[PATCH v3] Makefile: Tell compiler to generate bare-metal code

[Andre Przywara]

Our GCC invocation does not provide many parameters, which lets the
toolchain fill in its own default setup.
In case of a native build or when using a full-featured cross-compiler,
this probably means Linux userland, which is not what we want for a
bare-metal application like boot-wrapper.

Tell the compiler to forget about those standard settings, and only use
what we explicitly ask for. In particular that means to not use toolchain
provided libraries, since they might pull in more code than we want, and
might not run well in the boot-wrapper environment.

Disable the stack protector, as this adds code that relies on userland:
"If a guard check fails, an error message is printed and the program
exits." (from the gcc manpage).

Signed-off-by: Andre Przywara <andre.przywara at arm.com>
---
Hi,

compared to [PATCH v2 3/9] this drops the more contentious options (for
now, at least), and focuses on what's really needed. Including
-fno-stack-protector, as the need for this showed up in the cleanup series
already.

Cheers,
Andre

 Makefile.am | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/Makefile.am b/Makefile.am
index f941b07..581840e 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -125,6 +125,8 @@ CHOSEN_NODE	:= chosen {						\
 CPPFLAGS	+= $(INITRD_FLAGS)
 CFLAGS		+= -I$(top_srcdir)/include/ -I$(top_srcdir)/$(ARCH_SRC)/include/
 CFLAGS		+= -Wall -fomit-frame-pointer
+CFLAGS		+= -ffreestanding -nostdlib	# this is not for userland
+CFLAGS		+= -fno-stack-protector		# no terminal to print
 CFLAGS		+= -ffunction-sections -fdata-sections
 CFLAGS		+= -fno-pic -fno-pie
 LDFLAGS		+= --gc-sections
-- 
2.25.1