ovmf/gdb_uefi.py.in

"""
Allows loading TianoCore symbols into a GDB session attached to EFI
Firmware.

This is how it works: build GdbSyms - it's a dummy binary that
contains the relevant symbols needed to find and load image symbols.

$ gdb
(gdb) taget remote ....
(gdb) source Scripts/gdb_uefi.py
(gdb) reload-uefi -o /path/to/GdbSyms.dll

The -o option should be used if you've debugging EFI, where the PE
images were converted from MACH-O or ELF binaries.

"""

import array
import getopt
import binascii
import re

__license__ = "BSD"
__version = "1.0.0"
__maintainer__ = "Andrei Warkentin"
__email__ = "andrey.warkentin@gmail.com"
__status__ = "Works"


# FOR RPM PACKAGE replace the strings in the spec file 
build_path="__BUILD_PATH__"
source_path="__SOURCE_PATH__"
gdb_src_path="__GDB_SRC_PATH__"
flavor="__FLAVOR__"

class ReloadUefi (gdb.Command):
    """Reload UEFI symbols"""

    #
    # Various constants.
    #

    EINVAL = 0xffffffff
    CV_NB10 = 0x3031424E
    CV_RSDS = 0x53445352
    CV_MTOC = 0x434F544D
    DOS_MAGIC = 0x5A4D
    PE32PLUS_MAGIC = 0x20b
    EST_SIGNATURE = 0x5453595320494249
    DEBUG_GUID = [0x49152E77, 0x1ADA, 0x4764,
                  [0xB7,0xA2,0x7A,0xFE,
                   0xFE,0xD9,0x5E, 0x8B]]
    DEBUG_IS_UPDATING = 0x1

    #
    # If the images were built as ELF/MACH-O and then converted to PE,
    # then the base address needs to be offset by PE headers.
    #

    offset_by_headers = False

    def __init__ (self):
        super (ReloadUefi, self).__init__ ("reload-uefi", gdb.COMMAND_OBSCURE)

    #
    # Returns gdb.Type for a type.
    #

    def type (self, typename):
        return gdb.lookup_type (typename)

    #
    # Returns gdb.Type for a pointer to a type.
    #

    def ptype (self, typename):
        return gdb.lookup_type (typename).pointer ()

    #
    # Computes CRC32 on an array of data.
    #

    def crc32 (self, data):
        return binascii.crc32 (data) & 0xFFFFFFFF

    #
    # Sets a field in a struct to a value, i.e.
    #      value->field_name = data.
    #
    # Newer Py bindings to Gdb provide access to the inferior
    # memory, but not all, so have to do it this awkward way.
    #

    def set_field (self, value, field_name, data):
        gdb.execute ("set *(%s *) 0x%x = 0x%x" % \
                         (str (value[field_name].type), \
                              int (value[field_name].address), \
                              data))

    #
    # Returns data backing a gdb.Value as an array.
    # Same comment as above regarding newer Py bindings...
    #

    def value_data (self, value, bytes=0):
        value_address = gdb.Value (value.address)
        array_t = self.ptype ('UINT8')
        value_array = value_address.cast (array_t)
        if bytes == 0:
            bytes = value.type.sizeof
        data = array.array ('B')
        for i in range (0, bytes):
            data.append (value_array[i])
        return data

    #
    # Locates the EFI_SYSTEM_TABLE as per UEFI spec 17.4.
    # Returns base address or -1.
    #

    def search_est (self):
        address = 0
        estp_t = self.ptype ('EFI_SYSTEM_TABLE_POINTER')
        while True:
            estp = gdb.Value(address).cast(estp_t)
            if estp['Signature'] == self.EST_SIGNATURE:
                oldcrc = int (estp['Crc32'])
                self.set_field (estp, 'Crc32', 0)
                newcrc = self.crc32 (self.value_data (estp.dereference (), 0))
                self.set_field (estp, 'Crc32', int (oldcrc))
                if newcrc == oldcrc:
                    return estp['EfiSystemTableBase']

            address = address + 4*1024*1024
            if int (address) == 0:
                return gdb.Value(self.EINVAL)

