linux-kernel - [PATCH v2] x86, realmode: explicitly set entry via command line

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Message-Id: <20190924193310.132104-1-ndesaulniers@google.com>
Date:   Tue, 24 Sep 2019 12:33:08 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de
Cc:     clang-built-linux@...glegroups.com,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Tri Vo <trong@...roid.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Rob Herring <robh@...nel.org>,
        George Rimar <grimar@...esssoftek.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2] x86, realmode: explicitly set entry via command line

Linking with ld.lld via $ make LD=ld.lld produces the warning:
ld.lld: warning: cannot find entry symbol _start; defaulting to 0x1000

Linking with ld.bfd shows the default entry is 0x1000:
$ readelf -h arch/x86/realmode/rm/realmode.elf | grep Entry
  Entry point address:               0x1000

While ld.lld is being pedantic, just set the entry point explicitly,
instead of depending on the implicit default.

Link: https://github.com/ClangBuiltLinux/linux/issues/216
Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
---
Changes V1 -> V2:
* Use command line flag, rather than linker script, as ld.bfd produces a
  syntax error for `ENTRY(0x1000)` but is happy with `-e 0x1000`

 arch/x86/realmode/rm/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/realmode/rm/Makefile b/arch/x86/realmode/rm/Makefile
index f60501a384f9..338a00c5257f 100644
--- a/arch/x86/realmode/rm/Makefile
+++ b/arch/x86/realmode/rm/Makefile
@@ -46,7 +46,7 @@ $(obj)/pasyms.h: $(REALMODE_OBJS) FORCE
 targets += realmode.lds
 $(obj)/realmode.lds: $(obj)/pasyms.h
 
-LDFLAGS_realmode.elf := -m elf_i386 --emit-relocs -T
+LDFLAGS_realmode.elf := -m elf_i386 --emit-relocs -e 0x1000 -T
 CPPFLAGS_realmode.lds += -P -C -I$(objtree)/$(obj)
 
 targets += realmode.elf
-- 
2.23.0.351.gc4317032e6-goog