Source file src/runtime/stubs.go

Documentation: runtime

     1  // Copyright 2014 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package runtime
     6  
     7  import "unsafe"
     8  
     9  // Should be a built-in for unsafe.Pointer?
    10  //go:nosplit
    11  func add(p unsafe.Pointer, x uintptr) unsafe.Pointer {
    12  	return unsafe.Pointer(uintptr(p) + x)
    13  }
    14  
    15  // getg returns the pointer to the current g.
    16  // The compiler rewrites calls to this function into instructions
    17  // that fetch the g directly (from TLS or from the dedicated register).
    18  func getg() *g
    19  
    20  // mcall switches from the g to the g0 stack and invokes fn(g),
    21  // where g is the goroutine that made the call.
    22  // mcall saves g's current PC/SP in g->sched so that it can be restored later.
    23  // It is up to fn to arrange for that later execution, typically by recording
    24  // g in a data structure, causing something to call ready(g) later.
    25  // mcall returns to the original goroutine g later, when g has been rescheduled.
    26  // fn must not return at all; typically it ends by calling schedule, to let the m
    27  // run other goroutines.
    28  //
    29  // mcall can only be called from g stacks (not g0, not gsignal).
    30  //
    31  // This must NOT be go:noescape: if fn is a stack-allocated closure,
    32  // fn puts g on a run queue, and g executes before fn returns, the
    33  // closure will be invalidated while it is still executing.
    34  func mcall(fn func(*g))
    35  
    36  // systemstack runs fn on a system stack.
    37  // If systemstack is called from the per-OS-thread (g0) stack, or
    38  // if systemstack is called from the signal handling (gsignal) stack,
    39  // systemstack calls fn directly and returns.
    40  // Otherwise, systemstack is being called from the limited stack
    41  // of an ordinary goroutine. In this case, systemstack switches
    42  // to the per-OS-thread stack, calls fn, and switches back.
    43  // It is common to use a func literal as the argument, in order
    44  // to share inputs and outputs with the code around the call
    45  // to system stack:
    46  //
    47  //	... set up y ...
    48  //	systemstack(func() {
    49  //		x = bigcall(y)
    50  //	})
    51  //	... use x ...
    52  //
    53  //go:noescape
    54  func systemstack(fn func())
    55  
    56  var badsystemstackMsg = "fatal: systemstack called from unexpected goroutine"
    57  
    58  //go:nosplit
    59  //go:nowritebarrierrec
    60  func badsystemstack() {
    61  	sp := stringStructOf(&badsystemstackMsg)
    62  	write(2, sp.str, int32(sp.len))
    63  }
    64  
    65  // memclrNoHeapPointers clears n bytes starting at ptr.
    66  //
    67  // Usually you should use typedmemclr. memclrNoHeapPointers should be
    68  // used only when the caller knows that *ptr contains no heap pointers
    69  // because either:
    70  //
    71  // *ptr is initialized memory and its type is pointer-free, or
    72  //
    73  // *ptr is uninitialized memory (e.g., memory that's being reused
    74  // for a new allocation) and hence contains only "junk".
    75  //
    76  // The (CPU-specific) implementations of this function are in memclr_*.s.
    77  //go:noescape
    78  func memclrNoHeapPointers(ptr unsafe.Pointer, n uintptr)
    79  
    80  //go:linkname reflect_memclrNoHeapPointers reflect.memclrNoHeapPointers
    81  func reflect_memclrNoHeapPointers(ptr unsafe.Pointer, n uintptr) {
    82  	memclrNoHeapPointers(ptr, n)
    83  }
    84  
    85  // memmove copies n bytes from "from" to "to".
    86  //
    87  // memmove ensures that any pointer in "from" is written to "to" with
    88  // an indivisible write, so that racy reads cannot observe a
    89  // half-written pointer. This is necessary to prevent the garbage
    90  // collector from observing invalid pointers, and differs from memmove
    91  // in unmanaged languages. However, memmove is only required to do
    92  // this if "from" and "to" may contain pointers, which can only be the
    93  // case if "from", "to", and "n" are all be word-aligned.
    94  //
    95  // Implementations are in memmove_*.s.
    96  //
    97  //go:noescape
    98  func memmove(to, from unsafe.Pointer, n uintptr)
    99  
   100  //go:linkname reflect_memmove reflect.memmove
   101  func reflect_memmove(to, from unsafe.Pointer, n uintptr) {
   102  	memmove(to, from, n)
   103  }
   104  
   105  // exported value for testing
   106  var hashLoad = float32(loadFactorNum) / float32(loadFactorDen)
   107  
   108  //go:nosplit
   109  func fastrand() uint32 {
   110  	mp := getg().m
   111  	// Implement xorshift64+: 2 32-bit xorshift sequences added together.
