gcc链接脚本和启动文件详解
C代码生成可执行程序分为：预编译、编译、汇编、链接四个阶段。
- 预处理器把源程序聚合在一起，并把宏定义转换为源语言；
- 编译器根据预处理的源程序生成汇编程序；
- 汇编器处理汇编程序，生成可重定位的机器代码；
- 连接器将可重定位的目标代码和库文件连接到一起，生成可执行程序。
介绍几个常用命令，具体解释出自《The GNU linker》：
- SECTIONS命令
- MEMORY命令
- ENTRY命令
output sections：
下面是rtthread bsp下的一个连接脚本，逐字分析：
/*
* linker script for GD32F4xx with GNU ld
* bernard.xiong 2009-10-14
*/
/* Program Entry, set to mark it as "used" and avoid gc */
/* MEMORY命令，定义flash、ram的起始地址和长度，name也可改写成ROM和RAM，rx和rw表示属性，可读可执行和可读可写，ORIGIN可以写成org或o，LENGTH可以写成len或l */
MEMORY
{
CODE (rx) : ORIGIN = 0x08000000, LENGTH = 64k /* 64/512KB flash */
DATA (rw) : ORIGIN = 0x20000000, LENGTH = 256k /* 256KB sram */
}
/* entry point，也有其他写法 */
ENTRY(Reset_Handler)
/* 定义栈大小 */
_system_stack_size = 0x1000;
/* SECTIONS命令，定义了具体的flash和ram分布 */
SECTIONS
{
/* gcc在flash中主要包含text、data和bss三个section，text存放code，data存放initialized data，bss存放uninitialized data */
.text :
{
/* .表示the location counter，At the start of the ‘SECTIONS’ command, the location counter
has the value ‘0’，ALIGN(4)表示4字节对齐 */
. = ALIGN(4);
/* _stext表示text section的起始地址，在cmbacktrace中用到了_stext */
_stext = .;
/* 当垃圾回收开启时‘--gc-sections’，使用KEEP防止被清除，isr_vector在startup文件中被定义，从这里开始存放中断向量表 */
KEEP(*(.isr_vector)) /* Startup code */
. = ALIGN(4);
/* The ‘*’ is a wildcard which matches any file name. The expression ‘*(.text)’ means all ‘.text’ input sections in all input files. */
*(.text) /* remaining code */
/* 这里应该是text的结尾，怎么理解会比较好一点？ */
*(.text.*) /* remaining code */
*(.rodata) /* read-only data (constants) */
*(.rodata*)
/* 没找到glue_7的解释 */
*(.glue_7)
*(.glue_7t)
*(.gnu.linkonce.t*)
/* section information for finsh shell */
. = ALIGN(4);
__fsymtab_start = .;
KEEP(*(FSymTab))
__fsymtab_end = .;
. = ALIGN(4);
__vsymtab_start = .;
KEEP(*(VSymTab))
__vsymtab_end = .;
. = ALIGN(4);
/* section information for initial. */
. = ALIGN(4);
/* */
__rt_init_start = .;
/* typedef int (*init_fn_t)(void)
#define SECTION(x) __attribute__((section(x)))
#define INIT_EXPORT(fn, level) RT_USED const init_fn_t __rt_init_##fn SECTION(".rti_fn." level) = fn
init_fn_t是函数指针；
SECTION(".rti_fn." level)则表示把对象放在由括号中的名称所指代的section中；
INIT_EXPORT(rti_start, "0") => init_fn_t __rt_init_rti_start = rti_start SECTION(.rti_fn.0)
SORT is an alias for SORT_BY_NAME
实质就是将函数rti_start的首地址放到这个section中，并排序（启动顺序很重要） */
KEEP(*(SORT(.rti_fn*)))
__rt_init_end = .;
. = ALIGN(4);
. = ALIGN(4);
/* cmbacktrace中用到了这个地址 */
_etext = .;
} > CODE = 0/* CODE section中 */
/* .ARM.exidx is sorted, so has to go in its own output section. */
__exidx_start = .;
.ARM.exidx :
{
*(.ARM.exidx* .gnu.linkonce.armexidx.*)
/* This is used by the startup in order to initialize the .data secion */
_sidata = .;
} > CODE
__exidx_end = .;
/* .data section which is used for initialized data */
.data : AT (_sidata)
{
. = ALIGN(4);
/* This is used by the startup in order to initialize the .data secion */
_sdata = . ;
/* 所有初始化的数据 */
*(.data)
*(.data.*)
*(.gnu.linkonce.d*)
. = ALIGN(4);
/* This is used by the startup in order to initialize the .data secion */
_edata = . ;
} >DATA
.stack :
{
/* 栈，起始地址和大小 */
. = . + _system_stack_size;
/* 栈顶地址四字节对齐 */
. = ALIGN(4);
/* cmbacktrace中用到 */
_estack = .;
} >DATA
__bss_start = .;
.bss :
{
. = ALIGN(4);
/* This is used by the startup in order to initialize the .bss secion */
/* 实际上startup中使用了__bss_start和__bss_end地址 */
_sbss = .;
/* 所有未初始化的数据 */
*(.bss)
*(.bss.*)
/* COMMON好像没怎么见过，gcc中的说明是这样的：
A special notation is needed for common symbols, because in many object file formats
common symbols do not have a particular input section. The linker treats common symbols
as though they are in an input section named ‘COMMON’.
