LD和NOLOAD部分：了解奇怪的LMA值
我正在编写一个裸机内核，并且在NOLOAD部分的情况下我无法理解ld的输出。我声明只在MMU激活时存在的符号，所以VMA和LMA不一样。 我曾经声明这样那样的一个部分：LD和NOLOAD部分：了解奇怪的LMA值
_foobar_start = .; .foobar : AT(ADDR(.foobar) - VA_PA_OFFSET)
{
*.o(.foobar.section*)
}
_foobar_end = .;
现在我节的内容之一是通过引导加载器加载的，所以我只想申报VMA符号在运行时使用，访问数据，所以我尝试了NOLOAD属性：
_foobar_start = .; .foobar (NOLOAD) :
{
. += SIZE_OF_FOOBAR;
}
_foobar_end = .;
我知道，我不关心LMA在这种情况下，但我希望看到类似的东西，其中LMA = VMA（见LD manual）：
.foobar 0x000000004002c000 0x353c load address 0x000000004002c000 但我得到一个奇怪的LMA的东西，我不作感：
.foobar 0x000000004002c000 0x353c load address 0x0000000001900000 如果我使用
.foobar (NOLOAD) : AT(_foobar_start) 似乎一切都很好，我看迫使VMA = LMA脚本只有
.foobar 0x000000004002c000 0x353c 即使没有强制VMA = LMA，所产生的ELF是好的，但我得到的，因为其他部分的编译时间一些警告（toto是其他部分）：
warning: dot moved backwards before `.toto 我希望了解这些内容。
当我指定NOLOAD时，是否有原因导致LMA = VMA？
编辑：这里是全链接文件触发问题。我加了一些意见，针点问题
OUTPUT_ARCH(CONFIG_LINKER_ARCH) OUTPUT_FORMAT(CONFIG_LINKER_FORMAT)
_kern_phys_base = OCRAM_BASE_PA + OCRAM_OFFSET;
_kern_offset = KERNEL_VA_PA_OFFSET;
SECTIONS
{
. = _kern_phys_base;
_start_image_addr = .;
. = ALIGN(0x1000);
_early_text_start = .;
.early_text :
{
KEEP(*(.text.boot))
KEEP(*(.text.mmu))
}
. = ALIGN(4);
.early_rodata :
{
*(.rodata.boot*)
*(.rodata.mmu*)
}
_early_text_end = .;
. = ALIGN(0x1000);
_early_data_start = .;
.early_data :
{
*(.data.boot)
}
_early_data_end = .;
. = ALIGN(0x4000);
_early_bss_start = .;
.early_bss :
{
*(.bss.mmu)
*(.bss.boot)
}
. = ALIGN(16);
_early_bss_end = .;
_early_end = .;
/*
* The following part is accessed only once the MMU has been
* activated, so we first need to jump into "high" memory
*/
. += _kern_offset;
. = ALIGN(0x1000);
_text_start = .;
.text : AT(ADDR(.text) - _kern_offset)
{
*(.text .text.*)
}
_text_end = .;
. = ALIGN(0x1000);
_rodata_start = .;
.rodata : AT(ADDR(.rodata) - _kern_offset)
{
*(.rodata*)
}
_rodata_end = .;
. = ALIGN(4);
_arm_extab_start = .;
.ARM.extab : AT(ADDR(.ARM.extab) - _kern_offset)
{
*(.ARM.extab)
}
_arm_extab_end = .;
. = ALIGN(4);
_arm_exidx_start = .;
.ARM.exidx : AT(ADDR(.ARM.exidx) - _kern_offset)
{
*(.ARM.exidx)
}
_arm_exidx_end = .;
. = ALIGN(4);
_kernel_debug_info_start = .;
_kernel_debug_info_end = .;
. = ALIGN(4);
_emergency_code_vstart = .;
_emergency_code_vend = .;
/*
* This is where I use the NOLOAD, with AT this time
* This 'archive' part is not located in OCRAM, but some
* where else in RAM
*/
_archive_point_save = .;
. = DDR_BASE_VA;
. = ALIGN(512);
_archive_start = .;
.archive_data (NOLOAD) : AT(_archive_start)
{
codes.o(.rawdata*)
}
_archive_end = .;
. = _archive_point_save;
/* Back to OCRAM VMA */
. = ALIGN(0x1000);
_data_start = .;
.data : AT(ADDR(.data) - _kern_offset)
{
*(.data*)
}
_data_end = .;
. = ALIGN(32);
_bss_start = .;
.bss : AT(ADDR(.bss) - _kern_offset)
{
*(.bss .bss.*)
}
. = ALIGN(16);
_bss_end = .;
/*
* Second location, also in RAM, just after the '.archive_data' section
