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

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Date:   Mon, 11 May 2020 18:58:49 -0400
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     Ard Biesheuvel <ardb@...nel.org>,
        Mike Lothian <mike@...eburn.co.uk>
Cc:     linux-efi <linux-efi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        X86 ML <x86@...nel.org>
Subject: [PATCH] x86/boot: Mark global variables as static

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")
Signed-off-by: Arvind Sankar <nivedita@...m.mit.edu>
---
 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;
 
 /*----------------------------------------------------------------------*/
 
-- 
2.26.2