[PATCH] stackprotector: turn not having the right gcc into an #error

[Arjan van de Ven]

If the user selects the stack-protector config option, but does not have
a gcc that has the right bits enabled (for example because it isn't build
with a glibc that supports TLS, as is common for cross-compilers, but also
because it may be too old), then the runtime test fails right now.

Andrew rightfully points out that this is a condition we can detect at
build time, and we should error out at that point instead.

This patch adds an error message for this scenario. This error accomplishes
two goals
1) the user is informed that the security option he selective isn't available
2) the user is suggested to turn of the CONFIG option that won't work for him,
   and would make the runtime test fail anyway.

Signed-off-by: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
---
 arch/x86/Makefile |    2 +-
 kernel/panic.c    |    3 +++
 2 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 3cff3c8..c3e0eee 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -73,7 +73,7 @@ else
 
         stackp := $(CONFIG_SHELL) $(srctree)/scripts/gcc-x86_64-has-stack-protector.sh
         stackp-$(CONFIG_CC_STACKPROTECTOR) := $(shell $(stackp) \
-                "$(CC)" -fstack-protector )
+                "$(CC)" "-fstack-protector -DGCC_HAS_SP" )
         stackp-$(CONFIG_CC_STACKPROTECTOR_ALL) += $(shell $(stackp) \
                 "$(CC)" -fstack-protector-all )
 
diff --git a/kernel/panic.c b/kernel/panic.c
index c92c1e2..7cbcd8e 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -321,6 +321,9 @@ EXPORT_SYMBOL(warn_on_slowpath);
 
 #ifdef CONFIG_CC_STACKPROTECTOR
 
+#ifndef GCC_HAS_SP
+#error You have selected the CONFIG_CC_STACKPROTECTOR option, but the gcc used does not support this.
+#endif
 static unsigned long __stack_check_testing;
 /*
  * Self test function for the stack-protector feature.
-- 
1.5.4.5


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