* This time I didn't put the AT to show the difference in output
*/
_dyn_archive_point_save = .;
. = _archive_end;
. = ALIGN(0x1000);
_dyn_archive_start = .;
.dyn_archive (NOLOAD) :
{
. += _dyn_archive_space;
}
_dyn_archive_end = .;
. = _dyn_archive_point_save;
/* Back to OCRAM VMA */
. = ALIGN(0x1000);
_kernel_stack_guard = .;
. += 0x1000;
.stack (NOLOAD) :
{
_kernel_stack_end = .;
/* 2 pages of 4 kB */
. += 0x2000;
_kernel_stack_start = .;
}
_kernel_image_end = .;
}
这里是objdump -x输出：
build/kernel/kernel.elf: file format elf32-littlearm build/kernel/kernel.elf
architecture: arm, flags 0x00000102:
EXEC_P, D_PAGED
start address 0x00910000
Program Header:
0x70000001 off 0x0003072c vaddr 0x4003072c paddr 0x0093072c align 2**2
filesz 0x000000a0 memsz 0x000000a0 flags r--
LOAD off 0x00010000 vaddr 0x00910000 paddr 0x00910000 align 2**16
filesz 0x00002828 memsz 0x00008000 flags rwx
LOAD off 0x00018000 vaddr 0x40018000 paddr 0x00918000 align 2**16
filesz 0x000199e0 memsz 0x0001fa28 flags rwx
LOAD off 0x00038000 vaddr 0x41028000 paddr 0x01928000 align 2**16
filesz 0x00000000 memsz 0x00100000 flags rw-
LOAD off 0x00039000 vaddr 0x40039000 paddr 0x40039000 align 2**16
filesz 0x00000000 memsz 0x00002000 flags rw-
LOAD off 0x00040000 vaddr 0x41000000 paddr 0x41000000 align 2**16
filesz 0x00000000 memsz 0x00028000 flags rw-
private flags = 5000200: [Version5 EABI] [soft-float ABI]
Sections:
Idx Name Size VMA LMA File off Algn
0 .early_text 000015c0 00910000 00910000 00010000 2**5
CONTENTS, ALLOC, LOAD, READONLY, CODE
1 .early_rodata 00000030 009115c0 009115c0 000115c0 2**2
CONTENTS, ALLOC, LOAD, READONLY, DATA
2 .early_data 00000828 00912000 00912000 00012000 2**3
CONTENTS, ALLOC, LOAD, DATA
3 .early_bss 00004000 00914000 00914000 00012828 2**14
ALLOC
4 .text 000142d8 40018000 00918000 00018000 2**5
CONTENTS, ALLOC, LOAD, READONLY, CODE
5 .rodata 000036c0 4002d000 0092d000 0002d000 2**2
CONTENTS, ALLOC, LOAD, READONLY, DATA
6 .ARM.extab 0000006c 400306c0 009306c0 000306c0 2**2
CONTENTS, ALLOC, LOAD, READONLY, DATA
7 .ARM.exidx 000000a0 4003072c 0093072c 0003072c 2**2
CONTENTS, ALLOC, LOAD, READONLY, DATA
8 .archive_data 00028000 41000000 41000000 00040000 2**0
ALLOC
9 .data 000009e0 40031000 00931000 00031000 2**3
CONTENTS, ALLOC, LOAD, DATA
10 .bss 00006048 400319e0 009319e0 000319e0 2**3
ALLOC
11 .dyn_archive 00100000 41028000 01928000 00038000 2**0
ALLOC
12 .stack 00002000 40039000 40039000 00039000 2**0
ALLOC
13 .comment 0000002d 00000000 00000000 000319e0 2**0
CONTENTS, READONLY
14 .ARM.attributes 00000037 00000000 00000000 00031a0d 2**0
CONTENTS, READONLY
SYMBOL TABLE:
no symbols
正如你可以看到：.archive_data和.stack正确地得到VMA = LMA但.dyn_archive没有。如果我删除的.archive_data的AT，我得到比.dyn_archive相同的行为与地址0x1900000
回答：
看来我最后的评论是有效的，如证实（至少对扩大我们的手册中解释）on the binutils ML
由“LMA后退”场景触发的警告以及每次正确更新LMA都是手动更新的警告是正确的方法。
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