// Called from reflect·call or from runtime·morestack when a new
// stack segment is needed. Allocate a new stack big enough for
// m->moreframesize bytes, copy m->moreargsize bytes to the new frame,
// and then act as though runtime·lessstack called the function at
// m->morepc.
// 当需要一个新的栈段时调用，被reflect.call或者runtime.morestack调用
// 分配一个足够大的新栈，至少大于m->moreframesize。将m->moreargsize字节复制到新的栈帧。
// 然后伪装成在m->morepc处调用函数runtime.lessstack的样子。
void
runtime·newstack(void)
{
int32 framesize, minalloc, argsize;
Stktop *top;
byte *stk, *sp;
uintptr *src, *dst, *dstend;
G *gp;
Gobuf label;
bool reflectcall;
uintptr free;
framesize = m->moreframesize;
argsize = m->moreargsize;
gp = m->curg;
if(m->morebuf.sp < gp->stackguard - StackGuard) { //栈已经溢出
runtime·printf("runtime: split stack overflow: %p < %p\n", m->morebuf.sp, gp->stackguard - StackGuard);
runtime·throw("runtime: split stack overflow");
}
if(argsize % sizeof(uintptr) != 0) { //参数未对齐
runtime·printf("runtime: stack split with misaligned argsize %d\n", argsize);
runtime·throw("runtime: stack split argsize");
}
minalloc = 0;
reflectcall = framesize==1;
if(reflectcall) {
framesize = 0;
// moreframesize_minalloc is only set in runtime·gc(),
// that calls newstack via reflect·call().
minalloc = m->moreframesize_minalloc;
m->moreframesize_minalloc = 0;
if(framesize < minalloc)
framesize = minalloc;
}
if(reflectcall && minalloc == 0 && m->morebuf.sp - sizeof(Stktop) - argsize - 32 > gp->stackguard) {
// special case: called from reflect.call (framesize==1)
// to call code with an arbitrary argument size,
// and we have enough space on the current stack.
// the new Stktop* is necessary to unwind, but
// we don't need to create a new segment.
top = (Stktop*)(m->morebuf.sp - sizeof(*top));
stk = (byte*)gp->stackguard - StackGuard;
free = 0;
} else {
// 分配新空间
// framesize大小，必须包含参数大小部分，为调用runtime.morestack保留部分，并且至少大于StackMin。然后还要加上StackSystem部分
framesize += argsize;
framesize += StackExtra; // room for more functions, Stktop.
if(framesize < StackMin)
framesize = StackMin;
framesize += StackSystem;
stk = runtime·stackalloc(framesize);
top = (Stktop*)(stk+framesize-sizeof(*top));
free = framesize;
}
if(0) {
runtime·printf("newstack framesize=%d argsize=%d morepc=%p moreargp=%p gobuf=%p, %p top=%p old=%p\n",
framesize, argsize, m->morepc, m->moreargp, m->morebuf.pc, m->morebuf.sp, top, gp->stackbase);
}
//将一些重要信息从结构体g中移到栈顶Stktop中
top->stackbase = (byte*)gp->stackbase;
top->stackguard = (byte*)gp->stackguard;
top->gobuf = m->morebuf; //只是借助m结构体临时传了一下参数，morebuf中记录的是栈空间不够的那个函数的pc,sp,g
top->argp = m->moreargp; //参数
top->argsize = argsize; //参数大小
top->free = free; //可用空间大小
m->moreargp = nil;
m->morebuf.pc = nil;
m->morebuf.sp = (uintptr)nil;
// copy flag from panic
top->panic = gp->ispanic;
gp->ispanic = false;
gp->stackbase = (uintptr)top;
gp->stackguard = (uintptr)stk + StackGuard; //每个goroutine的g->stackguard设置成指向栈底上面StackGuard的位置。
//装饰栈顶的参数区域
sp = (byte*)top;
if(argsize > 0) { //将参数移过来
sp -= argsize;
dst = (uintptr*)sp;
dstend = dst + argsize/sizeof(*dst);
src = (uintptr*)top->argp;
while(dst < dstend)
*dst++ = *src++;
}
if(thechar == '5') { //编译器标识
// caller would have saved its LR below args.
sp -= sizeof(void*);
*(void**)sp = nil;
}
// Continue as if lessstack had just called m->morepc
// (the PC that decided to grow the stack).
