linux-kernel - Re: [PATCH] x86/e820: fix e820_search

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Message-ID: <20170125154838.GA8355@WeideMacBook-Pro.local>
Date:   Wed, 25 Jan 2017 23:48:38 +0800
From:   Wei Yang <richard.weiyang@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Wei Yang <richard.weiyang@...il.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Toshi Kani <toshi.kani@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/e820: fix e820_search_gap() error handling on x86-32

You are right. Thanks :-)

On Wed, Jan 11, 2017 at 03:49:04PM +0100, Arnd Bergmann wrote:
>gcc correctly points out that on 32-bit kernels, e820_search_gap()
>not finding a start now leads to pci_mem_start being set to an
>uninitialized value:
>
>arch/x86/kernel/e820.c: In function 'e820_setup_gap':
>arch/x86/kernel/e820.c:641:16: error: 'gapstart' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>
>This restores the behavior from before the cleanup, defaulting
>to address 0x10000000 if nothing was found.
>
>Fixes: b4ed1d15b453 ("x86/e820: Make e820_search_gap() static and remove unused variables")
>Signed-off-by: Arnd Bergmann <arnd@...db.de>
>---
> arch/x86/kernel/e820.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
>diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
>index 46f2afd3577a..b2bbad6ebe4d 100644
>--- a/arch/x86/kernel/e820.c
>+++ b/arch/x86/kernel/e820.c
>@@ -626,14 +626,16 @@ __init void e820_setup_gap(void)
> 	gapsize = 0x400000;
> 	found  = e820_search_gap(&gapstart, &gapsize);
> 
>-#ifdef CONFIG_X86_64
> 	if (!found) {
>+#ifdef CONFIG_X86_64
> 		gapstart = (max_pfn << PAGE_SHIFT) + 1024*1024;
> 		printk(KERN_ERR
> 	"e820: cannot find a gap in the 32bit address range\n"
> 	"e820: PCI devices with unassigned 32bit BARs may break!\n");
>-	}
>+#else
>+		gapstart = 0x10000000;
> #endif
>+	}
> 
> 	/*
> 	 * e820_reserve_resources_late protect stolen RAM already
>-- 
>2.9.0

-- 
Wei Yang
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