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From: "Madhavan T. Venkataraman" <>
To: Mark Brown <>
Subject: Re: [RFC PATCH v3 3/4] arm64: Handle miscellaneous functions in .text and .init.text
Date: Thu, 6 May 2021 10:30:21 -0500	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On 5/6/21 9:12 AM, Mark Brown wrote:
> On Mon, May 03, 2021 at 12:36:14PM -0500, wrote:
>> There are some SYM_CODE functions that are currently in ".text" or
>> ".init.text" sections. Some of these are functions that the unwinder
>> does not care about as they are not "interesting" to livepatch. These
>> will remain in their current sections. The rest I have moved into a
>> new section called ".code.text".
> I was thinking it'd be good to do this by modifying SYM_CODE_START() to
> emit the section, that way nobody can forget to put any SYM_CODE into a
> special section.  That does mean we'd have to first introduce a new
> variant for specifying a section that lets us override things that need
> to be in some specific section and convert everything that's in a
> special section over to that first which is a bit annoying but feels
> like it's worth it for the robustness.  It'd also put some of the don't
> cares into .code.text but so long as they are actually don't cares that
> should be fine!

OK. I could make the section an argument to SYM_CODE*() so that a developer
will never miss that. Some documentation may be in order so the guidelines
are clear. I will do the doc patch separately, if that is alright with
you all.

About the don't car functions - most of them are OK to be moved into
.code.text. But the hypervisor vector related code has a problem. I
have not debugged that yet. If I add that code in .code.text, KVM
initialization fails in one case. In another case, when I actually
test with a VM, the VM does not come up.

I am not sure. But it looks like there may be some reloc issue going on.
I don't have a handle on this yet. So, for now, I will leave the hypervisor
stuff in .text. But I will mark it as TBD in the cover letter so we don't
lose track of it.

>> Don't care functions
>> ====================
> We also have a bunch of things like __cpu_soft_restart which don't seem
> to be called out here but need to be in .idmap.text.

It is already in .idmap.text.

/* SPDX-License-Identifier: GPL-2.0-only */
 * CPU reset routines
 * Copyright (C) 2001 Deep Blue Solutions Ltd.
 * Copyright (C) 2012 ARM Ltd.
 * Copyright (C) 2015 Huawei Futurewei Technologies.

#include <linux/linkage.h>
#include <asm/assembler.h>
#include <asm/sysreg.h>
#include <asm/virt.h>

.pushsection    .idmap.text, "awx"

 * __cpu_soft_restart(el2_switch, entry, arg0, arg1, arg2) - Helper for
 * cpu_soft_restart.
 * @el2_switch: Flag to indicate a switch to EL2 is needed.
 * @entry: Location to jump to for soft reset.
 * arg0: First argument passed to @entry. (relocation list)
 * arg1: Second argument passed to @entry.(physical kernel entry)
 * arg2: Third argument passed to @entry. (physical dtb address)
 * Put the CPU into the same state as it would be if it had been reset, and
 * branch to what would be the reset vector. It must be executed with the
 * flat identity mapping.
        mov_q   x12, INIT_SCTLR_EL1_MMU_OFF
         * either disable EL1&0 translation regime or disable EL2&0 translation
         * regime if HCR_EL2.E2H == 1
        msr     sctlr_el1, x12

        cbz     x0, 1f                          // el2_switch?
        mov     x0, #HVC_SOFT_RESTART
        hvc     #0                              // no return

1:      mov     x8, x1                          // entry
        mov     x0, x2                          // arg0
        mov     x1, x3                          // arg1
        mov     x2, x4                          // arg2
        br      x8


I will double check all the *.S files and make sure that every function is accounted
for in version 4.

Stay tuned.



linux-arm-kernel mailing list

  reply	other threads:[~2021-05-06 15:32 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <65cf4dfbc439b010b50a0c46ec500432acde86d6>
2021-05-03 17:36 ` [RFC PATCH v3 0/4] arm64: Stack trace reliability checks in the unwinder madvenka
2021-05-03 17:36   ` [RFC PATCH v3 1/4] arm64: Introduce stack " madvenka
2021-05-04 15:50     ` Mark Brown
2021-05-04 19:14       ` Madhavan T. Venkataraman
2021-05-04 21:52     ` Josh Poimboeuf
2021-05-04 23:13       ` Madhavan T. Venkataraman
2021-05-05  0:07         ` Josh Poimboeuf
2021-05-05  0:21           ` Madhavan T. Venkataraman
2021-05-03 17:36   ` [RFC PATCH v3 2/4] arm64: Check the return PC against unreliable code sections madvenka
2021-05-04 16:05     ` Mark Brown
2021-05-04 19:03       ` Madhavan T. Venkataraman
2021-05-04 19:32         ` Madhavan T. Venkataraman
2021-05-05 16:46           ` Mark Brown
2021-05-05 18:48             ` Madhavan T. Venkataraman
2021-05-05 18:50               ` Madhavan T. Venkataraman
2021-05-06 13:45               ` Mark Brown
2021-05-06 15:21                 ` Madhavan T. Venkataraman
2021-05-05 16:34         ` Mark Brown
2021-05-05 17:51           ` Madhavan T. Venkataraman
2021-05-05 19:30     ` Ard Biesheuvel
2021-05-05 20:00       ` Madhavan T. Venkataraman
2021-05-03 17:36   ` [RFC PATCH v3 3/4] arm64: Handle miscellaneous functions in .text and .init.text madvenka
2021-05-06 14:12     ` Mark Brown
2021-05-06 15:30       ` Madhavan T. Venkataraman [this message]
2021-05-06 15:32         ` Madhavan T. Venkataraman
2021-05-06 15:44           ` Mark Brown
2021-05-06 15:56             ` Madhavan T. Venkataraman
2021-05-06 15:37         ` Mark Brown
2021-05-06 15:57           ` Madhavan T. Venkataraman
2021-05-03 17:36   ` [RFC PATCH v3 4/4] arm64: Handle funtion graph tracer better in the unwinder madvenka
2021-05-06 14:43     ` Mark Brown
2021-05-06 15:20       ` Madhavan T. Venkataraman

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