// 继续，伪装成好像是从m->morepc中调用lessstack函数的状态
// 跳转
label.sp = (uintptr)sp;
label.pc = (byte*)runtime·lessstack;
label.g = m->curg;
if(reflectcall)
runtime·gogocallfn(&label, (FuncVal*)m->morepc);
else
runtime·gogocall(&label, m->morepc, m->cret); //gogocall相当于一个直接的jmp，不是按函数协议跳转的
*(int32*)345 = 123; // never return
}
// Called from reflect·call or from runtime·morestack when a new
// stack segment is needed. Allocate a new stack big enough for
// m->moreframesize bytes, copy m->moreargsize bytes to the new frame,
// and then act as though runtime·lessstack called the function at
// m->morepc.
void
runtime·newstack(void)
{
int32 framesize, minalloc, argsize;
Stktop *top;
byte *stk, *sp;
uintptr *src, *dst, *dstend;
G *gp;
Gobuf label;
bool reflectcall;
uintptr free;
framesize = m->moreframesize;
argsize = m->moreargsize;
gp = m->curg;
if(m->morebuf.sp < gp->stackguard - StackGuard) {
runtime·printf("runtime: split stack overflow: %p < %p\n", m->morebuf.sp, gp->stackguard - StackGuard);
runtime·throw("runtime: split stack overflow");
}
if(argsize % sizeof(uintptr) != 0) {
runtime·printf("runtime: stack split with misaligned argsize %d\n", argsize);
runtime·throw("runtime: stack split argsize");
}
minalloc = 0;
reflectcall = framesize==1;
if(reflectcall) {
framesize = 0;
// moreframesize_minalloc is only set in runtime·gc(),
// that calls newstack via reflect·call().
minalloc = m->moreframesize_minalloc;
m->moreframesize_minalloc = 0;
if(framesize < minalloc)
framesize = minalloc;
}
if(reflectcall && minalloc == 0 && m->morebuf.sp - sizeof(Stktop) - argsize - 32 > gp->stackguard) {
// special case: called from reflect.call (framesize==1)
// to call code with an arbitrary argument size,
// and we have enough space on the current stack.
// the new Stktop* is necessary to unwind, but
// we don't need to create a new segment.
top = (Stktop*)(m->morebuf.sp - sizeof(*top));
stk = (byte*)gp->stackguard - StackGuard;
free = 0;
} else {
// allocate new segment.
framesize += argsize;
framesize += StackExtra; // room for more functions, Stktop.
if(framesize < StackMin)
framesize = StackMin;
framesize += StackSystem;
stk = runtime·stackalloc(framesize);
top = (Stktop*)(stk+framesize-sizeof(*top));
free = framesize;
}
if(0) {
runtime·printf("newstack framesize=%d argsize=%d morepc=%p moreargp=%p gobuf=%p, %p top=%p old=%p\n",
framesize, argsize, m->morepc, m->moreargp, m->morebuf.pc, m->morebuf.sp, top, gp->stackbase);
}
top->stackbase = (byte*)gp->stackbase;
top->stackguard = (byte*)gp->stackguard;
top->gobuf = m->morebuf;
top->argp = m->moreargp;
top->argsize = argsize;
top->free = free;
m->moreargp = nil;
m->morebuf.pc = nil;
m->morebuf.sp = (uintptr)nil;
// copy flag from panic
top->panic = gp->ispanic;
gp->ispanic = false;
gp->stackbase = (uintptr)top;
gp->stackguard = (uintptr)stk + StackGuard;
sp = (byte*)top;
if(argsize > 0) {
sp -= argsize;
dst = (uintptr*)sp;
dstend = dst + argsize/sizeof(*dst);
src = (uintptr*)top->argp;
while(dst < dstend)
*dst++ = *src++;
}
if(thechar == '5') {
// caller would have saved its LR below args.
sp -= sizeof(void*);
*(void**)sp = nil;
}
// Continue as if lessstack had just called m->morepc
// (the PC that decided to grow the stack).
label.sp = (uintptr)sp;
label.pc = (byte*)runtime·lessstack;
label.g = m->curg;
if(reflectcall)
runtime·gogocallfn(&label, (FuncVal*)m->morepc);
else
runtime·gogocall(&label, m->morepc, m->cret);
*(int32*)345 = 123; // never return
}