You may use file names with the ‘COMMON’ section just as with any other input sections.
You can use this to place common symbols from a particular input file in one section while
common symbols from other input files are placed in another section. */
*(COMMON)
/* 结尾地址四字节对齐 */
. = ALIGN(4);
/* This is used by the startup in order to initialize the .bss secion */
_ebss = . ;
/* 暂时没找到说明 */
*(.bss.init)
} > DATA
__bss_end = .;
_end = .;
/* 下面这些不知道干嘛的 */
/* Stabs debugging sections. */
.stab 0 : { *(.stab) }
.stabstr 0 : { *(.stabstr) }
.stab.excl 0 : { *(.stab.excl) }
.stab.exclstr 0 : { *(.stab.exclstr) }
.stab.index 0 : { *(.stab.index) }
.stab.indexstr 0 : { *(.stab.indexstr) }
.comment 0 : { *(.comment) }
/* DWARF debug sections.
* Symbols in the DWARF debugging sections are relative to the beginning
* of the section so we begin them at 0. */
/* DWARF 1 */
.debug 0 : { *(.debug) }
.line 0 : { *(.line) }
/* GNU DWARF 1 extensions */
.debug_srcinfo 0 : { *(.debug_srcinfo) }
.debug_sfnames 0 : { *(.debug_sfnames) }
/* DWARF 1.1 and DWARF 2 */
.debug_aranges 0 : { *(.debug_aranges) }
.debug_pubnames 0 : { *(.debug_pubnames) }
/* DWARF 2 */
.debug_info 0 : { *(.debug_info .gnu.linkonce.wi.*) }
.debug_abbrev 0 : { *(.debug_abbrev) }
.debug_line 0 : { *(.debug_line) }
.debug_frame 0 : { *(.debug_frame) }
.debug_str 0 : { *(.debug_str) }
.debug_loc 0 : { *(.debug_loc) }
.debug_macinfo 0 : { *(.debug_macinfo) }
/* SGI/MIPS DWARF 2 extensions */
.debug_weaknames 0 : { *(.debug_weaknames) }
.debug_funcnames 0 : { *(.debug_funcnames) }
.debug_typenames 0 : { *(.debug_typenames) }
.debug_varnames 0 : { *(.debug_varnames) }
}
下面是对应的启动文件：
;/*
; * Copyright (c) 2006-2021, RT-Thread Development Team
; *
; * SPDX-License-Identifier: Apache-2.0
; *
; * Change Logs:
; * Date Author Notes
; * 2018-05-22 tanek first implementation
; */
/* 指令语法集 统一的：ARM and THUMB instructions */
.syntax unified
/* Select the target processor */
.cpu cortex-m4
/* Select the floating-point unit to assemble for */
.fpu softvfp
/* This performs the same action as .code 16
thumb指令集，16bit */
.thumb
.global g_pfnVectors
.global Default_Handler
/* 意思是isr_vector的section，"a",%progbits啥意思不太明白 */
.section .isr_vector,"a",%progbits
/* 暂时没找到 */
.type g_pfnVectors, %object
g_pfnVectors:
/* On the OpenRISC, the .word directive produces a 32 bit value */
.word _estack // Top of Stack
.word Reset_Handler // Reset Handler
.word NMI_Handler // NMI Handler
.word HardFault_Handler // Hard Fault Handler
.word MemManage_Handler // MPU Fault Handler
.word BusFault_Handler // Bus Fault Handler
.word UsageFault_Handler // Usage Fault Handler
.word 0 // Reserved
.word 0 // Reserved
.word 0 // Reserved
.word 0 // Reserved
.word SVC_Handler // SVCall Handler
.word DebugMon_Handler // Debug Monitor Handler
.word 0 // Reserved
.word PendSV_Handler // PendSV Handler
