linux-kernel - Re: linux-next: changed messages in qemu boot

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Message-ID: <87czg3mzyi.fsf@mpe.ellerman.id.au>
Date:   Tue, 24 May 2022 12:22:45 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>
Cc:     Christophe Leroy <christophe.leroy@...roup.eu>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Next Mailing List <linux-next@...r.kernel.org>,
        PowerPC <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: linux-next: changed messages in qemu boot

"Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com> writes:
> Stephen Rothwell wrote:
>> Hi all,
>> 
>> Today's linux-next bboot of the powerpc pseries_le_defconfig build
>> produced these different kernel messages (diff from yesterday's tree):
>> 
>> - ftrace: allocating 33658 entries in 13 pages
>> - ftrace: allocated 13 pages with 3 groups
>> + ftrace-powerpc: Address of ftrace_regs_caller out of range of kernel_toc.
>
> Thanks for the report. I think that is due to:
> https://patchwork.ozlabs.org/project/linuxppc-dev/patch/bb6626e884acffe87b58736291df57db3deaa9b9.1652074503.git.christophe.leroy@csgroup.eu/

Yep, I bisected it there.

I should really read my email before bisecting :)

> The below diff fixes it for me:
>
> diff --git a/arch/powerpc/kernel/trace/ftrace.c b/arch/powerpc/kernel/trace/ftrace.c
> index 46c002a8388804..7418da705d43ac 100644
> --- a/arch/powerpc/kernel/trace/ftrace.c
> +++ b/arch/powerpc/kernel/trace/ftrace.c
> @@ -746,7 +746,7 @@ int __init ftrace_dyn_arch_init(void)
>  
>         reladdr = addr - kernel_toc_addr();
>  
> -       if (reladdr >= SZ_2G || reladdr < -SZ_2G) {
> +       if (reladdr >= SZ_2G || reladdr < -_UL(SZ_2G)) {
>                 pr_err("Address of %ps out of range of kernel_toc.\n",
>                                 (void *)addr);
>                 return -1;

I did:

	if (reladdr >= SZ_2G || reladdr < -(long)SZ_2G) {


Which more closely matches what the old code did, and I think is more
obvious? ie. we don't want to negate the unsigned value, we want a
signed value, and then the negative of that.

cheers