makefile - debug the environment used by make and port gcc from source -

i know how build gcc source, still have figure out exact environmental variables used gcc when configure , building gcc itself, i'm trying build compiler source using version of gcc different abi.

any idea on how kind of information beside "try grep variable starts $ inside makefiles , configuration files" ?

you can see list of environment variables affecting gcc.

to create completly independent gcc new toolset, have @ lfs, explain how build gcc existing os future os.

there page building gcc, talks boot_cflags='-o' , cflags_for_target , stage1_tflags , build_config. there additional variables cross-compiling , ada compiler.