• Russ Cox's avatar
    cmd/compile: add -linkobj flag to allow writing object file in two parts · feb6131b
    Russ Cox authored
    This flag is experimental and the semantics may change
    even after Go 1.7 is released. There are no changes to code
    not using the flag.
    
    The first part is for reading by future compiles.
    The second part is for reading by the final link step.
    Splitting the file this way allows distributed build systems
    to ship the compile-input part only to compile steps and
    the linker-input part only to linker steps.
    
    The first part is basically just the export data,
    and the second part is basically everything else.
    The overall files still have the same broad structure,
    so that existing tools will work with both halves.
    It's just that various pieces are empty in the two halves.
    
    This also copies the two bits of data the linker needed from
    export data into the object header proper, so that the linker
    doesn't need any export data at all. That eliminates a TODO
    that was left for switching to the binary export data.
    (Now the linker doesn't need to know about the switch.)
    
    The default is still to write out a combined output file.
    Nothing changes unless you pass -linkobj to the compiler.
    There is no support in the go command for -linkobj,
    since the go command doesn't copy objects around.
    The expectation is that other build systems (like bazel, say)
    might take advantage of this.
    
    The header adjustment and the option for the split output
    was intended as part of the zip archives, but the zip archives
    have been cut from Go 1.7. Doing this to the current archives
    both unblocks one step in the switch to binary export data
    and enables alternate build systems to experiment with the
    new flag using the Go 1.7 release.
    
    Change-Id: I8b6eab25b8a22b0a266ba0ac6d31e594f3d117f3
    Reviewed-on: https://go-review.googlesource.com/22500
    Run-TryBot: Russ Cox <rsc@golang.org>
    TryBot-Result: Gobot Gobot <gobot@golang.org>
    Reviewed-by: 's avatarIan Lance Taylor <iant@golang.org>
    Reviewed-by: 's avatarRobert Griesemer <gri@golang.org>
    feb6131b
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