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