[PATCH v2 0/3] Improve debugging of optimized code

[PATCH v2 0/3] Improve debugging of optimized code

[Bernd Edlinger]

I've rebased and re-tested the following patches
which are trying to improve the debug experience of
optimized gcc code.  This work was previously posted
quite some time ago here:
https://sourceware.org/pipermail/gdb-patches/2021-January/175617.html

These patches improve the debug experience with optimized
gcc code significantly, as can be seen by the test cases.
The problem is that there are cases where an inline function
has line table entries at the end of the inline subrange,
and it is unclear by the dwarf-5 debug info if these line
table entries belong to the called inline function or to
the calling outer function, while there are at least some
corner cases where by stepping into these lines e.g. the
return value might be inspected.  Also the call stack is
often displayed wrong because the line table entries
do not match with the block structure i.e. are obviously
not in the correct function.

Therefore this patch series tries to improve the issue by
introducing a heuristic, that marks some of the line table
entries that happen to be at the exact end of an inline
function range as weak.  This new line table flag can be
used to avoid to step into the inline function when a
step over was requested, and display the line belonging
to the correct function in the callstack.

I'm sorry, that this solution has quite some complexity,
but I promise it is worth it.  Please give this patch
a try and look for yourself how the debug experience is
improved in the test cases, and certainly also a number of
other programs, especially with C++, where inline functions
are pretty much used everywhere.


Bernd Edlinger (3):
  Fix handling of DW_AT_entry_pc of inlined subroutines
  Introduce a new line table flag is_weak
  Fix range end handling of inlined subroutines

 gdb/block.c                                   |  15 +-
 gdb/buildsym.c                                | 106 ++++++++--
 gdb/buildsym.h                                |   3 +
 gdb/dwarf2/read.c                             |  89 +++-----
 gdb/infcmd.c                                  |   3 +-
 gdb/infrun.c                                  |  30 ++-
 gdb/jit.c                                     |   1 +
 gdb/symmisc.c                                 |   6 +-
 gdb/symtab.c                                  |  17 +-
 gdb/symtab.h                                  |   5 +
 gdb/testsuite/gdb.base/empty-inline.c         |  39 ++++
 gdb/testsuite/gdb.base/empty-inline.exp       |  56 +++++
 gdb/testsuite/gdb.cp/empty-inline.cc          |  33 +++
 gdb/testsuite/gdb.cp/empty-inline.exp         |  51 +++++
 gdb/testsuite/gdb.cp/step-and-next-inline.cc  |   6 +-
 gdb/testsuite/gdb.cp/step-and-next-inline.exp | 194 +++++++-----------
 gdb/testsuite/gdb.dwarf2/dw2-ranges-base.exp  |   2 +-
 gdb/xcoffread.c                               |   1 +
 18 files changed, 444 insertions(+), 213 deletions(-)
 create mode 100644 gdb/testsuite/gdb.base/empty-inline.c
 create mode 100644 gdb/testsuite/gdb.base/empty-inline.exp
 create mode 100644 gdb/testsuite/gdb.cp/empty-inline.cc
 create mode 100644 gdb/testsuite/gdb.cp/empty-inline.exp

-- 
2.39.2

Re: [PATCH v2 0/3] Improve debugging of optimized code

[Sam James]

Bernd Edlinger <bernd.edlinger@hotmail.de> writes:

> I've rebased and re-tested the following patches
> which are trying to improve the debug experience of
> optimized gcc code.  This work was previously posted
> quite some time ago here:
> https://sourceware.org/pipermail/gdb-patches/2021-January/175617.html
>
> These patches improve the debug experience with optimized
> gcc code significantly, as can be seen by the test cases.
> The problem is that there are cases where an inline function
> has line table entries at the end of the inline subrange,
> and it is unclear by the dwarf-5 debug info if these line
> table entries belong to the called inline function or to
> the calling outer function, while there are at least some
> corner cases where by stepping into these lines e.g. the
> return value might be inspected.  Also the call stack is
> often displayed wrong because the line table entries
> do not match with the block structure i.e. are obviously
> not in the correct function.
>
> Therefore this patch series tries to improve the issue by
> introducing a heuristic, that marks some of the line table
> entries that happen to be at the exact end of an inline
> function range as weak.  This new line table flag can be
> used to avoid to step into the inline function when a
> step over was requested, and display the line belonging
> to the correct function in the callstack.
>
> I'm sorry, that this solution has quite some complexity,
> but I promise it is worth it.  Please give this patch
> a try and look for yourself how the debug experience is
> improved in the test cases, and certainly also a number of
> other programs, especially with C++, where inline functions
> are pretty much used everywhere.

I can't review this but I'm going to daily-drive it for a while and I'll
let you know of any issues. It sounds rather exciting to say the least.

thanks,
sam

>
>
> Bernd Edlinger (3):
>   Fix handling of DW_AT_entry_pc of inlined subroutines
>   Introduce a new line table flag is_weak
>   Fix range end handling of inlined subroutines
>
>  gdb/block.c                                   |  15 +-
>  gdb/buildsym.c                                | 106 ++++++++--
>  gdb/buildsym.h                                |   3 +
>  gdb/dwarf2/read.c                             |  89 +++-----
>  gdb/infcmd.c                                  |   3 +-
>  gdb/infrun.c                                  |  30 ++-
>  gdb/jit.c                                     |   1 +
>  gdb/symmisc.c                                 |   6 +-
>  gdb/symtab.c                                  |  17 +-
>  gdb/symtab.h                                  |   5 +
>  gdb/testsuite/gdb.base/empty-inline.c         |  39 ++++
>  gdb/testsuite/gdb.base/empty-inline.exp       |  56 +++++
>  gdb/testsuite/gdb.cp/empty-inline.cc          |  33 +++
>  gdb/testsuite/gdb.cp/empty-inline.exp         |  51 +++++
>  gdb/testsuite/gdb.cp/step-and-next-inline.cc  |   6 +-
>  gdb/testsuite/gdb.cp/step-and-next-inline.exp | 194 +++++++-----------
>  gdb/testsuite/gdb.dwarf2/dw2-ranges-base.exp  |   2 +-
>  gdb/xcoffread.c                               |   1 +
>  18 files changed, 444 insertions(+), 213 deletions(-)
>  create mode 100644 gdb/testsuite/gdb.base/empty-inline.c
>  create mode 100644 gdb/testsuite/gdb.base/empty-inline.exp
>  create mode 100644 gdb/testsuite/gdb.cp/empty-inline.cc
>  create mode 100644 gdb/testsuite/gdb.cp/empty-inline.exp