PPC - Branch absolute target restricted to 26/16 bits

[EdwardLarson]

For all branch instructions, the target address is passed in as the absolute address (see issue #108). Any address higher than 0x1fffffc throws an "Invalid Operand" error:

/# kstool ppc32be "b 0x1fffffc"
b 0x1fffffc = [ 49 ff ff fc ]
/# kstool ppc32be "b 0x2000000"
ERROR: failed on ks_asm() with count = 0, error = 'Invalid operand (KS_ERR_ASM_INVALIDOPERAND)' (code = 512)

This issue is present on ppc64, ppc64be, and ppc32be.

This behavior appears to be caused by a check that the target address fits the 26-bit limit for unconditional branch targets (16 bits for conditional). However for relative-offset branch instructions it is the offset which is restricted to 26/16 bits, not the target address. For example, the below is a valid branch to an instruction only 8 bytes ahead. The offset which will be encoded, 0x8, is well within the 26-bit limit, however since the target address is more than 26 bits wide, keystone fails:

/# kstool ppc32be "b 0x2000008" 0x2000000
ERROR: failed on ks_asm() with count = 0, error = 'Invalid operand (KS_ERR_ASM_INVALIDOPERAND)' (code = 512)

The expected behavior is that, like other architectures' implementations, keystone does not try to enforce range bounds at all. For example, in ARM64 the max branch range is 2**27 - 4 (0x7fffffc), but keystone will not enforce this limit:

/# kstool arm64 "b 0x1ffffffffffffffc" 0
b 0x1ffffffffffffffc = [ ff ff ff 17 ]

[EdwardLarson]

Long-resolved with #428