Commit 757b435a authored by Ard Biesheuvel's avatar Ard Biesheuvel Committed by Will Deacon

efi: arm64: Add vmlinux debug link to the Image binary

When building with debugging symbols, take the absolute path to the
vmlinux binary and add it to the special PE/COFF debug table entry.
This allows a debug EFI build to find the vmlinux binary, which is
very helpful in debugging, given that the offset where the Image is
first loaded by EFI is highly unpredictable.

On implementations of UEFI that choose to implement it, this
information is exposed via the EFI debug support table, which is a UEFI
configuration table that is accessible both by the firmware at boot time
and by the OS at runtime, and lists all PE/COFF images loaded by the

The format of the NB10 Codeview entry is based on the definition used
by EDK2, which is our primary reference when it comes to the use of
PE/COFF in the context of UEFI firmware.
Signed-off-by: default avatarArd Biesheuvel <>
[will: use realpath instead of shell invocation, as discussed on list]
Signed-off-by: default avatarWill Deacon <>
parent 965861d6
......@@ -95,6 +95,14 @@ config DEBUG_ALIGN_RODATA
If in doubt, say N.
config DEBUG_EFI
depends on EFI && DEBUG_INFO
bool "UEFI debugging"
Enable this option to include EFI specific debugging features into
the kernel that are only useful when using a debug build of the
UEFI firmware
source "drivers/hwtracing/coresight/Kconfig"
......@@ -55,3 +55,7 @@ obj-y += $(arm64-obj-y) vdso/ probes/
obj-m += $(arm64-obj-m)
head-y := head.o
extra-y += $(head-y)
ifeq ($(CONFIG_DEBUG_EFI),y)
AFLAGS_head.o += -DVMLINUX_PATH="\"$(realpath $(objtree)/vmlinux)\""
......@@ -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
.long efi_debug_table - _head // DebugTable
.long efi_debug_table_size
// Section table
......@@ -195,6 +200,46 @@ section_table:
.short 0 // NumberOfLineNumbers (0 for executables)
.long 0xe0500020 // Characteristics (section flags)
* The debug table is referenced via its Relative Virtual Address (RVA),
* which is only defined for those parts of the image that are covered
* by a section declaration. Since this header is not covered by any
* section, the debug table must be emitted elsewhere. So stick it in
* the .init.rodata section instead.
* Note that the EFI debug entry itself may legally have a zero RVA,
* which means we can simply put it right after the section headers.
.align 2
.long 0 // Characteristics
.long 0 // TimeDateStamp
.short 0 // MajorVersion
.short 0 // MinorVersion
.long efi_debug_entry_size // SizeOfData
.long 0 // RVA
.long efi_debug_entry - _head // FileOffset
.set efi_debug_table_size, . - efi_debug_table
.ascii "NB10" // Signature
.long 0 // Unknown
.long 0 // Unknown2
.long 0 // Unknown3
.set efi_debug_entry_size, . - efi_debug_entry
* EFI will load .text onwards at the 4k section alignment
* described in the PE/COFF header. To ensure that instruction
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