linux-kernel - Re: [PATCH v12 1/5] x86/boot: Add get_acpi_rsdp() to parse RSDP in cmdline from KEXEC

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Date:   Fri, 7 Dec 2018 10:10:55 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Masayoshi Mizuma <msys.mizuma@...il.com>,
        Chao Fan <fanc.fnst@...fujitsu.com>, bp@...en8.de,
        mingo@...hat.com
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org, tglx@...utronix.de,
        hpa@...or.com, keescook@...omium.org, indou.takao@...fujitsu.com,
        caoj.fnst@...fujitsu.com
Subject: Re: [PATCH v12 1/5] x86/boot: Add get_acpi_rsdp() to parse RSDP in
 cmdline from KEXEC

Hi,

On 11/29/18 at 04:10pm, Masayoshi Mizuma wrote:
> > diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
> > index 8dd1d5ccae58..e51713fe3add 100644
> > --- a/arch/x86/boot/compressed/misc.c
> > +++ b/arch/x86/boot/compressed/misc.c
> > @@ -12,6 +12,7 @@
> >   * High loaded stuff by Hans Lermen & Werner Almesberger, Feb. 1996
> >   */
> >  
> > +#define BOOT_CTYPE_H
> >  #include "misc.h"
> >  #include "error.h"
> >  #include "pgtable.h"
> > @@ -426,3 +427,7 @@ void fortify_panic(const char *name)
> >  {
> >  	error("detected buffer overflow");
> >  }
> > +
> > +#ifdef BOOT_STRING
> > +#include "../../../../lib/kstrtox.c"
> > +#endif
> > diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
> > index a1d5918765f3..809c31effa4b 100644
> > --- a/arch/x86/boot/compressed/misc.h
> > +++ b/arch/x86/boot/compressed/misc.h
> > @@ -116,3 +116,7 @@ static inline void console_init(void)
> >  void set_sev_encryption_mask(void);
> >  
> >  #endif
> > +
> > +/* acpitb.c */
> > +#define BOOT_STRING
> > +extern int kstrtoull(const char *s, unsigned int base, unsigned long long *res);
> > diff --git a/lib/kstrtox.c b/lib/kstrtox.c
> > index 1006bf70bf74..a0ac1b2257b8 100644
> > --- a/lib/kstrtox.c
> > +++ b/lib/kstrtox.c
> > @@ -126,6 +126,9 @@ int kstrtoull(const char *s, unsigned int base, unsigned long long *res)
> >  }
> >  EXPORT_SYMBOL(kstrtoull);
> >  
> > +/* Make compressed period code be able to use kstrtoull(). */
> > +#ifndef BOOT_STRING
> 
> I got the following build error.
> 
> ]$ make arch/x86/boot/compressed/misc.o
>   CALL    scripts/checksyscalls.sh
>   DESCEND  objtool
>   CC      arch/x86/boot/compressed/misc.o
> ld: -r and -pie may not be used together
> make[1]: *** [scripts/Makefile.build:294: arch/x86/boot/compressed/misc.o] Error 1
> make: *** [Makefile:1715: arch/x86/boot/compressed/misc.o] Error 2

I have met this issue when change code in boot/compressed/kaslr.c.

I remember Ingo merged my patch and found this build error. Since if 
CONFIG_MODULES=n EXPORT_SYMBOL is defined as empty in
include/linux/export.h, that's why you can only meet it only if
CONFIG_MODULES=y.

I remember I just muted it with below code, please check commit
d52e7d5a95.

+#define _LINUX_EXPORT_H
+#define EXPORT_SYMBOL(sym)

commit d52e7d5a952c5e35783f96e8c5b7fcffbb0d7c60
Author: Baoquan He <bhe@...hat.com>
Date:   Sat May 13 13:46:28 2017 +0800

    x86/KASLR: Parse all 'memmap=' boot option entries

Later in commit f922c4abdf76, Ard added a new switch __DISABLE_EXPORTS.
So you can just add #define __DISABLE_EXPORTS into misc.c. Then you
don't need to copy those lib functions to boot. Maintaining two copies
might have trouble if it has updates later.

commit f922c4abdf7648523589abee9460c87f51630d2f
Author: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Date:   Tue Aug 21 21:56:04 2018 -0700

    module: allow symbol exports to be disabled

Thanks
Baoquan

> ]$
> 
> I think this error gets fixed by changing the BOOT_STRING ifndef
> order before the EXPORT_SYMBOL, like this:
> 
> #ifndef BOOT_STRING
> EXPORT_SYMBOL(kstrtoull);
> 
> I'm not sure this change is a good way...
> 
> Thanks,
> Masa