[lldb-dev] changing register size on the fly?

Ted Woodward ted.woodward at codeaurora.org
Mon Dec 15 13:07:37 PST 2014

Thanks Greg.

My problem is we're using gdb-remote, and aren't subclassing RegisterContext.  Any advice?


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-----Original Message-----
From: Greg Clayton [mailto:gclayton at apple.com] 
Sent: Thursday, December 11, 2014 1:32 PM
To: Ted Woodward
Cc: lldb-dev at cs.uiuc.edu
Subject: Re: [lldb-dev] changing register size on the fly?

> On Dec 11, 2014, at 11:24 AM, Ted Woodward <ted.woodward at codeaurora.org> wrote:
> Some cores can change register sizes on the fly; for example, the Freescale e6500 can switch between 32 bit and 64 bit mode by writing the CM bit in the MSR. This causes the upper 32 bits of many 64 bit registers to be ignored.
> I’m working with a device that has registers that behave like this. I could display the larger size, but that’s confusing to a user who’s working with the smaller size.
> Is there a way to change register size on the fly?

Yes. Your RegisterContext subclass needs to override:

    virtual const RegisterInfo *
    GetRegisterInfoAtIndex (size_t reg) = 0;

So you can just return the correct RegisterInfo that contains "4" or "8" as the RegisterInfo.byte_size by grabbing using the m_thread to get to the process and somehow read the MSR and return the correct one dynamically.


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