Go Assembly中PCDATA的含义是什么

I'm compiling golang code to assembly using:

go build -gcflags -S .

In the assembly code I'm saying a lot of lines like:

PCDATA  $2, $1

What does it mean? In the quick guide to asm it states

The FUNCDATA and PCDATA directives contain information for use by the garbage collector; they are introduced by the compile

but there aren't many details