Recognize branch instruction on MIPS in gdb.trace/entry-values.exp

  The test entry-values.exp doesn't recognize the call instruction "jal"
on MIPS, so this patch sets call_insn "jal" first.

Currently, we assume the next instruction address of call instruction
is the address returned from foo, however it is not correct on MIPS
which has delay slot.  We extend variable call_insn to match one
instruction after jal, so that $returned_from_foo is correct on MIPS.

All tests in entry-values.exp are PASS.

gdb/testsuite:

2014-12-29  Yao Qi  <yao@codesourcery.com>

	* gdb.trace/entry-values.exp: Set call_insn for MIPS target.
---
 gdb/testsuite/gdb.trace/entry-values.exp | 10 ++++++++++
 1 file changed, 10 insertions(+)
  

On Mon, 29 Dec 2014, Yao Qi wrote:

> The test entry-values.exp doesn't recognize the call instruction "jal"
> on MIPS, so this patch sets call_insn "jal" first.
> 
> Currently, we assume the next instruction address of call instruction
> is the address returned from foo, however it is not correct on MIPS
> which has delay slot.  We extend variable call_insn to match one
> instruction after jal, so that $returned_from_foo is correct on MIPS.

 What's the semantics of the test case and the changes you're making?  

 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.

> 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.

  Maciej
  

"Maciej W. Rozycki" <macro@codesourcery.com> writes:

>  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.

>  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}

>> 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?
  

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