Re: [PATCH 0/2] Handle "line 0" ranges (PR26243, PR15314, PR15668)

[Simon Marchi <simark@simark.ca>]

On 2020-07-21 11:37 a.m., Pedro Alves wrote:
> PR 26243 shows that Clang associates some instructions in the middle
> of functions to line 0.  That is valid DWARF, but it wasn't noticed
> until recently, when the line info reading code was tweaked.
> Currently, "step" and "next" with Clang misbehave because these "line
> 0" instructions or instruction ranges aren't being handled.
> 
> This series fixes that in two parts:
> 
> #1 - By teaching infrun to step over such no-line-info instructions
>      automatically, when "set step-mode" is "off" (which is the
>      default).
> 
> #2 - By making "step" and "next" behave like "stepi" and "nexti"
>      respectively when a step is started at an instruction with no
>      line info.
> 
> I think that with the first patch, most users won't frequently notice
> these "no line info" regions unless they use stepi to run to them, or
> they set a breapoint by address in them.  But it can happen that you
> stop in one of them, and I think that making "step" not step out of
> the whole function is just a good idea if it does happen.  The second
> patch also fixes the older PR15314 and PR15668, because the error in
> question they are complaining about is removed by that patch.
> 
> I think we could also try to fix the issue addressed by #2 by making a
> "step" started at an instruction with no line info step until it finds
> an instruction with line info (maybe in the same function, maybe in a
> different function), instead of stepping out of the current function.
> I do think that the behavior I'm proposing is more intuitive, though.
> 
> Pedro Alves (2):
>   Keep stepping over "line 0" ranges (PR 26243)
>   Make step act as stepi if no line info (PR26243, PR15314, PR15668)
> 
>  gdb/doc/gdb.texinfo                               |  36 ++--
>  gdb/NEWS                                          |   5 +
>  gdb/infcmd.c                                      |  30 +--
>  gdb/infrun.c                                      |  47 +++--
>  gdb/testsuite/gdb.base/step-symless.exp           |  20 +-
>  gdb/testsuite/gdb.dwarf2/dw2-line-number-zero.c   |  61 ++++++
>  gdb/testsuite/gdb.dwarf2/dw2-line-number-zero.exp | 240 ++++++++++++++++++++++
>  7 files changed, 383 insertions(+), 56 deletions(-)
>  create mode 100644 gdb/testsuite/gdb.dwarf2/dw2-line-number-zero.c
>  create mode 100644 gdb/testsuite/gdb.dwarf2/dw2-line-number-zero.exp
> 
> 
> base-commit: 6d3d6e4ba779dc08b134cd1a09b055dbd88dbf8a
> -- 
> 2.14.5
> 

Because it can affect what kind of other bugfixes and mitigation we do
and how this patchset is discussed, my first question is: do you suggest
merging these patches before the GDB 10 branch is created or waiting
after the branch?

Simon