   112  	// Shift triplet [17,7,16] was calculated as indicated in Marsaglia's
   113  	// Xorshift paper: https://www.jstatsoft.org/article/view/v008i14/xorshift.pdf
   114  	// This generator passes the SmallCrush suite, part of TestU01 framework:
   115  	// http://simul.iro.umontreal.ca/testu01/tu01.html
   116  	s1, s0 := mp.fastrand[0], mp.fastrand[1]
   117  	s1 ^= s1 << 17
   118  	s1 = s1 ^ s0 ^ s1>>7 ^ s0>>16
   119  	mp.fastrand[0], mp.fastrand[1] = s0, s1
   120  	return s0 + s1
   121  }
   122  
   123  //go:nosplit
   124  func fastrandn(n uint32) uint32 {
   125  	// This is similar to fastrand() % n, but faster.
   126  	// See https://lemire.me/blog/2016/06/27/a-fast-alternative-to-the-modulo-reduction/
   127  	return uint32(uint64(fastrand()) * uint64(n) >> 32)
   128  }
   129  
   130  //go:linkname sync_fastrand sync.fastrand
   131  func sync_fastrand() uint32 { return fastrand() }
   132  
   133  // in asm_*.s
   134  //go:noescape
   135  func memequal(a, b unsafe.Pointer, size uintptr) bool
   136  
   137  // noescape hides a pointer from escape analysis.  noescape is
   138  // the identity function but escape analysis doesn't think the
   139  // output depends on the input.  noescape is inlined and currently
   140  // compiles down to zero instructions.
   141  // USE CAREFULLY!
   142  //go:nosplit
   143  func noescape(p unsafe.Pointer) unsafe.Pointer {
   144  	x := uintptr(p)
   145  	return unsafe.Pointer(x ^ 0)
   146  }
   147  
   148  func cgocallback(fn, frame unsafe.Pointer, framesize, ctxt uintptr)
   149  func gogo(buf *gobuf)
   150  func gosave(buf *gobuf)
   151  
   152  //go:noescape
   153  func jmpdefer(fv *funcval, argp uintptr)
   154  func asminit()
   155  func setg(gg *g)
   156  func breakpoint()
   157  
   158  // reflectcall calls fn with a copy of the n argument bytes pointed at by arg.
   159  // After fn returns, reflectcall copies n-retoffset result bytes
   160  // back into arg+retoffset before returning. If copying result bytes back,
   161  // the caller should pass the argument frame type as argtype, so that
   162  // call can execute appropriate write barriers during the copy.
   163  // Package reflect passes a frame type. In package runtime, there is only
   164  // one call that copies results back, in cgocallbackg1, and it does NOT pass a
   165  // frame type, meaning there are no write barriers invoked. See that call
   166  // site for justification.
   167  //
   168  // Package reflect accesses this symbol through a linkname.
   169  func reflectcall(argtype *_type, fn, arg unsafe.Pointer, argsize uint32, retoffset uint32)
   170  
   171  func procyield(cycles uint32)
   172  
   173  type neverCallThisFunction struct{}
   174  
   175  // goexit is the return stub at the top of every goroutine call stack.
   176  // Each goroutine stack is constructed as if goexit called the
   177  // goroutine's entry point function, so that when the entry point
   178  // function returns, it will return to goexit, which will call goexit1
   179  // to perform the actual exit.
   180  //
   181  // This function must never be called directly. Call goexit1 instead.
   182  // gentraceback assumes that goexit terminates the stack. A direct
   183  // call on the stack will cause gentraceback to stop walking the stack
   184  // prematurely and if there is leftover state it may panic.
   185  func goexit(neverCallThisFunction)
   186  
   187  // Not all cgocallback_gofunc frames are actually cgocallback_gofunc,
   188  // so not all have these arguments. Mark them uintptr so that the GC
   189  // does not misinterpret memory when the arguments are not present.
   190  // cgocallback_gofunc is not called from go, only from cgocallback,
   191  // so the arguments will be found via cgocallback's pointer-declared arguments.
   192  // See the assembly implementations for more details.
   193  func cgocallback_gofunc(fv, frame, framesize, ctxt uintptr)
   194  
   195  // publicationBarrier performs a store/store barrier (a "publication"
   196  // or "export" barrier). Some form of synchronization is required
   197  // between initializing an object and making that object accessible to
   198  // another processor. Without synchronization, the initialization
   199  // writes and the "publication" write may be reordered, allowing the
   200  // other processor to follow the pointer and observe an uninitialized
   201  // object. In general, higher-level synchronization should be used,
   202  // such as locking or an atomic pointer write. publicationBarrier is
   203  // for when those aren't an option, such as in the implementation of
   204  // the memory manager.
