C Programming Language

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How can I force the entry-point to be at start of .text? (programming.dev)

submitted 3 months ago* (last edited 3 months ago) by iliketurtiles@programming.dev to c/c_lang@programming.dev

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I'm trying to write a linker file to get C code running on a risc-v MCU (using riscv64-unknown-elf toolchain). My linker script looks like this, simplified:

MEMORY {
        IRAM (rx) : ORIGIN = 0x00000000, LENGTH = 1024
}

ENTRY(_start)

SECTIONS {
    .text : ALIGN(4) {
        *(.text)
    } >IRAM

...

readelf -h correctly shows the entry point's address to be the same as where _start is in the output executable. But I want _start to be at 0x0, not somewhere else, so that when I objcopy it to a flat binary, the start code will be at the beginning. How can I do this?

Right now I'm having the _start function go in a new section called ".boot" I've defined in the C file using __attribute__((section(".boot"))), then, placing this at the start of .text in the linker script like so

...
    .text : ALIGN(4) {
        *(.boot)
        *(.text)
...

But IDK if this how it should be done.

Thanks in advance :)

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[–] iliketurtiles@programming.dev 0 points 3 months ago (1 children)

I don't know what a .map file is, will look into that. This does work, when I objdump it _start is at 0x0. But I'm curious if there is a better solution, I'd like to learn how it's properly done.

[–] SpaceNoodle@lemmy.world 0 points 3 months ago (1 children)

That's generally how it's done.

[–] iliketurtiles@programming.dev 0 points 3 months ago

Oh I see, many thanks.