.word SysTick_Handler // SysTick Handler
// external interrupts handler
.word WWDGT_IRQHandler // 16:Window Watchdog Timer
.word LVD_IRQHandler // 17:LVD through EXTI Line detect
.word TAMPER_STAMP_IRQHandler // 18:Tamper and TimeStamp through EXTI Line detect
.word RTC_WKUP_IRQHandler // 19:RTC Wakeup through EXTI Line
.word FMC_IRQHandler // 20:FMC
.word RCU_CTC_IRQHandler // 21:RCU and CTC
.word EXTI0_IRQHandler // 22:EXTI Line 0
.word EXTI1_IRQHandler // 23:EXTI Line 1
.word EXTI2_IRQHandler // 24:EXTI Line 2
.word EXTI3_IRQHandler // 25:EXTI Line 3
.word EXTI4_IRQHandler // 26:EXTI Line 4
.word DMA0_Channel0_IRQHandler // 27:DMA0 Channel0
.word DMA0_Channel1_IRQHandler // 28:DMA0 Channel1
.word DMA0_Channel2_IRQHandler // 29:DMA0 Channel2
.word DMA0_Channel3_IRQHandler // 30:DMA0 Channel3
.word DMA0_Channel4_IRQHandler // 31:DMA0 Channel4
.word DMA0_Channel5_IRQHandler // 32:DMA0 Channel5
.word DMA0_Channel6_IRQHandler // 33:DMA0 Channel6
.word ADC_IRQHandler // 34:ADC
.word CAN0_TX_IRQHandler // 35:CAN0 TX
.word CAN0_RX0_IRQHandler // 36:CAN0 RX0
.word CAN0_RX1_IRQHandler // 37:CAN0 RX1
.word CAN0_EWMC_IRQHandler // 38:CAN0 EWMC
.word EXTI5_9_IRQHandler // 39:EXTI5 to EXTI9
.word TIMER0_BRK_TIMER8_IRQHandler // 40:TIMER0 Break and TIMER8
.word TIMER0_UP_TIMER9_IRQHandler // 41:TIMER0 Update and TIMER9
.word TIMER0_TRG_CMT_TIMER10_IRQHandler // 42:TIMER0 Trigger and Commutation and TIMER10
.word TIMER0_CC_IRQHandler // 43:TIMER0 Capture Compare
.word TIMER1_IRQHandler // 44:TIMER1
.word TIMER2_IRQHandler // 45:TIMER2
.word TIMER3_IRQHandler // 46:TIMER3
.word I2C0_EV_IRQHandler // 47:I2C0 Event
.word I2C0_ER_IRQHandler // 48:I2C0 Error
.word I2C1_EV_IRQHandler // 49:I2C1 Event
.word I2C1_ER_IRQHandler // 50:I2C1 Error
.word SPI0_IRQHandler // 51:SPI0
.word SPI1_IRQHandler // 52:SPI1
.word USART0_IRQHandler // 53:USART0
.word USART1_IRQHandler // 54:USART1
.word USART2_IRQHandler // 55:USART2
.word EXTI10_15_IRQHandler // 56:EXTI10 to EXTI15
.word RTC_Alarm_IRQHandler // 57:RTC Alarm
.word USBFS_WKUP_IRQHandler // 58:USBFS Wakeup
.word TIMER7_BRK_TIMER11_IRQHandler // 59:TIMER7 Break and TIMER11
.word TIMER7_UP_TIMER12_IRQHandler // 60:TIMER7 Update and TIMER12
.word TIMER7_TRG_CMT_TIMER13_IRQHandler // 61:TIMER7 Trigger and Commutation and TIMER13
.word TIMER7_CC_IRQHandler // 62:TIMER7 Capture Compare
.word DMA0_Channel7_IRQHandler // 63:DMA0 Channel7
.word EXMC_IRQHandler // 64:EXMC
.word SDIO_IRQHandler // 65:SDIO
.word TIMER4_IRQHandler // 66:TIMER4
.word SPI2_IRQHandler // 67:SPI2
.word UART3_IRQHandler // 68:UART3
.word UART4_IRQHandler // 69:UART4
.word TIMER5_DAC_IRQHandler // 70:TIMER5 and DAC0 DAC1 Underrun error
.word TIMER6_IRQHandler // 71:TIMER6
.word DMA1_Channel0_IRQHandler // 72:DMA1 Channel0
.word DMA1_Channel1_IRQHandler // 73:DMA1 Channel1
.word DMA1_Channel2_IRQHandler // 74:DMA1 Channel2
