tools/add-cfi.i386.awk

   1 # Insert GAS CFI directives ("control frame information") into x86-32 asm input
   2 #
   3 # CFI directives tell the assembler how to generate "stack frame" debug info
   4 # This information can tell a debugger (like gdb) how to find the current stack
   5 #   frame at any point in the program code, and how to find the values which
   6 #   various registers had at higher points in the call stack
   7 # With this information, the debugger can show a backtrace, and you can move up
   8 #   and down the call stack and examine the values of local variables
   9
  10 BEGIN {
  11   # don't put CFI data in the .eh_frame ELF section (which we don't keep)
  12   print ".cfi_sections .debug_frame"
  13
  14   # only emit CFI directives inside a function
  15   in_function = 0
  16
  17   # emit .loc directives with line numbers from original source
  18   printf ".file 1 \"%s\"\n", ARGV[1]
  19   line_number = 0
  20
  21   # used to detect "call label; label:" trick
  22   called = ""
  23 }
  24
  25 function get_const1() {
  26   # for instructions with 2 operands, get 1st operand (assuming it is constant)
  27   match($0, /-?(0x[0-9a-fA-F]+|[0-9]+),/)
  28   return parse_const(substr($0, RSTART, RLENGTH-1))
  29 }
  30
  31 function canonicalize_reg(register) {
  32   if (match(register, /^e/))
  33     return register
  34   else if (match(register, /[hl]$/)) # AH, AL, BH, BL, etc
  35     return "e" substr(register, 1, 1) "x"
  36   else # AX, BX, CX, etc
  37     return "e" register
  38 }
  39 function get_reg() {
  40   # only use if you already know there is 1 and only 1 register
  41   match($0, /%e?([abcd][hlx]|si|di|bp)/)
  42   return canonicalize_reg(substr($0, RSTART+1, RLENGTH-1))
  43 }
  44 function get_reg1() {
  45   # for instructions with 2 operands, get 1st operand (assuming it is register)
  46   match($0, /%e?([abcd][hlx]|si|di|bp),/)
  47   return canonicalize_reg(substr($0, RSTART+1, RLENGTH-2))
  48 }
  49 function get_reg2() {
  50   # for instructions with 2 operands, get 2nd operand (assuming it is register)
  51   match($0, /,%e?([abcd][hlx]|si|di|bp)/)
  52   return canonicalize_reg(substr($0, RSTART+2, RLENGTH-2))
  53 }
  54
  55 function adjust_sp_offset(delta) {
  56   if (in_function)
  57     printf ".cfi_adjust_cfa_offset %d\n", delta
  58 }
  59
  60 {
  61   line_number = line_number + 1
  62
  63   # clean the input up before doing anything else
  64   # delete comments
  65   gsub(/(#|\/\/).*/, "")
  66
  67   # canonicalize whitespace
  68   gsub(/[ \t]+/, " ") # mawk doesn't understand \s
  69   gsub(/ *, */, ",")
  70   gsub(/ *: */, ": ")
  71   gsub(/ $/, "")
  72   gsub(/^ /, "")
  73 }
  74
  75 # check for assembler directives which we care about
  76 /^\.(section|data|text)/ {
  77   # a .cfi_startproc/.cfi_endproc pair should be within the same section
  78   # otherwise, clang will choke when generating ELF output
  79   if (in_function) {
  80     print ".cfi_endproc"
  81     in_function = 0
  82   }
  83 }
  84 /^\.type [a-zA-Z0-9_]+,@function/ {
  85   functions[substr($2, 1, length($2)-10)] = 1
  86 }
  87 # not interested in assembler directives beyond this, just pass them through
  88 /^\./ {
  89   print
  90   next
  91 }
  92
  93 /^[a-zA-Z0-9_]+:/ {
  94   label = substr($1, 1, length($1)-1) # drop trailing :
  95
  96   if (called == label) {
  97     # note adjustment of stack pointer from "call label; label:"
  98     adjust_sp_offset(4)
  99   }
 100
 101   if (functions[label]) {
 102     if (in_function)
 103       print ".cfi_endproc"
 104
 105     in_function = 1
 106     print ".cfi_startproc"
 107
 108     for (register in saved)
 109       delete saved[register]
 110     for (register in dirty)
 111       delete dirty[register]
 112   }
 113
 114   # an instruction may follow on the same line, so continue processing
 115 }
 116
 117 /^$/ { next }
 118
 119 {
 120   called = ""
 121   printf ".loc 1 %d\n", line_number
 122   print
 123 }
 124
 125 # KEEPING UP WITH THE STACK POINTER
 126 # We do NOT attempt to understand foolish and ridiculous tricks like stashing
 127 #   the stack pointer and then using %esp as a scratch register, or bitshifting
 128 #   it or taking its square root or anything stupid like that.
