Re: [PATCH] Add MIPS UFR support

[Mike Frysinger <vapier at gentoo dot org>]

On Friday 08 November 2013 12:36:45 Andrew Bennett wrote:
> This patch adds support to the MIPS backend to deal with changing the FR
> mode in user mode (which I will now refer to as UFR).  The technical
> details are explained in the following paragraph.
> 
> The read only field UFR (at bit 28) in the floating point implementation
> register (CP1 control register 0) represents if the CPU supports UFR.  The
> UFR field (bit 2) in configuration register 5 (CP0 register 16, select 5)
> allows user mode to enable or disable UFR support.  The current value of
> the FR mode can be obtained if a read is made from the UFR register (CP1
> control register 1), and UFR support is enabled. If register zero is
> written to the UFR register, and UFR support is enabled, then the FR mode
> is set to 0. If register zero is written to the UNFR register (CP1 control
> register 4), and the UFR support is enabled, then the FR mode is set to 1.
> 
> To implement this I have firstly added the config 5 register to the
> simulator model, and added support to read and write to it.  Secondly, I
> have added support for the CTC1 and CFC1 instructions to write/read
> to/from the UFR and UNFR registers.

is this standard functionality available to all CPUs ?  your new status_UFRP 
bit overlaps with the existing status_CU0 bit, and you unconditionally enable 
this feature.

> I have also added a testcase to validate the implementation.  To run the
> testcase you will need to apply the following binutils patch:
> 
> https://sourceware.org/ml/binutils/2013-11/msg00065.html
> 
> 
> The simulator patch is attached to this email and the ChangeLog is shown
> below.

looks like your comments need tweaking to follow GNU style.  that means a 
period at the end followed by two spaces and then the closing */.  i also see 
"Unpredictable();" and that needs a space before the "(".

in your mips.igen change, the code changes the else case from a NOP to 
Unpredictable().  is that really what you want ?

> This is my first patch to gdb, so I am unsure the protocol on committing. 
> Would someone be able to clarify?

does your employer have copyright assignments in place ?

otherwise, we don't have a MIPS sim maintainer atm, so i'll do a crappy stand-
in job.
-mike

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