github.com/akaros/go-akaros@v0.0.0-20181004170632-85005d477eab/src/runtime/sys_x86.c (about) 1 // Copyright 2013 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 // +build amd64 amd64p32 386 6 7 #include "runtime.h" 8 9 // adjust Gobuf as it if executed a call to fn with context ctxt 10 // and then did an immediate gosave. 11 void 12 runtime·gostartcall(Gobuf *gobuf, void (*fn)(void), void *ctxt) 13 { 14 uintptr *sp; 15 16 sp = (uintptr*)gobuf->sp; 17 if(sizeof(uintreg) > sizeof(uintptr)) 18 *--sp = 0; 19 *--sp = (uintptr)gobuf->pc; 20 gobuf->sp = (uintptr)sp; 21 gobuf->pc = (uintptr)fn; 22 gobuf->ctxt = ctxt; 23 } 24 25 // Called to rewind context saved during morestack back to beginning of function. 26 // To help us, the linker emits a jmp back to the beginning right after the 27 // call to morestack. We just have to decode and apply that jump. 28 void 29 runtime·rewindmorestack(Gobuf *gobuf) 30 { 31 byte *pc; 32 33 pc = (byte*)gobuf->pc; 34 if(pc[0] == 0xe9) { // jmp 4-byte offset 35 gobuf->pc = gobuf->pc + 5 + *(int32*)(pc+1); 36 return; 37 } 38 if(pc[0] == 0xeb) { // jmp 1-byte offset 39 gobuf->pc = gobuf->pc + 2 + *(int8*)(pc+1); 40 return; 41 } 42 if(pc[0] == 0xcc) { 43 // This is a breakpoint inserted by gdb. We could use 44 // runtime·findfunc to find the function. But if we 45 // do that, then we will continue execution at the 46 // function entry point, and we will not hit the gdb 47 // breakpoint. So for this case we don't change 48 // gobuf->pc, so that when we return we will execute 49 // the jump instruction and carry on. This means that 50 // stack unwinding may not work entirely correctly 51 // (http://golang.org/issue/5723) but the user is 52 // running under gdb anyhow. 53 return; 54 } 55 runtime·printf("runtime: pc=%p %x %x %x %x %x\n", pc, pc[0], pc[1], pc[2], pc[3], pc[4]); 56 runtime·throw("runtime: misuse of rewindmorestack"); 57 }