 129 # %esp should only be adjusted by pushing/popping or adding/subtracting constants
 130 #
 131 /pushl?/ {
 132   if (match($0, / %(ax|bx|cx|dx|di|si|bp|sp)/))
 133     adjust_sp_offset(2)
 134   else
 135     adjust_sp_offset(4)
 136 }
 137 /popl?/ {
 138   if (match($0, / %(ax|bx|cx|dx|di|si|bp|sp)/))
 139     adjust_sp_offset(-2)
 140   else
 141     adjust_sp_offset(-4)
 142 }
 143 /addl? \$-?(0x[0-9a-fA-F]+|[0-9]+),%esp/ { adjust_sp_offset(-get_const1()) }
 144 /subl? \$-?(0x[0-9a-fA-F]+|[0-9]+),%esp/ { adjust_sp_offset(get_const1()) }
 145
 146 /call/ {
 147   if (match($0, /call [0-9]+f/)) # "forward" label
 148     called = substr($0, RSTART+5, RLENGTH-6)
 149   else if (match($0, /call [0-9a-zA-Z_]+/))
 150     called = substr($0, RSTART+5, RLENGTH-5)
 151 }
 152
 153 # TRACKING REGISTER VALUES FROM THE PREVIOUS STACK FRAME
 154 #
 155 /pushl? %e(ax|bx|cx|dx|si|di|bp)/ { # don't match "push (%reg)"
 156   # if a register is being pushed, and its value has not changed since the
 157   #   beginning of this function, the pushed value can be used when printing
 158   #   local variables at the next level up the stack
 159   # emit '.cfi_rel_offset' for that
 160
 161   if (in_function) {
 162     register = get_reg()
 163     if (!saved[register] && !dirty[register]) {
 164       printf ".cfi_rel_offset %s,0\n", register
 165       saved[register] = 1
 166     }
 167   }
 168 }
 169
 170 /movl? %e(ax|bx|cx|dx|si|di|bp),-?(0x[0-9a-fA-F]+|[0-9]+)?\(%esp\)/ {
 171   if (in_function) {
 172     register = get_reg()
 173     if (match($0, /-?(0x[0-9a-fA-F]+|[0-9]+)\(%esp\)/)) {
 174       offset = parse_const(substr($0, RSTART, RLENGTH-6))
 175     } else {
 176       offset = 0
 177     }
 178     if (!saved[register] && !dirty[register]) {
 179       printf ".cfi_rel_offset %s,%d\n", register, offset
 180       saved[register] = 1
 181     }
 182   }
 183 }
 184
 185 # IF REGISTER VALUES ARE UNCEREMONIOUSLY TRASHED
 186 # ...then we want to know about it.
 187 #
 188 function trashed(register) {
 189   if (in_function && !saved[register] && !dirty[register]) {
 190     printf ".cfi_undefined %s\n", register
 191   }
 192   dirty[register] = 1
 193 }
 194 # this does NOT exhaustively check for all possible instructions which could
 195 # overwrite a register value inherited from the caller (just the common ones)
 196 /mov.*,%e?([abcd][hlx]|si|di|bp)$/  { trashed(get_reg2()) }
 197 /(add|addl|sub|subl|and|or|xor|lea|sal|sar|shl|shr).*,%e?([abcd][hlx]|si|di|bp)$/ {
 198   trashed(get_reg2())
 199 }
 200 /^i?mul [^,]*$/                      { trashed("eax"); trashed("edx") }
 201 /^i?mul.*,%e?([abcd][hlx]|si|di|bp)$/ { trashed(get_reg2()) }
 202 /^i?div/                             { trashed("eax"); trashed("edx") }
 203 /(dec|inc|not|neg|pop) %e?([abcd][hlx]|si|di|bp)/  { trashed(get_reg()) }
 204 /cpuid/ { trashed("eax"); trashed("ebx"); trashed("ecx"); trashed("edx") }
 205
 206 END {
 207   if (in_function)
 208     print ".cfi_endproc"
 209 }