linux-kernel - Re: [PATCH 32/32] x86/boot/e820: Move index increments outside accessors in e820__update

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Message-ID: <aCiLaAWLu4OOmfyx@gmail.com>
Date: Sat, 17 May 2025 15:13:12 +0200
From: Ingo Molnar <mingo@...nel.org>
To: "H. Peter Anvin" <hpa@...or.com>
Cc: linux-kernel@...r.kernel.org, Andy Shevchenko <andy@...nel.org>,
	Arnd Bergmann <arnd@...nel.org>, Borislav Petkov <bp@...en8.de>,
	Juergen Gross <jgross@...e.com>, Kees Cook <keescook@...omium.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Mike Rapoport <rppt@...nel.org>,
	Paul Menzel <pmenzel@...gen.mpg.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	David Woodhouse <dwmw@...zon.co.uk>
Subject: Re: [PATCH 32/32] x86/boot/e820: Move index increments outside
 accessors in e820__update_table()


* H. Peter Anvin <hpa@...or.com> wrote:

> On May 15, 2025 5:05:48 AM PDT, Ingo Molnar <mingo@...nel.org> wrote:
> >This kind of code:
> >
> >	change_point[chg_idx++]->entry  = &entries[idx];
> >
> >Can be a bit confusing to human readers, and GCC-15 started
> >warning about these patterns.
> >
> >Move the index increment outside the accessor.
> >
> >Suggested-by: Andy Shevchenko <andy@...nel.org>
> >Signed-off-by: Ingo Molnar <mingo@...nel.org>
> >Cc: Arnd Bergmann <arnd@...nel.org>
> >Cc: David Woodhouse <dwmw@...zon.co.uk>
> >Cc: H. Peter Anvin <hpa@...or.com>
> >Cc: Kees Cook <keescook@...omium.org>
> >Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> >Cc: Mike Rapoport (Microsoft) <rppt@...nel.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 10c6e7dc72d7..afb312620c82 100644
> >--- a/arch/x86/kernel/e820.c
> >+++ b/arch/x86/kernel/e820.c
> >@@ -421,9 +421,11 @@ __init int e820__update_table(struct e820_table *table)
> > 	for (idx = 0; idx < table->nr_entries; idx++)	{
> > 		if (entries[idx].size != 0) {
> > 			change_point[chg_idx]->addr	= entries[idx].addr;
> >-			change_point[chg_idx++]->entry	= &entries[idx];
> >+			change_point[chg_idx]->entry	= &entries[idx];
> >+			chg_idx++;
> > 			change_point[chg_idx]->addr	= entries[idx].addr + entries[idx].size;
> >-			change_point[chg_idx++]->entry	= &entries[idx];
> >+			change_point[chg_idx]->entry	= &entries[idx];
> >+			chg_idx++;
> > 		}
> > 	}
> > 	chg_nr = chg_idx;
> 
> Really? That seems easier to miss to me.

Maybe writing it in two groups:

			change_point[chg_idx]->addr	= entries[idx].addr;
			change_point[chg_idx]->entry	= &entries[idx];
			chg_idx++;

			change_point[chg_idx]->addr	= entries[idx].addr + entries[idx].size;
			change_point[chg_idx]->entry	= &entries[idx];
			chg_idx++;

makes it a bit easier to read? The chg_idx++ are pretty prominent in 
that form, while it's easier to miss when it's embedded.

Thanks,

	Ingo