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From: Kees Cook <keescook@chromium.org>
To: Dmitry Osipenko <digetx@gmail.com>
Cc: Nick Desaulniers <ndesaulniers@google.com>,
	linux-kernel@vger.kernel.org,
	Russell King <linux@armlinux.org.uk>,
	clang-built-linux@googlegroups.com,
	Ingo Molnar <mingo@kernel.org>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v1] ARM: vfp: Use long jump to fix THUMB2 kernel compilation error
Date: Wed, 21 Oct 2020 16:40:34 -0700	[thread overview]
Message-ID: <202010211637.7CFD8435@keescook> (raw)
In-Reply-To: <20201021225737.739-1-digetx@gmail.com>

On Thu, Oct 22, 2020 at 01:57:37AM +0300, Dmitry Osipenko wrote:
> The vfp_kmode_exception() function now is unreachable using relative
> branching in THUMB2 kernel configuration, resulting in a "relocation
> truncated to fit: R_ARM_THM_JUMP19 against symbol `vfp_kmode_exception'"
> linker error. Let's use long jump in order to fix the issue.

Eek. Is this with gcc or clang?

> 
> Fixes: eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input sections")

Are you sure it wasn't 512dd2eebe55 ("arm/build: Add missing sections") ?
That commit may have implicitly moved the location of .vfp11_veneer,
though I thought I had chosen the correct position.

> Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
> ---
>  arch/arm/vfp/vfphw.S | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S
> index 4fcff9f59947..6e2b29f0c48d 100644
> --- a/arch/arm/vfp/vfphw.S
> +++ b/arch/arm/vfp/vfphw.S
> @@ -82,7 +82,8 @@ ENTRY(vfp_support_entry)
>  	ldr	r3, [sp, #S_PSR]	@ Neither lazy restore nor FP exceptions
>  	and	r3, r3, #MODE_MASK	@ are supported in kernel mode
>  	teq	r3, #USR_MODE
> -	bne	vfp_kmode_exception	@ Returns through lr
> +	ldr	r1, =vfp_kmode_exception
> +	bxne	r1			@ Returns through lr
>  
>  	VFPFMRX	r1, FPEXC		@ Is the VFP enabled?
>  	DBGSTR1	"fpexc %08x", r1

This seems like a workaround though? I suspect the vfp11_veneer needs
moving?

-- 
Kees Cook

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

WARNING: multiple messages have this Message-ID (diff)
From: Kees Cook <keescook@chromium.org>
To: Dmitry Osipenko <digetx@gmail.com>
Cc: Russell King <linux@armlinux.org.uk>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Ingo Molnar <mingo@kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com
Subject: Re: [PATCH v1] ARM: vfp: Use long jump to fix THUMB2 kernel compilation error
Date: Wed, 21 Oct 2020 16:40:34 -0700	[thread overview]
Message-ID: <202010211637.7CFD8435@keescook> (raw)
In-Reply-To: <20201021225737.739-1-digetx@gmail.com>

On Thu, Oct 22, 2020 at 01:57:37AM +0300, Dmitry Osipenko wrote:
> The vfp_kmode_exception() function now is unreachable using relative
> branching in THUMB2 kernel configuration, resulting in a "relocation
> truncated to fit: R_ARM_THM_JUMP19 against symbol `vfp_kmode_exception'"
> linker error. Let's use long jump in order to fix the issue.

Eek. Is this with gcc or clang?

> 
> Fixes: eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input sections")

Are you sure it wasn't 512dd2eebe55 ("arm/build: Add missing sections") ?
That commit may have implicitly moved the location of .vfp11_veneer,
though I thought I had chosen the correct position.

> Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
> ---
>  arch/arm/vfp/vfphw.S | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S
> index 4fcff9f59947..6e2b29f0c48d 100644
> --- a/arch/arm/vfp/vfphw.S
> +++ b/arch/arm/vfp/vfphw.S
> @@ -82,7 +82,8 @@ ENTRY(vfp_support_entry)
>  	ldr	r3, [sp, #S_PSR]	@ Neither lazy restore nor FP exceptions
>  	and	r3, r3, #MODE_MASK	@ are supported in kernel mode
>  	teq	r3, #USR_MODE
> -	bne	vfp_kmode_exception	@ Returns through lr
> +	ldr	r1, =vfp_kmode_exception
> +	bxne	r1			@ Returns through lr
>  
>  	VFPFMRX	r1, FPEXC		@ Is the VFP enabled?
>  	DBGSTR1	"fpexc %08x", r1

This seems like a workaround though? I suspect the vfp11_veneer needs
moving?

