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
5package runtime
6
7import "unsafe"
8
9type sigctxt struct {
10	info *siginfo
11	ctxt unsafe.Pointer
12}
13
14//go:nosplit
15//go:nowritebarrierrec
16func (c *sigctxt) regs() *regs64 { return &(*ucontext)(c.ctxt).uc_mcontext.ss }
17
18func (c *sigctxt) rax() uint64 { return c.regs().rax }
19func (c *sigctxt) rbx() uint64 { return c.regs().rbx }
20func (c *sigctxt) rcx() uint64 { return c.regs().rcx }
21func (c *sigctxt) rdx() uint64 { return c.regs().rdx }
22func (c *sigctxt) rdi() uint64 { return c.regs().rdi }
23func (c *sigctxt) rsi() uint64 { return c.regs().rsi }
24func (c *sigctxt) rbp() uint64 { return c.regs().rbp }
25func (c *sigctxt) rsp() uint64 { return c.regs().rsp }
26func (c *sigctxt) r8() uint64  { return c.regs().r8 }
27func (c *sigctxt) r9() uint64  { return c.regs().r9 }
28func (c *sigctxt) r10() uint64 { return c.regs().r10 }
29func (c *sigctxt) r11() uint64 { return c.regs().r11 }
30func (c *sigctxt) r12() uint64 { return c.regs().r12 }
31func (c *sigctxt) r13() uint64 { return c.regs().r13 }
32func (c *sigctxt) r14() uint64 { return c.regs().r14 }
33func (c *sigctxt) r15() uint64 { return c.regs().r15 }
34
35//go:nosplit
36//go:nowritebarrierrec
37func (c *sigctxt) rip() uint64 { return c.regs().rip }
38
39func (c *sigctxt) rflags() uint64  { return c.regs().rflags }
40func (c *sigctxt) cs() uint64      { return c.regs().cs }
41func (c *sigctxt) fs() uint64      { return c.regs().fs }
42func (c *sigctxt) gs() uint64      { return c.regs().gs }
43func (c *sigctxt) sigcode() uint64 { return uint64(c.info.si_code) }
44func (c *sigctxt) sigaddr() uint64 { return c.info.si_addr }
45
46func (c *sigctxt) set_rip(x uint64)     { c.regs().rip = x }
47func (c *sigctxt) set_rsp(x uint64)     { c.regs().rsp = x }
48func (c *sigctxt) set_sigcode(x uint64) { c.info.si_code = int32(x) }
49func (c *sigctxt) set_sigaddr(x uint64) { c.info.si_addr = x }
50
51//go:nosplit
52func (c *sigctxt) fixsigcode(sig uint32) {
53	switch sig {
54	case _SIGTRAP:
55		// OS X sets c.sigcode() == TRAP_BRKPT unconditionally for all SIGTRAPs,
56		// leaving no way to distinguish a breakpoint-induced SIGTRAP
57		// from an asynchronous signal SIGTRAP.
58		// They all look breakpoint-induced by default.
59		// Try looking at the code to see if it's a breakpoint.
60		// The assumption is that we're very unlikely to get an
61		// asynchronous SIGTRAP at just the moment that the
62		// PC started to point at unmapped memory.
63		pc := uintptr(c.rip())
64		// OS X will leave the pc just after the INT 3 instruction.
65		// INT 3 is usually 1 byte, but there is a 2-byte form.
66		code := (*[2]byte)(unsafe.Pointer(pc - 2))
67		if code[1] != 0xCC && (code[0] != 0xCD || code[1] != 3) {
68			// SIGTRAP on something other than INT 3.
69			c.set_sigcode(_SI_USER)
70		}
71
72	case _SIGSEGV:
73		// x86-64 has 48-bit virtual addresses. The top 16 bits must echo bit 47.
74		// The hardware delivers a different kind of fault for a malformed address
75		// than it does for an attempt to access a valid but unmapped address.
76		// OS X 10.9.2 mishandles the malformed address case, making it look like
77		// a user-generated signal (like someone ran kill -SEGV ourpid).
78		// We pass user-generated signals to os/signal, or else ignore them.
79		// Doing that here - and returning to the faulting code - results in an
80		// infinite loop. It appears the best we can do is rewrite what the kernel
81		// delivers into something more like the truth. The address used below
82		// has very little chance of being the one that caused the fault, but it is
83		// malformed, it is clearly not a real pointer, and if it does get printed
84		// in real life, people will probably search for it and find this code.
85		// There are no Google hits for b01dfacedebac1e or 0xb01dfacedebac1e
86		// as I type this comment.
87		//
88		// Note: if this code is removed, please consider
89		// enabling TestSignalForwardingGo for darwin-amd64 in
90		// misc/cgo/testcarchive/carchive_test.go.
91		if c.sigcode() == _SI_USER {
92			c.set_sigcode(_SI_USER + 1)
93			c.set_sigaddr(0xb01dfacedebac1e)
94		}
95	}
96}
97