I'm trying to implement semihosting on an arm board (precisely stm32f4D07, mounting a cortex-m4 processor) in order to facilitate the debugging of a program. I've followed the steps indicated in this nice article. I've installed openocd, compiled my program as it is shown in the example makefile and using the same linker script and startup file. Everything seems fine but when I start gdb and run the program this is what I get:
semihosting is enabled
target state: halted
target halted due to debug-request, current mode: Thread
xPSR: 0x01000000 pc: 0x2b007822 msp: 0x4c07b510, semihosting
Loading section .text, size 0xd3f4 lma 0x8000000
Loading section .ARM, size 0x8 lma 0x800d3f4
Loading section .init_array, size 0x8 lma 0x800d3fc
Loading section .fini_array, size 0x4 lma 0x800d404
Loading section .data, size 0x974 lma 0x800d408
Loading section .jcr, size 0x4 lma 0x800dd7c
Start address 0x800aa5c, load size 56704
Transfer rate: 17 KB/sec, 6300 bytes/write.
target state: halted
target halted due to debug-request, current mode: Thread
xPSR: 0x01000000 pc: 0x2b007822 msp: 0x4c07b510, semihosting
(gdb) info register pc
pc 0x800aa5c 0x800aa5c <Reset_Handler>
(gdb) c
Continuing.
^C
Program received signal SIGINT, Interrupt.
0xd0022b00 in ?? ()
The program counter ends up pointing at a random address. I've tried to track the execution flow placing breakpoints, but no matter where I place them they're never reached (I've even tried to place a breakpoint on the entry point of the program). Apparently for some reason the program starts at an unknown address. Probably I'm doing some colossal blunder related to something that I ignore, can someone help me please?
EDIT: This is the linker script (it's the same provided in the link above):
/* Entry Point */
ENTRY(Reset_Handler)
/* Highest address of the user mode stack */
_estack = 0x20020000; /* end of 128K RAM on AHB bus*/
/* Generate a link error if heap and stack don't fit into RAM */
_Min_Heap_Size = 0; /* required amount of heap */
_Min_Stack_Size = 0x400; /* required amount of stack */
/* Specify the memory areas */
MEMORY
{
FLASH (rx) : ORIGIN = 0x08000000, LENGTH = 1024K
RAM (xrw) : ORIGIN = 0x20000000, LENGTH = 192K
MEMORY_B1 (rx) : ORIGIN = 0x60000000, LENGTH = 0K
}
/* Define output sections */
SECTIONS
{
/* The startup code goes first into FLASH */
.isr_vector :
{
. = ALIGN(4);
KEEP(*(.isr_vector)) /* Startup code */
. = ALIGN(4);
} >FLASH
/* The program code and other data goes into FLASH */
.text :
{
. = ALIGN(4);
*(.text) /* .text sections (code) */
*(.text*) /* .text* sections (code) */
*(.rodata) /* .rodata sections (constants, strings, etc.) */
*(.rodata*) /* .rodata* sections (constants, strings, etc.) */
*(.glue_7) /* glue arm to thumb code */
*(.glue_7t) /* glue thumb to arm code */
*(.eh_frame)
KEEP (*(.init))
KEEP (*(.fini))
. = ALIGN(4);
_etext = .; /* define a global symbols at end of code */
_exit = .;
} >FLASH
.ARM.extab : { *(.ARM.extab* .gnu.linkonce.armextab.*) } >FLASH
.ARM : {
__exidx_start = .;
*(.ARM.exidx*)
__exidx_end = .;
} >FLASH
.preinit_array :
{
PROVIDE_HIDDEN (__preinit_array_start = .);
KEEP (*(.preinit_array*))
PROVIDE_HIDDEN (__preinit_array_end = .);
} >FLASH
.init_array :
{
PROVIDE_HIDDEN (__init_array_start = .);
KEEP (*(SORT(.init_array.*)))
KEEP (*(.init_array*))
PROVIDE_HIDDEN (__init_array_end = .);
} >FLASH
.fini_array :
{
PROVIDE_HIDDEN (__fini_array_start = .);
KEEP (*(.fini_array*))
KEEP (*(SORT(.fini_array.*)))
PROVIDE_HIDDEN (__fini_array_end = .);
} >FLASH
/* used by the startup to initialize data */
_sidata = .;
/* Initialized data sections goes into RAM, load LMA copy after code */
.data : AT ( _sidata )
{
. = ALIGN(4);
_sdata = .; /* create a global symbol at data start */
*(.data) /* .data sections */
*(.data*) /* .data* sections */
. = ALIGN(4);
_edata = .; /* define a global symbol at data end */
} >RAM
/* Uninitialized data section */
. = ALIGN(4);
.bss :
{
/* This is used by the startup in order to initialize the .bss secion */
_sbss = .; /* define a global symbol at bss start */
__bss_start__ = _sbss;
*(.bss)
*(.bss*)
*(COMMON)
. = ALIGN(4);
_ebss = .; /* define a global symbol at bss end */
__bss_end__ = _ebss;
} >RAM
/* User_heap_stack section, used to check that there is enough RAM left */
._user_heap_stack :
{
. = ALIGN(4);
PROVIDE ( end = . );
PROVIDE ( _end = . );
PROVIDE ( __end__ = . );
. = . + _Min_Heap_Size;
. = . + _Min_Stack_Size;
. = ALIGN(4);
} >RAM
/* MEMORY_bank1 section, code must be located here explicitly */
/* Example: extern int foo(void) __attribute__ ((section (".mb1text"))); */
.memory_b1_text :
{
*(.mb1text) /* .mb1text sections (code) */
*(.mb1text*) /* .mb1text* sections (code) */
*(.mb1rodata) /* read-only data (constants) */
*(.mb1rodata*)
} >MEMORY_B1
/* Remove information from the standard libraries */
/DISCARD/ :
{
libc.a ( * )
libm.a ( * )
libgcc.a ( * )
}
.ARM.attributes 0 : { *(.ARM.attributes) }
}
This is the code of the Reset_Handler function (again it is the same provided in the link above). This should be the entry point of the program as clearly stated in the linker script, but when I run it under gdb the pc goes somewhere else for some reason I don't understand.
.section .text.Reset_Handler
.weak Reset_Handler
.type Reset_Handler, %function
Reset_Handler:
/* Copy the data segment initializers from flash to SRAM */
movs r1, #0
b LoopCopyDataInit
CopyDataInit:
ldr r3, =_sidata
ldr r3, [r3, r1]
str r3, [r0, r1]
adds r1, r1, #4
LoopCopyDataInit:
ldr r0, =_sdata
ldr r3, =_edata
adds r2, r0, r1
cmp r2, r3
bcc CopyDataInit
ldr r2, =_sbss
b LoopFillZerobss
/* Zero fill the bss segment. */
FillZerobss:
movs r3, #0
str r3, [r2], #4
LoopFillZerobss:
ldr r3, = _ebss
cmp r2, r3
bcc FillZerobss
/* Call static constructors */
bl __libc_init_array
/* Call the application's entry point.*/
bl main
bx lr
.size Reset_Handler, .-Reset_Handler
