[PATCH] x86/e820: fix e820_search_gap() error handling on x86-32

[PATCH] x86/e820: fix e820_search_gap() error handling on x86-32

[Arnd Bergmann]

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@arndb.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

[tip:x86/boot] x86/e820/32: Fix e820_search_gap() error handling on x86-32

[tip-bot for Arnd Bergmann]

Commit-ID:  c19a5f35e315837170ee337eed21c7087ea94192
Gitweb:     http://git.kernel.org/tip/c19a5f35e315837170ee337eed21c7087ea94192
Author:     Arnd Bergmann <arnd@arndb.de>
AuthorDate: Wed, 11 Jan 2017 15:49:04 +0100
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Thu, 12 Jan 2017 09:40:06 +0100

x86/e820/32: Fix e820_search_gap() error handling on x86-32

GCC correctly points out that on 32-bit kernels, e820_search_gap()
not finding a start now leads to pci_mem_start ('gapstart') 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 this cleanup:

  b4ed1d15b453 ("x86/e820: Make e820_search_gap() static and remove unused variables")

... defaulting to address 0x10000000 if nothing was found.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Toshi Kani <toshi.kani@hpe.com>
Cc: Wei Yang <richard.weiyang@gmail.com>
Fixes: b4ed1d15b453 ("x86/e820: Make e820_search_gap() static and remove unused variables")
Link: http://lkml.kernel.org/r/20170111144926.695369-1-arnd@arndb.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 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 46f2afd..b2bbad6 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

Re: [PATCH] x86/e820: fix e820_search_gap() error handling on x86-32

[Wei Yang]

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@arndb.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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