-- 
Kees Cook

  reply	other threads:[~2020-10-21 23:42 UTC|newest]

Thread overview: 56+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-21 22:57 [PATCH v1] ARM: vfp: Use long jump to fix THUMB2 kernel compilation error Dmitry Osipenko
2020-10-21 22:57 ` Dmitry Osipenko
2020-10-21 23:40 ` Kees Cook [this message]
2020-10-21 23:40   ` Kees Cook
2020-10-22  0:00   ` Dmitry Osipenko
2020-10-22  0:00     ` Dmitry Osipenko
2020-10-22  3:28     ` Kees Cook
2020-10-22  3:28       ` Kees Cook
2020-10-22  7:06       ` Ard Biesheuvel
2020-10-22  7:06         ` Ard Biesheuvel
2020-10-22 15:57         ` Dmitry Osipenko
2020-10-22 15:57           ` Dmitry Osipenko
2020-10-22 16:06           ` Ard Biesheuvel
2020-10-22 16:06             ` Ard Biesheuvel
2020-10-22 16:11             ` Russell King - ARM Linux admin
2020-10-22 16:11               ` Russell King - ARM Linux admin
2020-10-22 16:20               ` Ard Biesheuvel
2020-10-22 16:20                 ` Ard Biesheuvel
2020-10-22 16:23                 ` Russell King - ARM Linux admin
2020-10-22 16:23                   ` Russell King - ARM Linux admin
2020-10-22 16:33                   ` Ard Biesheuvel
2020-10-22 16:33                     ` Ard Biesheuvel
2020-10-22 17:48                     ` Russell King - ARM Linux admin
2020-10-22 17:48                       ` Russell King - ARM Linux admin
2020-10-22 17:59                       ` Ard Biesheuvel
2020-10-22 17:59                         ` Ard Biesheuvel
2020-10-26  8:58                         ` Ard Biesheuvel
2020-10-26  8:58                           ` Ard Biesheuvel
2020-10-29  9:56                           ` Ard Biesheuvel
2020-10-29  9:56                             ` Ard Biesheuvel
2020-11-03  7:24                             ` Ard Biesheuvel
2020-11-03  7:24                               ` Ard Biesheuvel
2020-11-03  8:43                               ` Dmitry Osipenko
2020-11-03  8:43                                 ` Dmitry Osipenko
2020-11-09  7:25                                 ` Ard Biesheuvel
2020-11-09  7:25                                   ` Ard Biesheuvel
2020-11-10  7:44                                   ` Dmitry Osipenko
2020-11-10  7:44                                     ` Dmitry Osipenko
2020-11-10  7:45                                     ` Ard Biesheuvel
2020-11-10  7:45                                       ` Ard Biesheuvel
2020-10-22 16:34                   ` Dmitry Osipenko
2020-10-22 16:34                     ` Dmitry Osipenko
2020-10-22 17:38                     ` Russell King - ARM Linux admin
2020-10-22 17:38                       ` Russell King - ARM Linux admin
2020-10-22 17:47                       ` Ard Biesheuvel
2020-10-22 17:47                         ` Ard Biesheuvel
2020-10-22 17:50                         ` Russell King - ARM Linux admin
2020-10-22 17:50                           ` Russell King - ARM Linux admin
2020-10-22 17:51                           ` Ard Biesheuvel
2020-10-22 17:51                             ` Ard Biesheuvel
2020-10-22 19:05                       ` Dmitry Osipenko
2020-10-22 19:05                         ` Dmitry Osipenko
2020-10-22 14:57 ` Russell King - ARM Linux admin
2020-10-22 14:57   ` Russell King - ARM Linux admin
2020-10-22 15:56   ` Dmitry Osipenko
2020-10-22 15:56     ` Dmitry Osipenko

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