02 Feb, 2010

1 commit


17 Dec, 2009

1 commit

  • MIPS and some other architectures need this argument to handle
    big/little endian respectively.

    Signed-off-by: Wu Zhangjin
    Cc: Nicholas Mc Guire
    Cc: zhangfx@lemote.com
    Cc: Wu Zhangjin
    Cc: Ingo Molnar
    Cc: Thomas Gleixner
    Cc: Frederic Weisbecker
    Cc: linux-kernel@vger.kernel.org
    Cc: linux-mips@linux-mips.org
    Patchwork: http://patchwork.linux-mips.org/patch/674/
    Acked-by: Steven Rostedt
    Signed-off-by: Ralf Baechle

    Wu Zhangjin
     

21 Sep, 2009

1 commit

  • Adding a reference to to x86's causes
    the x86 linker script to have syntax errors, because the ALIGN and
    ENTRY keywords get redefined to the assembly implementations of those.
    One could fix this by adjusting the include structure, but I think any
    solution based on that approach would be fragile.

    Currently, it is impossible when writing a header to do something
    different for assembly files and linker scripts, even though there are
    clearly cases where one wants them to define macros differently for
    the two (ENTRY being an excellent example).
    So I think the right solution here is to introduce a new preprocessor
    definition, called LINKER_SCRIPT that is set along with __ASSEMBLY__
    for linker scripts, and to use that to not define ALIGN and ENTRY in
    linker scripts.
    I suspect we'll find other uses for this mechanism in
    the future.

    Signed-off-by: Tim Abbott
    Signed-off-by: Sam Ravnborg

    Tim Abbott
     

20 Sep, 2009

3 commits

  • Albin Tonnerre reported:

    Bash 4 filters out variables which contain a dot in them.
    This happends to be the case of CPPFLAGS_vmlinux.lds.
    This is rather unfortunate, as it now causes
    build failures when using SHELL=/bin/bash to compile,
    or when bash happens to be used by make (eg when it's /bin/sh)

    Remove the common definition of CPPFLAGS_vmlinux.lds by
    pushing relevant stuff to either Makefile.build or the
    arch specific kernel/Makefile where we build the linker script.

    This is also nice cleanup as we move the information out where
    it is used.

    Notes for the different architectures touched:

    arm - we use an already exported symbol
    cris - we use a config symbol aleady available
    [Not build tested]
    mips - the jiffies complexity has moved to vmlinux.lds.S where we need it.
    Added a few variables to CPPFLAGS - they are only used by
    the linker script.
    [Not build tested]
    powerpc - removed assignment that is not needed
    [not build tested]
    sparc - simplified it using $(BITS)
    um - introduced a few new exported variables to deal with this
    xtensa - added options to CPP invocation
    [not build tested]

    Cc: Albin Tonnerre
    Cc: Russell King
    Cc: Mikael Starvik
    Cc: Jesper Nilsson
    Cc: Benjamin Herrenschmidt
    Cc: Paul Mackerras
    Cc: "David S. Miller"
    Cc: Jeff Dike
    Cc: Chris Zankel
    Signed-off-by: Sam Ravnborg

    Sam Ravnborg
     
  • When this script fails the build should fail too. Otherwise there
    are mysterious build failures later.

    Signed-off-by: Andi Kleen
    Signed-off-by: Andrew Morton
    Signed-off-by: Sam Ravnborg

    Andi Kleen
     
  • I had some problems with record_mcount in the Makefile and it was hard
    to track down. Echo it by default to make it easier to diagnose.

    Signed-off-by: Andi Kleen
    Signed-off-by: Andrew Morton
    Signed-off-by: Sam Ravnborg

    Andi Kleen
     

19 Apr, 2009

1 commit

  • Following patch introduce support for setting options
    to gcc that has effect for current directory and all
    subdirectories.

    The typical use case are an architecture or a subsystem that
    decide to cover all files with -Werror.
    Today alpha, mips and sparc uses -Werror in almost all their
    Makefile- with subdir-ccflag-y it is now simpler to do so
    as only the top-level directories needs to be covered.

    Likewise if we decide to cover a full subsystem such
    as net/ with -Werror this is done by adding a single
    line to net/Makefile.

