18 /* Command line syntax: ./backtrace-child [--ptraceme|--gencore]
19    --ptraceme will call ptrace (PTRACE_TRACEME) in the two threads.
20    --gencore will call abort () at its end.
23    To test getting a signal at the very first instruction of a function:
24      PC will get changed to function 'jmp' by backtrace.c function
25      prepare_thread.  Then SIGUSR2 will be signalled to backtrace-child
26      which will invoke function sigusr2.
28      instruction of a function.  Properly handled unwind should not slip into
29      the previous unrelated function.
30      The tested functionality is arch-independent but the code reproducing it
31      has to be arch-specific.
32    On non-x86_64:
33      sigusr2 gets called by normal function call from function stdarg.
34    On any arch then sigusr2 calls raise (SIGUSR1) for --ptraceme.
35    abort () is called otherwise, expected for --gencore core dump.
40    # 1 0x7f7ab661af47 - 1  main
41    # 2 0x7f7ab5e3bb45 - 1  __libc_start_main
42    # 3 0x7f7ab661aa09 - 1  _start
45    # 1 0x7f7ab661ab3c - 1  sigusr2
48    # 4 0x7f7ab661ac92 - 1  stdarg
49    # 5 0x7f7ab661acba - 1  backtracegen
50    # 6 0x7f7ab661acd1 - 1  start
51    # 7 0x7f7ab61e2c53 - 1  start_thread
52    # 8 0x7f7ab5f0fdbd - 1  __clone
54    Expected non-x86_64 (i386) output; __kernel_vsyscall are skipped if found:
57    # 1 0xf7771466 - 1      raise
58    # 2 0xf77c1d07 - 1      main
59    # 3 0xf75bd963 - 1      __libc_start_main
60    # 4 0xf77c1761 - 1      _start
63    # 1 0xf7771466 - 1      raise
64    # 2 0xf77c18f4 - 1      sigusr2
65    # 3 0xf77c1a10 - 1      stdarg
66    # 4 0xf77c1a2c - 1      backtracegen
67    # 5 0xf77c1a48 - 1      start
68    # 6 0xf77699da - 1      start_thread
69    # 7 0xf769bbfe - 1      __clone
72    function in glibc to be the same as for the jmp() function. This is not always
93 main (int argc __attribute__ ((unused)), char **argv)  in main()
111 #define UNUSED __attribute__ ((unused))  macro
116 /* Execution will arrive here from jmp by an artificial ptrace-spawn signal.  */
125       /* Do not return as stack may be invalid due to ptrace-patched PC to the  in sigusr2()
126 	 jmp function.  */  in sigusr2()
131   /* Here we dump the core for --gencore.  */  in sigusr2()
147   /* Not reached, signal will get ptrace-spawn to jump into sigusr2.  */  in jmp()
159 stdarg (int f UNUSED, ...)  in stdarg()  argument
172       /* Execution will get PC patched into function jmp.  */  in stdarg()
192      function.  It must be stdarg so that it is a call and not jump (jump as  in backtracegen()
193      a tail-call).  */  in backtracegen()
203 start (void *arg UNUSED)  in start()  argument
211 main (int argc UNUSED, char **argv)  in main()  argument
215   ptraceme = (*argv && strcmp (*argv, "--ptraceme") == 0);  in main()
217   gencore = (*argv && strcmp (*argv, "--gencore") == 0);  in main()