linux-kernel - [PATCH 5/7] x86/boot: Mark global variables as static

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Message-Id: <20200517125754.8934-6-ardb@kernel.org>
Date:   Sun, 17 May 2020 14:57:52 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     linux-efi@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Ard Biesheuvel <ardb@...nel.org>, linux-kernel@...r.kernel.org,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Benjamin Thiel <b.thiel@...teo.de>,
        Borislav Petkov <bp@...en8.de>, Dave Young <dyoung@...hat.com>,
        Heinrich Schuchardt <xypron.glpk@....de>,
        Javier Martinez Canillas <javierm@...hat.com>,
        Jerry Snitselaar <jsnitsel@...hat.com>,
        Lenny Szubowicz <lszubowi@...hat.com>,
        linux-acpi@...r.kernel.org, Loic Yhuel <loic.yhuel@...il.com>,
        Matthew Garrett <mjg59@...gle.com>,
        Mike Lothian <mike@...eburn.co.uk>,
        Punit Agrawal <punit1.agrawal@...hiba.co.jp>
Subject: [PATCH 5/7] x86/boot: Mark global variables as static

From: Arvind Sankar <nivedita@...m.mit.edu>

Mike Lothian reports that after commit
  964124a97b97 ("efi/x86: Remove extra headroom for setup block")
gcc 10.1.0 fails with

  HOSTCC  arch/x86/boot/tools/build
  /usr/lib/gcc/x86_64-pc-linux-gnu/10.1.0/../../../../x86_64-pc-linux-gnu/bin/ld:
  error: linker defined: multiple definition of '_end'
  /usr/lib/gcc/x86_64-pc-linux-gnu/10.1.0/../../../../x86_64-pc-linux-gnu/bin/ld:
  /tmp/ccEkW0jM.o: previous definition here
  collect2: error: ld returned 1 exit status
  make[1]: *** [scripts/Makefile.host:103: arch/x86/boot/tools/build] Error 1
  make: *** [arch/x86/Makefile:303: bzImage] Error 2

The issue is with the _end variable that was added, to hold the end of
the compressed kernel from zoffsets.h (ZO__end). The name clashes with
the linker-defined _end symbol that indicates the end of the build
program itself.

Even when there is no compile-time error, this causes build to use
memory past the end of its .bss section.

To solve this, mark _end as static, and for symmetry, mark the rest of
the variables that keep track of symbols from the compressed kernel as
static as well.

Fixes: 964124a97b97 ("efi/x86: Remove extra headroom for setup block")
Reported-by: Mike Lothian <mike@...eburn.co.uk>
Tested-by: Mike Lothian <mike@...eburn.co.uk>
Signed-off-by: Arvind Sankar <nivedita@...m.mit.edu>
Link: https://lore.kernel.org/r/20200511225849.1311869-1-nivedita@alum.mit.edu
Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 arch/x86/boot/tools/build.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/arch/x86/boot/tools/build.c b/arch/x86/boot/tools/build.c
index 8f8c8e386cea..c8b8c1a8d1fc 100644
--- a/arch/x86/boot/tools/build.c
+++ b/arch/x86/boot/tools/build.c
@@ -59,14 +59,14 @@ u8 buf[SETUP_SECT_MAX*512];
 #define PECOFF_COMPAT_RESERVE 0x0
 #endif
 
-unsigned long efi32_stub_entry;
-unsigned long efi64_stub_entry;
-unsigned long efi_pe_entry;
-unsigned long efi32_pe_entry;
-unsigned long kernel_info;
-unsigned long startup_64;
-unsigned long _ehead;
-unsigned long _end;
+static unsigned long efi32_stub_entry;
+static unsigned long efi64_stub_entry;
+static unsigned long efi_pe_entry;
+static unsigned long efi32_pe_entry;
+static unsigned long kernel_info;
+static unsigned long startup_64;
+static unsigned long _ehead;
+static unsigned long _end;
 
 /*----------------------------------------------------------------------*/
 
-- 
2.17.1