    Signed-off-by: Sam Ravnborg
    Cc: Ingo Molnar
    Cc: "H. Peter Anvin"
    Cc: Thomas Gleixner

    Sam Ravnborg
     

03 Feb, 2009

1 commit


15 Jan, 2009

1 commit

  • This reverts commit ad7a953c522ceb496611d127e51e278bfe0ff483.

    And commit: ("allow stripping of generated symbols under CONFIG_KALLSYMS_ALL")
    9bb482476c6c9d1ae033306440c51ceac93ea80c

    These stripping patches has caused a set of issues:

    1) People have reported compatibility issues with binutils due to
    lack of support for `--strip-unneeded-symbols' with objcopy 2.15.92.0.2
    Reported by: Wenji
    2) ccache and distcc no longer works as expeced
    Reported by: Ted, Roland, + others
    3) The installed modules increased a lot in size
    Reported by: Ted, Davej + others

    Reported-by: Wenji Huang
    Reported-by: "Theodore Ts'o"
    Reported-by: Dave Jones
    Reported-by: Roland McGrath
    Signed-off-by: Sam Ravnborg

    Sam Ravnborg
     

14 Jan, 2009

1 commit


29 Dec, 2008

1 commit

  • * git://git.kernel.org/pub/scm/linux/kernel/git/sam/kbuild-next: (25 commits)
    allow stripping of generated symbols under CONFIG_KALLSYMS_ALL
    kbuild: strip generated symbols from *.ko
    kbuild: simplify use of genksyms
    kernel-doc: check for extra kernel-doc notations
    kbuild: add headerdep used to detect inclusion cycles in header files
    kbuild: fix string equality testing in tags.sh
    kbuild: fix make tags/cscope
    kbuild: fix make incompatibility
    kbuild: remove TAR_IGNORE
    setlocalversion: add git-svn support
    setlocalversion: print correct subversion revision
    scripts: improve the decodecode script
    scripts/package: allow custom options to rpm
    genksyms: allow to ignore symbol checksum changes
    genksyms: track symbol checksum changes
    tags and cscope support really belongs in a shell script
    kconfig: fix options to check-lxdialog.sh
    kbuild: gen_init_cpio expands shell variables in file names
    remove bashisms from scripts/extract-ikconfig
    kbuild: teach mkmakfile to be silent
    ...

    Linus Torvalds
     

20 Dec, 2008

2 commits

  • This patch changes the way __crc_ symbols are being resolved from
    using ld to do so to using the assembler, thus allowing these symbols
    to be marked local (the linker creates then as global ones) and hence
    allow stripping (for modules) or ignoring (for vmlinux) them. While at
    this, also strip other generated symbols during module installation.

    One potentially debatable point is the handling of the flags passeed
    to gcc when translating the intermediate assembly file into an object:
    passing $(c_flags) unchanged doesn't work as gcc passes --gdwarf2 to
    gas whenever is sees any -g* option, even for -g0, and despite the
    fact that the compiler would have already produced all necessary debug
    info in the C->assembly translation phase. I took the approach of just
    filtering out all -g* options, but an alternative to such negative
    filtering might be to have a positive filter which might, in the ideal
    case allow just all the -Wa,* options to pass through.

    Signed-off-by: Jan Beulich
    Signed-off-by: Sam Ravnborg

    Jan Beulich
     
  • Avoid duplicating long list of options in two places

    Signed-off-by: Sam Ravnborg

    Sam Ravnborg
     

04 Dec, 2008

1 commit

  • Sometimes it is preferable to avoid changes of exported symbol checksums
    (to avoid breaking externally provided modules). When a checksum change
    occurs, it can be hard to figure out what caused this change: underlying
    types may have changed, or additional type information may simply have
    become available at the point where a symbol is exported.

    Add a new --reference option to genksyms which allows it to report why
    checksums change, based on the type information dumps it creates with the
    --dump-types flag. Genksyms will read in such a dump from a previous run,
    and report which symbols have changed (and why).

    The behavior can be controlled for an entire build as follows: If
    KBUILD_SYMTYPES is set, genksyms uses --dump-types to produce *.symtypes
    dump files. If any *.symref files exist, those will be used as the
    reference to check against. If KBUILD_PRESERVE is set, checksum changes
    will fail the build.

