arguably the most annoying gdb script i've ever written

dbgscript

# written directly in conjunction with the following asm,
#
# ```
# bits 64
#
# d:
#  dq 0x0303030302020202
#   dq 0x0202020201010101
#
#   global _start
#_start:
#   mov eax, 1
#  mov ecx, 0
#   cpuid
#
#   movups xmm3, [d]
#  movups xmm4, [d]
#   pclmulqdq xmm3, xmm4, 0x11
#  mov rax, 60
#   pextrq rdi, xmm3, 1
#  syscall
# ```
#
# assembled and linked like
#
# nasm -f elf64 -o pclmulqdq.o pclmulqdq.s
# ld -o pclmulqdq pclmulqdq.o
#
# this can be run like
#
# gdb --batch-silent --command dbgscript -q --args taskset -ac 4 ./pclmulqdq
#
# to show that hiding the pclmulqdq bit in cpuid doesn't relate to the ability
# to actually execute that instruction.
#
# the MSR side of things looks something like
#
# ```
# > sudo rdmsr -x --processor 4 0xc0011004
# 7ed8320b178bfbff
# > sudo wrmsr --processor 4 0xc0011004 0x7ed83209178bfbff
# > sudo rdmsr -x --processor 4 0xc0011004
# 7ed83209178bfbff
# ```

set pagination off
set breakpoint pending on
set verbose off
b _start
r
c
set logging file /dev/stderr
set logging off
set $g=$pc

define hook-stop
  set logging on
  x/i $g
  set $g=$pc
  set logging off
end
si
si
set logging on
printf "# cpuid leaf: 0x%x\n", $rax
set logging off
si
set logging on
printf "# leaf 1 ecx: 0x%08x\n", $ecx
printf "# - bit 2 (pclmulqdq): %x\n", ($ecx & 2)
set logging off
si
si
si
si
si
define hook-stop
end
set logging on
x/i $pc
si
printf "# exit code: %d\n", $_exitcode
q