[Lldb-commits] [PATCH] D22231: Implement trampoline step-through for Windows-x86.

[Stephane Sezer via lldb-commits]

sas created this revision.
sas added reviewers: clayborg, zturner.
sas added a subscriber: lldb-commits.

This is required to be able to step through calls to external functions
that are not properly marked with __declspec(dllimport). When a call
like this is emitted, the linker will inject a trampoline to produce an
indirect call through the IAT.

http://reviews.llvm.org/D22231

Files:
  source/Plugins/DynamicLoader/Windows-DYLD/DynamicLoaderWindowsDYLD.cpp

Index: source/Plugins/DynamicLoader/Windows-DYLD/DynamicLoaderWindowsDYLD.cpp
===================================================================
--- source/Plugins/DynamicLoader/Windows-DYLD/DynamicLoaderWindowsDYLD.cpp
+++ source/Plugins/DynamicLoader/Windows-DYLD/DynamicLoaderWindowsDYLD.cpp
@@ -12,6 +12,9 @@
 #include "lldb/Core/PluginManager.h"
 #include "lldb/Target/Process.h"
 #include "lldb/Target/Target.h"
+#include "lldb/Target/RegisterContext.h"
+#include "lldb/Target/ExecutionContext.h"
+#include "lldb/Target/ThreadPlanStepInstruction.h"
 
 #include "llvm/ADT/Triple.h"
 
@@ -100,5 +103,46 @@
 ThreadPlanSP
 DynamicLoaderWindowsDYLD::GetStepThroughTrampolinePlan(Thread &thread, bool 
stop)
 {
-    return ThreadPlanSP();
+    auto arch = m_process->GetTarget().GetArchitecture();
+    if (arch.GetMachine() != llvm::Triple::x86)
+    {
+        return ThreadPlanSP();
+    }
+
+    uint64_t pc = thread.GetRegisterContext()->GetPC();
+    // Max size of an instruction in x86 is 15 bytes.
+    AddressRange range(pc, 2 * 15);
+
+    ExecutionContext exe_ctx(m_process->GetTarget());
+    DisassemblerSP disassembler_sp = Disassembler::DisassembleRange(arch, 
nullptr, nullptr, exe_ctx, range, true);
+    if (!disassembler_sp)
+    {
+        return ThreadPlanSP();
+    }
+
+    InstructionList *insn_list = &disassembler_sp->GetInstructionList();
+    if (insn_list == nullptr)
+    {
+        return ThreadPlanSP();
+    }
+
+    // First instruction in a x86 Windows trampoline is going to be an indirect
+    // jump through the IAT and the next one will be a nop (usually there for
+    // alignment purposes). e.g.:
+    //     0x70ff4cfc <+956>: jmpl   *0x7100c2a8
+    //     0x70ff4d02 <+962>: nop
+
+    auto first_insn = insn_list->GetInstructionAtIndex(0);
+    auto second_insn = insn_list->GetInstructionAtIndex(1);
+
+    if (first_insn == nullptr || second_insn == nullptr ||
+        strcmp(first_insn->GetMnemonic(&exe_ctx), "jmpl") != 0 ||
+        strcmp(second_insn->GetMnemonic(&exe_ctx), "nop") != 0)
+    {
+        return ThreadPlanSP();
+    }
+
+    assert(first_insn->DoesBranch() && !second_insn->DoesBranch());
+
+    return ThreadPlanSP(new ThreadPlanStepInstruction(thread, false, false, 
eVoteNoOpinion, eVoteNoOpinion));
 }



Index: source/Plugins/DynamicLoader/Windows-DYLD/DynamicLoaderWindowsDYLD.cpp
===================================================================
--- source/Plugins/DynamicLoader/Windows-DYLD/DynamicLoaderWindowsDYLD.cpp
+++ source/Plugins/DynamicLoader/Windows-DYLD/DynamicLoaderWindowsDYLD.cpp
@@ -12,6 +12,9 @@
 #include "lldb/Core/PluginManager.h"
 #include "lldb/Target/Process.h"
 #include "lldb/Target/Target.h"
+#include "lldb/Target/RegisterContext.h"
+#include "lldb/Target/ExecutionContext.h"
+#include "lldb/Target/ThreadPlanStepInstruction.h"
 
 #include "llvm/ADT/Triple.h"
 
@@ -100,5 +103,46 @@
 ThreadPlanSP
 DynamicLoaderWindowsDYLD::GetStepThroughTrampolinePlan(Thread &thread, bool stop)
 {
-    return ThreadPlanSP();
+    auto arch = m_process->GetTarget().GetArchitecture();
+    if (arch.GetMachine() != llvm::Triple::x86)
+    {
+        return ThreadPlanSP();
+    }
+
+    uint64_t pc = thread.GetRegisterContext()->GetPC();
+    // Max size of an instruction in x86 is 15 bytes.
+    AddressRange range(pc, 2 * 15);
+
+    ExecutionContext exe_ctx(m_process->GetTarget());
+    DisassemblerSP disassembler_sp = Disassembler::DisassembleRange(arch, nullptr, nullptr, exe_ctx, range, true);
+    if (!disassembler_sp)
+    {
+        return ThreadPlanSP();
+    }
+
+    InstructionList *insn_list = &disassembler_sp->GetInstructionList();
+    if (insn_list == nullptr)
+    {
+        return ThreadPlanSP();
+    }
+
+    // First instruction in a x86 Windows trampoline is going to be an indirect
+    // jump through the IAT and the next one will be a nop (usually there for
+    // alignment purposes). e.g.:
+    //     0x70ff4cfc <+956>: jmpl   *0x7100c2a8
+    //     0x70ff4d02 <+962>: nop
+
+    auto first_insn = insn_list->GetInstructionAtIndex(0);
+    auto second_insn = insn_list->GetInstructionAtIndex(1);
+
+    if (first_insn == nullptr || second_insn == nullptr ||
+        strcmp(first_insn->GetMnemonic(&exe_ctx), "jmpl") != 0 ||
+        strcmp(second_insn->GetMnemonic(&exe_ctx), "nop") != 0)
+    {
+        return ThreadPlanSP();
+    }
+
+    assert(first_insn->DoesBranch() && !second_insn->DoesBranch());
+
+    return ThreadPlanSP(new ThreadPlanStepInstruction(thread, false, false, eVoteNoOpinion, eVoteNoOpinion));
 }

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