linux-kernel - [PATCH] um: Support LTO

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Message-Id: <20230113-umlto-v1-1-9795842411e7@pefoley.com>
Date:   Fri, 13 Jan 2023 12:03:00 -0500
From:   Peter Foley <pefoley2@...oley.com>
To:     Richard Weinberger <richard@....at>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        Johannes Berg <johannes@...solutions.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>
Cc:     linux-um@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Peter Foley <pefoley2@...oley.com>
Subject: [PATCH] um: Support LTO

Only a handful of changes are necessary to get it to work.

Signed-off-by: Peter Foley <pefoley2@...oley.com>
---
 arch/um/Kconfig           | 2 ++
 arch/um/Makefile          | 2 +-
 arch/x86/um/vdso/Makefile | 2 +-
 3 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/um/Kconfig b/arch/um/Kconfig
index ad4ff3b0e91e..7c94ca7ff758 100644
--- a/arch/um/Kconfig
+++ b/arch/um/Kconfig
@@ -25,6 +25,8 @@ config UML
 	select GENERIC_IRQ_SHOW
 	select GENERIC_CPU_DEVICES
 	select HAVE_GCC_PLUGINS
+	select ARCH_SUPPORTS_LTO_CLANG
+	select ARCH_SUPPORTS_LTO_CLANG_THIN
 	select TRACE_IRQFLAGS_SUPPORT
 	select TTY # Needed for line.c
 	select HAVE_ARCH_VMAP_STACK
diff --git a/arch/um/Makefile b/arch/um/Makefile
index f1d4d67157be..a41dde204b08 100644
--- a/arch/um/Makefile
+++ b/arch/um/Makefile
@@ -142,7 +142,7 @@ endif
 LD_FLAGS_CMDLINE = $(foreach opt,$(KBUILD_LDFLAGS),-Wl,$(opt))
 
 # Used by link-vmlinux.sh which has special support for um link
-export CFLAGS_vmlinux := $(LINK-y) $(LINK_WRAPS) $(LD_FLAGS_CMDLINE)
+export CFLAGS_vmlinux := $(LINK-y) $(LINK_WRAPS) $(LD_FLAGS_CMDLINE) $(CC_FLAGS_LTO)
 export LDFLAGS_vmlinux := $(LDFLAGS_EXECSTACK)
 
 # When cleaning we don't include .config, so we don't include
diff --git a/arch/x86/um/vdso/Makefile b/arch/x86/um/vdso/Makefile
index 6fbe97c52c99..6825e146a62f 100644
--- a/arch/x86/um/vdso/Makefile
+++ b/arch/x86/um/vdso/Makefile
@@ -61,7 +61,7 @@ CFLAGS_REMOVE_um_vdso.o = -pg -fprofile-arcs -ftest-coverage
 #
 quiet_cmd_vdso = VDSO    $@
       cmd_vdso = $(CC) -nostdlib -o $@ \
-		       $(VDSO_LDFLAGS) $(VDSO_LDFLAGS_$(filter %.lds,$(^F))) \
+		       $(CC_FLAGS_LTO) $(VDSO_LDFLAGS) $(VDSO_LDFLAGS_$(filter %.lds,$(^F))) \
 		       -Wl,-T,$(filter %.lds,$^) $(filter %.o,$^) && \
 		 sh $(srctree)/$(src)/checkundef.sh '$(NM)' '$@'
 

---
base-commit: d9fc1511728c15df49ff18e49a494d00f78b7cd4
change-id: 20230113-umlto-c7f6731306e7

Best regards,
-- 
Peter Foley <pefoley2@...oley.com>