    #
    # Searches for a vendor-specific configuration table (in EST),
    # given a vendor-specific table GUID. GUID is a list like -
    # [32-bit, 16-bit, 16-bit, [8 bytes]]
    #

    def search_config (self, cfg_table, count, guid):
        index = 0
        while index != count:
            cfg_entry = cfg_table[index]['VendorGuid']
            if cfg_entry['Data1'] == guid[0] and \
                    cfg_entry['Data2'] == guid[1] and \
                    cfg_entry['Data3'] == guid[2] and \
                    self.value_data (cfg_entry['Data4']).tolist () == guid[3]:
                return cfg_table[index]['VendorTable']
            index = index + 1
        return gdb.Value(self.EINVAL)

    #
    # Returns a UTF16 string corresponding to a (CHAR16 *) value in EFI.
    #

    def parse_utf16 (self, value):
        index = 0
        data = array.array ('H')
        while value[index] != 0:
            data.append (value[index])
            index = index + 1
        return data.tostring ().decode ('utf-16')

    #
    # Returns offset of a field within structure. Useful
    # for getting container of a structure.
    #

    def offsetof (self, typename, field):
        t = gdb.Value (0).cast (self.ptype (typename))
        return int (t[field].address)

    #
    # Returns sizeof of a type.
    #

    def sizeof (self, typename):
        return self.type (typename).sizeof

    #
    # Returns the EFI_IMAGE_NT_HEADERS32 pointer, given
    # an ImageBase address as a gdb.Value.
    #

    def pe_headers (self, imagebase):
        dosh_t = self.ptype ('EFI_IMAGE_DOS_HEADER')
        head_t = self.ptype ('EFI_IMAGE_OPTIONAL_HEADER_UNION')
        dosh = imagebase.cast(dosh_t)
        h_addr = imagebase
        if dosh['e_magic'] == self.DOS_MAGIC:
            h_addr = h_addr + dosh['e_lfanew']
        return gdb.Value(h_addr).cast (head_t)

    #
    # Returns True if pe_headers refer to a PE32+ image.
    #

    def pe_is_64 (self, pe_headers):
        if pe_headers['Pe32']['OptionalHeader']['Magic'] == self.PE32PLUS_MAGIC:
            return True
        return False

    #
    # Returns the PE (not so) optional header.
    #

    def pe_optional (self, pe):
        if self.pe_is_64 (pe):
            return pe['Pe32Plus']['OptionalHeader']
        else:
            return pe['Pe32']['OptionalHeader']

    #
    # Returns the symbol file name for a PE image.
    #

    def pe_parse_debug (self, pe):
        opt = self.pe_optional (pe)
        debug_dir_entry = opt['DataDirectory'][6]
        dep = debug_dir_entry['VirtualAddress'] + opt['ImageBase']
        dep = dep.cast (self.ptype ('EFI_IMAGE_DEBUG_DIRECTORY_ENTRY'))
        cvp = dep.dereference ()['RVA'] + opt['ImageBase']
        cvv = cvp.cast(self.ptype ('UINT32')).dereference ()
        if cvv == self.CV_NB10:
            return cvp + self.sizeof('EFI_IMAGE_DEBUG_CODEVIEW_NB10_ENTRY')
        elif cvv == self.CV_RSDS:
            return cvp + self.sizeof('EFI_IMAGE_DEBUG_CODEVIEW_RSDS_ENTRY')
        elif cvv == self.CV_MTOC:
            return cvp + self.sizeof('EFI_IMAGE_DEBUG_CODEVIEW_MTOC_ENTRY')
        return gdb.Value(self.EINVAL)

    #
    # Parses an EFI_LOADED_IMAGE_PROTOCOL, figuring out the symbol file name.
    # This file name is then appended to list of loaded symbols.
    #
    # TBD: Support TE images.
    #

    def parse_image (self, image, syms):
        base = image['ImageBase']
        pe = self.pe_headers (base)
        opt = self.pe_optional (pe)
        sym_name = self.pe_parse_debug (pe)

