Commit Graph

3 Commits

Author SHA1 Message Date
Nick Desaulniers 27f2a4db76 Makefile: fix GDB warning with CONFIG_RELR
GDB produces the following warning when debugging kernels built with
CONFIG_RELR:

BFD: /android0/linux-next/vmlinux: unknown type [0x13] section `.relr.dyn'

when loading a kernel built with CONFIG_RELR into GDB. It can also
prevent debugging symbols using such relocations.

Peter sugguests:
  [That flag] means that lld will use dynamic tags and section type
  numbers in the OS-specific range rather than the generic range. The
  kernel itself doesn't care about these numbers; it determines the
  location of the RELR section using symbols defined by a linker script.

Link: https://github.com/ClangBuiltLinux/linux/issues/1057
Suggested-by: Peter Collingbourne <pcc@google.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Link: https://lore.kernel.org/r/20210522012626.2811297-1-ndesaulniers@google.com
Signed-off-by: Will Deacon <will@kernel.org>
2021-06-08 13:09:34 +01:00
Ilie Halip 65e1f38d9a scripts/tools-support-relr.sh: un-quote variables
When the CC variable contains quotes, e.g. when using
ccache (make CC="ccache <compiler>"), this script always
fails, so CONFIG_RELR is never enabled, even when the
toolchain supports this feature. Removing the /dev/null
redirect and invoking the script manually shows the issue:

    $ CC='/usr/bin/ccache clang' ./scripts/tools-support-relr.sh
    ./scripts/tools-support-relr.sh: 7: ./scripts/tools-support-relr.sh: /usr/bin/ccache clang: not found

Fix this by un-quoting the variables.

Before:
    $ make ARCH=arm64 CC='/usr/bin/ccache clang' LD=ld.lld \
        NM=llvm-nm OBJCOPY=llvm-objcopy defconfig
    $ grep RELR .config
    CONFIG_ARCH_HAS_RELR=y

With this change:
    $ make ARCH=arm64 CC='/usr/bin/ccache clang' LD=ld.lld \
        NM=llvm-nm OBJCOPY=llvm-objcopy defconfig
    $ grep RELR .config
    CONFIG_TOOLS_SUPPORT_RELR=y
    CONFIG_ARCH_HAS_RELR=y
    CONFIG_RELR=y

Fixes: 5cf896fb6b ("arm64: Add support for relocating the kernel with RELR relocations")
Reported-by: Dmitry Golovin <dima@golovin.in>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Reviewed-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Link: https://github.com/ClangBuiltLinux/linux/issues/769
Cc: Peter Collingbourne <pcc@google.com>
Signed-off-by: Ilie Halip <ilie.halip@gmail.com>
Signed-off-by: Will Deacon <will@kernel.org>
2019-11-13 10:52:05 +00:00
Peter Collingbourne 5cf896fb6b arm64: Add support for relocating the kernel with RELR relocations
RELR is a relocation packing format for relative relocations.
The format is described in a generic-abi proposal:
https://groups.google.com/d/topic/generic-abi/bX460iggiKg/discussion

The LLD linker can be instructed to pack relocations in the RELR
format by passing the flag --pack-dyn-relocs=relr.

This patch adds a new config option, CONFIG_RELR. Enabling this option
instructs the linker to pack vmlinux's relative relocations in the RELR
format, and causes the kernel to apply the relocations at startup along
with the RELA relocations. RELA relocations still need to be applied
because the linker will emit RELA relative relocations if they are
unrepresentable in the RELR format (i.e. address not a multiple of 2).

Enabling CONFIG_RELR reduces the size of a defconfig kernel image
with CONFIG_RANDOMIZE_BASE by 3.5MB/16% uncompressed, or 550KB/5%
compressed (lz4).

Signed-off-by: Peter Collingbourne <pcc@google.com>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
2019-08-05 12:35:35 +01:00