From: Arvind Sankar <nivedita@xxxxxxxxxxxx> There are use cases for storing the offset of a symbol in kernel_info. For example, the trenchboot series [0] needs to store the offset of the Measured Launch Environment header in kernel_info. Since commit (note: commit ID from tip/master) commit 527afc212231 ("x86/boot: Check that there are no run-time relocations") run-time relocations are not allowed in the compressed kernel, so simply using the symbol in kernel_info, as .long symbol will cause a linker error because this is not position-independent. With kernel_info being a separate object file and in a different section from startup_32, there is no way to calculate the offset of a symbol from the start of the image in a position-independent way. To enable such use cases, put kernel_info into its own section which is placed at a predetermined offset (KERNEL_INFO_OFFSET) via the linker script. This will allow calculating the symbol offset in a position-independent way, by adding the offset from the start of kernel_info to KERNEL_INFO_OFFSET. Ensure that kernel_info is aligned, and use the SYM_DATA.* macros instead of bare labels. This stores the size of the kernel_info structure in the ELF symbol table. Signed-off-by: Arvind Sankar <nivedita@xxxxxxxxxxxx> Cc: Ross Philipson <ross.philipson@xxxxxxxxxx> Signed-off-by: Ross Philipson <ross.philipson@xxxxxxxxxx> --- arch/x86/boot/compressed/kernel_info.S | 19 +++++++++++++++---- arch/x86/boot/compressed/kernel_info.h | 12 ++++++++++++ arch/x86/boot/compressed/vmlinux.lds.S | 6 ++++++ 3 files changed, 33 insertions(+), 4 deletions(-) create mode 100644 arch/x86/boot/compressed/kernel_info.h diff --git a/arch/x86/boot/compressed/kernel_info.S b/arch/x86/boot/compressed/kernel_info.S index f818ee8fba38..c18f07181dd5 100644 --- a/arch/x86/boot/compressed/kernel_info.S +++ b/arch/x86/boot/compressed/kernel_info.S @@ -1,12 +1,23 @@ /* SPDX-License-Identifier: GPL-2.0 */ +#include <linux/linkage.h> #include <asm/bootparam.h> +#include "kernel_info.h" - .section ".rodata.kernel_info", "a" +/* + * If a field needs to hold the offset of a symbol from the start + * of the image, use the macro below, eg + * .long rva(symbol) + * This will avoid creating run-time relocations, which are not + * allowed in the compressed kernel. + */ + +#define rva(X) (((X) - kernel_info) + KERNEL_INFO_OFFSET) - .global kernel_info + .section ".rodata.kernel_info", "a" -kernel_info: + .balign 16 +SYM_DATA_START(kernel_info) /* Header, Linux top (structure). */ .ascii "LToP" /* Size. */ @@ -19,4 +30,4 @@ kernel_info: kernel_info_var_len_data: /* Empty for time being... */ -kernel_info_end: +SYM_DATA_END_LABEL(kernel_info, SYM_L_LOCAL, kernel_info_end) diff --git a/arch/x86/boot/compressed/kernel_info.h b/arch/x86/boot/compressed/kernel_info.h new file mode 100644 index 000000000000..c127f84aec63 --- /dev/null +++ b/arch/x86/boot/compressed/kernel_info.h @@ -0,0 +1,12 @@ +/* SPDX-License-Identifier: GPL-2.0 */ + +#ifndef BOOT_COMPRESSED_KERNEL_INFO_H +#define BOOT_COMPRESSED_KERNEL_INFO_H + +#ifdef CONFIG_X86_64 +#define KERNEL_INFO_OFFSET 0x500 +#else /* 32-bit */ +#define KERNEL_INFO_OFFSET 0x100 +#endif + +#endif /* BOOT_COMPRESSED_KERNEL_INFO_H */ diff --git a/arch/x86/boot/compressed/vmlinux.lds.S b/arch/x86/boot/compressed/vmlinux.lds.S index 083ec6d7722a..718c52f3f1e6 100644 --- a/arch/x86/boot/compressed/vmlinux.lds.S +++ b/arch/x86/boot/compressed/vmlinux.lds.S @@ -7,6 +7,7 @@ OUTPUT_FORMAT(CONFIG_OUTPUT_FORMAT) #include <asm/cache.h> #include <asm/page_types.h> +#include "kernel_info.h" #ifdef CONFIG_X86_64 OUTPUT_ARCH(i386:x86-64) @@ -27,6 +28,11 @@ SECTIONS HEAD_TEXT _ehead = . ; } + .rodata.kernel_info KERNEL_INFO_OFFSET : { + *(.rodata.kernel_info) + } + ASSERT(ABSOLUTE(kernel_info) == KERNEL_INFO_OFFSET, "kernel_info at bad address!") + .rodata..compressed : { *(.rodata..compressed) } -- 2.39.3