efi/x86: Move x86 back to libstub

This reverts commit 84be880560fb, which itself reverted my original
attempt to move x86 from #include'ing .c files from across the tree
to using the EFI stub built as a static library.

The issue that affected the original approach was that splitting
the implementation into several .o files resulted in the variable
'efi_early' becoming a global with external linkage, which under
-fPIC implies that references to it must go through the GOT. However,
dealing with this additional GOT entry turned out to be troublesome
on some EFI implementations. (GCC's visibility=hidden attribute is
supposed to lift this requirement, but it turned out not to work on
the 32-bit build.)

Instead, use a pure getter function to get a reference to efi_early.
This approach results in no additional GOT entries being generated,
so there is no need for any changes in the early GOT handling.

Tested-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>

1 files changed, 4 insertions, 4 deletions

diff --git a/arch/x86/boot/compressed/eboot.c b/arch/x86/boot/compressed/eboot.c
index 1acf605a646d..92b9a5f2aed6 100644
--- a/arch/x86/boot/compressed/eboot.c
+++ b/arch/x86/boot/compressed/eboot.c
@@ -21,8 +21,10 @@ static efi_system_table_t *sys_table;
 
 static struct efi_config *efi_early;
 
-#define efi_call_early(f, ...)						\
-	efi_early->call(efi_early->f, __VA_ARGS__);
+__pure const struct efi_config *__efi_early(void)
+{
+	return efi_early;
+}
 
 #define BOOT_SERVICES(bits)						\
 static void setup_boot_services##bits(struct efi_config *c)		\
@@ -285,8 +287,6 @@ void efi_char16_printk(efi_system_table_t *table, efi_char16_t *str)
 	}
 }
 
-#include "../../../../drivers/firmware/efi/libstub/efi-stub-helper.c"
-
 static void find_bits(unsigned long mask, u8 *pos, u8 *size)
 {
 	u8 first, len;