Garama masala is a blend of toasted ground spices used in South Asian cuisine, most especially in Northern India. As is the case with curry powder, different brands will have different amounts of the spices, and sometimes other spices added.
Many garam masalas will include black pepper, cinnamon, cumin, cloves, cardamom, and sometimes coriander. Because these spices quickly lose their aroma and strength once ground, it is best and most effective to use whole spices and create the mix as needed. In this case, the spices are toasted first, then ground together. Sometimes a liquid is added to make a paste. Bay leaves, nutmeg, garlic, or onion may be included. In store-bought garam masala, there is often a higher proportion of less expensive spices, sometimes including ground ginger and dried garlic.
The pre-made garam masala I have on hand includes coriander, black pepper, cumin, cardamom, and cinnamon.
GF - because garam masala is not a single spice, there is a very slight
possibility of gluten in some brands. The McCormick company is very
dependable on this subject and does not hide wheat on their labels (if
it's there, it'll say "wheat", not "natural flavours"). At the time of
this writing, McCormick garam masala is gluten-free, as are the vast majority of brands (I've yet to find one that isn't).