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Date:   Mon, 27 Jan 2020 11:35:47 -0800
Message-Id: <20200127193549.187419-1-brendanhiggins@google.com>
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Subject: [RFC v1 0/2] arch: um: turn BTF_TYPEINFO support off
From:   Brendan Higgins <brendanhiggins@google.com>
To:     jdike@addtoit.com, richard@nod.at, anton.ivanov@cambridgegreys.com,
        akpm@linux-foundation.org, changbin.du@intel.com,
        yamada.masahiro@socionext.com, rdunlap@infradead.org,
        keescook@chromium.org, andriy.shevchenko@linux.intel.com
Cc:     linux-um@lists.infradead.org, linux-kernel@vger.kernel.org,
        davidgow@google.com, heidifahim@google.com,
        Brendan Higgins <brendanhiggins@google.com>
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Sender: linux-kernel-owner@vger.kernel.org
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As a part of my quest to get allyesconfig working on UML, I found a new
build error, with CONFIG_DEBUG_INFO_BTF=y:

scripts/link-vmlinux.sh: line 106: 17463 Segmentation fault      LLVM_OBJCOPY=${OBJCOPY} ${PAHOLE} -J ${1}
objcopy: --change-section-vma .BTF=0x0000000000000000 never used
objcopy: --change-section-lma .BTF=0x0000000000000000 never used
objcopy: error: the input file '.btf.vmlinux.bin' is empty
Failed to generate BTF for vmlinux
Try to disable CONFIG_DEBUG_INFO_BTF
make: *** [Makefile:1078: vmlinux] Error 1

The most interesting bit seems to be the:

objcopy: error: the input file '.btf.vmlinux.bin' is empty

Thinking about it, I am not sure if it makes sense for UML to produce
BTF type information, so I proposed a fix here that:

 1. Adds the ability for architectures to turn BTF support off.
 2. Turns BTF support off for UML.

I am also totally fine with just saying that DEBUG_INFO_BTF
depends on !UML, but I figured people would prefer this approach more.

Brendan Higgins (2):
  kbuild: add arch specific dependency for BTF support
  arch: um: turn BTF_TYPEINFO support off

 arch/um/Kconfig   | 1 +
 lib/Kconfig.debug | 5 ++++-
 2 files changed, 5 insertions(+), 1 deletion(-)

-- 
2.25.0.341.g760bfbb309-goog