jasonmolenda created this revision.
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This is a change I need on Darwin systems, so I'm trying to decide whether I
put the test case in API/functionalities or in macosx, but I think it may apply
on Linux as well.
With a __builtin_debugtrap() in a program, we want the debugger to stop
execution there, but we want the user to get past it with a 'continue' or
next/step. With a __builtin_trap(), we want the debugger to stop on that
instruction and not advance unless the user rewrites $pc manually or something.
On x86, __builtin_debugtrap() is 0xcc (the breakpoint instruction); when you
hit that, the pc has advanced past the 0xcc. In debugserver
(DNBArchImplX86_64::NotifyException) when we've hit an 0xcc that was NOT a
breakpoint debugserver inserted, it leaves the $pc past the 0xcc, so continuing
will work.
On arm64, __builtin_debugtrap is 'brk #0xf000', this patch recognizes that
specific instruction in DNBArchMachARM64::NotifyException and advances the pc
past it so we get the same behavior.
The test case hits a __builtin_debugtrap(), continues past it, hits a
__builtin_trap(), and checks that it cannot advance past that. With this
debugserver patch, that's how lldb behaves on both x86 darwin and arm64 darwin.
Pretty simple stuff; the only real question is whether we should make this a
macos-only tested behavior, or include Linux as well. Anyone know how this
works with lldb-server on linux?
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D91238
Files:
lldb/test/API/functionalities/builtin-debugtrap/Makefile
lldb/test/API/functionalities/builtin-debugtrap/TestBuiltinDebugTrap.py
lldb/test/API/functionalities/builtin-debugtrap/main.cpp
lldb/tools/debugserver/source/MacOSX/arm64/DNBArchImplARM64.cpp
Index: lldb/tools/debugserver/source/MacOSX/arm64/DNBArchImplARM64.cpp
===================================================================
--- lldb/tools/debugserver/source/MacOSX/arm64/DNBArchImplARM64.cpp
+++ lldb/tools/debugserver/source/MacOSX/arm64/DNBArchImplARM64.cpp
@@ -524,6 +524,25 @@
return true;
}
+ // detect a __builtin_debugtrap instruction pattern ("brk #0xf000")
+ // and advance the $pc past it, so that the user can continue execution.
+ if (exc.exc_data.size() == 2 && exc.exc_data[0] == EXC_ARM_BREAKPOINT) {
+ nub_addr_t pc = GetPC(INVALID_NUB_ADDRESS);
+ if (pc != INVALID_NUB_ADDRESS && pc > 0) {
+ DNBBreakpoint *bp =
+ m_thread->Process()->Breakpoints().FindByAddress(pc);
+ if (bp == nullptr) {
+ uint8_t insnbuf[4];
+ if (m_thread->Process()->ReadMemory(pc, 4, insnbuf) == 4) {
+ uint8_t builtin_debugtrap_insn[4] = {0x00, 0x00, 0x3e,
+ 0xd4}; // brk #0xf000
+ if (memcmp(insnbuf, builtin_debugtrap_insn, 4) == 0) {
+ SetPC(pc + 4);
+ }
+ }
+ }
+ }
+ }
break;
}
return false;
Index: lldb/test/API/functionalities/builtin-debugtrap/main.cpp
===================================================================
--- /dev/null
+++ lldb/test/API/functionalities/builtin-debugtrap/main.cpp
@@ -0,0 +1,11 @@
+#include <stdio.h>
+int global = 0;
+int main()
+{
+ global = 5; // Set a breakpoint here
+ __builtin_debugtrap();
+ global = 10;
+ __builtin_trap();
+ global = 15;
+ return global;
+}
Index: lldb/test/API/functionalities/builtin-debugtrap/TestBuiltinDebugTrap.py
===================================================================
--- /dev/null
+++ lldb/test/API/functionalities/builtin-debugtrap/TestBuiltinDebugTrap.py
@@ -0,0 +1,65 @@
+"""
+Test that lldb can continue past a __builtin_debugtrap, but not a __builtin_trap
+"""
+
+import lldb
+import lldbsuite.test.lldbutil as lldbutil
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+
+class BuiltinDebugTrapTestCase(TestBase):
+
+ mydir = TestBase.compute_mydir(__file__)
+
+ NO_DEBUG_INFO_TESTCASE = True
+ @skipIfWindows
+ @skipUnlessDarwin
+
+ def test(self):
+ self.build()
+ (target, process, thread, bkpt) = lldbutil.run_to_source_breakpoint(
+ self, "// Set a breakpoint here", lldb.SBFileSpec("main.cpp"))
+
+ # Continue to __builtin_debugtrap()
+ process.Continue()
+ if self.TraceOn():
+ self.runCmd("f")
+ self.runCmd("bt")
+ self.runCmd("ta v global")
+
+ self.assertEqual(process.GetSelectedThread().GetStopReason(),
+ lldb.eStopReasonException)
+
+ list = target.FindGlobalVariables("global", 1, lldb.eMatchTypeNormal)
+ self.assertEqual(list.GetSize(), 1)
+ global_value = list.GetValueAtIndex(0)
+
+ self.assertEqual(global_value.GetValueAsUnsigned(), 5)
+
+ # Continue to the __builtin_trap() -- we should be able to
+ # continue past __builtin_debugtrap.
+ process.Continue()
+ if self.TraceOn():
+ self.runCmd("f")
+ self.runCmd("bt")
+ self.runCmd("ta v global")
+
+ self.assertEqual(process.GetSelectedThread().GetStopReason(),
+ lldb.eStopReasonException)
+
+ # "global" is now 10.
+ self.assertEqual(global_value.GetValueAsUnsigned(), 10)
+
+ # We should be at the same point as before -- cannot advance
+ # past a __builtin_trap().
+ process.Continue()
+ if self.TraceOn():
+ self.runCmd("f")
+ self.runCmd("bt")
+ self.runCmd("ta v global")
+
+ self.assertEqual(process.GetSelectedThread().GetStopReason(),
+ lldb.eStopReasonException)
+
+ # "global" is still 10.
+ self.assertEqual(global_value.GetValueAsUnsigned(), 10)
Index: lldb/test/API/functionalities/builtin-debugtrap/Makefile
===================================================================
--- /dev/null
+++ lldb/test/API/functionalities/builtin-debugtrap/Makefile
@@ -0,0 +1,3 @@
+CXX_SOURCES := main.cpp
+
+include Makefile.rules
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