On PPC r0 always contains 0 by definition (that is, it is not a real register). I think this is working as intended.

Yeah, R0 is always 0 in the Go ABI.

And what happens when Go code calls C code built by gcc where it is not always 0? Does it reinitialize it when it returns?

On 27/02/2016 8:44 am, "laboger" notifications@github.com wrote:

And what happens when Go code calls C code built by gcc where it is not
always 0? Does it reinitialize it when it returns?

Yes.

Thanks for the responses.

ianlancetaylor wrote:

On PPC r0 always contains 0 by definition (that is, it is not a real register).

To be pedantic, r0 is a real register and can contain non-zero data. In fact, we use r0 as a scratch register in GCC all the time, as well as when we save/restore the link register in the prologue/epilogue.

That said, there are instructions where the contents of r0 are ignored and the value zero is used instead. For example, the base register in load and store instructions and addi and addis, etc. but only if r0 is the RA operand. If r0 isn't reset whenever r0 is used like calling non GO routines (eg, C), or whenever making syscalls (r0 holds the syscall number), then you can't guarantee that r0 is zero.