• Russ Cox's avatar
    liblink, runtime: diagnose and fix C code running on Go stack · c81a0ed3
    Russ Cox authored
    This CL contains compiler+runtime changes that detect C code
    running on Go (not g0, not gsignal) stacks, and it contains
    corrections for what it detected.
    
    The detection works by changing the C prologue to use a different
    stack guard word in the G than Go prologue does. On the g0 and
    gsignal stacks, that stack guard word is set to the usual
    stack guard value. But on ordinary Go stacks, that stack
    guard word is set to ^0, which will make any stack split
    check fail. The C prologue then calls morestackc instead
    of morestack, and morestackc aborts the program with
    a message about running C code on a Go stack.
    
    This check catches all C code running on the Go stack
    except NOSPLIT code. The NOSPLIT code is allowed,
    so the check is complete. Since it is a dynamic check,
    the code must execute to be caught. But unlike the static
    checks we've been using in cmd/ld, the dynamic check
    works with function pointers and other indirect calls.
    For example it caught sigpanic being pushed onto Go
    stacks in the signal handlers.
    
    Fixes #8667.
    
    LGTM=khr, iant
    R=golang-codereviews, khr, iant
    CC=golang-codereviews, r
    https://golang.org/cl/133700043
    c81a0ed3
os_linux.c 8.2 KB