.word DMA1_Channel3_IRQHandler // 75:DMA1 Channel3
.word DMA1_Channel4_IRQHandler // 76:DMA1 Channel4
.word ENET_IRQHandler // 77:Ethernet
.word ENET_WKUP_IRQHandler // 78:Ethernet Wakeup through EXTI Line
.word CAN1_TX_IRQHandler // 79:CAN1 TX
.word CAN1_RX0_IRQHandler // 80:CAN1 RX0
.word CAN1_RX1_IRQHandler // 81:CAN1 RX1
.word CAN1_EWMC_IRQHandler // 82:CAN1 EWMC
.word USBFS_IRQHandler // 83:USBFS
.word DMA1_Channel5_IRQHandler // 84:DMA1 Channel5
.word DMA1_Channel6_IRQHandler // 85:DMA1 Channel6
.word DMA1_Channel7_IRQHandler // 86:DMA1 Channel7
.word USART5_IRQHandler // 87:USART5
.word I2C2_EV_IRQHandler // 88:I2C2 Event
.word I2C2_ER_IRQHandler // 89:I2C2 Error
.word USBHS_EP1_Out_IRQHandler // 90:USBHS Endpoint 1 Out
.word USBHS_EP1_In_IRQHandler // 91:USBHS Endpoint 1 in
.word USBHS_WKUP_IRQHandler // 92:USBHS Wakeup through EXTI Line
.word USBHS_IRQHandler // 93:USBHS
.word DCI_IRQHandler // 94:DCI
.word 0 // 95:Reserved
.word TRNG_IRQHandler // 96:TRNG
.word FPU_IRQHandler // 97:FPU
.word UART6_IRQHandler // 98:UART6
.word UART7_IRQHandler // 99:UART7
.word SPI3_IRQHandler // 100:SPI3
.word SPI4_IRQHandler // 101:SPI4
.word SPI5_IRQHandler // 102:SPI5
.word 0 // 103:Reserved
.word TLI_IRQHandler // 104:TLI
.word TLI_ER_IRQHandler // 105:TLI Error
.word IPA_IRQHandler // 106:IPA
.size g_pfnVectors, .-g_pfnVectors
.section .text.Reset_Handler
.weak Reset_Handler
.type Reset_Handler, %function
Reset_Handler:
ldr r1, =_sidata
ldr r2, =_sdata
ldr r3, =_edata
subs r3, r2
ble fill_bss_start
loop_copy_data:
subs r3, #4
ldr r0, [r1,r3]
str r0, [r2,r3]
bgt loop_copy_data
fill_bss_start:
ldr r1, =__bss_start
ldr r2, =__bss_end
movs r0, 0
subs r2, r1
ble startup_enter
loop_fill_bss:
subs r2, #4
str r0, [r1, r2]
bgt loop_fill_bss
startup_enter:
bl SystemInit
bl main
/* Exception Handlers */
.weak NMI_Handler
.type NMI_Handler, %function
NMI_Handler:
b .
.size NMI_Handler, . - NMI_Handler
.weak MemManage_Handler
.type MemManage_Handler, %function
MemManage_Handler:
b .
.size MemManage_Handler, . - MemManage_Handler
.weak BusFault_Handler
.type BusFault_Handler, %function
BusFault_Handler:
b .
.size BusFault_Handler, . - BusFault_Handler
.weak UsageFault_Handler
.type UsageFault_Handler, %function
UsageFault_Handler:
b .
.size UsageFault_Handler, . - UsageFault_Handler
.weak SVC_Handler
.type SVC_Handler, %function
SVC_Handler:
b .
.size SVC_Handler, . - SVC_Handler
.weak DebugMon_Handler
.type DebugMon_Handler, %function
DebugMon_Handler:
b .
.size DebugMon_Handler, . - DebugMon_Handler
.weak PendSV_Handler
.type PendSV_Handler, %function
PendSV_Handler:
b .
.size PendSV_Handler, . - PendSV_Handler
.weak SysTick_Handler
.type SysTick_Handler, %function
SysTick_Handler:
b .
.size SysTick_Handler, . - SysTick_Handler
/* IQR Handler */
.section .text.Default_Handler,"ax",%progbits
.type Default_Handler, %function
Default_Handler:
b .
