Linker script, init C variables

Question

I try find answer long time. Sorry but I really can't find it.

I use gcc,ld,gcc(for assembler compilation).

I wrote ld script:

SECTIONS
{
  .text : *{.text}
}
LS_size = (SIZEOF(.text) + 2048 ) & ( 0xF800 ) >> 9 ;

I try use LS_size from assembler:

_rom_size:
.byte LS_size

Its work fine, but on C code I can't set value to variable:

struct my_struct vari = {
  .codesize = LS_size,
}

If I extern LS_size, I got:

error: initializer element is not constant

How can I set default value for my constant C variables from variables, which are produced in ld scripts?

LS_size isn't known at compile time, since it's a linker script variable. You could try adding an extern const size_t LS_size; declaration in your C code, and move the initialization of vari.codesize to some function. — Michael
– Michael, Commented Oct 9, 2013 at 10:24
Then I compile the asm(.S) source I got: 0x00, (it is a _rom_size). But then I link it i got: 0x04. This means that I can specify which object file what data need to write to link stage. But I don't know how I can to write this on C code. — ASM
– ASM, Commented Oct 9, 2013 at 10:39
Well, I might be wrong, but I when you initialize the struct while declaring it I think the RHS must be a compile-time constant. Hence the suggestion to move the initialization in my previous comment. — Michael
– Michael, Commented Oct 9, 2013 at 10:49

Jose Luis Quiroga Beltran · Accepted Answer · 2017-05-08 16:34:35Z

1

Write in C:

struct my_st { 
    long the_code_sz;
};

struct my_st vv = {
  .the_code_sz = ((long)(&LS_size))
};

Then you can use

vv.the_code_sz

LS_size is a symbol and the address of that symbol is the value you gave it in the linker script.

answered May 8, 2017 at 16:34

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Comments

Pica · Accepted Answer · 2015-05-05 17:29:22Z

0

Also remember that linkerskript variables are not datatypes. They represent adresses- and what is stored there is completely arbitrary

Its bascially what you get with &VariableName in C.

answered May 5, 2015 at 17:29

Pica

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