    Signed-off-by: Andreas Gruenbacher
    Cc: Randy Dunlap
    Signed-off-by: Andrew Morton
    Signed-off-by: Sam Ravnborg

    Andreas Gruenbacher
     

31 Oct, 2008

1 commit


23 Oct, 2008

1 commit

  • The recordmcount script requires that the actual arch is passed in.
    This works well when ARCH=i386 or ARCH=x86_64 but does not handle the
    case of ARCH=x86.

    This patch adds a parameter to the function to pass in the number of
    bits of the architecture. So that it can determine if x86 should be
    run for x86_64 or i386 archs.

    Signed-off-by: Steven Rostedt
    Signed-off-by: Ingo Molnar

    Steven Rostedt
     

14 Oct, 2008

3 commits

  • CHK include/linux/version.h
    CHK include/linux/utsrelease.h
    CC scripts/mod/empty.o
    /bin/sh: /usr/src/25/scripts/recordmcount.pl: Permission denied

    We shouldn't assume that files have their `x' bits set. There are various
    ways in which file permissions get lost, including use of patch(1).

    It might not be correct to assume that perl lives in $PATH?

    Signed-off-by: Andrew Morton
    Signed-off-by: Ingo Molnar

    Andrew Morton
     
  • I'm seeing when I use separate src/build dirs:

    make[3]: *** [arch/x86/kernel/time_32.o] Error 1
    /bin/sh: scripts/recordmcount.pl: No such file or directory
    make[3]: *** [arch/x86/kernel/irq_32.o] Error 1
    /bin/sh: scripts/recordmcount.pl: No such file or directory
    make[3]: *** [arch/x86/kernel/ldt.o] Error 1
    /bin/sh: scripts/recordmcount.pl: No such file or directory
    make[3]: *** [arch/x86/kernel/i8259.o] Error 1
    /bin/sh: scripts/recordmcount.pl: No such file or directory

    This fixes it.

    Signed-off-by: Ingo Molnar

    Jeremy Fitzhardinge
     
  • This patch creates a section in the kernel called "__mcount_loc".
    This will hold a list of pointers to the mcount relocation for
    each call site of mcount.

    For example:

    objdump -dr init/main.o
    [...]
    Disassembly of section .text:

    0000000000000000 :
    0: 55 push %rbp
    [...]
    000000000000017b :
    17b: 55 push %rbp
    17c: 48 89 e5 mov %rsp,%rbp
    17f: 53 push %rbx
    180: 48 83 ec 08 sub $0x8,%rsp
    184: e8 00 00 00 00 callq 189
    185: R_X86_64_PC32 mcount+0xfffffffffffffffc
    [...]

    We will add a section to point to each function call.

    .section __mcount_loc,"a",@progbits
    [...]
    .quad .text + 0x185
    [...]

    The offset to of the mcount call site in init_post is an offset from
    the start of the section, and not the start of the function init_post.
    The mcount relocation is at the call site 0x185 from the start of the
    .text section.

    .text + 0x185 == init_post + 0xa

    We need a way to add this __mcount_loc section in a way that we do not
    lose the relocations after final link. The .text section here will
    be attached to all other .text sections after final link and the
    offsets will be meaningless. We need to keep track of where these
    .text sections are.

    To do this, we use the start of the first function in the section.
    do_one_initcall. We can make a tmp.s file with this function as a reference
    to the start of the .text section.

    .section __mcount_loc,"a",@progbits
    [...]
    .quad do_one_initcall + 0x185
    [...]

    Then we can compile the tmp.s into a tmp.o

    gcc -c tmp.s -o tmp.o

    And link it into back into main.o.

    ld -r main.o tmp.o -o tmp_main.o
    mv tmp_main.o main.o

    But we have a problem. What happens if the first function in a section
    is not exported, and is a static function. The linker will not let
    the tmp.o use it. This case exists in main.o as well.

    Disassembly of section .init.text:

    0000000000000000 :
    0: 55 push %rbp
    1: 48 89 e5 mov %rsp,%rbp
    4: e8 00 00 00 00 callq 9
    5: R_X86_64_PC32 mcount+0xfffffffffffffffc

    The first function in .init.text is a static function.

    00000000000000a8 t __setup_set_reset_devices
    000000000000105f t __setup_str_set_reset_devices
    0000000000000000 t set_reset_devices

    The lowercase 't' means that set_reset_devices is local and is not exported.
    If we simply try to link the tmp.o with the set_reset_devices we end
    up with two symbols: one local and one global.

