linux-kernel - [PATCH v3] x86, realmode: explicitly set entry via ENTRY in linker script

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Date:   Wed, 25 Sep 2019 11:09:06 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de
Cc:     clang-built-linux@...glegroups.com, maskray@...gle.com,
        grimar@...esssoftek.com, ruiu@...gle.com,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Peter Smith <Peter.Smith@....com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v3] x86, realmode: explicitly set entry via ENTRY in linker script

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. The symbol pa_text_start
refers to the start of the .text section, which may not be at 0x1000 if
the preceding sections listed in arch/x86/realmode/rm/realmode.lds.S
were large enough. This matches behavior in arch/x86/boot/setup.ld.

Link: https://github.com/ClangBuiltLinux/linux/issues/216
Suggested-by: Borislav Petkov <bp@...en8.de>
Suggested-by: Peter Smith <Peter.Smith@....com>
Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
---
 arch/x86/realmode/rm/realmode.lds.S | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/realmode/rm/realmode.lds.S b/arch/x86/realmode/rm/realmode.lds.S
index 3bb980800c58..64d135d1ee63 100644
--- a/arch/x86/realmode/rm/realmode.lds.S
+++ b/arch/x86/realmode/rm/realmode.lds.S
@@ -11,6 +11,7 @@
 
 OUTPUT_FORMAT("elf32-i386")
 OUTPUT_ARCH(i386)
+ENTRY(pa_text_start)
 
 SECTIONS
 {
-- 
2.23.0.351.gc4317032e6-goog