Undefined reference to 'r11'/Compiler failed in iaux.c

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Jamie
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Undefined reference to 'r11'/Compiler failed in iaux.c

Postby Jamie » Tue Jul 13, 2010 11:14 am

I'm getting these (pretty unspecified) errors when I'm trying to link an object compiled from XC code with loads of inline assembly in it. The line which seems to be causing the error is:

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asm("ldw %0, cp[%1]" : "=r"(procAddr) : "r"(procIndex));
Which produces:

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kernel/functions.xc: Error: Undefined reference to 'r11'
And when I express this line slightly differently:

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asm("mov r11, %0" :: "r"(procIndex) : "r11");
asm("ldw %0, cp[r11]" : "=r"(procAddr) :: "r11");
The compiler gives the error:

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Compiler failed in iaux.c, line 66
o != ((void *)0)
It could well be something that I'm doing wrong or a problem to do with register allocation but I've got no idea about how to go about fixing this based on these strange error messages?!
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segher
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Postby segher » Tue Jul 13, 2010 11:57 am

ldwcp takes an immediate argument as the offset from cp, not a register.

You might want an ldawcp / ldw combo?


Segher
richard
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Postby richard » Tue Jul 13, 2010 12:11 pm

The offset of ldwcp must be an immediate. There is no version of ldwcp which takes a register offset from the cp. When you write:

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asm("ldw %0, cp[%1]" : "=r"(procAddr) : "r"(procIndex));
After substitution the assembler will see something like:

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ldw r0, cp[r11]
Because there is no register offset version of ldwcp the assembler assumes r11 in this context refers to a symbol. When no definition of this symbol is found at link time the mapper errors. I think the following (untested) piece of inline asm should work:

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asm("ldaw r11, cp[0]; ldw %0, r11[%1]" : "=r"(procAddr) : "r"(procIndex) : "r11");
when I express this line slightly differently:

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asm("mov r11, %0" :: "r"(procIndex) : "r11");
asm("ldw %0, cp[r11]" : "=r"(procAddr) :: "r11");
The compiler gives the error:

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Compiler failed in iaux.c, line 66
o != ((void *)0)
This also won't work for the reasons given above, but the compiler shouldn't fail like that. I've haven't been able to recreate this behaviour from just that snippet of code. Are you able to submit a ticket with the source code necessary to recreate the compiler failure?
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Jamie
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Postby Jamie » Tue Jul 13, 2010 12:15 pm

dwcp takes an immediate argument as the offset from cp, not a register.

You might want an ldawcp / ldw combo?
Whoops! Good spot - I guess it shouldn't have got passed the assembler though.

Even after correcting this, the 'Compiler failed' error is still occuring.

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asm("ldaw r11, cp[0]" ::: "r11");
asm("ldw %0, r11[%1]" : "=r"(procAddr) : "r"(procIndex) : "r11");
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Jamie
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Postby Jamie » Tue Jul 13, 2010 12:35 pm

This also won't work for the reasons given above, but the compiler shouldn't fail like that. I've haven't been able to recreate this behaviour from just that snippet of code. Are you able to submit a ticket with the source code necessary to recreate the compiler failure?
I've submitted a ticket for it. Although the ammended version still prodcues the error, it only does so with compiler optimisations enabled.
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segher
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Postby segher » Tue Jul 13, 2010 1:33 pm

Jamie wrote: Even after correcting this, the 'Compiler failed' error is still occuring.

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asm("ldaw r11, cp[0]" ::: "r11");
asm("ldw %0, r11[%1]" : "=r"(procAddr) : "r"(procIndex) : "r11");
The clobber on the first asm is wrong: it should be an output instead, since you use
r11 later.
The clobber on the second asm is wrong: it should be an input.

Alternatively, write the whole thing as a single asm, e.g.

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asm("ldaw r11,cp[0] ; ldw %0,r11[%1]" : "=r"(procAddr) : "r"(procIndex) : "r11");
Or, probably best, just write this in C code instead of asm; or if you really want to use asm,
write the whole thing in assembler, i.e. a .s file.


Segher
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Jamie
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Postby Jamie » Tue Jul 13, 2010 4:15 pm

The clobber on the first asm is wrong: it should be an output instead, since you use
r11 later.
The clobber on the second asm is wrong: it should be an input.
So how do you write "r11" as an output in the first asm and as an input on the second one? Or have I missed the point a bit and the correct way to write it is as a single asm as you have suggested?
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segher
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Postby segher » Tue Jul 13, 2010 4:43 pm

I don't know if there is a register contstraint to say "r11". Writing it as a single
asm() is certainly easier.
JohnR
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Postby JohnR » Tue Jul 13, 2010 7:12 pm

Hi
Or, probably best, just write this in C code instead of asm; or if you really want to use asm,
write the whole thing in assembler, i.e. a .s file.
Or write initially in XC, compile to a .S file and see what's generated.

John.

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