[tip: x86/boot] x86/realmode: Explicitly set entry point via ENTRY in linker script

[tip-bot2 for Nick Desaulniers]

The following commit has been merged into the x86/boot branch of tip:

Commit-ID:     3f5f909bc331a7ff9120b11c8e0e320d60b01c89
Gitweb:        https://git.kernel.org/tip/3f5f909bc331a7ff9120b11c8e0e320d60b01c89
Author:        Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
AuthorDate:    Wed, 25 Sep 2019 11:09:06 -07:00
Committer:     Borislav Petkov <bp@xxxxxxx>
CommitterDate: Tue, 01 Oct 2019 12:17:58 +02:00

x86/realmode: Explicitly set entry point 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.

Suggested-by: Borislav Petkov <bp@xxxxxxxxx>
Suggested-by: Peter Smith <Peter.Smith@xxxxxxx>
Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: clang-built-linux@xxxxxxxxxxxxxxxx
Cc: grimar@xxxxxxxxxxxxxxxx
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: maskray@xxxxxxxxxx
Cc: ruiu@xxxxxxxxxx
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: x86-ml <x86@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20190925180908.54260-1-ndesaulniers@xxxxxxxxxx
Link: https://github.com/ClangBuiltLinux/linux/issues/216
---
 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 3bb9808..64d135d 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
 {