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[02/20] efi/libstub/x86: force 'hidden' visibility for extern declarations

Message ID 20200103113953.9571-3-ardb@kernel.org
State New
Headers show
Series More EFI updates for v5.6 | expand

Commit Message

Ard Biesheuvel Jan. 3, 2020, 11:39 a.m. UTC
Commit c3710de5065d ("efi/libstub/x86: Drop __efi_early() export and
efi_config struct") introduced a reference from C code in eboot.c to
the startup_32 symbol defined in the .S startup code. This results in
a GOT based reference to startup_32, and since GOT entries carry
absolute addresses, they need to be fixed up before they can be used.

On modern toolchains (binutils 2.26 or later), this reference is
relaxed into a R_386_GOTOFF relocation (or the analogous X86_64 one)
which never uses the absolute address in the entry, and so we get
away with not fixing up the GOT table before calling the EFI entry
point. However, GCC 4.6 combined with a binutils of the era (2.24)
will produce a true GOT indirected reference, resulting in a wrong
value to be returned for the address of startup_32() if the boot
code is not running at the address it was linked at.

Fortunately, we can easily override this behavior, and force GCC to
emit the GOTOFF relocations explicitly, by setting the visibility
pragma 'hidden'.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 arch/x86/boot/compressed/eboot.c | 2 ++
 1 file changed, 2 insertions(+)
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Patch

diff --git a/arch/x86/boot/compressed/eboot.c b/arch/x86/boot/compressed/eboot.c
index da04948d75ed..565ee4733579 100644
--- a/arch/x86/boot/compressed/eboot.c
+++ b/arch/x86/boot/compressed/eboot.c
@@ -6,6 +6,8 @@ 
  *
  * ----------------------------------------------------------------------- */
 
+#pragma GCC visibility push(hidden)
+
 #include <linux/efi.h>
 #include <linux/pci.h>