On Tue, Nov 17, 2020 at 10:03:29PM +1100, Michael Ellerman wrote:

Nathan Chancellor [off-list ref] writes:

quoted

Currently, '--orphan-handling=warn' is spread out across four different
architectures in their respective Makefiles, which makes it a little
unruly to deal with in case it needs to be disabled for a specific
linker version (in this case, ld.lld 10.0.1).

To make it easier to control this, hoist this warning into Kconfig and
the main Makefile so that disabling it is simpler, as the warning will
only be enabled in a couple places (main Makefile and a couple of
compressed boot folders that blow away LDFLAGS_vmlinx) and making it
conditional is easier due to Kconfig syntax. One small additional
benefit of this is saving a call to ld-option on incremental builds
because we will have already evaluated it for CONFIG_LD_ORPHAN_WARN.

To keep the list of supported architectures the same, introduce
CONFIG_ARCH_WANT_LD_ORPHAN_WARN, which an architecture can select to
gain this automatically after all of the sections are specified and size
asserted. A special thanks to Kees Cook for the help text on this
config.

Link: https://github.com/ClangBuiltLinux/linux/issues/1187
Signed-off-by: Nathan Chancellor <redacted>
---
 Makefile                          | 6 ++++++
 arch/Kconfig                      | 9 +++++++++
 arch/arm/Kconfig                  | 1 +
 arch/arm/Makefile                 | 4 ----
 arch/arm/boot/compressed/Makefile | 4 +++-
 arch/arm64/Kconfig                | 1 +
 arch/arm64/Makefile               | 4 ----
 arch/powerpc/Kconfig              | 1 +
 arch/powerpc/Makefile             | 1 -

Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)

quoted

 arch/x86/Kconfig                  | 1 +
 arch/x86/Makefile                 | 3 ---
 arch/x86/boot/compressed/Makefile | 4 +++-
 init/Kconfig                      | 3 +++
 13 files changed, 28 insertions(+), 14 deletions(-)

diff --git a/Makefile b/Makefile
index 008aba5f1a20..c443afd61886 100644
--- a/Makefile
+++ b/Makefile

@@ -984,6 +984,12 @@ ifeq ($(CONFIG_RELR),y)
 LDFLAGS_vmlinux	+= --pack-dyn-relocs=relr
 endif
 
+# We never want expected sections to be placed heuristically by the
+# linker. All sections should be explicitly named in the linker script.
+ifeq ($(CONFIG_LD_ORPHAN_WARN),y)
+LDFLAGS_vmlinux += --orphan-handling=warn
+endif

This is a nit, but you can use ifdef with bool CONFIG symbols in
Makefiles, which reads a bit nicer, eg:

ifdef CONFIG_LD_ORPHAN_WARN
LDFLAGS_vmlinux += --orphan-handling=warn
endif

That is indeed cleaner, I did not realize I could do that as long as the
config was a boolean. I will use that in v2, which I will send along
within the next few days to give Masahiro some time to comment.

Cheers,
Nathan

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