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Instantiate Error in Target::GetEntryPointAddress() only when necessary
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When `Target::GetEntryPointAddress()` calls `exe_module->GetObjectFile()->GetEntryPointAddress()`, and the returned
`entry_addr` is valid, it can immediately be returned.

However, just before that, an `llvm::Error` value has been setup, but in this case it is not consumed before returning, like is done further below in the function.

In https://bugs.freebsd.org/248745 we got a bug report for this, where a very simple test case aborts and dumps core:

```
* thread #1, name = 'testcase', stop reason = breakpoint 1.1
    frame #0: 0x00000000002018d4 testcase`main(argc=1, argv=0x00007fffffffea18) at testcase.c:3:5
   1	int main(int argc, char *argv[])
   2	{
-> 3	    return 0;
   4	}
(lldb) p argc
Program aborted due to an unhandled Error:
Error value was Success. (Note: Success values must still be checked prior to being destroyed).

Thread 1 received signal SIGABRT, Aborted.
thr_kill () at thr_kill.S:3
3	thr_kill.S: No such file or directory.
(gdb) bt
#0  thr_kill () at thr_kill.S:3
#1  0x00000008049a0004 in __raise (s=6) at /usr/src/lib/libc/gen/raise.c:52
rust-lang#2  0x0000000804916229 in abort () at /usr/src/lib/libc/stdlib/abort.c:67
rust-lang#3  0x000000000451b5f5 in fatalUncheckedError () at /usr/src/contrib/llvm-project/llvm/lib/Support/Error.cpp:112
rust-lang#4  0x00000000019cf008 in GetEntryPointAddress () at /usr/src/contrib/llvm-project/llvm/include/llvm/Support/Error.h:267
rust-lang#5  0x0000000001bccbd8 in ConstructorSetup () at /usr/src/contrib/llvm-project/lldb/source/Target/ThreadPlanCallFunction.cpp:67
rust-lang#6  0x0000000001bcd2c0 in ThreadPlanCallFunction () at /usr/src/contrib/llvm-project/lldb/source/Target/ThreadPlanCallFunction.cpp:114
rust-lang#7  0x00000000020076d4 in InferiorCallMmap () at /usr/src/contrib/llvm-project/lldb/source/Plugins/Process/Utility/InferiorCallPOSIX.cpp:97
rust-lang#8  0x0000000001f4be33 in DoAllocateMemory () at /usr/src/contrib/llvm-project/lldb/source/Plugins/Process/FreeBSD/ProcessFreeBSD.cpp:604
rust-lang#9  0x0000000001fe51b9 in AllocatePage () at /usr/src/contrib/llvm-project/lldb/source/Target/Memory.cpp:347
rust-lang#10 0x0000000001fe5385 in AllocateMemory () at /usr/src/contrib/llvm-project/lldb/source/Target/Memory.cpp:383
rust-lang#11 0x0000000001974da2 in AllocateMemory () at /usr/src/contrib/llvm-project/lldb/source/Target/Process.cpp:2301
rust-lang#12 CanJIT () at /usr/src/contrib/llvm-project/lldb/source/Target/Process.cpp:2331
rust-lang#13 0x0000000001a1bf3d in Evaluate () at /usr/src/contrib/llvm-project/lldb/source/Expression/UserExpression.cpp:190
rust-lang#14 0x00000000019ce7a2 in EvaluateExpression () at /usr/src/contrib/llvm-project/lldb/source/Target/Target.cpp:2372
rust-lang#15 0x0000000001ad784c in EvaluateExpression () at /usr/src/contrib/llvm-project/lldb/source/Commands/CommandObjectExpression.cpp:414
rust-lang#16 0x0000000001ad86ae in DoExecute () at /usr/src/contrib/llvm-project/lldb/source/Commands/CommandObjectExpression.cpp:646
rust-lang#17 0x0000000001a5e3ed in Execute () at /usr/src/contrib/llvm-project/lldb/source/Interpreter/CommandObject.cpp:1003
rust-lang#18 0x0000000001a6c4a3 in HandleCommand () at /usr/src/contrib/llvm-project/lldb/source/Interpreter/CommandInterpreter.cpp:1762
