arm64/efi: set PE/COFF section alignment to 4 KB

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@linaro.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 8c06c9d..8ae84d8 100644 (file)
--- 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)