Merge tag 'core-build-2020-10-12' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull orphan section checking from Ingo Molnar:
 "Orphan link sections were a long-standing source of obscure bugs,
  because the heuristics that various linkers & compilers use to handle
  them (include these bits into the output image vs discarding them
  silently) are both highly idiosyncratic and also version dependent.

  Instead of this historically problematic mess, this tree by Kees Cook
  (et al) adds build time asserts and build time warnings if there's any
  orphan section in the kernel or if a section is not sized as expected.

  And because we relied on so many silent assumptions in this area, fix
  a metric ton of dependencies and some outright bugs related to this,
  before we can finally enable the checks on the x86, ARM and ARM64
  platforms"

* tag 'core-build-2020-10-12' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (36 commits)
  x86/boot/compressed: Warn on orphan section placement
  x86/build: Warn on orphan section placement
  arm/boot: Warn on orphan section placement
  arm/build: Warn on orphan section placement
  arm64/build: Warn on orphan section placement
  x86/boot/compressed: Add missing debugging sections to output
  x86/boot/compressed: Remove, discard, or assert for unwanted sections
  x86/boot/compressed: Reorganize zero-size section asserts
  x86/build: Add asserts for unwanted sections
  x86/build: Enforce an empty .got.plt section
  x86/asm: Avoid generating unused kprobe sections
  arm/boot: Handle all sections explicitly
  arm/build: Assert for unwanted sections
  arm/build: Add missing sections
  arm/build: Explicitly keep .ARM.attributes sections
  arm/build: Refactor linker script headers
  arm64/build: Assert for unwanted sections
  arm64/build: Add missing DWARF sections
  arm64/build: Use common DISCARDS in linker script
  arm64/build: Remove .eh_frame* sections due to unwind tables
  ...

1 files changed, 19 insertions, 0 deletions

diff --git a/include/linux/hidden.h b/include/linux/hidden.h
new file mode 100644
index 000000000000..49a17b6b5962
--- /dev/null
+++ b/include/linux/hidden.h
@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * When building position independent code with GCC using the -fPIC option,
+ * (or even the -fPIE one on older versions), it will assume that we are
+ * building a dynamic object (either a shared library or an executable) that
+ * may have symbol references that can only be resolved at load time. For a
+ * variety of reasons (ELF symbol preemption, the CoW footprint of the section
+ * that is modified by the loader), this results in all references to symbols
+ * with external linkage to go via entries in the Global Offset Table (GOT),
+ * which carries absolute addresses which need to be fixed up when the
+ * executable image is loaded at an offset which is different from its link
+ * time offset.
+ *
+ * Fortunately, there is a way to inform the compiler that such symbol
+ * references will be satisfied at link time rather than at load time, by
+ * giving them 'hidden' visibility.
+ */
+
+#pragma GCC visibility push(hidden)