linux-kernel - [tip:efi/core] arm/efi: Remove pointless dummy .reloc section

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Message-ID: <tip-574cea724cd81f4063491ed1c0534d81a094a913@git.kernel.org>
Date:   Mon, 21 Aug 2017 02:18:38 -0700
From:   tip-bot for Ard Biesheuvel <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     matt@...eblueprint.co.uk, linux-kernel@...r.kernel.org,
        torvalds@...ux-foundation.org, peterz@...radead.org,
        tglx@...utronix.de, ard.biesheuvel@...aro.org, hpa@...or.com,
        mingo@...nel.org
Subject: [tip:efi/core] arm/efi: Remove pointless dummy .reloc section

Commit-ID:  574cea724cd81f4063491ed1c0534d81a094a913
Gitweb:     http://git.kernel.org/tip/574cea724cd81f4063491ed1c0534d81a094a913
Author:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
AuthorDate: Fri, 18 Aug 2017 20:49:42 +0100
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Mon, 21 Aug 2017 09:43:50 +0200

arm/efi: Remove pointless dummy .reloc section

The kernel's EFI PE/COFF header contains a dummy .reloc section, and
an explanatory comment that claims that this is required for the EFI
application loader to accept the Image as a relocatable image (i.e.,
one that can be loaded at any offset and fixed up in place)

This was inherited from the x86 implementation, which has elaborate host
tooling to mangle the PE/COFF header post-link time, and which populates
the .reloc section with a single dummy base relocation. On ARM, no such
tooling exists, and the .reloc section remains empty, and is never even
exposed via the BaseRelocationTable directory entry, which is where the
PE/COFF loader looks for it.

The PE/COFF spec is unclear about relocatable images that do not require
any fixups, but the EDK2 implementation, which is the de facto reference
for PE/COFF in the UEFI space, clearly does not care, and explicitly
mentions (in a comment) that relocatable images with no base relocations
are perfectly fine, as long as they don't have the RELOCS_STRIPPED
attribute set (which is not the case for our PE/COFF image)

So simply remove the .reloc section altogether.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Matt Fleming <matt@...eblueprint.co.uk>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: linux-efi@...r.kernel.org
Link: http://lkml.kernel.org/r/20170818194947.19347-10-ard.biesheuvel@linaro.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/arm/boot/compressed/efi-header.S | 18 +-----------------
 1 file changed, 1 insertion(+), 17 deletions(-)

diff --git a/arch/arm/boot/compressed/efi-header.S b/arch/arm/boot/compressed/efi-header.S
index 4169b90..309d619 100644
--- a/arch/arm/boot/compressed/efi-header.S
+++ b/arch/arm/boot/compressed/efi-header.S
@@ -41,7 +41,7 @@ pe_header:
 
 coff_header:
 		.short	0x01c2			@ ARM or Thumb
-		.short	2			@ nr_sections
+		.short	1			@ nr_sections
 		.long	0 			@ TimeDateStamp
 		.long	0			@ PointerToSymbolTable
 		.long	0			@ NumberOfSymbols
@@ -96,22 +96,6 @@ extra_header_fields:
 		.quad	0			@ BaseRelocationTable
 
 section_table:
-		@
-		@ The EFI application loader requires a relocation section
-		@ because EFI applications must be relocatable. This is a
-		@ dummy section as far as we are concerned.
-		@
-		.ascii	".reloc\0\0"
-		.long	0			@ VirtualSize
-		.long	0			@ VirtualAddress
-		.long	0			@ SizeOfRawData
-		.long	0			@ PointerToRawData
-		.long	0			@ PointerToRelocations
-		.long	0			@ PointerToLineNumbers
-		.short	0			@ NumberOfRelocations
-		.short	0			@ NumberOfLineNumbers
-		.long	0x42000040		@ Characteristics
-
 		.ascii	".text\0\0\0"
 		.long	_end - __efi_start	@ VirtualSize
 		.long	__efi_start		@ VirtualAddress