Is there any reference to "main" in the default linker scripts of arm-none-eabi that could interfere when linking from the command line - gcc

Question

When using the gnu toolchain particularly arm-none-eabi is there any reason why when using the command line linker option it resorts to what seems an incorrect address to the start of 'main'. However, when 'main' is anything else the correct starting address and stack is initialized. For example,
.thumb
.syntax unified
.globl _start
_start:
.word 0x20001000
.word reset
reset:
bl main
b .
int main ( void )
{
return(0);
}
arm-none-eabi-gcc -O2 -c -mthumb main.c -o main.o
arm-none-eabi-as start.s -o start.o
arm-none-eabi-gcc -O2 -c -mthumb main.c -o main.o
arm-none-eabi-ld -Ttext=0x08000000 start.o main.o -o main.elf
arm-none-eabi-objdump -d main.elf
main.elf: file format elf32-littlearm
Disassembly of section .text:
08000000 <main>:
8000000: 2000 movs r0, #0
8000002: 4770 bx lr
08000004 <_start>:
8000004: 20001000 .word 0x20001000
8000008: 0800000c .word 0x0800000c
0800000c <reset>:
800000c: f7ff fff8 bl 8000000 <main>
8000010: e7fe b.n 8000010 <reset+0x4>
in the disassembly the output above doesn't initialize the stack 0x20001000 and start of rom 0x08000000 correctly from what I notice, but..
.thumb
.syntax unified
.globl _start
_start:
.word 0x20001000
.word reset
reset:
bl notmain
b .
int notmain ( void )
{
return(0);
}
arm-none-eabi-gcc -O2 -c -mthumb main.c -o main.o
arm-none-eabi-as start.s -o start.o
arm-none-eabi-gcc -O2 -c -mthumb main.c -o main.o
arm-none-eabi-ld -Ttext=0x08000000 start.o main.o -o main.elf
arm-none-eabi-objdump -d main.elf
main.elf: file format elf32-littlearm
Disassembly of section .text:
08000000 <_start>:
8000000: 20001000 .word 0x20001000
8000004: 08000008 .word 0x08000008
08000008 <reset>:
8000008: f000 f802 bl 8000010 <xmain>
800000c: e7fe b.n 800000c <reset+0x4>
...
08000010 <notmain>:
8000010: 2000 movs r0, #0
8000012: 4770 bx lr
I tried looking through the toolchain in my files to find any other reference to main pertaining to linker scripts and got some other help along the way, but there doesnt seem to be a clear solution as to why this is. Of course, if you create your own linker or a generated one you wont run into this problem, but I was just curious as I am trying to learn the tool a bit more.

Answer 1

..but I was just curious as I am trying to learn the tool a bit more
The arm-eabi-none is meant to be used with newlib (as a guess because you have not stated otherwise). This can process elf format files and it is a 'library', but there is no OS. If newlib mechanics want main() to be first, the tool will set things up like this. You don't want an elf file, but a binary. If you want a binary (ihex, srec, etc), then use a linker script! This is what it is meant for.
Use ld --verbose to see the default linker script. You are complaining about the order of emitted .text, but you have done nothing to define the ordering. The linker script may need main to be first so that some other library feature may work. You have a reset vector and a CPU which initializes the stack and 'reset vector' or initial code.
This is still emitted in the 'bad case', but it is not placed correctly. You need to have a custom linker script and position this a the first thing in the binary. Relying on the linker to place it correctly is error prone. An upgrade of tools can definitely change the order.
See: Can _start be a thumb function, were you have options like, -nostartfiles -static -nostdlib and use a custom linker script as an elf binary is unlikely to be understood and you need to flash/burn a binary to whatever boot device (or CPU built-in) is going to read the reset vectors.