.size Default_Handler, . - Default_Handler
.macro IRQ handler
.weak \handler
.set \handler, Default_Handler
.endm
IRQ WWDGT_IRQHandler
IRQ LVD_IRQHandler
IRQ TAMPER_STAMP_IRQHandler
IRQ RTC_WKUP_IRQHandler
IRQ FMC_IRQHandler
IRQ RCU_CTC_IRQHandler
IRQ EXTI0_IRQHandler
IRQ EXTI1_IRQHandler
IRQ EXTI2_IRQHandler
IRQ EXTI3_IRQHandler
IRQ EXTI4_IRQHandler
IRQ DMA0_Channel0_IRQHandler
IRQ DMA0_Channel1_IRQHandler
IRQ DMA0_Channel2_IRQHandler
IRQ DMA0_Channel3_IRQHandler
IRQ DMA0_Channel4_IRQHandler
IRQ DMA0_Channel5_IRQHandler
IRQ DMA0_Channel6_IRQHandler
IRQ ADC_IRQHandler
IRQ CAN0_TX_IRQHandler
IRQ CAN0_RX0_IRQHandler
IRQ CAN0_RX1_IRQHandler
IRQ CAN0_EWMC_IRQHandler
IRQ EXTI5_9_IRQHandler
IRQ TIMER0_BRK_TIMER8_IRQHandler
IRQ TIMER0_UP_TIMER9_IRQHandler
IRQ TIMER0_TRG_CMT_TIMER10_IRQHandler
IRQ TIMER0_CC_IRQHandler
IRQ TIMER1_IRQHandler
IRQ TIMER2_IRQHandler
IRQ TIMER3_IRQHandler
IRQ I2C0_EV_IRQHandler
IRQ I2C0_ER_IRQHandler
IRQ I2C1_EV_IRQHandler
IRQ I2C1_ER_IRQHandler
IRQ SPI0_IRQHandler
IRQ SPI1_IRQHandler
IRQ USART0_IRQHandler
IRQ USART1_IRQHandler
IRQ USART2_IRQHandler
IRQ EXTI10_15_IRQHandler
IRQ RTC_Alarm_IRQHandler
IRQ USBFS_WKUP_IRQHandler
IRQ TIMER7_BRK_TIMER11_IRQHandler
IRQ TIMER7_UP_TIMER12_IRQHandler
IRQ TIMER7_TRG_CMT_TIMER13_IRQHandler
IRQ TIMER7_CC_IRQHandler
IRQ DMA0_Channel7_IRQHandler
IRQ EXMC_IRQHandler
IRQ SDIO_IRQHandler
IRQ TIMER4_IRQHandler
IRQ SPI2_IRQHandler
IRQ UART3_IRQHandler
IRQ UART4_IRQHandler
IRQ TIMER5_DAC_IRQHandler
IRQ TIMER6_IRQHandler
IRQ DMA1_Channel0_IRQHandler
IRQ DMA1_Channel1_IRQHandler
IRQ DMA1_Channel2_IRQHandler
IRQ DMA1_Channel3_IRQHandler
IRQ DMA1_Channel4_IRQHandler
IRQ ENET_IRQHandler
IRQ ENET_WKUP_IRQHandler
IRQ CAN1_TX_IRQHandler
IRQ CAN1_RX0_IRQHandler
IRQ CAN1_RX1_IRQHandler
IRQ CAN1_EWMC_IRQHandler
IRQ USBFS_IRQHandler
IRQ DMA1_Channel5_IRQHandler
IRQ DMA1_Channel6_IRQHandler
IRQ DMA1_Channel7_IRQHandler
IRQ USART5_IRQHandler
IRQ I2C2_EV_IRQHandler
IRQ I2C2_ER_IRQHandler
IRQ USBHS_EP1_Out_IRQHandler
IRQ USBHS_EP1_In_IRQHandler
IRQ USBHS_WKUP_IRQHandler
IRQ USBHS_IRQHandler
IRQ DCI_IRQHandler
IRQ TRNG_IRQHandler
IRQ FPU_IRQHandler
IRQ UART6_IRQHandler
IRQ UART7_IRQHandler
IRQ SPI3_IRQHandler
IRQ SPI4_IRQHandler
IRQ SPI5_IRQHandler
IRQ TLI_IRQHandler
IRQ TLI_ER_IRQHandler
IRQ IPA_IRQHandler