linux-kernel - Re: [PATCH] [RFC] ARM: move __bug_table into .data for XIP

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Date:   Fri, 28 Jul 2017 11:27:38 -0400 (EDT)
From:   Nicolas Pitre <nicolas.pitre@...aro.org>
To:     Arnd Bergmann <arnd@...db.de>
cc:     linux-arm-kernel@...ts.infradead.org,
        Peter Zijlstra <peterz@...radead.org>,
        Matt Hart <matthew.hart@...aro.org>,
        Stefan Agner <stefan@...er.ch>,
        Chris Brandt <chris.brandt@...esas.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Russell King <rmk+kernel@....linux.org.uk>,
        Russell King <linux@...linux.org.uk>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [RFC] ARM: move __bug_table into .data for XIP_KERNEL

On Fri, 28 Jul 2017, Arnd Bergmann wrote:

> Matt Hart reports that vf610m4_defconfig kernels grew to 2GB
> xipImage size after the __bug_table change.
> 
> I tried out a few things and found that moving the bug table
> into the .data section avoids this problem. However, the
> linker script magic is beyond my capabilities here, so this
> is almost certainly not correct.

Well, before your patch the BUG_TABLE location as well as its runtime 
functionality were completely wrong and broken.

> I've added a few people to Cc that understand this better
> than I do, hopefully someone can turn my bogus patch into
> a proper one.

Your patch isn't as bad as you make it, but maybe the following will 
avoid open recoding BUG_TABLE locally:

diff --git a/arch/arm/kernel/vmlinux-xip.lds.S b/arch/arm/kernel/vmlinux-xip.lds.S
index 8265b11621..21b4b29c2f 100644
--- a/arch/arm/kernel/vmlinux-xip.lds.S
+++ b/arch/arm/kernel/vmlinux-xip.lds.S
@@ -237,13 +237,13 @@ SECTIONS
 		 */
 		DATA_DATA
 		CONSTRUCTORS
-
-		_edata = .;
 	}
-	_edata_loc = __data_loc + SIZEOF(.data);
 
 	BUG_TABLE
 
+	_edata = .;
+	_edata_loc = __data_loc + SIZEOF(.data);
+
 #ifdef CONFIG_HAVE_TCM
         /*
 	 * We align everything to a page boundary so we can


Nicolas