    .section __mcount_loc,"a",@progbits
    .quad set_reset_devices + 0x10

    00000000000000a8 t __setup_set_reset_devices
    000000000000105f t __setup_str_set_reset_devices
    0000000000000000 t set_reset_devices
    U set_reset_devices

    We still have an undefined reference to set_reset_devices, and if we try
    to compile the kernel, we will end up with an undefined reference to
    set_reset_devices, or even worst, it could be exported someplace else,
    and then we will have a reference to the wrong location.

    To handle this case, we make an intermediate step using objcopy.
    We convert set_reset_devices into a global exported symbol before linking
    it with tmp.o and set it back afterwards.

    00000000000000a8 t __setup_set_reset_devices
    000000000000105f t __setup_str_set_reset_devices
    0000000000000000 T set_reset_devices

    00000000000000a8 t __setup_set_reset_devices
    000000000000105f t __setup_str_set_reset_devices
    0000000000000000 T set_reset_devices

    00000000000000a8 t __setup_set_reset_devices
    000000000000105f t __setup_str_set_reset_devices
    0000000000000000 t set_reset_devices

    Now we have a section in main.o called __mcount_loc that we can place
    somewhere in the kernel using vmlinux.ld.S and access it to convert
    all these locations that call mcount into nops before starting SMP
    and thus, eliminating the need to do this with kstop_machine.

    Note, A well documented perl script (scripts/recordmcount.pl) is used
    to do all this in one location.

    Signed-off-by: Steven Rostedt
    Signed-off-by: Ingo Molnar

    Steven Rostedt
     

26 Apr, 2008

1 commit


29 Jan, 2008

2 commits

  • Setting the option DEBUG_SECTION_MISMATCH will
    report additional section mismatch'es but this
    should in the end makes it possible to get rid of
    all of them.

    See help text in lib/Kconfig.debug for details.

    Signed-off-by: Sam Ravnborg

    Sam Ravnborg
     
  • When multiple built-in modules (especially drivers) provide the same
    capability, they're prioritized by link order specified by the order
    listed in Makefile. This implicit ordering is lost for loadable
    modules.

    When driver modules are loaded by udev, what comes first in
    modules.alias file is selected. However, the order in this file is
    indeterministic (depends on filesystem listing order of installed
    modules). This causes confusion.

    The solution is two-parted. This patch updates kbuild such that it
    generates and installs modules.order which contains the name of
    modules ordered according to Makefile. The second part is update to
    depmod such that it generates output files according to this file.

    Note that both obj-y and obj-m subdirs can contain modules and
    ordering information between those two are lost from beginning.
    Currently obj-y subdirs are put before obj-m subdirs.

    Sam Ravnborg cleaned up Makefile modifications and suggested using awk
    to remove duplicate lines from modules.order instead of using separate
    C program.

    Signed-off-by: Tejun Heo
    Acked-by: Greg Kroah-Hartman
    Cc: Bill Nottingham
    Cc: Rusty Russell
    Cc: Kay Sievers
    Cc: Jon Masters
    Signed-off-by: Sam Ravnborg

    Tejun Heo
     

16 Oct, 2007

1 commit

  • Introduce ccflags-y, asflags-y and ldflags-y so we soon can
    deprecate use of EXTRA_CFLAGS, EXTRA_AFLAGS and EXTRA_LDFLAGS.
    This patch does not touch any in-tree users - thats next round.
    Lets get this committed first and then fix the users of the
    soon to be deprecated variants next.

    The rationale behind this change is to introduce support for
    makefile fragments like:

    ccflags-$(CONFIG_WHATEVER_DEBUG) := -DDEBUG

    As a replacement for the uglier:
    ifeq ($(CONFIG_WHATEVER_DEBUG),y)
    EXTRA_CFLAGS := -DDEBUG
    endif

    Signed-off-by: Sam Ravnborg

    Sam Ravnborg
     

15 Oct, 2007

1 commit

  • External modules have in a few cases modifed gcc option
    by modifying CFLAGS. This has never been documented and
    was a bad practice.
    With the check to use KBUILD_CFLAGS it will no longer work
    so we better error out and tell what was wrong as a service
    to the external module users.

