corefiles/2273: Invalid relocation if executable is marked as ET_DYN

Bernhard Walle bwalle@suse.de
Mon Jun 18 13:28:00 GMT 2007


The following reply was made to PR corefiles/2273; it has been noted by GNATS.

From: Bernhard Walle <bwalle@suse.de>
To: gdb-gnats@sources.redhat.com
Cc:  
Subject: Re: corefiles/2273: Invalid relocation if executable is marked as ET_DYN
Date: Mon, 18 Jun 2007 15:21:26 +0200

 As I don't know how to send multiple attachments, here's the kernel
 patch inline:
 
 -----
 From ebiederm@xmission.com  Wed May 30 23:15:10 2007
 Date: Mon, 30 Apr 2007 09:12:39 -0600
 From: "Eric W. Biederman" <ebiederm@xmission.com>
 To: Andi Kleen <ak@suse.de>, Andrew Morton <akpm@linux-foundation.org>
 Cc: Helge Hafting <helgehaf@aitel.hist.no>, Horms <horms@verge.net.au>,
 	Kexec Mailing List <kexec@lists.infradead.org>,
 	Jurriaan <thunder7@xs4all.nl>, linux-kernel@vger.kernel.org
 Subject: [PATCH 1/2] x86_64: Reflect the relocatability of the kernel in the
 	ELF header.
 
 
 Currently because vmlinux does not reflect that the kernel is relocatable
 we still have to support CONFIG_PHYSICAL_START.  So this patch adds a small
 c program to do what we cannot do with a linker script set the elf header
 type to ET_DYN.
 
 Since last time I have fixed the type to be in my code ET_DYN (oops),
 and verified this works with kexec.  I realized while testing that we
 don't have anyway of identifying a kernel vmlinux as linux so we
 probably want to add an ELF note but that will be another patch.
 
 Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
 ---
  arch/x86_64/Kconfig  |    4 +++
  arch/x86_64/Makefile |   10 +++++++
  scripts/Makefile     |   11 ++++---
  scripts/mketrel.c    |   70 ++++++++++++++++++++++++++++++++++++++++++++++++++
  4 files changed, 90 insertions(+), 5 deletions(-)
  create mode 100644 scripts/mketrel.c
 
 diff --git a/arch/x86_64/Kconfig b/arch/x86_64/Kconfig
 index b00adb9..95949c3 100644
 --- a/arch/x86_64/Kconfig
 +++ b/arch/x86_64/Kconfig
 @@ -121,6 +121,10 @@ config ARCH_HAS_ILOG2_U64
  	bool
  	default n
  
 +config ELF_RELOCATABLE
 +	bool
 +	default y
 +
  source "init/Kconfig"
  
  
 diff --git a/arch/x86_64/Makefile b/arch/x86_64/Makefile
 index a81a84a..7c0434c 100644
 --- a/arch/x86_64/Makefile
 +++ b/arch/x86_64/Makefile
 @@ -125,6 +125,16 @@ define archhelp
    echo  '  isoimage     - Create a boot CD-ROM image'
  endef
  
 +ifeq ($(CONFIG_RELOCATABLE),y)
 +define cmd_vmlinux__
 +      $(LD) $(LDFLAGS) $(LDFLAGS_vmlinux) -o $@ \
 +      -T $(vmlinux-lds) $(vmlinux-init)		\
 +      --start-group $(vmlinux-main) --end-group	\
 +      $(filter-out $(vmlinux-lds) $(vmlinux-init) $(vmlinux-main) FORCE ,$^) \
 +      && scripts/mketrel $@
 +endef
 +endif
 +
  CLEAN_FILES += arch/$(ARCH)/boot/fdimage \
  	       arch/$(ARCH)/boot/image.iso \
  	       arch/$(ARCH)/boot/mtools.conf
 diff --git a/scripts/Makefile b/scripts/Makefile
 index 1c73c5a..ddba550 100644
 --- a/scripts/Makefile
 +++ b/scripts/Makefile
 @@ -7,11 +7,12 @@
  # conmakehash:   Create chartable
  # conmakehash:	 Create arrays for initializing the kernel console tables
  
