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Re: determine whether code is running in a signal handler context
On 10/18/2017 09:07 PM, Yubin Ruan wrote:
> By "auxiliary information", do you mean those auxiliary information
> provided by the kernel (to the dynamic loader), e.g., environment
> variables, or what? It seems to me that if we have the frame pointers,
> it would be a lot easier. And it would be better if we limit our code
> to X86/64.
No, by 'auxiliary information' I mean .eh_frame/.debug_frame, the information
that tells you where the current frame's data is located (on stack or in
registers), so you can, from your current IP, find enough data to attempt
a frame unwind.
> Yes. I should have emphasized that I need only detect that the code is
> *in* a signal handler, and that is all I want. So if anyone can
> provide more info/heuristic about that (just about that) I will be
> very thankful.
You have to do architecture specific things, which I don't have immediately
off the top of my head.
gdb has a architecture-specific signal call recognizer:
gdb/gdb/i386-linux-tdep.c:
71 /* Recognizing signal handler frames. */
72
73 /* GNU/Linux has two flavors of signals. Normal signal handlers, and
74 "realtime" (RT) signals. The RT signals can provide additional
75 information to the signal handler if the SA_SIGINFO flag is set
76 when establishing a signal handler using `sigaction'. It is not
77 unlikely that future versions of GNU/Linux will support SA_SIGINFO
78 for normal signals too. */
...
gdb/gdb/aarch64-linux-tdep.c:
49 /* Signal frame handling.
50
51 +------------+ ^
52 | saved lr | |
53 +->| saved fp |--+
54 | | |
55 | | |
56 | +------------+
57 | | saved lr |
58 +--| saved fp |
59 ^ | |
60 | | |
61 | +------------+
62 ^ | |
63 | | signal |
64 | | | SIGTRAMP_FRAME (struct rt_sigframe)
65 | | saved regs |
66 +--| saved sp |--> interrupted_sp
67 | | saved pc |--> interrupted_pc
68 | | |
69 | +------------+
70 | | saved lr |--> default_restorer (movz x8, NR_sys_rt_sigreturn; svc 0)
71 +--| saved fp |<- FP
72 | | NORMAL_FRAME
73 | |<- SP
74 +------------+
75
76 On signal delivery, the kernel will create a signal handler stack
77 frame and setup the return address in LR to point at restorer stub.
78 The signal stack frame is defined by:
....
And so on and so forth...
--
Cheers,
Carlos.