    This check can be overruled if
    KBUILD_NOPEDANTIC is set to something.
    Addid this possibility may allow older external
    module to build without any code modifications but potentially
    only loosing some un-important gcc options.

    Signed-off-by: Sam Ravnborg

    Sam Ravnborg
     

13 Oct, 2007

2 commits

  • These checks has been present for several kernel releases (> 5).
    So lets just get rid of them.
    With this we no longer check for use of:
    EXTRA_TARGETS, O_TARGET, L_TARGET, list-multi, export-objs

    There were three remaining in-tree users of O_TARGET in some
    unmaintained sh64 code - mail sent to the maintainer + list.

    Signed-off-by: Sam Ravnborg

    Sam Ravnborg
     
  • EXTRA_ARFLAGS have never been used so no need to carry
    around on this.
    A google search did not reveal any external module
    using this either.

    Signed-off-by: Sam Ravnborg

    Sam Ravnborg
     

26 Jul, 2007

1 commit

  • Sam Ravnborg pointed out that Documentation/kbuild/makefiles.txt already
    says this is what it's for. This patch makes the reality live up to the
    documentation. This fixes the problem of LDFLAGS_BUILD_ID getting into too
    many places.

    Signed-off-by: Roland McGrath
    Signed-off-by: Sam Ravnborg

    Roland McGrath
     

17 Jul, 2007

1 commit


06 May, 2007

1 commit


25 Sep, 2006

1 commit

  • Consistently decide when to rebuild a target across all of
    if_changed, if_changed_dep, if_changed_rule.
    PHONY targets are now treated alike (ignored) for all targets

    While add it make Kbuild.include almost readable by factoring out a few
    bits to some common variables and reuse this in Makefile.build.

    Signed-off-by: Sam Ravnborg

    Sam Ravnborg
     

01 Jul, 2006

1 commit

  • kbuild used $¤(*F to get filename of target without extension.
    This was used in several places all over kbuild, but introducing
    make -rR broke his for all cases where we specified full path to
    target/prerequsite. It is assumed that make -rR disables old style
    suffix-rules which is why is suddenly failed.

    ia64 was impacted by this change because several div* routines in
    arch/ia64/lib are build using explicit paths and then kbuild failed.

    Thanks to David Mosberger-Tang for an explanation
    what was the root-cause and for testing on ia64.

    This patch also fixes two uses of $(*F) in arch/um

    Signed-off-by: Sam Ravnborg

    Sam Ravnborg
     

27 Jun, 2006

1 commit

  • This reverts commit e5c44fd88c146755da6941d047de4d97651404a9.

    Thanks to Daniel Ritz and Michal Piotrowski for noticing the problem.

    Daniel says:

    "[The] reason is a recent change that made modules always shows as
    module.mod. it breaks modprobe and probably many scripts..besides
    lsmod looking horrible

    stuff like this in modprobe.conf:
    install pcmcia_core /sbin/modprobe --ignore-install pcmcia_core; /sbin/modprobe pcmcia
    makes modprobe fork/exec endlessly calling itself...until oom
    interrupts it"

    Signed-off-by: Linus Torvalds

    Linus Torvalds
     

25 Jun, 2006

2 commits

  • Here is a patch that adds a new -T option to genksyms for generating dumps of
    the type definition that makes up the symbol version hashes. This allows to
    trace modversion changes back to what caused them. The dump format is the
    name of the type defined, followed by its definition (which is almost C):

    s#list_head struct list_head { s#list_head * next , * prev ; }

    The s#, u#, e#, and t# prefixes stand for struct, union, enum, and typedef.
    The exported symbols do not define types, and thus do not have an x# prefix:

    nfs4_acl_get_whotype int nfs4_acl_get_whotype ( char * , t#u32 )

    The symbol type defintion of a single file can be generated with:

    make fs/jbd/journal.symtypes

    If KBUILD_SYMTYPES is defined, all the *.symtypes of all object files that
    export symbols are generated.

    The single *.symtypes files can be combined into a single file after a kernel
    build with a script like the following:

    for f in $(find -name '*.symtypes' | sort); do
    f=${f#./}
    echo "/* ${f%.symtypes}.o */"
    cat $f
    echo
    done \
    | sed -e '\:UNKNOWN:d' \
    -e 's:[,;] }:}:g' \
    -e 's:\([[({]\) :\1:g' \
    -e 's: \([])},;]\):\1:g' \
    -e 's: $::' \
    $f \
    | awk '
    /^.#/ { if (defined[$1] == $0) {
    print $1
    next
    }
    defined[$1] = $0
    }
    { print }
    '

    When the kernel ABI changes, diffing individual *.symtype files, or the
    combined files, against each other will show which symbol changes caused the
    ABI changes. This can save a tremendous amount of time.

