[PATCH v2 2/2] arm64: efi: add vmlinux debug link to the Image binary

[ard.biesheuvel@linaro.org (Ard Biesheuvel)]

When building with debugging symbols, take the absolute path to the
vmlinux binary and add it to the special PE/COFF debug table entry.

These entries are used internally by EDK2 based* debug builds of UEFI
to populate the DebugImageInfo table, which can be used by debuggers
as well as by the OS itself to retrieve information about all loaded
PE/COFF executables. This is highly useful for source level debugging
of the UEFI stub.

* for AArch64, this probably means all of them

Cc: Matt Fleming <matt@codeblueprint.co.uk>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
 arch/arm64/kernel/Makefile |  4 +++
 arch/arm64/kernel/head.S   | 34 +++++++++++++++++++-
 arch/arm64/kernel/image.h  |  3 ++
 3 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
index 7d66bbaafc0c..6dbc0e5527f5 100644
--- a/arch/arm64/kernel/Makefile
+++ b/arch/arm64/kernel/Makefile
@@ -55,3 +55,7 @@ obj-y					+= $(arm64-obj-y) vdso/ probes/
 obj-m					+= $(arm64-obj-m)
 head-y					:= head.o
 extra-y					+= $(head-y) vmlinux.lds
+
+ifeq ($(CONFIG_EFI)$(CONFIG_DEBUG_INFO),yy)
+AFLAGS_head.o += -DVMLINUX_PATH="\"$(shell readlink -f $(objtree)/vmlinux)\""
+endif
diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 4b1abac3485a..b462ab1f11ef 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -149,7 +149,7 @@ extra_header_fields:
 	.quad	0				// SizeOfHeapReserve
 	.quad	0				// SizeOfHeapCommit
 	.long	0				// LoaderFlags
-	.long	0x6				// NumberOfRvaAndSizes
+	.long	(section_table - .) / 8		// NumberOfRvaAndSizes
 
 	.quad	0				// ExportTable
 	.quad	0				// ImportTable
@@ -158,6 +158,11 @@ extra_header_fields:
 	.quad	0				// CertificationTable
 	.quad	0				// BaseRelocationTable
 
+#ifdef CONFIG_DEBUG_INFO
+	.long	efi_debug_table - _head		// DebugTable
+	.long	efi_debug_table_size
+#endif
+
 	// Section table
 section_table:
 
@@ -204,6 +209,33 @@ section_table:
 	 */
 	.align 12
 efi_header_end:
+
+#ifdef CONFIG_DEBUG_INFO
+	__INITDATA
+
+efi_debug_table:
+	// EFI_IMAGE_DEBUG_DIRECTORY_ENTRY
+	.long	0			// Characteristics
+	.long	0			// TimeDateStamp
+	.short	0			// MajorVersion
+	.short	0			// MinorVersion
+	.long	2			// Type == EFI_IMAGE_DEBUG_TYPE_CODEVIEW
+	.long	efi_debug_entry_size	// SizeOfData
+	.long	efi_debug_entry_offset	// RVA
+	.long	efi_debug_entry_offset	// FileOffset
+
+ENTRY(efi_debug_entry)
+	// EFI_IMAGE_DEBUG_CODEVIEW_NB10_ENTRY
+	.long	0x3031424E		// Signature
+	.long	0			// Unknown
+	.long	0			// Unknown2
+	.long	0			// Unknown3
+
+	.asciz	VMLINUX_PATH
+
+	.set	efi_debug_entry_size, . - efi_debug_entry
+	.set	efi_debug_table_size, . - efi_debug_table
+#endif
 #endif
 
 	__INIT
diff --git a/arch/arm64/kernel/image.h b/arch/arm64/kernel/image.h
index c7fcb232fe47..ad5406f011c2 100644
--- a/arch/arm64/kernel/image.h
+++ b/arch/arm64/kernel/image.h
@@ -116,6 +116,9 @@ __efistub__end			= KALLSYMS_HIDE(_end);
 __efistub__edata		= KALLSYMS_HIDE(_edata);
 __efistub_screen_info		= KALLSYMS_HIDE(screen_info);
 
+#ifdef CONFIG_DEBUG_INFO
+efi_debug_entry_offset = efi_debug_entry - _text;
+#endif
 #endif
 
 #endif /* __ASM_IMAGE_H */
-- 
2.7.4