 -hostprogs-$(CONFIG_KALLSYMS)     += kallsyms
 -hostprogs-$(CONFIG_LOGO)         += pnmtologo
 -hostprogs-$(CONFIG_VT)           += conmakehash
 -hostprogs-$(CONFIG_PROM_CONSOLE) += conmakehash
 -hostprogs-$(CONFIG_IKCONFIG)     += bin2c
 +hostprogs-$(CONFIG_KALLSYMS)        += kallsyms
 +hostprogs-$(CONFIG_LOGO)            += pnmtologo
 +hostprogs-$(CONFIG_VT)              += conmakehash
 +hostprogs-$(CONFIG_PROM_CONSOLE)    += conmakehash
 +hostprogs-$(CONFIG_IKCONFIG)        += bin2c
 +hostprogs-$(CONFIG_ELF_RELOCATABLE) += mketrel
  
  always		:= $(hostprogs-y) $(hostprogs-m)
  
 diff --git a/scripts/mketrel.c b/scripts/mketrel.c
 new file mode 100644
 index 0000000..aa0408a
 --- /dev/null
 +++ b/scripts/mketrel.c
 @@ -0,0 +1,70 @@
 +#include <sys/types.h>
 +#include <sys/stat.h>
 +#include <fcntl.h>
 +#include <unistd.h>
 +#include <elf.h>
 +#include <stdio.h>
 +#include <errno.h>
 +#include <string.h>
 +#include <stdarg.h>
 +#include <stdlib.h>
 +
 +static int fd;
 +unsigned char e_ident[EI_NIDENT];
 +
 +void die(const char * str, ...)
 +{
 +	va_list args;
 +	va_start(args, str);
 +	vfprintf(stderr, str, args);
 +	fputc('\n', stderr);
 +	exit(1);
 +}
 +
 +void file_open(const char *name)
 +{
 +	if ((fd = open(name, O_RDWR, 0)) < 0)
 +		die("Unable to open `%s': %m", name);
 +}
 +
 +static void mketrel(void)
 +{
 +	unsigned char e_type[2];
 +	if (read(fd, &e_ident, sizeof(e_ident)) != sizeof(e_ident))
 +		die("Cannot read ELF header: %s\n", strerror(errno));
 +
 +	if (memcmp(e_ident, ELFMAG, 4) != 0)
 +		die("No ELF magic\n");
 +
 +	if ((e_ident[EI_CLASS] != ELFCLASS64) &&
 +	    (e_ident[EI_CLASS] != ELFCLASS32))
 +		die("Unrecognized ELF class: %x\n", e_ident[EI_CLASS]);
 +	
 +	if ((e_ident[EI_DATA] != ELFDATA2LSB) &&
 +	    (e_ident[EI_DATA] != ELFDATA2MSB))
 +		die("Unrecognized ELF data encoding: %x\n", e_ident[EI_DATA]);
 +
 +	if (e_ident[EI_VERSION] != EV_CURRENT)
 +		die("Unknown ELF version: %d\n", e_ident[EI_VERSION]);
 +
 +	if (e_ident[EI_DATA] == ELFDATA2LSB) {
 +		e_type[0] = ET_DYN & 0xff;
 +		e_type[1] = ET_DYN >> 8;
 +	} else {
 +		e_type[1] = ET_DYN & 0xff;
 +		e_type[0] = ET_DYN >> 8;
 +	}
 +
 +	if (write(fd, &e_type, sizeof(e_type)) != sizeof(e_type))
 +		die("Cannot write ELF type: %s\n", strerror(errno));
 +}
 +
 +int main(int argc, char **argv)
 +{
 +	if (argc != 2)
 +		die("Usage: mketrel: vmlinux");
 +	file_open(argv[1]);
 +	mketrel();
 +	close(fd);
 +	return 0;
 +}
 -- 
 1.5.1.1.181.g2de0
 
 
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