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Re: How to control location of startup code?

Richard Earnshaw wrote:

Is there any way to control how the default startup code ends up in

  the output file/the virutal address it gets and/or what output
  section it's included in?

I do it by putting it in a seperate segment. More specifically, I have
my own "crt0.s" it contains the reset vector and other IRQ like things
below is the relavent snippit in ARM assembly

.section .vectors


The *PROBLEM* with this is by default the '.vectors' segment is not
tagged as loadable perhaps there is a way to do this in GAS, it was
not obvious to me.

You need to set the section flags when you create the section, something like:

.section .vectors, code, "ax"

which tells the assembler that the section contains code, has to be _A_llocated at load time and is e_X_ecutable.


OK. Thanks to you both.

I really think there ought to be some way to match the startup code by file name in the linker script, though... Also, in the meantime, I've started wonder if I raelly want to handle crt0 this way. The alternative is to keep it in the normal code section, and have something like

	ldr	pc, Reset_Addr
	ldr	pc, Undefined_Addr	/* Undefined instructions */
	ldr	pc, SWI_Addr
	ldr	pc, Prefetch_Addr	/* Prefetch abort*/
	ldr	pc, Abort_Addr		/* Data abort */
	nop				/* Reserved vector */
	ldr	pc, IRQ_Addr
	ldr	pc, FIQ_Addr
[ ... ]

	[ initial system setup ]
	ldr	pc, Start_Addr

	.align 0
Reset_Addr:	.word resetHandler
[ ... ]
Start_Addr:	.word _start

in a separate file, and direct the associated object code to a different output section (which is easy.) Actually, I'm quite sure I want to keep the vectors separate, the question is really whether to target vectors *and* crt0 for the area starting at address 0, or just the vectors.

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