Date:   Wed, 22 Apr 2020 17:43:28 +0000
From:   Atish Patra <Atish.Patra@....com>
To:     "palmer@...belt.com" <palmer@...belt.com>
CC:     "linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "xypron.glpk@....de" <xypron.glpk@....de>,
        "masahiroy@...nel.org" <masahiroy@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "ardb@...nel.org" <ardb@...nel.org>
Subject: Re: [v4 PATCH 2/3] RISC-V: Add PE/COFF header for EFI stub

On Tue, 2020-04-21 at 13:02 -0700, Palmer Dabbelt wrote:
> [I just saw there's a v4, so I'm moving over here]
> 
> On Mon, 20 Apr 2020 20:33:35 PDT (-0700), Atish Patra wrote:
> > Linux kernel Image can appear as an EFI application With
> > appropriate
> > PE/COFF header fields in the beginning of the Image header. An EFI
> > application loader can directly load a Linux kernel Image and an
> > EFI
> > stub residing in kernel can boot Linux kernel directly.
> > 
> > Add the necessary PE/COFF header.
> > 
> > Signed-off-by: Atish Patra <atish.patra@....com>
> > ---
> >  arch/riscv/include/asm/sections.h | 13 ++++
> >  arch/riscv/kernel/Makefile        |  4 ++
> >  arch/riscv/kernel/efi-header.S    | 99
> > +++++++++++++++++++++++++++++++
> >  arch/riscv/kernel/head.S          | 16 +++++
> >  arch/riscv/kernel/image-vars.h    | 53 +++++++++++++++++
> >  arch/riscv/kernel/vmlinux.lds.S   | 20 ++++++-
> >  6 files changed, 203 insertions(+), 2 deletions(-)
> >  create mode 100644 arch/riscv/include/asm/sections.h
> >  create mode 100644 arch/riscv/kernel/efi-header.S
> >  create mode 100644 arch/riscv/kernel/image-vars.h
> > 
> > diff --git a/arch/riscv/include/asm/sections.h
> > b/arch/riscv/include/asm/sections.h
> > new file mode 100644
> > index 000000000000..3a9971b1210f
> > --- /dev/null
> > +++ b/arch/riscv/include/asm/sections.h
> > @@ -0,0 +1,13 @@
> > +/* SPDX-License-Identifier: GPL-2.0-only */
> > +/*
> > + * Copyright (C) 2020 Western Digital Corporation or its
> > affiliates.
> > + */
> > +#ifndef __ASM_SECTIONS_H
> > +#define __ASM_SECTIONS_H
> > +
> > +#include <asm-generic/sections.h>
> > +
> > +extern char _start[];
> > +extern char _start_kernel[];
> > +
> > +#endif /* __ASM_SECTIONS_H */
> > diff --git a/arch/riscv/kernel/Makefile
> > b/arch/riscv/kernel/Makefile
> > index 86c83081044f..86ca755f8a9f 100644
> > --- a/arch/riscv/kernel/Makefile
> > +++ b/arch/riscv/kernel/Makefile
> > @@ -32,6 +32,10 @@ obj-y	+= patch.o
> >  obj-$(CONFIG_MMU) += vdso.o vdso/
> > 
> >  obj-$(CONFIG_RISCV_M_MODE)	+= clint.o traps_misaligned.o
> > +OBJCOPYFLAGS := --prefix-symbols=__efistub_
> > +$(obj)/%.stub.o: $(obj)/%.o FORCE
> > +	$(call if_changed,objcopy)
> > +
> >  obj-$(CONFIG_FPU)		+= fpu.o
> >  obj-$(CONFIG_SMP)		+= smpboot.o
> >  obj-$(CONFIG_SMP)		+= smp.o
> > diff --git a/arch/riscv/kernel/efi-header.S
> > b/arch/riscv/kernel/efi-header.S
> > new file mode 100644
> > index 000000000000..69dde8268527
> > --- /dev/null
> > +++ b/arch/riscv/kernel/efi-header.S
> > @@ -0,0 +1,99 @@
> > +/* SPDX-License-Identifier: GPL-2.0-only */
> > +/*
> > + * Copyright (C) 2020 Western Digital Corporation or its
> > affiliates.
