Don't set a software stepping breakpoint at 0 on arm or mips.

[jmajors]

Summary

Added a test for the next_pc being zero before setting a software breakpoint
in arm32 and mips.
Reenabled the crash during step test for android/linux.

[labath]

Could you make two more changes to this patch?

source/Plugins/Process/Linux/NativeProcessLinux.cpp

1359

You can put the code behind this switch on the architecture below, so we don't duplicate it needlessly -- I don't know of any arch which uses software single stepping and is not arm or mips, so probably the else branch is dead code, but even if such arch existed, this should be correct for it as well. (Also, probably the whole switch should be a bit deduplicated but that's for a different change).

1371

I don't think the thread should be added to this list if setting the breakpoint failed, as we will then just try to remove (and fail) the non-existing breakpoint in SignalIfAllThreadsStopped().

[jmajors]

Restructured the code to skip setting a software breakpoint at 0.

[labath]

Thanks. I've committed this as r285187.

packages/Python/lldbsuite/test/functionalities/thread/crash_during_step/TestCrashDuringStep.py

class CreateDuringStepTestCase(TestBase):
 
     mydir = TestBase.compute_mydir(__file__)
 
     def setUp(self):
         TestBase.setUp(self)
         self.breakpoint = line_number('main.cpp', '// Set breakpoint here')
 
     @expectedFailureAll(oslist=["windows"], bugnumber="llvm.org/pr24778")
-    @expectedFailureAndroid("llvm.org/pr24497", archs=['arm', 'aarch64'])
-    @expectedFailureAll(
-        oslist=["linux"],
-        archs=["arm"],
-        bugnumber="llvm.org/pr24497")
     # IO error due to breakpoint at invalid address
     @expectedFailureAll(triple=re.compile('^mips'))
     def test_step_inst_with(self):
         """Test thread creation during step-inst handling."""
         self.build(dictionary=self.getBuildFlags())
         exe = os.path.join(os.getcwd(), "a.out")
 
         target = self.dbg.CreateTarget(exe)

source/Plugins/Process/Linux/NativeProcessLinux.cpp

if (next_flags & 0x20) {
       // Arm mode
       error = SetSoftwareBreakpoint(next_pc, 4);
     }
   } else if (m_arch.GetMachine() == llvm::Triple::mips64 ||
              m_arch.GetMachine() == llvm::Triple::mips64el ||
              m_arch.GetMachine() == llvm::Triple::mips ||
              m_arch.GetMachine() == llvm::Triple::mipsel)
     error = SetSoftwareBreakpoint(next_pc, 4);
   else {
     // No size hint is given for the next breakpoint
     error = SetSoftwareBreakpoint(next_pc, 0);
   }
 
-  if (error.Fail())
+  // If setting the breakpoint fails because next_pc is out of
+  // the address space, ignore it and let the debugee segfault.
+  if (error.GetError() == EIO || error.GetError() == EFAULT) {
+    return Error();
+  } else if (error.Fail())
     return error;
 
   m_threads_stepping_with_breakpoint.insert({thread.GetID(), next_pc});
 
   return Error();
 }
 
 bool NativeProcessLinux::SupportHardwareSingleStepping() const {
   if (m_arch.GetMachine() == llvm::Triple::arm ||
       m_arch.GetMachine() == llvm::Triple::mips64 ||
       m_arch.GetMachine() == llvm::Triple::mips64el ||