$getg() function for gdb

getg.py

import gdb

_Gdead = 6

class SliceValue:
    """Wrapper for slice values."""

    def __init__(self, val):
        self.val = val

    @property
    def len(self):
        return int(self.val['len'])

    @property
    def cap(self):
        return int(self.val['cap'])

    def __getitem__(self, i):
        if i < 0 or i >= self.len:
            raise IndexError(i)
        ptr = self.val["array"]
        return (ptr + i).dereference()

def getg(sp=None, n=None):
    if sp is None and n is None:
        sp = gdb.parse_and_eval('$sp')

    found = [None]
    def checkg(gp):
        if gp == 0:
            return
        if gp['atomicstatus'] == _Gdead:
            return
        if sp != None and gp['stack']['lo'] < sp and sp <= gp['stack']['hi']:
            if found[0] is not None:
                raise gdb.GdbError('multiple Gs with overlapping stacks!')
            found[0] = gp
        if n != None and gp['goid'] == n:
            if found[0] is not None:
                raise gdb.GdbError('multiple Gs with same goid!')
            found[0] = gp

    # Check allgs.
    for gp in SliceValue(gdb.parse_and_eval("'runtime.allgs'")):
        checkg(gp)

    # Check g0s and gsignals, which aren't on allgs.
    if sp is not None:
        mp = gdb.parse_and_eval("'runtime.allm'")
        while mp != 0:
            checkg(mp['g0'])
            checkg(mp['gsignal'])
            mp = mp['alllink']

    return found[0]

class GetG(gdb.Function):
    """Return the current *g."""

    def __init__(self):
        super(GetG, self).__init__("getg")

    def invoke(self, n=None):
        g = getg(n=n)
        if g is None:
            raise gdb.GdbError('G not found')
        return g
GetG()