RE: [PATCH 1/1] gdb: Avoid warning for the jump command inside an inline function.

["Willgerodt, Felix" <felix.willgerodt@intel.com>]

> -----Original Message-----
> From: Bruno Larsen <blarsen@redhat.com>
> Sent: Freitag, 17. März 2023 14:34
> To: Willgerodt, Felix <felix.willgerodt@intel.com>; gdb-
> patches@sourceware.org
> Subject: Re: [PATCH 1/1] gdb: Avoid warning for the jump command inside
> an inline function.
> 
> On 17/03/2023 13:56, Willgerodt, Felix wrote:
> >> -----Original Message-----
> >> From: Bruno Larsen <blarsen@redhat.com>
> >> Sent: Freitag, 17. März 2023 11:14
> >> To: Willgerodt, Felix <felix.willgerodt@intel.com>; gdb-
> >> patches@sourceware.org
> >> Cc: Cristian Sandu <cristian.sandu@intel.com>
> >> Subject: Re: [PATCH 1/1] gdb: Avoid warning for the jump command
> inside
> >> an inline function.
> >>
> >> On 24/01/2023 16:19, Felix Willgerodt via Gdb-patches wrote:
> >>> When stopped inside an inline function, trying to jump to a different line
> >>> of the same function currently results in a warning about jumping to
> >> another
> >>> function.  Fix this by taking inline functions into account.
> >>>
> >>> Before:
> >>>     Breakpoint 1, function_inline (x=510) at jump-inline.cpp:22
> >>>     22        a = a + x;             /* inline-funct */
> >>>     (gdb) j 21
> >>>     Line 21 is not in `function_inline(int)'.  Jump anyway? (y or n)
> >>>
> >>> After:
> >>>     Breakpoint 2, function_inline (x=510) at jump-inline.cpp:22
> >>>     22        a = a + x;            /* inline-funct */
> >>>     (gdb) j 21
> >>>     Continuing at 0x400679.
> >>>
> >>>     Breakpoint 1, function_inline (x=510) at jump-inline.cpp:21
> >>>     21        a += 1020 + a;                /* increment-funct */
> >>>
> >>> This was regression-tested on X86-64 Linux.
> >>>
> >>> Co-Authored-by: Cristian Sandu <cristian.sandu@intel.com>
> >>> ---
> >>>    gdb/infcmd.c                           |  3 +-
> >>>    gdb/testsuite/gdb.base/jump-inline.c   | 30 +++++++++++++++++
> >>>    gdb/testsuite/gdb.base/jump-inline.exp | 45
> >> ++++++++++++++++++++++++++
> >>>    3 files changed, 77 insertions(+), 1 deletion(-)
> >>>    create mode 100644 gdb/testsuite/gdb.base/jump-inline.c
> >>>    create mode 100644 gdb/testsuite/gdb.base/jump-inline.exp
> >>>
> >>> diff --git a/gdb/infcmd.c b/gdb/infcmd.c
> >>> index fd88b8ca328..40414bc9260 100644
> >>> --- a/gdb/infcmd.c
> >>> +++ b/gdb/infcmd.c
> >>> @@ -1091,7 +1091,8 @@ jump_command (const char *arg, int from_tty)
> >>>
> >>>      /* See if we are trying to jump to another function.  */
> >>>      fn = get_frame_function (get_current_frame ());
> >>> -  sfn = find_pc_function (sal.pc);
> >>> +  sfn = find_pc_sect_containing_function (sal.pc,
> >>> +					  find_pc_mapped_section (sal.pc));
> >> Hi Felix,
> >>
> >> Thanks for doing this, it is a good improvement, but I don't know if
> >> this is the best way to go about it. Is there a reason why
> >> find_pc_function should not return inlined functions?
> >>
> >> I feel like most of the time we want to know the function, knowing if
> >> we're in an inlined one would be desirable, but I might be wrong. Does
> >> anyone know?
> >>
> > Hi Bruno,
> >
> > I don't know the details, but the comments in symtab.h are rather explicit
> > about it, so I assume there is a reason:
> >
> >
> > /* lookup the function symbol corresponding to the address.  The
> >     return value will not be an inlined function; the containing
> >     function will be returned instead.  */
> >
> > extern struct symbol *find_pc_function (CORE_ADDR);
> >
> > /* lookup the function symbol corresponding to the address and
> >     section.  The return value will be the closest enclosing function,
> >     which might be an inline function.  */
> >
> > extern struct symbol *find_pc_sect_containing_function
> >    (CORE_ADDR pc, struct obj_section *section);
> 
> Hi Felix,
> 
> I thought it was mostly a descriptive comment, rather than prescriptive.
> I tested changing find_pc_function locally and there were only 2
> regressions, which might just be broken assumptions, but our testsuite
> is probably not very comprehensive on inlined functions, so I don't know
> how representative this test actually is.
> 

Hi Bruno,

Could you share what changes you have done locally?
Did you basically just change find_pc_function to call
find_pc_sec_containing_function?

I saw that there is another comment in blockframe.c about
"backwards compatibility", but that has been in the code for ages and
I couldn't find anything interesting related to it.

When git blaming the comments in symtab.h, I saw they were added 
by Pedro a couple years ago:
https://sourceware.org/git/?p=binutils-gdb.git;a=commit;f=gdb/symtab.h;h=cd2bb709940d33668fe6dbe8d4ffee0ed44c25e6
Maybe he can help shed some light on this?

Thanks,
Felix
Intel Deutschland GmbH
Registered Address: Am Campeon 10, 85579 Neubiberg, Germany
Tel: +49 89 99 8853-0, www.intel.de <http://www.intel.de>
Managing Directors: Christin Eisenschmid, Sharon Heck, Tiffany Doon Silva  
Chairperson of the Supervisory Board: Nicole Lau
Registered Office: Munich
Commercial Register: Amtsgericht Muenchen HRB 186928