linux-kernel - Re: [PATCH 7/8] x86/xen: Add unwind hint annotations

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Date:   Tue, 12 Sep 2017 14:56:52 +0200
From:   Jiri Slaby <jslaby@...e.cz>
To:     Josh Poimboeuf <jpoimboe@...hat.com>, x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH 7/8] x86/xen: Add unwind hint annotations

On 08/31/2017, 10:23 PM, Josh Poimboeuf wrote:
> Add unwind hint annotations to the xen head code so the ORC unwinder can
> read head_64.o.

xen-head.S is included also in head_32.S, so we see:
arch/x86/kernel/../../x86/xen/xen-head.S:47: Error: no such instruction:
`unwind_hint_empty'
scripts/Makefile.build:413: recipe for target
'arch/x86/kernel/head_32.o' failed

To fix this, I use:

--- a/arch/x86/kernel/head_32.S
+++ b/arch/x86/kernel/head_32.S
@@ -25,6 +25,7 @@
 #include <asm/bootparam.h>
 #include <asm/export.h>
 #include <asm/pgtable_32.h>
+#include "../entry/calling.h"

 /* Physical address */
 #define pa(X) ((X) - __PAGE_OFFSET)


> hypercall_page needs empty annotations at 32-byte intervals to match the
> 'xen_hypercall_*' ELF functions at those locations.
> 
> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
> ---
>  arch/x86/xen/xen-head.S | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S
> index 9753225289e8..8f9741cbb32f 100644
> --- a/arch/x86/xen/xen-head.S
> +++ b/arch/x86/xen/xen-head.S
> @@ -19,6 +19,7 @@
>  #ifdef CONFIG_XEN_PV
>  	__INIT
>  ENTRY(startup_xen)
> +	UNWIND_HINT_EMPTY
>  	cld
>  
>  	/* Clear .bss */
> @@ -40,7 +41,10 @@ END(startup_xen)
>  .pushsection .text
>  	.balign PAGE_SIZE
>  ENTRY(hypercall_page)
> -	.skip PAGE_SIZE
> +	.rept (PAGE_SIZE / 32)
> +		UNWIND_HINT_EMPTY
> +		.skip 32
> +	.endr
>  
>  #define HYPERCALL(n) \
>  	.equ xen_hypercall_##n, hypercall_page + __HYPERVISOR_##n * 32; \
> 


-- 
js
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