[PATCH v2 02/10] arm64/efi: set PE/COFF section alignment to 4 KB

[Ard Biesheuvel]

Position independent AArch64 code needs to be linked and loaded at the
same relative offset from a 4 KB boundary, or adrp/add and adrp/ldr
pairs will not work correctly. (This is how PC relative symbol
references with a 4 GB reach are emitted)

We need to declare this in the PE/COFF header, otherwise the PE/COFF
loader may load the Image and invoke the stub at an offset which
violates this rule.

Reviewed-by: Roy Franz <roy.franz at linaro.org>
Acked-by: Mark Rutland <mark.rutland at arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
---
v2: added comment explaining '.align 12' in head.S
---
 arch/arm64/kernel/head.S | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 8c06c9d269d2..8ae84d8c2a8c 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -161,7 +161,7 @@ optional_header:
 
 extra_header_fields:
 	.quad	0				// ImageBase
-	.long	0x20				// SectionAlignment
+	.long	0x1000				// SectionAlignment
 	.long	0x8				// FileAlignment
 	.short	0				// MajorOperatingSystemVersion
 	.short	0				// MinorOperatingSystemVersion
@@ -228,7 +228,15 @@ section_table:
 	.short	0		// NumberOfRelocations  (0 for executables)
 	.short	0		// NumberOfLineNumbers  (0 for executables)
 	.long	0xe0500020	// Characteristics (section flags)
-	.align 5
+
+	/*
+	 * EFI will load stext onwards at the 4k section alignment
+	 * described in the PE/COFF header. To ensure that instruction
+	 * sequences using an adrp and a :lo12: immediate will function
+	 * correctly at this alignment, we must ensure that stext is
+	 * placed at a 4k boundary in the Image to begin with.
+	 */
+	.align 12
 #endif
 
 ENTRY(stext)
-- 
1.8.3.2