        # For ELF and Mach-O-derived images...
        if self.offset_by_headers:
            base = base + opt['SizeOfHeaders']
        if sym_name != self.EINVAL:
            sym_name = sym_name.cast (self.ptype('CHAR8')).string ()
            # Ignore the driver from qemu
            if re.search (r"\.efidrv$", sym_name):
                return
            # FOR RPM PACKAGE substitute the build path
            sym_name = re.sub(r"^"+re.escape(build_path), "/usr/lib/debug/"+flavor, sym_name)
            sym_name = re.sub(r"\.dll$", ".debug", sym_name)
            syms.append ("add-symbol-file %s 0x%x" % \
                             (sym_name,
                              int (base)))

    #
    # Parses table EFI_DEBUG_IMAGE_INFO structures, builds
    # a list of add-symbol-file commands, and reloads debugger
    # symbols.
    #

    def parse_edii (self, edii, count):
        index = 0
        syms = []
        while index != count:
            entry = edii[index]
            if entry['ImageInfoType'].dereference () == 1:
                entry = entry['NormalImage']
                self.parse_image(entry['LoadedImageProtocolInstance'], syms)
            else:
                print ('Skipping unknown EFI_DEBUG_IMAGE_INFO (Type 0x%x)' % \
                entry['ImageInfoType'].dereference ())
            index = index + 1
        gdb.execute ("symbol-file")
        print ('Loading new symbols...')
        for sym in syms:
            print (sym)
            gdb.execute (sym)

    #
    # Parses EFI_DEBUG_IMAGE_INFO_TABLE_HEADER, in order to load
    # image symbols.
    #

    def parse_dh (self, dh):
        dh_t = self.ptype ('EFI_DEBUG_IMAGE_INFO_TABLE_HEADER')
        dh = dh.cast (dh_t)
        print ('DebugImageInfoTable @ 0x%x, 0x%x entries' \
            % (int (dh['EfiDebugImageInfoTable']), dh['TableSize']))
        if dh['UpdateStatus'] & self.DEBUG_IS_UPDATING:
            print ('EfiDebugImageInfoTable update in progress, retry later')
            return
        self.parse_edii (dh['EfiDebugImageInfoTable'], dh['TableSize'])

    #
    # Parses EFI_SYSTEM_TABLE, in order to load image symbols.
    #

    def parse_est (self, est):
        est_t = self.ptype ('EFI_SYSTEM_TABLE')
        est = est.cast (est_t)
        print ('Connected to %s (Rev. 0x%x)' % \
            (self.parse_utf16 (est['FirmwareVendor']), \
                 int (est['FirmwareRevision'])))
        print ('ConfigurationTable @ 0x%x, 0x%x entries' \
            % (int (est['ConfigurationTable']), est['NumberOfTableEntries']))

        dh = self.search_config(est['ConfigurationTable'],
                                    est['NumberOfTableEntries'],
                                    self.DEBUG_GUID)
        if dh == self.EINVAL:
            print ('No EFI_DEBUG_IMAGE_INFO_TABLE_HEADER')
            return
        self.parse_dh (dh)

    #
    # Usage information.
    #

    def usage (self):
        print ('Usage: reload-uefi [-o] /path/to/GdbSyms.dll')

    #
    # Handler for reload-uefi.
    #

    def invoke (self, arg, from_tty):
        args = arg.split(' ')
        try:
            opts, args = getopt.getopt(args, "o", ["offset-by-headers"])
        except (getopt.GetoptError, err):
            self.usage ()
            return
        for opt, arg in opts:
            if opt == "-o":
                self.offset_by_headers = True

        if len(args) < 1:
            self.usage ()
            return

        # FOR RPM PACKAGE substitute the path of the source code
        gdb.execute ("set substitute-path "+source_path+" "+gdb_src_path)

        gdb.execute ("symbol-file")
        gdb.execute ("symbol-file %s" % args[0])
        est = self.search_est ()
        if est == self.EINVAL:
            print ('No EFI_SYSTEM_TABLE...')
            return

        print ('EFI_SYSTEM_TABLE @ 0x%x' % est)
        self.parse_est (est)

ReloadUefi ()