# Utility module for 'icache.py': interpret tag tables and indirect nodes.
# (This module is a bit chatty when confronted with the unexpected.)
import regexp
import string
import ifile
# Get the tag table of an open file, as a dictionary.
# Seeks around in the file; after reading, the position is undefined.
# Return an empty tag table if none is found.
#
def get_tags(f):
#
# First see if the last "node" is the end of tag table marker.
#
f.seek(0, 2) # Seek to EOF
end = f.tell()
buf = ifile.backup_node(f, end)
if not labelmatch(buf, 0, 'end tag table\n'):
return {} # No succes
#
# Next backup to the previous "node" -- the tag table itself.
#
###print 'Getting prebuilt tag table...'
end = f.tell() - len(buf)
buf = ifile.backup_node(f, end)
label = 'tag table:\n'
if not labelmatch(buf, 0, label):
print 'Weird: end tag table marker but no tag table?'
print 'Node begins:', `buf[:50]`
return {}
#
# Now read the whole tag table.
#
end = f.tell() - len(buf) # Do this first!
buf = ifile.read_node(f, buf)
#
# First check for an indirection table.
#
indirlist = []
if labelmatch(buf, len(label), '(indirect)\n'):
indirbuf = ifile.backup_node(f, end)
if not labelmatch(indirbuf, 0, 'indirect:\n'):
print 'Weird: promised indirection table not found'
print 'Node begins:', `indirbuf[:50]`
# Carry on. Things probably won't work though.
else:
indirbuf = ifile.read_node(f, indirbuf)
indirlist = parse_indirlist(indirbuf)
#
# Now parse the tag table.
#
findtag = regexp.compile('^(.*[nN]ode:[ \t]*(.*))\177([0-9]+)$').match
i = 0
tags = {}
while 1:
match = findtag(buf, i)
if not match:
break
(a,b), (a1,b1), (a2,b2), (a3,b3) = match
i = b
line = buf[a1:b1]
node = string.lower(buf[a2:b2])
offset = eval(buf[a3:b3]) # XXX What if it overflows?
if tags.has_key(node):
print 'Duplicate key in tag table:', `node`
file, offset = map_offset(offset, indirlist)
tags[node] = file, offset, line
#
return tags
# Return true if buf[i:] begins with a label, after lower case conversion.
# The label argument must be in lower case.
#
def labelmatch(buf, i, label):
return string.lower(buf[i:i+len(label)]) == label
# Parse the indirection list.
# Return a list of (filename, offset) pairs ready for use.
#
def parse_indirlist(buf):
list = []
findindir = regexp.compile('^(.+):[ \t]*([0-9]+)$').match
i = 0
while 1:
match = findindir(buf, i)
if not match:
break
(a,b), (a1,b1), (a2,b2) = match
file = buf[a1:b1]
offset = eval(buf[a2:b2]) # XXX What if this gets overflow?
list.append((file, offset))
i = b
return list
# Map an offset through the indirection list.
# Return (filename, new_offset).
# If the list is empty, return the given offset and an empty file name.
#
def map_offset(offset, indirlist):
if not indirlist:
return '', offset
#
# XXX This could be done more elegant.
#
filex, offx = indirlist[0]
for i in range(len(indirlist)):
file1, off1 = indirlist[i]
if i+1 >= len(indirlist):
file2, off2 = '', 0x7fffffff
else:
file2, off2 = indirlist[i+1]
if off1 <= offset < off2:
# Add offx+2 to compensate for extra header.
# No idea whether this is always correct.
return file1, offset-off1 + offx+2
#
# XXX Shouldn't get here.
#
print 'Oops, map_offset fell through'
return '', offset # Not likely to get good results
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