[LLVMdev] Keyword documenation for target, deplibs ...

[Chris Lattner]

On Sun, 5 Mar 2006, Wink Saville wrote:
> My goal is to create a language which can compile itself, therefore I
> feel I need to understand the Assembler/Byte code format.

ok.

> Starting with a C hello world program there are statements at the
> beginning of the disassembled bc file that I couldn't find any
> documentation:

Sorry, this really should be in the LangRef.html file, but isn't for some 
reason.

> These are "self-explantory" but what are the possible values and what
> other items should I be prepared to output.

>    target endian = little
>    target pointersize = 32

Three possible options for each of these:

1) big/little/nothing
2) 32/64/nothing

Note that if your front-end is "type safe", i.e. it's not possible to 
write bad pointer casts, and your front-end isn't doing pointer arithmetic 
in a bad way, you shoouldn't need these.

>    target triple = "i686-pc-linux-gnu"

This is a standard target triple.  The ones supported by the X86 backend 
are listed here:
http://llvm.cs.uiuc.edu/docs/CodeGenerator.html#x86

>    deplibs = [ "c", "crtend" ]

This is information passed on to the linker to specify which libraries the 
code depends on.  In this case, the linker will try to link in libc and 
libcrtend.  Generally you want to add the runtime library for your 
langauge to this list.  If your language has the capability to figure out 
which libraries are required by the user application, you can also have it 
add them here.

This is to support things like a hypothetical C compiler with a pragma in 
"math.h".  Whenever the user code #includes math.h, this pragma would 
inform the linker to link in libm.

-Chris

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