Re: [PATCH] Recognize branch instruction on MIPS in gdb.trace/entry-values.exp

["Maciej W. Rozycki" <macro at codesourcery dot com>]

On Tue, 30 Dec 2014, Yao Qi wrote:

> >  What's the semantics of the test case and the changes you're making?  
> >
> 
> dwarf assembler is used to generate debug info with DW_TAG_GNU_call_site
> and DW_TAG_GNU_call_site_parameter to exercise GDB.  The change I am
> making in this patch is to recognize branch instruction on MIPS, so that
> we can compute the address returned from foo, and fill it in the
> generated debug info.

 Ah, OK.

> >  I'm asking because the MIPS architecture has several instructions used to 
> > make procedure calls, depending on the ISA and ABI selected, and also 
> > compiler options.  Besides JAL these instructions include JALS, JALX, 
> > JALR, JALRC, JALRS, BAL and BALS.  It looks to me you need to modify the 
> > pattern here to take these into account; JALRC does not have a delay slot.
> >
> 
> I'll update the pattern to {jalrc|(?:jal|bal)[^\r\n]+\r\n}

 I think {jalrc|[jb]al[^\r\n]+\r\n} will be a little bit more efficient, 
but please make sure too that the right-hand side branch does not swallow 
`jalrc' with its following instruction by greedy matching:

"An RE consisting of two or more branches connected by the | operator 
prefers longest match."

(from the TCL Reference Manual) -- so I think you'll have to modify your 
regexp further yet.

> >> All tests in entry-values.exp are PASS.
> >
> >  Which target and ABI(s) did you ran your testing on?  Please try at least 
> > these: o32/MIPS, o32/MIPS16, o32/microMIPS, n64 on a Linux and a 
> > bare-metal target each; testing o32/MIPS16 with the `-mflip-mips16' GCC 
> > option too will be appreciated.  These combinations should trigger some 
> > (although not all) of the other possible instructions.
> 
> To avoid of misunderstanding, let me map them to the following concrete gcc
> options (I don't find -mabi=o32 nor -mabi=n64 in
> https://gcc.gnu.org/onlinedocs/gcc/MIPS-Options.html),
> 
>   -mabi=32 
>   -mabi=32 -mips16
>   -mabi=32 -mips16 -mflip-mips16
>   -mabi=32 -mmicromips
>   -mabi=64 on both linux and bare-metal target
> 
> are they what you want?

 Yes, except I meant both Linux and bare-metal across all the variations, 
not n64 only (missing comma after `n64' in my original sentence).  Here 
n64 matters as it covers PIC calling sequences.

  Maciej