linux-kernel - Re: [PATCH v5 2/2] x86/purgatory: Add linker script

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Date:   Thu, 30 Mar 2023 11:15:23 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Ricardo Ribalda <ribalda@...omium.org>
Cc:     Eric Biederman <ebiederm@...ssion.com>,
        Baoquan He <bhe@...hat.com>, Philipp Rudo <prudo@...hat.com>,
        kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Ross Zwisler <zwisler@...gle.com>,
        Simon Horman <horms@...nel.org>,
        "x86@...nel.org" <x86@...nel.org>, Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH v5 2/2] x86/purgatory: Add linker script


Hmm, this patch may need some more eyes. At least from the x86 maintainers.

-- Steve


On Thu, 30 Mar 2023 11:44:48 +0200
Ricardo Ribalda <ribalda@...omium.org> wrote:

> Make sure that the .text section is not divided in multiple overlapping
> sections. This is not supported by kexec_file.
> 
> Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> ---
>  arch/x86/purgatory/.gitignore        |  2 ++
>  arch/x86/purgatory/Makefile          | 20 +++++++++----
>  arch/x86/purgatory/kexec-purgatory.S |  2 +-
>  arch/x86/purgatory/purgatory.lds.S   | 57 ++++++++++++++++++++++++++++++++++++
>  4 files changed, 74 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/x86/purgatory/.gitignore b/arch/x86/purgatory/.gitignore
> index d2be1500671d..1fe71fe5945d 100644
> --- a/arch/x86/purgatory/.gitignore
> +++ b/arch/x86/purgatory/.gitignore
> @@ -1 +1,3 @@
>  purgatory.chk
> +purgatory.lds
> +purgatory
> diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
> index 17f09dc26381..4dc96d409bec 100644
> --- a/arch/x86/purgatory/Makefile
> +++ b/arch/x86/purgatory/Makefile
> @@ -16,10 +16,11 @@ CFLAGS_sha256.o := -D__DISABLE_EXPORTS
>  
>  # When linking purgatory.ro with -r unresolved symbols are not checked,
>  # also link a purgatory.chk binary without -r to check for unresolved symbols.
> -PURGATORY_LDFLAGS := -e purgatory_start -z nodefaultlib
> -LDFLAGS_purgatory.ro := -r $(PURGATORY_LDFLAGS)
> -LDFLAGS_purgatory.chk := $(PURGATORY_LDFLAGS)
> -targets += purgatory.ro purgatory.chk
> +PURGATORY_LDFLAGS := -nostdlib -z nodefaultlib
> +LDFLAGS_purgatory := -r $(PURGATORY_LDFLAGS) -T
> +LDFLAGS_purgatory.chk := -e purgatory_start $(PURGATORY_LDFLAGS)
> +
> +targets += purgatory.lds purgatory.ro purgatory.chk
>  
>  # Sanitizer, etc. runtimes are unavailable and cannot be linked here.
>  GCOV_PROFILE	:= n
> @@ -72,10 +73,17 @@ CFLAGS_string.o			+= $(PURGATORY_CFLAGS)
>  AFLAGS_REMOVE_setup-x86_$(BITS).o	+= -Wa,-gdwarf-2
>  AFLAGS_REMOVE_entry64.o			+= -Wa,-gdwarf-2
>  
> -$(obj)/purgatory.ro: $(PURGATORY_OBJS) FORCE
> +OBJCOPYFLAGS_purgatory.ro := -O elf64-x86-64
> +OBJCOPYFLAGS_purgatory.ro += --remove-section='*debug*'
> +OBJCOPYFLAGS_purgatory.ro += --remove-section='.comment'
> +OBJCOPYFLAGS_purgatory.ro += --remove-section='.note.*'
> +$(obj)/purgatory.ro: $(obj)/purgatory FORCE
> +		$(call if_changed,objcopy)
> +
> +$(obj)/purgatory.chk: $(obj)/purgatory FORCE
>  		$(call if_changed,ld)
>  
> -$(obj)/purgatory.chk: $(obj)/purgatory.ro FORCE
> +$(obj)/purgatory: $(obj)/purgatory.lds $(PURGATORY_OBJS) FORCE
>  		$(call if_changed,ld)
>  
>  $(obj)/kexec-purgatory.o: $(obj)/purgatory.ro $(obj)/purgatory.chk
> diff --git a/arch/x86/purgatory/kexec-purgatory.S b/arch/x86/purgatory/kexec-purgatory.S
> index 8530fe93b718..54b0d0b4dc42 100644
> --- a/arch/x86/purgatory/kexec-purgatory.S
> +++ b/arch/x86/purgatory/kexec-purgatory.S
> @@ -5,7 +5,7 @@
>  	.align	8
>  kexec_purgatory:
>  	.globl	kexec_purgatory
> -	.incbin	"arch/x86/purgatory/purgatory.ro"
> +	.incbin	"arch/x86/purgatory/purgatory"
>  .Lkexec_purgatory_end:
>  
>  	.align	8
> diff --git a/arch/x86/purgatory/purgatory.lds.S b/arch/x86/purgatory/purgatory.lds.S
> new file mode 100644
> index 000000000000..610da88aafa0
> --- /dev/null
> +++ b/arch/x86/purgatory/purgatory.lds.S
> @@ -0,0 +1,57 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#include <asm-generic/vmlinux.lds.h>
> +
> +OUTPUT_FORMAT(CONFIG_OUTPUT_FORMAT)
> +
> +#undef i386
> +
> +#include <asm/cache.h>
> +#include <asm/page_types.h>
> +
> +ENTRY(purgatory_start)
> +
> +SECTIONS
> +{
> +	. = 0;
> +	.head.text : {
> +		_head = . ;
> +		HEAD_TEXT
> +		_ehead = . ;
> +	}
> +	.rodata : {
> +		_rodata = . ;
> +		*(.rodata)	 /* read-only data */
> +		*(.rodata.*)
> +		_erodata = . ;
> +	}
> +	.text :	{
> +		_text = .; 	/* Text */
> +		*(.text)
> +		*(.text.*)
> +		*(.noinstr.text)
> +		_etext = . ;
> +	}
> +	.data :	{
> +		_data = . ;
> +		*(.data)
> +		*(.data.*)
> +		*(.bss.efistub)
> +		_edata = . ;
> +	}
> +	. = ALIGN(L1_CACHE_BYTES);
> +	.bss : {
> +		_bss = . ;
> +		*(.bss)
> +		*(.bss.*)
> +		*(COMMON)
> +		. = ALIGN(8);	/* For convenience during zeroing */
> +		_ebss = .;
> +	}
> +
> +	/* Sections to be discarded */
> +	/DISCARD/ : {
> +		*(.eh_frame)
> +		*(*__ksymtab*)
> +		*(___kcrctab*)
> +	}
> +}
>