x86/boot: Extract error reporting functions

Currently to use warn(), a caller would need to include misc.h. However,
this means they would get the (unavailable during compressed boot)
gcc built-in memcpy family of functions. But since string.c is defining
these memcpy functions for use by misc.c, we end up in a weird circular
dependency.

To break this loop, move the error reporting functions outside of misc.c
with their own header so that they can be independently included by
other sources. Since the screen-writing routines use memmove(), keep the
low-level *_putstr() functions in misc.c.
Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Baoquan He <bhe@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Borislav Petkov <bp@suse.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Lasse Collin <lasse.collin@tukaani.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Yinghai Lu <yinghai@kernel.org>
Link: http://lkml.kernel.org/r/1462229461-3370-2-git-send-email-keescook@chromium.orgSigned-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/boot/compressed/Makefile

@@ -70,7 +70,7 @@ $(obj)/../voffset.h: vmlinux FORCE
 $(obj)/misc.o: $(obj)/../voffset.h
 
 vmlinux-objs-y := $(obj)/vmlinux.lds $(obj)/head_$(BITS).o $(obj)/misc.o \
-	$(obj)/string.o $(obj)/cmdline.o \
+	$(obj)/string.o $(obj)/cmdline.o $(obj)/error.o \
 	$(obj)/piggy.o $(obj)/cpuflags.o
 
 vmlinux-objs-$(CONFIG_EARLY_PRINTK) += $(obj)/early_serial_console.o

arch/x86/boot/compressed/error.c

+/*
+ * Callers outside of misc.c need access to the error reporting routines,
+ * but the *_putstr() functions need to stay in misc.c because of how
+ * memcpy() and memmove() are defined for the compressed boot environment.
+ */
+#include "misc.h"
+
+void warn(char *m)
+{
+	error_putstr("\n\n");
+	error_putstr(m);
+	error_putstr("\n\n");
+}
+
+void error(char *m)
+{
+	warn(m);
+	error_putstr(" -- System halted");
+
+	while (1)
+		asm("hlt");
+}

arch/x86/boot/compressed/error.h

+#ifndef BOOT_COMPRESSED_ERROR_H
+#define BOOT_COMPRESSED_ERROR_H
+
+void warn(char *m);
+void error(char *m);
+
+#endif /* BOOT_COMPRESSED_ERROR_H */

arch/x86/boot/compressed/kaslr.c

@@ -10,6 +10,7 @@
  *
  */
 #include "misc.h"
+#include "error.h"
 
 #include <asm/msr.h>
 #include <asm/archrandom.h>

arch/x86/boot/compressed/misc.c

@@ -12,6 +12,7 @@
  */
 
 #include "misc.h"
+#include "error.h"
 #include "../string.h"
 #include "../voffset.h"
 
@@ -36,7 +37,6 @@
 #define memmove		memmove
 
 /* Functions used by the included decompressor code below. */
-static void error(char *m);
 void *memmove(void *dest, const void *src, size_t n);
 
 /*
@@ -169,22 +169,6 @@ void __puthex(unsigned long value)
 	}
 }
 
-void warn(char *m)
-{
-	error_putstr("\n\n");
-	error_putstr(m);
-	error_putstr("\n\n");
-}
-
-static void error(char *m)
-{
-	warn(m);
-	error_putstr(" -- System halted");
-
-	while (1)
-		asm("hlt");
-}
-
 #if CONFIG_X86_NEED_RELOCS
 static void handle_relocations(void *output, unsigned long output_len)
 {

arch/x86/boot/compressed/misc.h

@@ -35,7 +35,6 @@ extern memptr free_mem_end_ptr;
 extern struct boot_params *boot_params;
 void __putstr(const char *s);
 void __puthex(unsigned long value);
-void warn(char *m);
 #define error_putstr(__x)  __putstr(__x)
 #define error_puthex(__x)  __puthex(__x)
 

arch/x86/boot/compressed/string.c

@@ -5,6 +5,8 @@
  * trust the gcc built-in implementations as they may do unexpected things
  * (e.g. FPU ops) in the minimal decompression stub execution environment.
  */
+#include "error.h"
+
 #include "../string.c"
 
 #ifdef CONFIG_X86_32