Travesal Through The Go Compiler, Part 2

`Builder.build`

Builder.build generate an archive for a single package.

Builder.build gets building information from two sources:
- internal/cfg package. It contains some global variables saving build flags.
- load.Package. It contains information for the current building package.
- Builder.build will build a need flag, finish the step and uncheck the finished bits one by one.
Set up caching information by action, its package, and package’s target.
Set up objects output directory.
Setup cgo cache & vet cache.
Set up building target directory.
Set up non-Go files overlay. This step is to copy the non-Go files to the object directory.
Preprocess coverage files and replace the file path of original *.go files.
- It runs go tool cover -mode=b.coverMode -var="varName" -o dst.go src.go to generate the coverage files.
Build cgo files.
- After the build, the cfiles will be cleared and generated go files will be added to gofiles
Cache all source files. It’s all *.go files now
Generate import configuration and package dependencies information.
Generate embedded files configuration.
Run BuildToolchain.gc. This is the actual go build stage.
Run BuildToolchain.cc. This is the actual cgo build stage.
Run BuildToolchain.asm. This is the actual *.s build stage.
Run BuildToolchain.pack. This will generate the object archive (*.a).
Update the BuildID accordingly.

Builder.link links a package and generates the final binary. It’s very simple compared with the build stage.