package sys Import Path runtime/internal/sys (on go.dev) Dependency Relation imports 2 packages, and imported by one packageInvolved Source Files consts.go consts_norace.go intrinsics.go nih.go package sys contains system- and configuration- and architecture-specific constants used by the runtime. zversion.goPackage-Level Type Names (only one)NotInHeap is a type must never be allocated from the GC'd heap or on the stack, and is called not-in-heap. Other types can embed NotInHeap to make it not-in-heap. Specifically, pointers to these types must always fail the `runtime.inheap` check. The type may be used for global variables, or for objects in unmanaged memory (e.g., allocated with `sysAlloc`, `persistentalloc`, r`fixalloc`, or from a manually-managed span). Specifically: 1. `new(T)`, `make(T)`, `append(T, ...)` and implicit heap allocation of T are disallowed. (Though implicit allocations are disallowed in the runtime anyway.) 2. A pointer to a regular type (other than `unsafe.Pointer`) cannot be converted to a pointer to a not-in-heap type, even if they have the same underlying type. 3. Any type that containing a not-in-heap type is itself considered as not-in-heap. - Structs and arrays are not-in-heap if their elements are not-in-heap. - Maps and channels contains no-in-heap types are disallowed. 4. Write barriers on pointers to not-in-heap types can be omitted. The last point is the real benefit of NotInHeap. The runtime uses it for low-level internal structures to avoid memory barriers in the scheduler and the memory allocator where they are illegal or simply inefficient. This mechanism is reasonably safe and does not compromise the readability of the runtime.Package-Level Functions (total 12)Bswap32 returns its input with byte order reversed 0x01020304 -> 0x04030201Bswap64 returns its input with byte order reversed 0x0102030405060708 -> 0x0807060504030201LeadingZeros64 returns the number of leading zero bits in x; the result is 64 for x == 0.LeadingZeros8 returns the number of leading zero bits in x; the result is 8 for x == 0.Len64 returns the minimum number of bits required to represent x; the result is 0 for x == 0. nosplit because this is used in src/runtime/histogram.go, which make run in sensitive contexts.Len8 returns the minimum number of bits required to represent x; the result is 0 for x == 0.OnesCount64 returns the number of one bits ("population count") in x.Prefetch prefetches data from memory addr to cache AMD64: Produce PREFETCHT0 instruction ARM64: Produce PRFM instruction with PLDL1KEEP optionPrefetchStreamed prefetches data from memory addr, with a hint that this data is being streamed. That is, it is likely to be accessed very soon, but only once. If possible, this will avoid polluting the cache. AMD64: Produce PREFETCHNTA instruction ARM64: Produce PRFM instruction with PLDL1STRM optionTrailingZeros32 returns the number of trailing zero bits in x; the result is 32 for x == 0.TrailingZeros64 returns the number of trailing zero bits in x; the result is 64 for x == 0.TrailingZeros8 returns the number of trailing zero bits in x; the result is 8 for x == 0.Package-Level Constants (total 6)DefaultPhysPageSize is the default physical page size.Int64Align is the required alignment for a 64-bit integer (4 on 32-bit systems, 8 on 64-bit).MinFrameSize is the size of the system-reserved words at the bottom of a frame (just above the architectural stack pointer). It is zero on x86 and PtrSize on most non-x86 (LR-based) systems. On PowerPC it is larger, to cover three more reserved words: the compiler word, the link editor word, and the TOC save word.PCQuantum is the minimal unit for a program counter (1 on x86, 4 on most other systems). The various PC tables record PC deltas pre-divided by PCQuantum.StackAlign is the required alignment of the SP register. The stack must be at least word aligned, but some architectures require more.AIX requires a larger stack for syscalls. The race build also needs more stack. See issue 54291. This arithmetic must match that in cmd/internal/objabi/stack.go:stackGuardMultiplier.
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