Hi Amol,
On Wed, Aug 11, 2021 at 08:25:24AM +0530, Amol via Gcc-help wrote:
> When compiling the following lines with ppc64le-linux-gnu-gcc, version 11.2.0,
> an incorrect instruction is assembled.
>
> unsigned long val;
> asm volatile ("mfpir %0" : "=r"(val));
> // ppc64le-linux-gnu-gcc -mcpu=power9 a.c
>
> The output binary contains
> mfspr r9, 286
>
> instead of
>
> mfspr r9, 1023
>
> ----
> It turns out that the assembler doesn't actually recognize the mfpir
> opcode, but,
> since gcc forces -many on the assembler, it is coaxed into assembling an
> instruction that isn't the correct one for the power9 arch. The resulting binary
> misbehaves. Another instance of this problem at [1].
>
> Is there a way gcc can be told to not force -many on the assembler,
> or, otherwise
> be made to correctly support mfpir?
There is no "mfpir" instruction on Power9, there is an extended mnemonic
though, and apparently GAS does not implement it yet. Please file a bug
in the binutils bugzilla for that. (We probably should implement the
extended mnemonics for many more mfspr/mtspr btw).
GCC will stop using -many as soon as that is possible to do, GCC 12 if
that works out, but that will still not solve your problem: it then will
give an error on mfpir. If GAS *does* implement the Power9 extended
mnemonic, it will work with as well as without -many.
Segher
