• Russ Cox's avatar
    cmd/gc: disable link-time copying of un-Go-initialized globals · e5c10503
    Russ Cox authored
    If you write:
    
            var x = 3
    
    then the compiler arranges for x to be initialized in the linker
    with an actual 3 from the data segment, rather than putting
    x in the bss and emitting init-time "x = 3" assignment code.
    
    If you write:
    
            var y = x
            var x = 3
    
    then the compiler is clever and treats this the same as if
    the code said 'y = 3': they both end up in the data segment
    with no init-time assignments.
    
    If you write
    
            var y = x
            var x int
    
    then the compiler was treating this the same as if the
    code said 'x = 0', making both x and y zero and avoiding
    any init-time assignment.
    
    This copying optimization to avoid init-time assignment of y
    is incorrect if 'var x int' doesn't mean 'x = 0' but instead means
    'x is initialized in C or assembly code'. The program ends up
    with 'y = 0' instead of 'y = the value specified for x in that other code'.
    
    Disable the propagation if there is no initializer for x.
    
    This comes up in some uses of cgo, because cgo generates
    Go globals that are initialized in accompanying C files.
    
    Fixes #7665.
    
    LGTM=iant
    R=golang-codereviews, iant
    CC=golang-codereviews
    https://golang.org/cl/93200044
    e5c10503
sinit.c 28.7 KB