linux-kernel - Re: [PATCH v4 2/2] x86/purgatory: Make sure we fail the build if purgatory.ro has missing symbols

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Message-ID: <e96ea0cc-954d-2cd3-8d9d-53d57856d8aa@redhat.com>
Date:   Thu, 12 Mar 2020 18:46:44 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Arvind Sankar <nivedita@...m.mit.edu>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/2] x86/purgatory: Make sure we fail the build if
 purgatory.ro has missing symbols

Hi,

On 3/12/20 1:10 AM, Arvind Sankar wrote:
> On Wed, Mar 11, 2020 at 10:46:01PM +0100, Hans de Goede wrote:
>> Since we link purgatory.ro with -r aka we enable "incremental linking"
>> no checks for unresolved symbols is done while linking purgatory.ro.
>>
> 
> Do we actually need to link purgatory with -r? We could use
> --emit-relocs to get the relocation sections generated the way the main
> x86 kernel does, no?
> 
> Eg like the below? This would avoid the double-link creating
> purgatory.chk.

So I've changed the patch for this in my local tree over to the version
suggested below and tested kexec with this (and I can confirm that it
still works)

I'm wondering though if it would not be better to keep the purgatory.ro name ?  :

1. The generated ELF binary should still be relocatable
2. .ro files are part of the global .gitignore settings, for the
    new purgatory name we need to add an arch/x86/purgatory/.gitignore file
3. Keeping the purgatory.ro name will make the diff easier to read

Regards,

Hans


> 
> diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
> index fb4ee5444379..5332f95ca1d3 100644
> --- a/arch/x86/purgatory/Makefile
> +++ b/arch/x86/purgatory/Makefile
> @@ -14,8 +14,8 @@ $(obj)/sha256.o: $(srctree)/lib/crypto/sha256.c FORCE
>   
>   CFLAGS_sha256.o := -D__DISABLE_EXPORTS
>   
> -LDFLAGS_purgatory.ro := -e purgatory_start -r --no-undefined -nostdlib -z nodefaultlib
> -targets += purgatory.ro
> +LDFLAGS_purgatory := -e purgatory_start --emit-relocs -nostdlib -z nodefaultlib
> +targets += purgatory
>   
>   KASAN_SANITIZE	:= n
>   KCOV_INSTRUMENT := n
> @@ -55,7 +55,7 @@ CFLAGS_sha256.o			+= $(PURGATORY_CFLAGS)
>   CFLAGS_REMOVE_string.o		+= $(PURGATORY_CFLAGS_REMOVE)
>   CFLAGS_string.o			+= $(PURGATORY_CFLAGS)
>   
> -$(obj)/purgatory.ro: $(PURGATORY_OBJS) FORCE
> +$(obj)/purgatory: $(PURGATORY_OBJS) FORCE
>   		$(call if_changed,ld)
>   
>   targets += kexec-purgatory.c
> @@ -63,7 +63,7 @@ targets += kexec-purgatory.c
>   quiet_cmd_bin2c = BIN2C   $@
>         cmd_bin2c = $(objtree)/scripts/bin2c kexec_purgatory < $< > $@
>   
> -$(obj)/kexec-purgatory.c: $(obj)/purgatory.ro FORCE
> +$(obj)/kexec-purgatory.c: $(obj)/purgatory FORCE
>   	$(call if_changed,bin2c)
>   
>   obj-$(CONFIG_KEXEC_FILE)	+= kexec-purgatory.o
>