[PATCH 1/2] kbuild: add '-fno-stack-check' to barebox build options

[Ahmad Fatoum]

This ports over Linux commit 3ce120b16cc5 ("kbuild: add
'-fno-stack-check' to kernel build options"):

  Author:     Linus Torvalds <torvalds at linux-foundation.org>

    kbuild: add '-fno-stack-check' to kernel build options

    It appears that hardened gentoo enables "-fstack-check" by default for
    gcc.

    That doesn't work _at_all_ for the kernel, because the kernel stack
    doesn't act like a user stack at all: it's much smaller, and it doesn't
    auto-expand on use.  So the extra "probe one page below the stack" code
    generated by -fstack-check just breaks the kernel in horrible ways,
    causing infinite double faults etc.

    [ I have to say, that the particular code gcc generates looks very
      stupid even for user space where it works, but that's a separate
      issue.  ]

    Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>

I am porting it, because it may become more acute with the incoming
support for multiple stacks (via initjmp).

Signed-off-by: Ahmad Fatoum <ahmad at a3f.at>
---
 Makefile | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/Makefile b/Makefile
index f3c85cff9430..fa7fbbeb35f0 100644
--- a/Makefile
+++ b/Makefile
@@ -622,6 +622,9 @@ KBUILD_CFLAGS += $(call cc-option, -fno-delete-null-pointer-checks,)
 # disable invalid "can't wrap" optimizations for signed / pointers
 KBUILD_CFLAGS	+= $(call cc-option,-fno-strict-overflow)
 
+# Make sure -fstack-check isn't enabled (like gentoo apparently did)
+KBUILD_CFLAGS  += $(call cc-option,-fno-stack-check)
+
 KBUILD_CFLAGS   += $(call cc-disable-warning, address-of-packed-member)
 
 # Align the bit size of userspace programs with the kernel
-- 
2.30.0