> > + * Adapted from arch/arm64/kernel/efi-header.S
> > + */
> > +
> > +#include <linux/pe.h>
> > +#include <linux/sizes.h>
> > +
> > +	.macro	__EFI_PE_HEADER
> > +	.long	PE_MAGIC
> > +coff_header:
> > +	.short	IMAGE_FILE_MACHINE_RISCV64		// Machine
> > +	.short	section_count				//
> > NumberOfSections
> > +	.long	0 					//
> > TimeDateStamp
> > +	.long	0					//
> > PointerToSymbolTable
> > +	.long	0					//
> > NumberOfSymbols
> > +	.short	section_table - optional_header		//
> > SizeOfOptionalHeader
> > +	.short	IMAGE_FILE_DEBUG_STRIPPED | \
> > +		IMAGE_FILE_EXECUTABLE_IMAGE | \
> > +		IMAGE_FILE_LINE_NUMS_STRIPPED		//
> > Characteristics
> > +
> > +optional_header:
> > +	.short	PE_OPT_MAGIC_PE32PLUS			// PE32+
> > format
> > +	.byte	0x02					//
> > MajorLinkerVersion
> > +	.byte	0x14					//
> > MinorLinkerVersion
> > +	.long	__text_end - efi_header_end		//
> > SizeOfCode
> > +	.long	_end - __text_end			//
> > SizeOfInitializedData
> > +	.long	0					//
> > SizeOfUninitializedData
> > +	.long	__efistub_efi_entry - _start		//
> > AddressOfEntryPoint
> > +	.long	efi_header_end - _start			//
> > BaseOfCode
> > +
> > +extra_header_fields:
> > +	.quad	0					//
> > ImageBase
> > +	.long	SZ_4K					//
> > SectionAlignment
> > +	.long	PECOFF_FILE_ALIGNMENT			//
> > FileAlignment
> > +	.short	0					//
> > MajorOperatingSystemVersion
> > +	.short	0					//
> > MinorOperatingSystemVersion
> > +	.short	LINUX_EFISTUB_MAJOR_VERSION		//
> > MajorImageVersion
> > +	.short	LINUX_EFISTUB_MINOR_VERSION		//
> > MinorImageVersion
> > +	.short	0					//
> > MajorSubsystemVersion
> > +	.short	0					//
> > MinorSubsystemVersion
> > +	.long	0					//
> > Win32VersionValue
> > +
> > +	.long	_end - _start				//
> > SizeOfImage
> > +
> > +	// Everything before the kernel image is considered part of the
> > header
> > +	.long	efi_header_end - _start			//
> > SizeOfHeaders
> > +	.long	0					// CheckSum
> > +	.short	IMAGE_SUBSYSTEM_EFI_APPLICATION		//
> > Subsystem
> > +	.short	0					//
> > DllCharacteristics
> > +	.quad	0					//
> > SizeOfStackReserve
> > +	.quad	0					//
> > SizeOfStackCommit
> > +	.quad	0					//
> > SizeOfHeapReserve
> > +	.quad	0					//
> > SizeOfHeapCommit
> > +	.long	0					//
> > LoaderFlags
> > +	.long	(section_table - .) / 8			//
> > NumberOfRvaAndSizes
> > +
> > +	.quad	0					//
> > ExportTable
> > +	.quad	0					//
> > ImportTable
> > +	.quad	0					//
> > ResourceTable
> > +	.quad	0					//
> > ExceptionTable
> > +	.quad	0					//
> > CertificationTable
> > +	.quad	0					//
> > BaseRelocationTable
> > +
> > +	// Section table
> > +section_table:
> > +	.ascii	".text\0\0\0"
> > +	.long	__text_end - efi_header_end		//
> > VirtualSize
> > +	.long	efi_header_end - _start			//
> > VirtualAddress
> > +	.long	__text_end - efi_header_end		//
> > SizeOfRawData
> > +	.long	efi_header_end - _start			//
> > PointerToRawData
> > +
> > +	.long	0					//
