[lldb-dev] How to get the error message while creating an invalid target?

[Greg Clayton via lldb-dev]

The SBDebugger::CreateTarget() call take an "SBError &error" as the last argument. The error will contain any error message:

    lldb::SBTarget
    CreateTarget (const char *filename,
                  const char *target_triple,
                  const char *platform_name,
                  bool add_dependent_modules,
                  lldb::SBError& error);



This function is the one that should be used. Any of the "const char *" arguments can be NULL. But typically you want to specify at least the filename. The triple is only really needed if you are debugging files that have more than one architecture or if the file you are debugging doesn't completely specify what you want to debug. The triple can be "x86_64" or more specific like "x86_64-apple-ios". The platform name only needs to be specified if your executable file (ELF file, mach-o file, or other exe format) doesn't have enough information inside of it to extract the triple from the object file. ELF has very sparse information inside of it to help us identify what platform it can/should be used for. You will know if you need to specify the platform if LLDB gets it wrong. To see what happens, try things out from the command line:


(lldb) target create /tmp/a.out
(lldb) target list
Current targets:
* target #0: /tmp/a.out ( arch=x86_64-apple-macosx, platform=host )

We see that the "host" platform was auto selected and the architecture was extracted from the executable as "x86_64-apple-macosx". 

To see a list of platform names you can do:

(lldb) platform select <TAB> 
Available completions:
	remote-freebsd
	remote-linux
	remote-netbsd
	remote-windows
	kalimba
	remote-android
	remote-ios
	remote-macosx
	ios-simulator
	darwin-kernel
	tvos-simulator
	watchos-simulator
	remote-tvos
	remote-watchos
	remote-gdb-server

So if you have an iOS binary that was targeting a device (not a simulator), you could create your target with:

lldb::SBError error;
lldb::SBTarget target = debugger.CreateTarget("/tmp/a.out", "armv7-apple-ios", "remote-ios", false, error);


> On Mar 8, 2016, at 5:22 PM, Jeffrey Tan via lldb-dev <lldb-dev at lists.llvm.org> wrote:
> 
> Hi,
> 
> In lldb, when I try to "target create [invalid_target]", I got some meaningful error message like:
> error: 'XXX' doesn't contain any 'host' platform architectures: x86_64h, x86_64, i386
> 
> What is the python API to get this from? I tried to check SBTarget.IsValid() and then use SBTarget.GetDescription(eDescriptionLevelVerbose), but that does not return the error message. 
> 
> Thanks
> Jeffrey
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