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@@ -0,0 +1,80 @@
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+Mini FAQ about the misc libc/gcc crt files.
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+
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+
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+Some definitions:
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+PIC - position independent code (-fPIC)
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+PIE - position independent executable (-fPIE -pie)
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+crt - C runtime
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+
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+
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+
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+crt0.o crt1.o etc...
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+ Some systems use crt0.o, while some use crt1.o (and a few even use crt2.o
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+ or higher). Most likely due to a transitionary phase that some targets
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+ went through. The specific number is otherwise entirely arbitrary -- look
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+ at the internal gcc port code to figure out what your target expects. All
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+ that matters is that whatever gcc has encoded, your C library better use
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+ the same name.
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+
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+ This object is expected to contain the _start symbol which takes care of
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+ bootstrapping the initial execution of the program. What exactly that
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+ entails is highly libc dependent and as such, the object is provided by
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+ the C library and cannot be mixed with other ones.
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+
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+ On uClibc/glibc systems, this object initializes very early ABI requirements
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+ (like the stack or frame pointer), setting up the argc/argv/env values, and
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+ then passing pointers to the init/fini/main funcs to the internal libc main
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+ which in turn does more general bootstrapping before finally calling the real
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+ main function.
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+
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+ glibc ports call this file 'start.S' while uClibc ports call this crt0.S or
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+ crt1.S (depending on what their gcc expects).
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+
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+crti.o
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+ Defines the function prologs for the .init and .fini sections (with the _init
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+ and _fini symbols respectively). This way they can be called directly. These
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+ symbols also trigger the linker to generate DT_INIT/DT_FINI dynamic ELF tags.
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+
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+ These are to support the old style constructor/destructor system where all
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+ .init/.fini sections get concatenated at link time. Not to be confused with
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+ newer prioritized constructor/destructor .init_array/.fini_array sections and
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+ DT_INIT_ARRAY/DT_FINI_ARRAY ELF tags.
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+
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+ glibc ports used to call this 'initfini.c', but now use 'crti.S'. uClibc
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+ also uses 'crti.S'.
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+
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+crtn.o
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+ Defines the function epilogs for the .init/.fini sections. See crti.o.
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+
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+ glibc ports used to call this 'initfini.c', but now use 'crtn.S'. uClibc
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+ also uses 'crtn.S'.
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+
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+Scrt1.o
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+ Used in place of crt1.o when generating PIEs.
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+gcrt1.o
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+ Used in place of crt1.o when generating code with profiling information.
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+ Compile with -pg. Produces output suitable for the gprof util.
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+Mcrt1.o
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+ Like gcrt1.o, but is used with the prof utility. glibc installs this as
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+ a dummy file as it's useless on linux systems.
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+
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+crtbegin.o
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+ GCC uses this to find the start of the constructors.
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+crtbeginS.o
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+ Used in place of crtbegin.o when generating shared objects/PIEs.
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+crtbeginT.o
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+ Used in place of crtbegin.o when generating static executables.
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+crtend.o
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+ GCC uses this to find the start of the destructors.
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+crtendS.o
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+ Used in place of crtend.o when generating shared objects/PIEs.
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+
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+
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+
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+General linking order:
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+crt1.o crti.o crtbegin.o [-L paths] [user objects] [gcc libs] [C libs] [gcc libs] crtend.o crtn.o
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+
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+
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+
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+More references:
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+ http://gcc.gnu.org/onlinedocs/gccint/Initialization.html
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