github.com/afumu/libc@v0.0.6/musl/tools/add-cfi.i386.awk (about)

     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  }