linux-kernel - [PATCH 02/12] firmware: declare {__start,__end}_builtin

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Date:   Sun, 16 Oct 2016 17:16:06 +0200
From:   Vegard Nossum <vegard.nossum@...cle.com>
To:     linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Jiri Slaby <jslaby@...e.cz>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "Luis R . Rodriguez" <mcgrof@...nel.org>,
        Vegard Nossum <vegard.nossum@...cle.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        stable@...r.kernel.org
Subject: [PATCH 02/12] firmware: declare {__start,__end}_builtin_fw as external array

The test in this loop:

  for (b_fw = __start_builtin_fw; b_fw != __end_builtin_fw; b_fw++) {

was getting completely compiled out by my gcc, 7.0.0 20160520. The result
was that the loop was going beyond the end of the builtin_fw array and
giving me a page fault when trying to dereference b_fw->name inside
strcmp().

By using the new external array helper macros we get the expected
behaviour.

Reported-by: Jiri Slaby <jslaby@...e.cz>
Cc: Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: stable@...r.kernel.org
Signed-off-by: Vegard Nossum <vegard.nossum@...cle.com>
---
 arch/x86/kernel/cpu/microcode/core.c | 5 ++---
 drivers/base/firmware_class.c        | 9 +++++----
 include/asm-generic/vmlinux.lds.h    | 2 +-
 3 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index 5ce5155..6669746 100644
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -91,15 +91,14 @@ static bool __init check_loader_disabled_bsp(void)
 	return *res;
 }
 
-extern struct builtin_fw __start_builtin_fw[];
-extern struct builtin_fw __end_builtin_fw[];
+DECLARE_EXTARRAY(struct builtin_fw, builtin_fw);
 
 bool get_builtin_firmware(struct cpio_data *cd, const char *name)
 {
 #ifdef CONFIG_FW_LOADER
 	struct builtin_fw *b_fw;
 
-	for (b_fw = __start_builtin_fw; b_fw != __end_builtin_fw; b_fw++) {
+	ext_for_each(b_fw, builtin_fw) {
 		if (!strcmp(name, b_fw->name)) {
 			cd->size = b_fw->size;
 			cd->data = b_fw->data;
diff --git a/drivers/base/firmware_class.c b/drivers/base/firmware_class.c
index 22d1760..b85d943e6 100644
--- a/drivers/base/firmware_class.c
+++ b/drivers/base/firmware_class.c
@@ -9,6 +9,7 @@
 
 #include <linux/capability.h>
 #include <linux/device.h>
+#include <linux/extarray.h>
 #include <linux/module.h>
 #include <linux/init.h>
 #include <linux/timer.h>
@@ -43,15 +44,14 @@ MODULE_LICENSE("GPL");
 
 #ifdef CONFIG_FW_LOADER
 
-extern struct builtin_fw __start_builtin_fw[];
-extern struct builtin_fw __end_builtin_fw[];
+DECLARE_EXTARRAY(struct builtin_fw, builtin_fw)
 
 static bool fw_get_builtin_firmware(struct firmware *fw, const char *name,
 				    void *buf, size_t size)
 {
 	struct builtin_fw *b_fw;
 
-	for (b_fw = __start_builtin_fw; b_fw != __end_builtin_fw; b_fw++) {
+	ext_for_each(b_fw, builtin_fw) {
 		if (strcmp(name, b_fw->name) == 0) {
 			fw->size = b_fw->size;
 			fw->data = b_fw->data;
@@ -69,9 +69,10 @@ static bool fw_is_builtin_firmware(const struct firmware *fw)
 {
 	struct builtin_fw *b_fw;
 
-	for (b_fw = __start_builtin_fw; b_fw != __end_builtin_fw; b_fw++)
+	ext_for_each(b_fw, builtin_fw) {
 		if (fw->data == b_fw->data)
 			return true;
+	}
 
 	return false;
 }
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 3074796..d6121ac 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -317,7 +317,7 @@
 	.builtin_fw        : AT(ADDR(.builtin_fw) - LOAD_OFFSET) {	\
 		VMLINUX_SYMBOL(__start_builtin_fw) = .;			\
 		*(.builtin_fw)						\
-		VMLINUX_SYMBOL(__end_builtin_fw) = .;			\
+		VMLINUX_SYMBOL(__stop_builtin_fw) = .;			\
 	}								\
 									\
 	TRACEDATA							\
-- 
2.10.0.479.g221bd91