GNU linker - How to fill unused memory space - gcc

Question

Some sections within my program are located at different places in memory and there are some unused memory locations. The following is a part of the object file of my program:
a0000128: 20cf8f93 addi t6,t6,524 # a0000330 <region_1>
a000012c: 000f8067 jr t6
Disassembly of section .fill:
00000000a0000130 <_end-0x800290>:
a0000130: deaa sw a0,124(sp)
a0000132: c0ad beqz s1,a0000194 <_start+0x194>
a0000134: dede sw s7,124(sp)
a0000136: c0ad beqz s1,a0000198 <_start+0x198>
...
Disassembly of section .s_region_1:
00000000a0000330 <region_1>:
a0000330: 00400f97 auipc t6,0x400
a0000334: 00cf8f93 addi t6,t6,12 # a040033c <region_2>
a0000338: 000f8067 jr t6
As shown, instruction at address 0xa000012c jumps to another instruction at address 0xa0000330. Since there are unused memory locations, I used FILL command in linker script. However, corresponding HEX file (generated with objcopy -O verilog) does not include the machine code of region_1. That is, HEX file only includes .text section and the data that is used to pad unused memory region:
13 0F 00 00 9B 0F 10 00 93 9F FF 01 1B 08 F0 FF
13 18 38 03 13 08 18 04 13 18 C8 00 13 08 98 12
73 10 18 30 97 0F 00 00 93 8F CF 20 67 80 0F 00
#A0000130
AA DE AD C0 DE DE AD C0 DE DE AD C0 DE DE AD C0
DE DE AD C0 DE DE AD C0 DE DE AD C0 DE DE AD C0
DE DE AD C0 DE DE AD C0 DE DE AD C0 DE DE AD C0
DE DE AD C0 DE DE AD C0 DE DE AD C0 DE DE AD C0
...
The following is the content of the linker script:
SECTIONS
{
. = 0xA0000000;
.text : { *(.text) }
.fill :
{
FILL(0xDEADC0DE);
BYTE(0xAA);
. = . + 0x1FF;
}
.s_region_1 : { *(s_region_1) }
.bss : { *(.bss) }
_end = .;
}
What is wrong with the linker script above?
This is the memory map I want to generate:
/*************************/
.text
/*************************/
/* EMPTY REGION */
/*************************/
.section_1
/*************************/

Answer 1

I noticed that I have to add "aw" flags within my assembly code when defining the section:
.section ".sregion1","aw"
region_1:
la x31, region_2
jr x31
After adding "aw" flags, the HEX file was generated by objcopy as expected:
#80000000
1B 00 10 00 13 10 F0 01 B7 F0 0F 00 9B 80 70 81
93 90 C0 00 93 80 90 A5 13 01 80 00 93 01 80 00
1B 02 10 00 13 12 F2 01 B7 B2 0F 00 9B 82 12 FB
...
#80400130
97 0F 00 00 93 8F CF 00 67 80 0F 00 97 0F 00 00
93 8F 0F 00 67 80 0F 00
The following is the final version of my linker file:
OUTPUT_ARCH( "riscv" )
ENTRY(_start)
/*
MEMORY {
text (RX): o = 0x80000000, LENGTH = 128M
s_region_1 (RX): o = 0x80400000, LENGTH = 256K
}
*/
SECTIONS
{
. = 0x80000000;
.text :
{
*(.text);
}
. = . + 0x400000;
.sregion1 : { *(.sregion1) }
. = . + 0x400000;
.bss : { *(.bss) }
_end = .;
}