Every. Single. Giant. Will. Warn. You. As. You. Come. Close. Before. They. Attack.
And not every giant will attack you, Ive walked next to plenty of giants, they are always protective of their mammoths or territory.
This. I've walked up to plenty of giants that were cool with me walking beside them (very close beside them).
Just approach slowly. See if the giant is getting agitated. Don't get near or screw with their herds of mammoths or goats (some herd goats). And don't stroll into one of their camps all willy-nilly.
I found a named giant once, but couldn't talk to him.