Cannot create a new section modifying the default linker script. #1162
Description
I do not know if this is the right forum, but I tried the raspberry pi forums to no avail.
My requirement is to have a portion of the RAM reserved for holding code created at runtime, and for the section to be writable. Plus, I want to load some of its content by copy a portion of the FLASH at boot-up. The purpose is to have dynamic generation of code.
I have a minimal sample that is modeled after the USB stdio sample for the SDK examples. It simply prints a string. I have attempted to create a modified linker script (based on the default script) as follows:
main.cpp:
#include <stdio.h>
extern "C" void forth();
int main()
{
forth();
return 0;
}
forth() is defined in an assembly file called test.s
test.s:
.syntax unified
.thumb
.section .data
.align 2
data: .asciz "ABC12345"
.section .user_section, "awx" @ putting function in .user_section
@ .section .text
.align 2
.global forth
.thumb_func
forth:
PUSH {LR}
BL stdio_init_all
LDR R0, =data
BL puts
POP {PC}
The linker file has the following mods:
MEMORY
{
FLASH(rx) : ORIGIN = 0x10000000, LENGTH = 2048k
RAM(rwx) : ORIGIN = 0x20000000, LENGTH = 128k
FORTH(rwx) : ORIGIN = 0x20020000, LENGTH = 128k
SCRATCH_X(rwx) : ORIGIN = 0x20040000, LENGTH = 4k
SCRATCH_Y(rwx) : ORIGIN = 0x20041000, LENGTH = 4k
}
and the section definition of user_section as follows:
.user_section : {
*(.user_section.*)
. = ALIGN(4);
} > FORTH AT> FLASH
The .dis file looks like this:
Sections:
Idx Name Size VMA LMA File off Algn
0 .boot2 00000100 10000000 10000000 00001000 2**0
CONTENTS, ALLOC, LOAD, READONLY, CODE
1 .text 000071e8 10000100 10000100 00001100 2**3
CONTENTS, ALLOC, LOAD, READONLY, CODE
2 .rodata 000016b0 100072e8 100072e8 000082e8 2**3
CONTENTS, ALLOC, LOAD, READONLY, DATA
3 .binary_info 00000020 10008998 10008998 00009998 2**2
CONTENTS, ALLOC, LOAD, DATA
4 .ram_vector_table 000000c0 20000000 20000000 0000b038 2**2
CONTENTS
5 .data 00000460 200000c0 100089b8 0000a0c0 2**4
CONTENTS, ALLOC, LOAD, READONLY, CODE
6 .uninitialized_data 00000000 20000520 20000520 0000b0f8 2**0
CONTENTS
7 .user_section 00000038 20020000 10008e18 0000b000 2**3
CONTENTS, ALLOC, LOAD, READONLY, CODE
8 .scratch_x 00000000 20040000 20040000 0000b0f8 2**0
CONTENTS
9 .scratch_y 00000000 20041000 20041000 0000b0f8 2**0
CONTENTS
10 .bss 00000d84 20000520 20000520 0000b520 2**3
ALLOC
11 .heap 00000800 200012a4 200012a4 0000b0f8 2**2
CONTENTS, READONLY
The .dis file appears to be correct, but the program does not run. If I change the section to just .text (see comment in test.s), it works fine. If I additionally use the copy_to_ram linker script distributed with the SDK, the code is loaded in RAM on boot. What I want is a combination of the two, in that user_section should be copied from FLASH to ram and should allow for additional code to be placed at runtime.
I think I am doing all the right things but am stumped as to what I am missing. Any suggestions on making this work are appreciated.