# Insert GAS CFI directives ("control frame information") into x86-32 asm input
#
# CFI directives tell the assembler how to generate "stack frame" debug info
# This information can tell a debugger (like gdb) how to find the current stack
# frame at any point in the program code, and how to find the values which
# various registers had at higher points in the call stack
# With this information, the debugger can show a backtrace, and you can move up
# and down the call stack and examine the values of local variables
BEGIN {
# don't put CFI data in the .eh_frame ELF section (which we don't keep)
print ".cfi_sections .debug_frame"
# only emit CFI directives inside a function
in_function = 0
# emit .loc directives with line numbers from original source
printf ".file 1 \"%s\"\n", ARGV[1]
line_number = 0
# used to detect "call label; label:" trick
called = ""
}
function get_const1() {
# for instructions with 2 operands, get 1st operand (assuming it is constant)
match($0, /-?(0x[0-9a-fA-F]+|[0-9]+),/)
return parse_const(substr($0, RSTART, RLENGTH-1))
}
function canonicalize_reg(register) {
if (match(register, /^e/))
return register
else if (match(register, /[hl]$/)) # AH, AL, BH, BL, etc
return "e" substr(register, 1, 1) "x"
else # AX, BX, CX, etc
return "e" register
}
function get_reg() {
# only use if you already know there is 1 and only 1 register
match($0, /%e?([abcd][hlx]|si|di|bp)/)
return canonicalize_reg(substr($0, RSTART+1, RLENGTH-1))
}
function get_reg1() {
# for instructions with 2 operands, get 1st operand (assuming it is register)
match($0, /%e?([abcd][hlx]|si|di|bp),/)
return canonicalize_reg(substr($0, RSTART+1, RLENGTH-2))
}
function get_reg2() {
# for instructions with 2 operands, get 2nd operand (assuming it is register)
match($0, /,%e?([abcd][hlx]|si|di|bp)/)
return canonicalize_reg(substr($0, RSTART+2, RLENGTH-2))
}
function adjust_sp_offset(delta) {
if (in_function)
printf ".cfi_adjust_cfa_offset %d\n", delta
}
{
line_number = line_number + 1
# clean the input up before doing anything else
# delete comments
gsub(/(#|\/\/).*/, "")
# canonicalize whitespace
gsub(/[ \t]+/, " ") # mawk doesn't understand \s
gsub(/ *, */, ",")
gsub(/ *: */, ": ")
gsub(/ $/, "")
gsub(/^ /, "")
}
# check for assembler directives which we care about
/^\.(section|data|text)/ {
# a .cfi_startproc/.cfi_endproc pair should be within the same section
# otherwise, clang will choke when generating ELF output
if (in_function) {
print ".cfi_endproc"
in_function = 0
}
}
/^\.type [a-zA-Z0-9_]+,\@function/ {
functions[substr($2, 1, length($2)-10)] = 1
}
# not interested in assembler directives beyond this, just pass them through
/^\./ {
print
next
}
/^[a-zA-Z0-9_]+:/ {
label = substr($1, 1, length($1)-1) # drop trailing :
if (called == label) {
# note adjustment of stack pointer from "call label; label:"
adjust_sp_offset(4)
}
if (functions[label]) {
if (in_function)
print ".cfi_endproc"
in_function = 1
print ".cfi_startproc"
for (register in saved)
delete saved[register]
for (register in dirty)
delete dirty[register]
}
# an instruction may follow on the same line, so continue processing
}
/^$/ { next }
{
called = ""
printf ".loc 1 %d\n", line_number
print
}
# KEEPING UP WITH THE STACK POINTER
# We do NOT attempt to understand foolish and ridiculous tricks like stashing
# the stack pointer and then using %esp as a scratch register, or bitshifting
# it or taking its square root or anything stupid like that.
# %esp should only be adjusted by pushing/popping or adding/subtracting constants
#
/pushl?/ {
if (match($0, / %(ax|bx|cx|dx|di|si|bp|sp)/))
adjust_sp_offset(2)
else
adjust_sp_offset(4)
}
/popl?/ {
if (match($0, / %(ax|bx|cx|dx|di|si|bp|sp)/))
adjust_sp_offset(-2)
else
adjust_sp_offset(-4)
}
/addl? \$-?(0x[0-9a-fA-F]+|[0-9]+),%esp/ { adjust_sp_offset(-get_const1()) }
/subl? \$-?(0x[0-9a-fA-F]+|[0-9]+),%esp/ { adjust_sp_offset(get_const1()) }
/call/ {
if (match($0, /call [0-9]+f/)) # "forward" label
called = substr($0, RSTART+5, RLENGTH-6)
else if (match($0, /call [0-9a-zA-Z_]+/))
called = substr($0, RSTART+5, RLENGTH-5)
}
# TRACKING REGISTER VALUES FROM THE PREVIOUS STACK FRAME
#
/pushl? %e(ax|bx|cx|dx|si|di|bp)/ { # don't match "push (%reg)"
# if a register is being pushed, and its value has not changed since the
# beginning of this function, the pushed value can be used when printing
# local variables at the next level up the stack
# emit '.cfi_rel_offset' for that
if (in_function) {
register = get_reg()
if (!saved[register] && !dirty[register]) {
printf ".cfi_rel_offset %s,0\n", register
saved[register] = 1
}
}
}
/movl? %e(ax|bx|cx|dx|si|di|bp),-?(0x[0-9a-fA-F]+|[0-9]+)?\(%esp\)/ {
if (in_function) {
register = get_reg()
if (match($0, /-?(0x[0-9a-fA-F]+|[0-9]+)\(%esp\)/)) {
offset = parse_const(substr($0, RSTART, RLENGTH-6))
} else {
offset = 0
}
if (!saved[register] && !dirty[register]) {
printf ".cfi_rel_offset %s,%d\n", register, offset
saved[register] = 1
}
}
}
# IF REGISTER VALUES ARE UNCEREMONIOUSLY TRASHED
# ...then we want to know about it.
#
function trashed(register) {
if (in_function && !saved[register] && !dirty[register]) {
printf ".cfi_undefined %s\n", register
}
dirty[register] = 1
}
# this does NOT exhaustively check for all possible instructions which could
# overwrite a register value inherited from the caller (just the common ones)
/mov.*,%e?([abcd][hlx]|si|di|bp)$/ { trashed(get_reg2()) }
/(add|addl|sub|subl|and|or|xor|lea|sal|sar|shl|shr).*,%e?([abcd][hlx]|si|di|bp)$/ {
trashed(get_reg2())
}
/^i?mul [^,]*$/ { trashed("eax"); trashed("edx") }
/^i?mul.*,%e?([abcd][hlx]|si|di|bp)$/ { trashed(get_reg2()) }
/^i?div/ { trashed("eax"); trashed("edx") }
/(dec|inc|not|neg|pop) %e?([abcd][hlx]|si|di|bp)/ { trashed(get_reg()) }
/cpuid/ { trashed("eax"); trashed("ebx"); trashed("ecx"); trashed("edx") }
END {
if (in_function)
print ".cfi_endproc"
}