   205  //
   206  // There's no corresponding barrier for the read side because the read
   207  // side naturally has a data dependency order. All architectures that
   208  // Go supports or seems likely to ever support automatically enforce
   209  // data dependency ordering.
   210  func publicationBarrier()
   211  
   212  // getcallerpc returns the program counter (PC) of its caller's caller.
   213  // getcallersp returns the stack pointer (SP) of its caller's caller.
   214  // The implementation may be a compiler intrinsic; there is not
   215  // necessarily code implementing this on every platform.
   216  //
   217  // For example:
   218  //
   219  //	func f(arg1, arg2, arg3 int) {
   220  //		pc := getcallerpc()
   221  //		sp := getcallersp()
   222  //	}
   223  //
   224  // These two lines find the PC and SP immediately following
   225  // the call to f (where f will return).
   226  //
   227  // The call to getcallerpc and getcallersp must be done in the
   228  // frame being asked about.
   229  //
   230  // The result of getcallersp is correct at the time of the return,
   231  // but it may be invalidated by any subsequent call to a function
   232  // that might relocate the stack in order to grow or shrink it.
   233  // A general rule is that the result of getcallersp should be used
   234  // immediately and can only be passed to nosplit functions.
   235  
   236  //go:noescape
   237  func getcallerpc() uintptr
   238  
   239  //go:noescape
   240  func getcallersp() uintptr // implemented as an intrinsic on all platforms
   241  
   242  // getclosureptr returns the pointer to the current closure.
   243  // getclosureptr can only be used in an assignment statement
   244  // at the entry of a function. Moreover, go:nosplit directive
   245  // must be specified at the declaration of caller function,
   246  // so that the function prolog does not clobber the closure register.
   247  // for example:
   248  //
   249  //	//go:nosplit
   250  //	func f(arg1, arg2, arg3 int) {
   251  //		dx := getclosureptr()
   252  //	}
   253  //
   254  // The compiler rewrites calls to this function into instructions that fetch the
   255  // pointer from a well-known register (DX on x86 architecture, etc.) directly.
   256  func getclosureptr() uintptr
   257  
   258  //go:noescape
   259  func asmcgocall(fn, arg unsafe.Pointer) int32
   260  
   261  func morestack()
   262  func morestack_noctxt()
   263  func rt0_go()
   264  
   265  // return0 is a stub used to return 0 from deferproc.
   266  // It is called at the very end of deferproc to signal
   267  // the calling Go function that it should not jump
   268  // to deferreturn.
   269  // in asm_*.s
   270  func return0()
   271  
   272  // in asm_*.s
   273  // not called directly; definitions here supply type information for traceback.
   274  func call32(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
   275  func call64(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
   276  func call128(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
   277  func call256(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
   278  func call512(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
   279  func call1024(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
   280  func call2048(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
   281  func call4096(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
   282  func call8192(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
   283  func call16384(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
   284  func call32768(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
   285  func call65536(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
   286  func call131072(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
   287  func call262144(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
   288  func call524288(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
   289  func call1048576(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
   290  func call2097152(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
   291  func call4194304(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
   292  func call8388608(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
   293  func call16777216(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
   294  func call33554432(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
   295  func call67108864(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
   296  func call134217728(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
   297  func call268435456(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
   298  func call536870912(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
   299  func call1073741824(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
   300  
   301  func systemstack_switch()
   302  
   303  // alignUp rounds n up to a multiple of a. a must be a power of 2.
   304  func alignUp(n, a uintptr) uintptr {
   305  	return (n + a - 1) &^ (a - 1)
   306  }
   307  
   308  // alignDown rounds n down to a multiple of a. a must be a power of 2.
   309  func alignDown(n, a uintptr) uintptr {
   310  	return n &^ (a - 1)
   311  }
   312  
   313  // checkASM reports whether assembly runtime checks have passed.
   314  func checkASM() bool
   315  
   316  func memequal_varlen(a, b unsafe.Pointer) bool
   317  
   318  // bool2int returns 0 if x is false or 1 if x is true.
   319  func bool2int(x bool) int {
   320  	// Avoid branches. In the SSA compiler, this compiles to
   321  	// exactly what you would want it to.
   322  	return int(uint8(*(*uint8)(unsafe.Pointer(&x))))
   323  }
   324  
   325  // abort crashes the runtime in situations where even throw might not
   326  // work. In general it should do something a debugger will recognize
   327  // (e.g., an INT3 on x86). A crash in abort is recognized by the
   328  // signal handler, which will attempt to tear down the runtime
   329  // immediately.
   330  func abort()
   331  
   332  // Called from compiled code; declared for vet; do NOT call from Go.
   333  func gcWriteBarrier()
   334  func duffzero()
   335  func duffcopy()
   336  
   337  // Called from linker-generated .initarray; declared for go vet; do NOT call from Go.
   338  func addmoduledata()
   339  

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