[PATCH] gendwarfksyms: define __GENKSYMS__ when processing asm-protoypes.h

[Ard Biesheuvel <ardb+git@google.com>]

From: Ard Biesheuvel <ardb@kernel.org>

Ensure that __GENKSYMS__ is #define'd when passing asm/asm-prototypes.h
through the compiler to capture the exported symbols. This ensures that
exported symbols such as __ref_stack_chk_guard on x86, which is declared
conditionally, is visible to the tool.

Otherwise, an error such as the below may be raised, breaking the build
when CONFIG_GENDWARFKSYMS=y

  <stdin>:4:15: error: use of undeclared identifier '__ref_stack_chk_guard'

Cc: Sami Tolvanen <samitolvanen@google.com>
Reported-by: syzbot+06fd1a3613c50d36129e@syzkaller.appspotmail.com
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 scripts/Makefile.build | 1 +
 1 file changed, 1 insertion(+)

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 993708d11874..7855cdc4e763 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -305,6 +305,7 @@ $(obj)/%.rs: $(obj)/%.rs.S FORCE
 getasmexports =								\
    { echo "\#include <linux/kernel.h>" ;				\
      echo "\#include <linux/string.h>" ;				\
+     echo "\#define  __GENKSYMS__" ;					\
      echo "\#include <asm/asm-prototypes.h>" ;				\
      $(call getexportsymbols,EXPORT_SYMBOL(\1);) ; }
 
-- 
2.49.0.rc1.451.g8f38331e32-goog