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From:   Zhenzhong Duan <zhenzhong.duan@oracle.com>
To:     linux-kernel@vger.kernel.org
Cc:     Zhenzhong Duan <zhenzhong.duan@oracle.com>,
        "Kirill A. Shutemov" <kirill@shutemov.name>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>, x86-ml <x86@kernel.org>
Subject: [PATCH] x86/boot/compressed/64: Fix 'may be used uninitialized' issue
Date:   Mon,  2 Sep 2019 17:30:24 +0800
Message-Id: <1567416624-26727-1-git-send-email-zhenzhong.duan@oracle.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Builds kernel with "make bzImage EXTRA_CFLAGS=-Wall", gcc complains:

arch/x86/boot/compressed/pgtable_64.c: In function 'paging_prepare':
arch/x86/boot/compressed/pgtable_64.c:92:7: warning: 'new' may be used uninitialized in this function [-Wmaybe-uninitialized]
   new = round_down(new, PAGE_SIZE);

In theory a random value of variable new may pass all the check and be
assigned to bios_start, fixing it by assigning it an initial value.

Fixes: 0a46fff2f910 ("x86/boot/compressed/64: Fix boot on machines with broken E820 table")
Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86-ml <x86@kernel.org>
---
 arch/x86/boot/compressed/pgtable_64.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/boot/compressed/pgtable_64.c b/arch/x86/boot/compressed/pgtable_64.c
index 2faddeb..c886269 100644
--- a/arch/x86/boot/compressed/pgtable_64.c
+++ b/arch/x86/boot/compressed/pgtable_64.c
@@ -72,7 +72,7 @@ static unsigned long find_trampoline_placement(void)
 
 	/* Find the first usable memory region under bios_start. */
 	for (i = boot_params->e820_entries - 1; i >= 0; i--) {
-		unsigned long new;
+		unsigned long new = bios_start;
 
 		entry = &boot_params->e820_table[i];
 
-- 
1.8.3.1