linux-kernel - Re: [PATCH] bootconfig: Fix unaligned access when building footer

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Message-Id: <20250724101044.d32c46958f6605ae22016851@kernel.org>
Date: Thu, 24 Jul 2025 10:10:44 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Ben Hutchings <benh@...ian.org>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH] bootconfig: Fix unaligned access when building footer

On Wed, 23 Jul 2025 22:20:35 +0200
Ben Hutchings <benh@...ian.org> wrote:

> On Thu, 2025-07-24 at 00:37 +0900, Masami Hiramatsu wrote:
> > On Wed, 23 Jul 2025 12:49:25 +0200
> > Ben Hutchings <benh@...ian.org> wrote:
> [...]
> > >  static int apply_xbc(const char *path, const char *xbc_path)
> > >  {
> > > -	char *buf, *data, *p;
> > > +	struct {
> > > +		uint32_t size;
> > > +		uint32_t csum;
> > > +		char magic[BOOTCONFIG_MAGIC_LEN];
> > > +	} footer;
> > 
> > Don't we need __attribute__((__packed__)) for the footer?
> 
> I don't see any reason for there to be padding in this structure, since
> it has an alignment of 4 and the size of each member is a multiple of 4.
> 
> I included an assertion that there is no padding:
> 
> [...]
> > > +	memcpy(footer.magic, BOOTCONFIG_MAGIC, BOOTCONFIG_MAGIC_LEN);
> > > +	static_assert(sizeof(footer) == BOOTCONFIG_FOOTER_SIZE);
> > > +	memcpy(data + size, &footer, BOOTCONFIG_FOOTER_SIZE);
> [...]

OK, if we saw the assertion error, we'll add packed attribute.
Let me pick it as it is.

Thank you!


> 
> Ben.
> 
> -- 
> Ben Hutchings - Debian developer, member of kernel, installer and LTS
> teams


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>