> > PointerToRelocations
> > +	.long	0					//
> > PointerToLineNumbers
> > +	.short	0					//
> > NumberOfRelocations
> > +	.short	0					//
> > NumberOfLineNumbers
> > +	.long	IMAGE_SCN_CNT_CODE | \
> > +		IMAGE_SCN_MEM_READ | \
> > +		IMAGE_SCN_MEM_EXECUTE			//
> > Characteristics
> > +
> > +	.ascii	".data\0\0\0"
> > +	.long	__data_virt_size			//
> > VirtualSize
> > +	.long	__text_end - _start			//
> > VirtualAddress
> > +	.long	__data_raw_size				//
> > SizeOfRawData
> > +	.long	__text_end - _start			//
> > PointerToRawData
> > +
> > +	.long	0					//
> > PointerToRelocations
> > +	.long	0					//
> > PointerToLineNumbers
> > +	.short	0					//
> > NumberOfRelocations
> > +	.short	0					//
> > NumberOfLineNumbers
> > +	.long	IMAGE_SCN_CNT_INITIALIZED_DATA | \
> > +		IMAGE_SCN_MEM_READ | \
> > +		IMAGE_SCN_MEM_WRITE			// Characteristics
> > +
> > +	.set	section_count, (. - section_table) / 40
> > +
> > +efi_header_end:
> > +	.endm
> > diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
> > index 98a406474e7d..ddd613dac9d6 100644
> > --- a/arch/riscv/kernel/head.S
> > +++ b/arch/riscv/kernel/head.S
> > @@ -13,6 +13,7 @@
> >  #include <asm/csr.h>
> >  #include <asm/hwcap.h>
> >  #include <asm/image.h>
> > +#include "efi-header.S"
> > 
> >  __HEAD
> >  ENTRY(_start)
> > @@ -22,10 +23,18 @@ ENTRY(_start)
> >  	 * Do not modify it without modifying the structure and all
> > bootloaders
> >  	 * that expects this header format!!
> >  	 */
> > +#ifdef CONFIG_EFI
> > +	/*
> > +	 * This instruction decodes to "MZ" ASCII required by UEFI.
> > +	 */
> > +	li s4,-13
> 
> This needs to be a c.li in order to encode as "MZ".  It'd be cleaner
> to
> explicitly write it that way rather that having the assembler
> transparently
> compress it, but we definately need to have Kconfig make EFI select
> ISA_C.
> 

Sure. I will add that.

> > +	j _start_kernel
> > +#else
> >  	/* jump to start kernel */
> >  	j _start_kernel
> >  	/* reserved */
> >  	.word 0
> > +#endif
> >  	.balign 8
> >  #if __riscv_xlen == 64
> >  	/* Image load offset(2MB) from start of RAM */
> > @@ -43,7 +52,14 @@ ENTRY(_start)
> >  	.ascii RISCV_IMAGE_MAGIC
> >  	.balign 4
> >  	.ascii RISCV_IMAGE_MAGIC2
> > +#ifdef CONFIG_EFI
> > +	.word pe_head_start - _start
> > +pe_head_start:
> > +
> > +	__EFI_PE_HEADER
> > +#else
> >  	.word 0
> > +#endif
> > 
> >  .align 2
> >  #ifdef CONFIG_MMU
> > diff --git a/arch/riscv/kernel/image-vars.h
> > b/arch/riscv/kernel/image-vars.h
> > new file mode 100644
> > index 000000000000..bd8b764f0ad9
> > --- /dev/null
> > +++ b/arch/riscv/kernel/image-vars.h
> > @@ -0,0 +1,53 @@
> > +/* SPDX-License-Identifier: GPL-2.0-only */
> > +/*
> > + * Copyright (C) 2020 Western Digital Corporation or its
> > affiliates.
> > + * Linker script variables to be set after section resolution, as
> > + * ld.lld does not like variables assigned before SECTIONS is
> > processed.
