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Filename Latest commit message Latest commit date
Fangrui Song f04d1e880f bpf: Support llvm-objcopy for vmlinux BTF
commit 90ceddcb495008ac8ba7a3dce297841efcd7d584 upstream.

Simplify gen_btf logic to make it work with llvm-objcopy. The existing
'file format' and 'architecture' parsing logic is brittle and does not
work with llvm-objcopy/llvm-objdump.

'file format' output of llvm-objdump>=11 will match GNU objdump, but
'architecture' (bfdarch) may not.

.BTF in .tmp_vmlinux.btf is non-SHF_ALLOC. Add the SHF_ALLOC flag
because it is part of vmlinux image used for introspection. C code
can reference the section via linker script defined __start_BTF and
__stop_BTF. This fixes a small problem that previous .BTF had the
SHF_WRITE flag (objcopy -I binary -O elf* synthesized .data).

Additionally, `objcopy -I binary` synthesized symbols
_binary__btf_vmlinux_bin_start and _binary__btf_vmlinux_bin_stop (not
used elsewhere) are replaced with more commonplace __start_BTF and
__stop_BTF.

Add 2>/dev/null because GNU objcopy (but not llvm-objcopy) warns
"empty loadable segment detected at vaddr=0xffffffff81000000, is this intentional?"

We use a dd command to change the e_type field in the ELF header from
ET_EXEC to ET_REL so that lld will accept .btf.vmlinux.bin.o.  Accepting
ET_EXEC as an input file is an extremely rare GNU ld feature that lld
does not intend to support, because this is error-prone.

The output section description .BTF in include/asm-generic/vmlinux.lds.h
avoids potential subtle orphan section placement issues and suppresses
--orphan-handling=warn warnings.

Fixes: df786c9b9476 ("bpf: Force .BTF section start to zero when dumping from vmlinux")
Fixes: cb0cc635c7a9 ("powerpc: Include .BTF section")
Reported-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Fangrui Song <maskray@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Tested-by: Stanislav Fomichev <sdf@google.com>
Tested-by: Andrii Nakryiko <andriin@fb.com>
Reviewed-by: Stanislav Fomichev <sdf@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
Link: https://github.com/ClangBuiltLinux/linux/issues/871
Link: https://lore.kernel.org/bpf/20200318222746.173648-1-maskray@google.com
Signed-off-by: Maria Teguiani <teguiani@google.com>
Tested-by: Matthias Maennich <maennich@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-06-17 16:40:20 +02:00
arch bpf: Support llvm-objcopy for vmlinux BTF 2020-06-17 16:40:20 +02:00
block
certs
crypto
Documentation x86/speculation: Add Ivy Bridge to affected list 2020-06-10 20:24:58 +02:00
drivers vxlan: Avoid infinite loop when suppressing NS messages with invalid options 2020-06-17 16:40:20 +02:00
fs
include bpf: Support llvm-objcopy for vmlinux BTF 2020-06-17 16:40:20 +02:00
init
ipc
kernel bpf: Support llvm-objcopy for vmlinux BTF 2020-06-17 16:40:20 +02:00
lib
LICENSES
mm
net bridge: Avoid infinite loop when suppressing NS messages with invalid options 2020-06-17 16:40:20 +02:00
samples
scripts bpf: Support llvm-objcopy for vmlinux BTF 2020-06-17 16:40:20 +02:00
security
sound
tools
usr
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Makefile Linux 5.4.46 2020-06-10 20:24:58 +02:00
README

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.