gdbutil

# -*- gdb-script -*-

# Utility functions to pretty-print x86 segment/interrupt descriptors.
# To load this file, run "source gdbutil" in gdb.
# printdesc and printdescs are the main entry points.

# IA32 2007, Volume 3A, Table 3-2
set $STS_T16A = 0x1
set $STS_LDT  = 0x2
set $STS_T16B = 0x3
set $STS_CG16 = 0x4
set $STS_TG   = 0x5
set $STS_IG16 = 0x6
set $STS_TG16 = 0x7
set $STS_T32A = 0x9
set $STS_T32B = 0xB
set $STS_CG32 = 0xC
set $STS_IG32 = 0xE
set $STS_TG32 = 0xF

define outputsts
  while 1
    if $arg0 == $STS_T16A
      echo STS_T16A
      loop_break
    end
    if $arg0 == $STS_LDT
      echo STS_LDT\ 
      loop_break
    end
    if $arg0 == $STS_T16B
      echo STS_T16B
      loop_break
    end
    if $arg0 == $STS_CG16
      echo STS_CG16
      loop_break
    end
    if $arg0 == $STS_TG
      echo STS_TG\ \ 
      loop_break
    end
    if $arg0 == $STS_IG16
      echo STS_IG16
      loop_break
    end
    if $arg0 == $STS_TG16
      echo STS_TG16
      loop_break
    end
    if $arg0 == $STS_T32A
      echo STS_T32A
      loop_break
    end
    if $arg0 == $STS_T32B
      echo STS_T32B
      loop_break
    end
    if $arg0 == $STS_CG32
      echo STS_CG32
      loop_break
    end
    if $arg0 == $STS_IG32
      echo STS_IG32
      loop_break
    end
    if $arg0 == $STS_TG32
      echo STS_TG32
      loop_break
    end
    echo Reserved
    loop_break
  end
end  

# IA32 2007, Volume 3A, Table 3-1
set $STA_X = 0x8
set $STA_E = 0x4
set $STA_C = 0x4
set $STA_W = 0x2
set $STA_R = 0x2
set $STA_A = 0x1

define outputsta
  if $arg0 & $STA_X
    # Code segment
    echo code
    if $arg0 & $STA_C
      echo |STA_C
    end
    if $arg0 & $STA_R
      echo |STA_R
    end
  else
    # Data segment
    echo data
    if $arg0 & $STA_E
      echo |STA_E
    end
    if $arg0 & $STA_W
      echo |STA_W
    end
  end
  if $arg0 & $STA_A
    echo |STA_A
  else
    printf "      "
  end
end

# xv6-specific
set $SEG_KCODE = 1
set $SEG_KDATA = 2
set $SEG_KCPU  = 3
set $SEG_UCODE = 4
set $SEG_UDATA = 5
set $SEG_TSS   = 6

define outputcs
  if ($arg0 & 4) == 0
    if $arg0 >> 3 == $SEG_KCODE
      printf "SEG_KCODE<<3"
    end
    if $arg0 >> 3 == $SEG_KDATA
      printf "SEG_KDATA<<3"
    end
    if $arg0 >> 3 == $SEG_KCPU
      printf "SEG_KCPU<<3"
    end
    if $arg0 >> 3 == $SEG_UCODE
      printf "SEG_UCODE<<3"
    end
    if $arg0 >> 3 == $SEG_UDATA
      printf "SEG_UDATA<<3"
    end
    if $arg0 >> 3 == $SEG_TSS
      printf "SEG_TSS<<3"
    end
    if ($arg0 >> 3 < 1) + ($arg0 >> 3 > 6)
      printf "GDT[%d]", $arg0 >> 3
    end
  else
    printf "LDT[%d]", $arg0 >> 3
  end
  if ($arg0 & 3) > 0
    printf "|"
    outputdpl ($arg0&3)
  end
end

define outputdpl
  if $arg0 == 0
    printf "DPL_KERN"
  else
    if $arg0 == 3
      printf "DPL_USER"
    else
      printf "DPL%d", $arg0
    end
  end
end

