[PATCH 3/3] add CFI generation script for x86_64

[Alex Dowad <alexinbeijing@gmail.com>]

this makes debugging more pleasant when you have to dig into x86_64 assembly,
since GCC can obtain accurate stack traces. it turns out that the parts we care
about are almost exactly like i386, except for the register names!
---
 tools/add-cfi.x86_64.awk | 196 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 196 insertions(+)
 create mode 100644 tools/add-cfi.x86_64.awk

diff --git a/tools/add-cfi.x86_64.awk b/tools/add-cfi.x86_64.awk
new file mode 100644
index 0000000..bbc90da
--- /dev/null
+++ b/tools/add-cfi.x86_64.awk
@@ -0,0 +1,196 @@
+# Insert GAS CFI directives ("control frame information") into x86-64 asm input
+
+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($0, RSTART, RLENGTH-1))
+}
+
+function canonicalize_reg(register) {
+  if (match(register, /^r/))
+    return register
+  else if (match(register, /^e/))
+    return "r" substr(register, 2, length(register)-1)
+  else if (match(register, /[hl]$/)) # AH, AL, BH, BL, etc
+    return "r" substr(register, 1, 1) "x"
+  else # AX, BX, CX, etc
+    return "r" register
+}
+function get_reg() {
+  # only use if you already know there is 1 and only 1 register
+  match($0, /%[er]?([abcd][xlh]|si|di|bp|8|9|10|11|12|13|14|15)/)
+  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, /%[er]?([abcd][xlh]|si|di|bp|8|9|10|11|12|13|14|15),/)
+  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, /,%[er]?([abcd][xlh]|si|di|bp|8|9|10|11|12|13|14|15)/)
+  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($1)-1) # drop trailing :
+
+  if (called == label) {
+    # note adjustment of stack pointer from "call label; label:"
+    adjust_sp_offset(8)
+  }
+
+  if (functions[label]) {
+    if (in_function)
+      print ".cfi_endproc"
+
+    in_function = 1
+    print ".cfi_startproc"
+
+    for (register in saved)
+      delete saved[register]
+    for (register in dirty)
+      delete dirty[register]
+  }
+
+  # an instruction may follow on the same line, so continue processing
+}
+
+/^$/ { next }
+
+{
+  called = ""
+  printf ".loc 1 %d\n", line_number
+  print
+}
+
+# KEEPING UP WITH THE STACK POINTER
+# %rsp should only be adjusted by pushing/popping or adding/subtracting constants
+#
+/pushl?/ {
+  adjust_sp_offset(8)
+}
+/popl?/ {
+  adjust_sp_offset(-8)
+}
+/addl? \$-?(0x[0-9a-fA-F]+|[0-9]+),%rsp/ { adjust_sp_offset(-get_const1()) }
+/subl? \$-?(0x[0-9a-fA-F]+|[0-9]+),%rsp/ { 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? %r(ax|bx|cx|dx|si|di|bp|8|9|10|11|12|13|14|15)/ { # 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? %r(ax|bx|cx|dx|si|di|bp|8|9|10|11|12|13|14|15),-?(0x[0-9a-fA-F]+|[0-9]+)?\(%rsp\)/ {
+  if (in_function) {
+    register = get_reg()
+    if (match($0, /-?(0x[0-9a-fA-F]+|[0-9]+)\(%rsp\)/)) {
+      offset = parse_const(substr($0, RSTART, RLENGTH-6))
+    } else {
+      offset = 0
+    }
+    if (!saved[register] && !dirty[register]) {
+      printf ".cfi_rel_offset %s,%d\n", register, offset
+      saved[register] = 1
+    }
+  }
+}
+
+# IF REGISTER VALUES ARE UNCEREMONIOUSLY TRASHED
+# ...then we want to know about it.
+#
+function trashed(register) {
+  if (in_function && !saved[register] && !dirty[register]) {
+    printf ".cfi_undefined %s\n", register
+  }
+  dirty[register] = 1
+}
+# this does NOT exhaustively check for all possible instructions which could
+# overwrite a register value inherited from the caller (just the common ones)
+/mov.*,%[er]?([abcd][xlh]|si|di|bp|8|9|10|11|12|13|14|15)$/ { trashed(get_reg2()) }
+/(add|addl|sub|subl|and|or|xor|lea|sal|sar|shl|shr).*,%[er]?([abcd][xlh]|si|di|bp|8|9|10|11|12|13|14|15)$/ {
+  trashed(get_reg2())
+}
+/^i?mul [^,]*$/ { trashed("rax"); trashed("rdx") }
+/^i?mul.*,%[er]?([abcd][xlh]|si|di|bp|8|9|10|11|12|13|14|15)$/ { trashed(get_reg2()) }
+/^i?div/ { trashed("rax"); trashed("rdx") }
+
+/(dec|inc|not|neg|pop) %[er]?([abcd][xlh]|si|di|bp|8|9|10|11|12|13|14|15)/  { trashed(get_reg()) }
+/cpuid/ { trashed("rax"); trashed("rbx"); trashed("rcx"); trashed("rdx") }
+
+END {
+  if (in_function)
+    print ".cfi_endproc"
+}
-- 
2.0.0.GIT