Mini FAQ about the misc libc/gcc crt files.
Some definitions:
PIC - position independent code (-fPIC)
PIE - position independent executable (-fPIE -pie)
crt - C runtime
crt0.o
Older style of the initial runtime code ? No one generates this anymore.
crt1.o
Newer style of the initial runtime code. Contains the _start symbol which
sets up the env with argc/argv/libc _init/libc _fini before jumping to the
libc main. glibc calls this file 'start.S'.
crti.o
Defines the function prolog; _init in the .init section and _fini in the
.fini section. glibc calls this 'initfini.c'.
crtn.o
Defines the function epilog. glibc calls this 'initfini.c'.
Scrt1.o
Used in place of crt1.o when generating PIEs.
gcrt1.o
Used in place of crt1.o when generating code with profiling information.
Compile with -pg. Produces output suitable for the gprof util.
mcrt1.o
Like gcrt1.o, but is used with the prof utility. glibc installs this as
a dummy file as it's useless on linux systems.
crtbegin.o
GCC uses this to find the start of the constructors.
crtbeginS.o
Used in place of crtbegin.o when generating shared objects/PIEs.
crtbeginT.o
Used in place of crtbegin.o when generating static executables.
crtend.o
GCC uses this to find the start of the deconstructors.
crtendS.o
Used in place of crtendS.o when generating shared objects/PIEs.
General linking order:
crt1.o crti.o crtbegin.o [-L paths] [user objects] [gcc libs] [C libs] [gcc libs] crtend.o crtn.o
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