rust-lang#19 0x0000000001a6f98c in IOHandlerInputComplete () at /usr/src/contrib/llvm-project/lldb/source/Interpreter/CommandInterpreter.cpp:2760
rust-lang#20 0x0000000001a90b08 in Run () at /usr/src/contrib/llvm-project/lldb/source/Core/IOHandler.cpp:548
rust-lang#21 0x00000000019a6c6a in ExecuteIOHandlers () at /usr/src/contrib/llvm-project/lldb/source/Core/Debugger.cpp:903
rust-lang#22 0x0000000001a70337 in RunCommandInterpreter () at /usr/src/contrib/llvm-project/lldb/source/Interpreter/CommandInterpreter.cpp:2946
rust-lang#23 0x0000000001d9d812 in RunCommandInterpreter () at /usr/src/contrib/llvm-project/lldb/source/API/SBDebugger.cpp:1169
rust-lang#24 0x0000000001918be8 in MainLoop () at /usr/src/contrib/llvm-project/lldb/tools/driver/Driver.cpp:675
rust-lang#25 0x000000000191a114 in main () at /usr/src/contrib/llvm-project/lldb/tools/driver/Driver.cpp:890```

Fix the incorrect error catch by only instantiating an `Error` object if it is necessary.

Reviewed By: JDevlieghere

Differential Revision: https://reviews.llvm.org/D86355
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DimitryAndric committed Aug 22, 2020
1 parent 5e7e216 commit 1ce07cd
Showing 1 changed file with 15 additions and 16 deletions.
31 changes: 15 additions & 16 deletions lldb/source/Target/Target.cpp
Original file line number Diff line number Diff line change
Expand Up @@ -2407,21 +2407,13 @@ lldb::addr_t Target::GetPersistentSymbol(ConstString name) {

llvm::Expected<lldb_private::Address> Target::GetEntryPointAddress() {
Module *exe_module = GetExecutableModulePointer();
llvm::Error error = llvm::Error::success();
assert(!error); // Check the success value when assertions are enabled.

if (!exe_module || !exe_module->GetObjectFile()) {
error = llvm::make_error<llvm::StringError>("No primary executable found",
llvm::inconvertibleErrorCode());
} else {
// Try to find the entry point address in the primary executable.
const bool has_primary_executable = exe_module && exe_module->GetObjectFile();
if (has_primary_executable) {
Address entry_addr = exe_module->GetObjectFile()->GetEntryPointAddress();
if (entry_addr.IsValid())
return entry_addr;

error = llvm::make_error<llvm::StringError>(
"Could not find entry point address for executable module \"" +
exe_module->GetFileSpec().GetFilename().GetStringRef() + "\"",
llvm::inconvertibleErrorCode());
}

const ModuleList &modules = GetImages();
Expand All @@ -2432,14 +2424,21 @@ llvm::Expected<lldb_private::Address> Target::GetEntryPointAddress() {
continue;

Address entry_addr = module_sp->GetObjectFile()->GetEntryPointAddress();
if (entry_addr.IsValid()) {
// Discard the error.
llvm::consumeError(std::move(error));
if (entry_addr.IsValid())
return entry_addr;
}
}

return std::move(error);
// We haven't found the entry point address. Return an appropriate error.
if (!has_primary_executable)
return llvm::make_error<llvm::StringError>(
"No primary executable found and could not find entry point address in "
"any executable module",
llvm::inconvertibleErrorCode());

return llvm::make_error<llvm::StringError>(
"Could not find entry point address for primary executable module \"" +
exe_module->GetFileSpec().GetFilename().GetStringRef() + "\"",
llvm::inconvertibleErrorCode());
}

lldb::addr_t Target::GetCallableLoadAddress(lldb::addr_t load_addr,
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