    Dump the types that make up modversions

    Signed-off-by: Andreas Gruenbacher
    Signed-off-by: Sam Ravnborg

    Andreas Gruenbacher
     
  • make failed to supply the filename when using make -rR and using $(*F)
    to get target filename without extension.
    This bug was not reproduceable in small scale but using:
    $(basename $(notdir $@)) fixes it with same functionality.

    Signed-off-by: Sam Ravnborg

    Sam Ravnborg
     

09 Jun, 2006

1 commit

  • This fixes one of the worst kbuild warts left - the broken dependencies used
    to check and regenerate the .config file. This was done via an indirect
    dependency and the .config itself had an empty command, which can cause make
    not to reread the changed .config file.

    Instead of this we generate now a new file include/config/auto.conf from
    .config, which is used for kbuild and has the proper dependencies. It's also
    the main make target now for all files generated during this step (and thus
    replaces include/linux/autoconf.h).

    This also means we can now relax the syntax requirements for the .config file
    and we don't have to rewrite it all the time, i.e. silentoldconfig only
    writes .config now when it's necessary to keep it in sync with the Kconfig
    files and even this can be suppressed by setting the environment variable
    KCONFIG_NOSILENTUPDATE, so the update can (and must) be done manually.

    Signed-off-by: Roman Zippel
    Signed-off-by: Andrew Morton
    Signed-off-by: Sam Ravnborg

    Roman Zippel
     

13 Mar, 2006

2 commits

  • Add -fverbose-asm to i386 Makefile rule for building .s files. This makes
    the assembler output much more readable for humans.

    Suggested by Der Herr Hofrat

    Signed-off-by: Chuck Ebbert
    Signed-off-by: Andrew Morton
    Signed-off-by: Sam Ravnborg

    Chuck Ebbert
     
  • genksyms needs to know when a symbol must have a "_" prefex as is
    true for a few architectures.
    Pass $(ARCH) as commandline argument and hardcode what architectures that
    needs this info.
    Previous attemt to take it from elfconfig.h was br0ken since elfconfig.h
    is a generated file.

    Signed-off-by: Sam Ravnborg

    Sam Ravnborg
     

06 Mar, 2006

1 commit

  • The kbuild system takes advantage of an incorrect behavior in GNU make.
    Once this behavior is fixed, all files in the kernel rebuild every time,
    even if nothing has changed. This patch ensures kbuild works with both
    the incorrect and correct behaviors of GNU make.

    For more details on the incorrect behavior, see:

    http://lists.gnu.org/archive/html/bug-make/2006-03/msg00003.html

    Changes in this patch:
    - Keep all targets that are to be marked .PHONY in a variable, PHONY.
    - Add .PHONY: $(PHONY) to mark them properly.
    - Remove any $(PHONY) files from the $? list when determining whether
    targets are up-to-date or not.

    Signed-off-by: Paul Smith
    Signed-off-by: Sam Ravnborg

    Paul Smith
     

19 Feb, 2006

2 commits

  • While the recent change to also escape # symbols when storing C-file
    compilation command lines was helpful, it should be in effect for all
    command lines, as much as the dollar escaping should be in effect for
    C-source compilation commands. Additionally, for better readability and
    maintenance, consolidating all the escaping (single quotes, dollars,
    and now sharps) was also desirable.

    Signed-Off-By: Jan Beulich
    Signed-off-by: Sam Ravnborg

    Jan Beulich
     
  • Move $(CC) support functions to Kbuild.include so they are available
    in the kbuild files.
    In addition the following was done:
    o as-option documented in Documentation/kbuild/makefiles.txt
    o Moved documentation to new section to match
    new scope of functions
    o added cc-ifversion used to conditionally select a text string
    dependent on actual $(CC) version
    o documented cc-ifversion
    o change so Kbuild.include is read before the kbuild file

    Signed-off-by: Sam Ravnborg

    Sam Ravnborg