[PATCH kexec-tools v3] arm-zImage: prepare for more malloc requirements of zstd

[Simon Horman]

On Tue, Sep 22, 2026 at 12:25:59PM +0200, Andreas Kemnade wrote:
> As there are plans for zstd in zImage for ARM, which requires more malloc
> size fo, decompression, look at the header for the required size.
> 
> References:
> https://lore.kernel.org/lkml/ZFDMRst2O+RJUYuu@shell.armlinux.org.uk/#t
> https://lore.kernel.org/lkml/20260828-zstd2-v2-0-4d9ce7150877@kemnade.info/
> 
> Suggested-by: Russell King (Oracle) <linux at armlinux.org.uk>
> Signed-off-by: Andreas Kemnade <andreas at kemnade.info>
> ---
> To: kexec at lists.infradead.org
> To: Andrew Morton <akpm at linux-foundation.org>
> To: Baoquan He <baoquan.he at linux.dev>
> To: Mike Rapoport <rppt at kernel.org>
> To: Pasha Tatashin <pasha.tatashin at soleen.com>
> To: Pratyush Yadav <pratyush at kernel.org>
> To: Simon Horman <horms at kernel.org>
> Cc: Russell King <linux at armlinux.org.uk>
> Cc: j.neuschaefer at gmx.net
> ---
> Changes in v3:
> - calculate zImage size requirement before the if (tag) to simplify code
> - Link to v2: https://patch.msgid.link/20260912-malloc-fix-v2-1-eb0c3ca681cd@kemnade.info
> 
> Changes in v2:
> - extract malloc size from zImage header
> - Link to v1: https://patch.msgid.link/20260829094607.689485-1-andreas@kemnade.info

Thanks, and sorry for the delay.

I have applied this as:

[1] arm-zImage: prepare for more malloc requirements of zstd
    https://git.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git/commit/?id=e128675241fa


This required a manual merge due to conflicts with the following,
which I had applied just beforehand.

[2] arm: use the zImage tag's real TEXT_OFFSET for kernel placement
    https://git.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git/commit/?id=c1a526c87eb1

In particular:

a. The text_offset member no longer needs to be added to struct zimage_tag
   by [1] as it was added by [2].

b. There is some fuzz in the 2nd hunk of [2] as [1] adds some
   logic earlier on in zImage_arm_load().

FTR, the patch I applied is as follows.
If I've messed something up, please let me know.


>From e128675241fa7777dcce613a2df191458c320f5b Mon Sep 17 00:00:00 2001
From: Andreas Kemnade <andreas at kemnade.info>
Date: Tue, 22 Sep 2026 12:25:59 +0200
Subject: [PATCH] arm-zImage: prepare for more malloc requirements of zstd

As there are plans for zstd in zImage for ARM, which requires more malloc
size fo, decompression, look at the header for the required size.

References:
https://lore.kernel.org/lkml/ZFDMRst2O+RJUYuu@shell.armlinux.org.uk/#t
https://lore.kernel.org/lkml/20260828-zstd2-v2-0-4d9ce7150877@kemnade.info/

Suggested-by: Russell King (Oracle) <linux at armlinux.org.uk>
Signed-off-by: Andreas Kemnade <andreas at kemnade.info>
Reviewed-by: Tom Fitzhenry <tom at tom-fitzhenry.me.uk>
Tested-by: Tom Fitzhenry <tom at tom-fitzhenry.me.uk>
Signed-off-by: Simon Horman <horms at kernel.org>
---
 kexec/arch/arm/kexec-zImage-arm.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/kexec/arch/arm/kexec-zImage-arm.c b/kexec/arch/arm/kexec-zImage-arm.c
index 892fca0cf09c..b1ee6ca2158b 100644
--- a/kexec/arch/arm/kexec-zImage-arm.c
+++ b/kexec/arch/arm/kexec-zImage-arm.c
@@ -132,6 +132,7 @@ struct zimage_tag {
 			uint32_t size_ptr;
 			uint32_t bss_size;
 			uint32_t text_offset;
+			uint32_t malloc_size;
 		} krnl_size;
 	} u;
 };
@@ -679,9 +680,15 @@ int zImage_arm_load(int argc, char **argv, const char *buf, off_t len,
 
 	/*
 	 * The zImage length does not include its stack (4k) or its
-	 * malloc space (64k).  Include this.
+	 * malloc space.
 	 */
-	len += 0x11000;
+	len += 0x1000;
+
+	/* include malloc space */
+	if (tag && le32_to_cpu(tag->hdr.size) >= 6)
+		len += le32_to_cpu(tag->u.krnl_size.malloc_size);
+	else
+		len += 0x10000;
 
 	dbgprintf("zImage requires 0x%08llx bytes\n", (unsigned long long)len);
 
-- 
2.47.3