linux-kernel - [PATCH] LoongArch: Implement physical address with ELF program header

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Message-Id: <20250714083856.910856-1-maobibo@loongson.cn>
Date: Mon, 14 Jul 2025 16:38:56 +0800
From: Bibo Mao <maobibo@...ngson.cn>
To: Huacai Chen <chenhuacai@...nel.org>
Cc: WANG Xuerui <kernel@...0n.name>,
	Xi Ruoyao <xry111@...111.site>,
	loongarch@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: [PATCH] LoongArch: Implement physical address with ELF program header

With structure elf64_phdr, field p_paddr is physical address of the
segment. And it is convenient for qemu to calculate the physical
address when directly boot ELF kernel image.

Otherwise QEMU needs convert virtual address p_vaddr into physical
address, the conversion logic assumes that DMW method is used where
48 bit physical address is supported. However with direct MMU mapping
method with start address from 0xFFFF800000000000, only 47 bit physical
address is supported. QEMU cannot assume the kernel behavior at kernel
loading stage.

Here add physical address indication in ELF program header, it is
convenient to get kernel loading physical address.

Here is output with command readelf -l vmlinux with patch:
  Elf file type is EXEC (Executable file)
  Entry point 0x90000000015f5000
  There are 2 program headers, starting at offset 64
  Program Headers:
    Type           Offset             VirtAddr           PhysAddr
                   FileSiz            MemSiz              Flags  Align
    LOAD           0x0000000000010000 0x9000000000200000 0x0000000000200000
                   0x000000000293b000 0x0000000002a79b98  RWE    0x10000

And output with command readelf -l vmlinux without the patch:
  Elf file type is EXEC (Executable file)
  Entry point 0x90000000015f5000
  There are 2 program headers, starting at offset 64
  Program Headers:
    Type           Offset             VirtAddr           PhysAddr
                   FileSiz            MemSiz              Flags  Align
    LOAD           0x0000000000010000 0x9000000000200000 0x9000000000200000
                   0x000000000293b000 0x0000000002a79b98  RWE    0x10000

Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
---
 arch/loongarch/kernel/vmlinux.lds.S | 31 +++++++++++++++++++----------
 1 file changed, 20 insertions(+), 11 deletions(-)

diff --git a/arch/loongarch/kernel/vmlinux.lds.S b/arch/loongarch/kernel/vmlinux.lds.S
index 08ea921cdec1..bb936d92b334 100644
--- a/arch/loongarch/kernel/vmlinux.lds.S
+++ b/arch/loongarch/kernel/vmlinux.lds.S
@@ -3,10 +3,12 @@
 #include <asm/asm-offsets.h>
 #include <asm/thread_info.h>
 #include <asm/orc_lookup.h>
+#include <asm/addrspace.h>
 
 #define PAGE_SIZE _PAGE_SIZE
 #define RO_EXCEPTION_TABLE_ALIGN	4
 #define PHYSADDR_MASK			0xffffffffffff /* 48-bit */
+#define LOAD_OFFSET			CACHE_BASE
 
 /*
  * Put .bss..swapper_pg_dir as the first thing in .bss. This will
@@ -42,7 +44,7 @@ SECTIONS
 
 	. = ALIGN(PECOFF_SEGMENT_ALIGN);
 	_stext = .;
-	.text : {
+	.text : AT(ADDR(.text) - LOAD_OFFSET) {
 		TEXT_TEXT
 		SCHED_TEXT
 		LOCK_TEXT
@@ -60,7 +62,7 @@ SECTIONS
 	__inittext_begin = .;
 
 	INIT_TEXT_SECTION(PAGE_SIZE)
-	.exit.text : {
+	.exit.text : AT(ADDR(.exit.text) - LOAD_OFFSET) {
 		EXIT_TEXT
 	}
 
@@ -82,7 +84,7 @@ SECTIONS
 	}
 
 	INIT_DATA_SECTION(16)
-	.exit.data : {
+	.exit.data : AT(ADDR(.exit.data) - LOAD_OFFSET) {
 		EXIT_DATA
 	}
 
@@ -90,7 +92,7 @@ SECTIONS
 	PERCPU_SECTION(1 << CONFIG_L1_CACHE_SHIFT)
 #endif
 
-	.init.bss : {
+	.init.bss : AT(ADDR(.init.bss) - LOAD_OFFSET) {
 		*(.init.bss)
 	}
 	. = ALIGN(PECOFF_SEGMENT_ALIGN);
@@ -101,27 +103,34 @@ SECTIONS
 	_sdata = .;
 	RO_DATA(4096)
 
-	.got : ALIGN(16) { *(.got) }
-	.plt : ALIGN(16) { *(.plt) }
-	.got.plt : ALIGN(16) { *(.got.plt) }
+	. =  ALIGN(16);
+	.got : AT(ADDR(.got) - LOAD_OFFSET) { *(.got) }
+	. =  ALIGN(16);
+	.plt : AT(ADDR(.plt) - LOAD_OFFSET) { *(.plt) }
+	. =  ALIGN(16);
+	.got.plt : AT(ADDR(.got.plt) - LOAD_OFFSET) { *(.got.plt) }
 
 	RW_DATA(1 << CONFIG_L1_CACHE_SHIFT, PAGE_SIZE, THREAD_SIZE)
 
-	.rela.dyn : ALIGN(8) {
+	. = ALIGN(8);
+	.rela.dyn : AT(ADDR(.rela.dyn) - LOAD_OFFSET) {
 		__rela_dyn_begin = .;
 		 *(.rela.dyn) *(.rela*)
 		__rela_dyn_end = .;
 	}
 
 #ifdef CONFIG_RELR
-	.relr.dyn : ALIGN(8) {
+	. = ALIGN(8);
+	.relr.dyn : AT(ADDR(.relr.dyn) - LOAD_OFFSET) {
 		__relr_dyn_begin = .;
 		 *(.relr.dyn)
 		__relr_dyn_end = .;
 	}
 #endif
 
-	.data.rel : { *(.data.rel*) }
+	.data.rel : AT(ADDR(.data.rel) - LOAD_OFFSET) {
+		*(.data.rel*)
+	}
 
 #ifdef CONFIG_RELOCATABLE
 	. = ALIGN(8);
@@ -134,7 +143,7 @@ SECTIONS
 
 	ORC_UNWIND_TABLE
 
-	.sdata : {
+	.sdata : AT(ADDR(.sdata) - LOAD_OFFSET) {
 		*(.sdata)
 	}
 	.edata_padding : { BYTE(0); . = ALIGN(PECOFF_FILE_ALIGN); }

base-commit: 347e9f5043c89695b01e66b3ed111755afcf1911
-- 
2.39.3