> > + * Based on arch/arm64/kerne/image-vars.h
> > + */
> > +#ifndef __RISCV_KERNEL_IMAGE_VARS_H
> > +#define __RISCV_KERNEL_IMAGE_VARS_H
> > +
> > +#ifndef LINKER_SCRIPT
> > +#error This file should only be included in vmlinux.lds.S
> > +#endif
> > +
> > +#ifdef CONFIG_EFI
> > +
> > +__efistub_stext_offset = _start_kernel - _start;
> > +
> > +/*
> > + * The EFI stub has its own symbol namespace prefixed by
> > __efistub_, to
> > + * isolate it from the kernel proper. The following symbols are
> > legally
> > + * accessed by the stub, so provide some aliases to make them
> > accessible.
> > + * Only include data symbols here, or text symbols of functions
> > that are
> > + * guaranteed to be safe when executed at another offset than they
> > were
> > + * linked at. The routines below are all implemented in assembler
> > in a
> > + * position independent manner
> > + */
> > +__efistub_memcmp		= memcmp;
> > +__efistub_memchr		= memchr;
> > +__efistub_memcpy		= memcpy;
> > +__efistub_memmove		= memmove;
> > +__efistub_memset		= memset;
> > +__efistub_strlen		= strlen;
> > +__efistub_strnlen		= strnlen;
> > +__efistub_strcmp		= strcmp;
> > +__efistub_strncmp		= strncmp;
> > +__efistub_strrchr		= strrchr;
> > +
> > +#ifdef CONFIG_KASAN
> > +__efistub___memcpy		= memcpy;
> > +__efistub___memmove		= memmove;
> > +__efistub___memset		= memset;
> > +#endif
> > +
> > +__efistub__start		= _start;
> > +__efistub__start_kernel		= _start_kernel;
> > +__efistub__end			= _end;
> > +__efistub__edata		= _edata;
> > +__efistub_screen_info		= screen_info;
> > +
> > +#endif
> > +
> > +#endif /* __RISCV_KERNEL_IMAGE_VARS_H */
> > diff --git a/arch/riscv/kernel/vmlinux.lds.S
> > b/arch/riscv/kernel/vmlinux.lds.S
> > index 0339b6bbe11a..20ebf7e8c215 100644
> > --- a/arch/riscv/kernel/vmlinux.lds.S
> > +++ b/arch/riscv/kernel/vmlinux.lds.S
> > @@ -10,6 +10,7 @@
> >  #include <asm/cache.h>
> >  #include <asm/thread_info.h>
> >  #include <asm/set_memory.h>
> > +#include "image-vars.h"
> > 
> >  #include <linux/sizes.h>
> >  OUTPUT_ARCH(riscv)
> > @@ -17,6 +18,14 @@ ENTRY(_start)
> > 
> >  jiffies = jiffies_64;
> > 
> > +PECOFF_FILE_ALIGNMENT = 0x200;
> > +#ifdef CONFIG_EFI
> > +#define PECOFF_EDATA_PADDING	\
> > +	.pecoff_edata_padding : { BYTE(0); . =
> > ALIGN(PECOFF_FILE_ALIGNMENT); }
> > +#else
> > +#define PECOFF_EDATA_PADDING
> > +#endif
> > +
> >  SECTIONS
> >  {
> >  	/* Beginning of code and text segment */
> > @@ -62,6 +71,8 @@ SECTIONS
> >  		_etext = .;
> >  	}
> > 
> > +	__text_end = .;
> > +
> >  	/* Start of data section */
> >  	_sdata = .;
> >  	RO_DATA(SECTION_ALIGN)
> > @@ -78,9 +89,12 @@ SECTIONS
> >  	.sdata : {
> >  		__global_pointer$ = . + 0x800;
> >  		*(.sdata*)
> > -		/* End of data section */
> > -		_edata = .;
> >  	}
> > +	PECOFF_EDATA_PADDING
> > +	__data_raw_size = ABSOLUTE(. - __text_end);
> > +
> > +	/* End of data section */
> > +	_edata = .;
> > 
> >  	BSS_SECTION(PAGE_SIZE, PAGE_SIZE, 0)
> > 
> > @@ -88,6 +102,8 @@ SECTIONS
> >  		*(.rel.dyn*)
> >  	}
> > 
> > +	__data_virt_size = ABSOLUTE(. - __text_end);
> > +
> >  	_end = .;
> > 
> >  	STABS_DEBUG

-- 
Regards,
Atish

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