define printdesc
  if $argc != 1
    echo Usage: printdesc expr
  else
    _printdesc ((uint*)&($arg0))[0] ((uint*)&($arg0))[1]
    printf "\n"
  end
end

document printdesc
Print an x86 segment or gate descriptor.
printdesc EXPR
EXPR must evaluate to a descriptor value.  It can be of any C type.
end

define _printdesc
  _printdesc1 $arg0 $arg1 ($arg1>>15&1) ($arg1>>13&3) ($arg1>>12&1) ($arg1>>8&15)
end

define _printdesc1
  # 2:P 3:DPL 4:S 5:Type
  if $arg2 == 0
    printf "P = 0 (Not present)"
  else
    printf "type = "
    if $arg4 == 0
      # System segment
      outputsts $arg5
      printf " (0x%x)    ", $arg5
      _printsysdesc $arg0 $arg1 $arg5
    else
      # Code/data segment
      outputsta $arg5
      printf "  "
      _printsegdesc $arg0 $arg1
    end

    printf "  DPL = "
    outputdpl $arg3
    printf " (%d)", $arg3
  end
end

define _printsysdesc
  # 2:Type
  # GDB's || is buggy
  if ($arg2 == $STS_TG) + (($arg2&7) == $STS_IG16) + (($arg2&7) == $STS_TG16)
    # Gate descriptor
    _printgate $arg2 ($arg0>>16) ($arg0&0xFFFF) ($arg1>>16)
  else
    # System segment descriptor
    _printsegdesc $arg0 $arg1
  end
end

define _printgate
  # IA32 2007, Voume 3A, Figure 5-2
  # 0:Type 1:CS 2:Offset 15..0 3:Offset 31..16
  printf "CS = "
  outputcs $arg1
  printf " (%d)", $arg1

  if (($arg0&7) == $STS_IG16) + (($arg0&7) == $STS_TG16)
    printf "  Offset = "
    output/a $arg3 << 16 | $arg2
  end
end

define _printsegdesc
  # IA32 20007, Volume 3A, Figure 3-8 and Figure 4-1
  _printsegdesc1 ($arg0>>16) ($arg1&0xFF) ($arg1>>24) ($arg0&0xFFFF) ($arg1>>16&15) ($arg1>>23&1)
  if ($arg1>>12&1) == 1
    printf "  AVL = %d", $arg1>>20&1
    if ($arg1>>11&1) == 0
      # Data segment
      if ($arg1>>22&1) == 0
        printf "  B = small (0) "
      else
        printf "  B = big (1)   "
      end
    else
      # Code segment
      printf "  D = "
      if ($arg1>>22&1) == 0
        printf "16-bit (0)"
      else
        printf "32-bit (1)"
      end
    end
  end
end

define _printsegdesc1
  # 0:Base 0..15  1:Base 16..23  2:Base 24..32  3:Limit 0..15  4:Limit 16..19  5:G
  printf "base = 0x%08x", $arg0 | ($arg1<<16) | ($arg2<<24)
  printf "  limit = 0x"
  if $arg5 == 0
    printf "%08x", $arg3 | ($arg4<<16)
  else
    printf "%08x", (($arg3 | ($arg4<<16)) << 12) | 0xFFF
  end
end

define printdescs
  if $argc < 1 || $argc > 2
    echo Usage: printdescs expr [count]
  else
    if $argc == 1
      _printdescs ($arg0) (sizeof($arg0)/sizeof(($arg0)[0]))
    else
      _printdescs ($arg0) ($arg1)
    end
  end
end

document printdescs
Print an array of x86 segment or gate descriptors.
printdescs EXPR [COUNT]
EXPR must evaluate to an array of descriptors.
end

define _printdescs
  set $i = 0
  while $i < $arg1
    printf "[%d] ", $i
    printdesc $arg0[$i]
    set $i = $i + 1
  end
end