeps/unix/sysv/linux/mips/configure.ac b/sysdeps/unix/sysv/linux/mips/configure.ac
index 9147aa4..3db1b32 100644
--- a/sysdeps/unix/sysv/linux/mips/configure.ac
+++ b/sysdeps/unix/sysv/linux/mips/configure.ac
@@ -134,3 +134,35 @@ if test -z "$arch_minimum_kernel"; then
     arch_minimum_kernel=4.5.0
   fi
 fi
+
+# Check if we are supposed to run on kernels older than 4.8.0. If so,
+# force executable stack to avoid potential runtime problems with fpu
+# emulation.
+# NOTE: The check below assumes that in absence of user-provided minumum_kernel
+# we will default to arch_minimum_kernel which is currently less than 4.8.0 for
+# all known configurations. If this changes, the check must be updated.
+AC_CACHE_CHECK([whether the compiler must use executable stack],
+        libc_cv_mips_force_execstack, [dnl
+libc_cv_mips_force_execstack=no
+  if test $libc_mips_float = hard; then
+    if test -n "$minimum_kernel"; then
+       changequote(,)
+       min_version=$((`echo "$minimum_kernel.0.0.0" | sed 's/\([0-9]*\)\.\([0-9]*\)\.\([0-9]*\).*/\1 \* 65536 + \2 \* 256 + \3/'`))
+       changequote([,])
+       if test $min_version -lt 264192; then
+         libc_cv_mips_force_execstack=yes
+       fi
+    else
+      libc_cv_mips_force_execstack=yes
+    fi
+  fi])
+
+libc_mips_has_gnustack=$libc_cv_as_noexecstack
+
+if test $libc_cv_mips_force_execstack = yes; then
+  libc_mips_has_gnustack=no
+  AC_MSG_WARN([forcing executable stack for pre-4.8.0 Linux kernels])
+fi
+
+LIBC_CONFIG_VAR([mips-force-execstack],[${libc_cv_mips_force_execstack}])
+LIBC_CONFIG_VAR([mips-has-gnustack],[${libc_mips_has_gnustack}])
-- 
1.9.1