linux-kernel - [PATCHv2] x86/purgatory: don't generate debug info for purgatory.ro

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Date:   Mon,  3 Aug 2020 13:49:48 +0800
From:   Pingfan Liu <kernelfans@...il.com>
To:     x86@...nel.org
Cc:     Pingfan Liu <kernelfans@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Steve Wahl <steve.wahl@....com>, linux-kernel@...r.kernel.org,
        kexec@...ts.infradead.org
Subject: [PATCHv2] x86/purgatory: don't generate debug info for purgatory.ro

Purgatory.ro is a standalone binary that is not linked against the rest of
the kernel.  Its image is copied into an array that is linked to the
kernel, and from there kexec relocates it wherever it desires.

Unlike the debug info for vmlinux, which can be used for analyzing crash
such info is useless in purgatory.ro. And discarding them can save about
200K space.

Original:
  259080  kexec-purgatory.o
Stripped debug info:
   29152  kexec-purgatory.o

Signed-off-by: Pingfan Liu <kernelfans@...il.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Hans de Goede <hdegoede@...hat.com>
Cc: Nick Desaulniers <ndesaulniers@...gle.com>
Cc: Arvind Sankar <nivedita@...m.mit.edu>
Cc: Steve Wahl <steve.wahl@....com>
Cc: linux-kernel@...r.kernel.org
Cc: kexec@...ts.infradead.org
To: x86@...nel.org
---
 arch/x86/purgatory/Makefile | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
index 088bd76..d24b43a 100644
--- a/arch/x86/purgatory/Makefile
+++ b/arch/x86/purgatory/Makefile
@@ -32,7 +32,7 @@ KCOV_INSTRUMENT := n
 # make up the standalone purgatory.ro
 
 PURGATORY_CFLAGS_REMOVE := -mcmodel=kernel
-PURGATORY_CFLAGS := -mcmodel=large -ffreestanding -fno-zero-initialized-in-bss
+PURGATORY_CFLAGS := -mcmodel=large -ffreestanding -fno-zero-initialized-in-bss -g0
 PURGATORY_CFLAGS += $(DISABLE_STACKLEAK_PLUGIN) -DDISABLE_BRANCH_PROFILING
 PURGATORY_CFLAGS += $(call cc-option,-fno-stack-protector)
 
@@ -64,6 +64,9 @@ CFLAGS_sha256.o			+= $(PURGATORY_CFLAGS)
 CFLAGS_REMOVE_string.o		+= $(PURGATORY_CFLAGS_REMOVE)
 CFLAGS_string.o			+= $(PURGATORY_CFLAGS)
 
+AFLAGS_REMOVE_setup-x86_$(BITS).o	+= -Wa,-gdwarf-2
+AFLAGS_REMOVE_entry64.o			+= -Wa,-gdwarf-2
+
 $(obj)/purgatory.ro: $(PURGATORY_OBJS) FORCE
 		$(call if_changed,ld)
 
-- 
2.7.5