powerpc64: Fix "show spr" command on ELFv2 kernels
Summary: When compiling for ELFv2, it is necessary to adjust the offset to
get_spr and factor in the function prologue to ensure the correct instruction is
being edited.
Test Plan:
Before:
db> show spr 110
KDB: reentering
KDB: stack backtrace:
0xc008000020fb96e0: at 0xc000000002bb2e34 = kdb_backtrace+0x68
0xc008000020fb97f0: at 0xc000000002bb3798 = kdb_reenter+0x54
0xc008000020fb9860: at 0xc000000002f87090 = trap+0x4e4
0xc008000020fb9990: at 0xc000000002f78a60 = powerpc_interrupt+0x110
0xc008000020fb9a20: kernel trap 0xe40 by 0xc000000002401978 = get_spr+0x8: srr1=0x9000000000001032
r1=0xc008000020fb9cd0 cr=0x80009438 xer=0x20040000 ctr=0xc000000002f7b40c r2=0xc0000000037fd000
saved LR(0xfffffffffffffffb) is invalid.After:
db> show spr 110 SPR 272(110): c000000003cae900
Submitted by: git_bdragon.rtk0.net
Differential Revision: https://reviews.freebsd.org/D17813