PowerPC EABI - prepending ecrti/crtbegin

[Marco Awater]

On 30-3-2011 19:26, Ian Lance Taylor wrote:
> Why do ecrti.o and crtbegin.o cause trouble?  Are you assuming that your
> code is the very first in the file?  If that is the problem, I would
> recommend adjusting your linker script to put your vector table at the
> front.  I think that will be simpler than fighting against the compiler
> here.

Thank you for your response. I had indeed assumed that my code would be 
the first to appear in the file. I had placed the start of the vector 
table at the start of the .text section by passing the object with the 
vector table as the first argument to the linker. Unfortunately, ecrti.o 
and crtbegin.o were prepended to the .text section by the compiler and 
thus moved the vector code.

The trouble caused by these files stems from the fact that their code is 
executed without proper context. Imagine the following as the first code 
executed after a cold boot (at which point neither r0 nor r1 contain 
valid values yet):

00000000 <__do_global_dtors_aux>:
    0:	94 21 ff e8 	stwu    r1,-24(r1)
    4:	7c 08 02 a6 	mflr    r0
    8:	93 e1 00 14 	stw     r31,20(r1)

I'd initially tried to use the linkerscript, but ran into some issues 
(which have now been fixed) thus prompting me to experiment with 
-nostartfiles. But the whole thing had made me wonder how these files 
(ecrti.o and crtbegin.o) were intended to be used.. they are now 
basically dead code as far as my application is concerned; I don't call 
any of the code in these files since I don't need C++ support.

Is this the intended manner to implement this - tweak the linkerscript 
or use -nostartfiles (and provide your own EABI definitions) - or how 
does one go about this for OS-less C-only targets?

>
> Ian

-- 
With kind regards,
Met vriendelijke groet,
     Marco Awater
     Software Engineer

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