[Bug testsuite/29813] New: [gdb/testsuite, powerpc64le] FAIL: gdb.base/vla-optimized-out.exp: o1: printed size of optimized out vla

[Bug testsuite/29813] New: [gdb/testsuite, powerpc64le] FAIL: gdb.base/vla-optimized-out.exp: o1: printed size of optimized out vla

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29813

            Bug ID: 29813
           Summary: [gdb/testsuite, powerpc64le] FAIL:
                    gdb.base/vla-optimized-out.exp: o1: printed size of
                    optimized out vla
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: testsuite
          Assignee: unassigned at sourceware dot org
          Reporter: vries at gcc dot gnu.org
  Target Milestone: ---

On powerpc64le, with gcc 7.5.0, I run into:
...
(gdb) PASS: gdb.base/vla-optimized-out.exp: o1: printed optimized out vla
p sizeof (a)^M
$2 = <optimized out>^M
(gdb) FAIL: gdb.base/vla-optimized-out.exp: o1: printed size of optimized out
vla
...

The dwarf expression that needs evaluating is:
...
    <155>   DW_AT_upper_bound : 13 byte block: f3 1 53 23 1 8 20 24 8 20 26 31
1c       (DW_OP_GNU_entry_value: (DW_OP_reg3 (r3)); DW_OP_plus_uconst: 1;
DW_OP_const1u: 32; DW_OP_shl; DW_OP_const1u: 32; DW_OP_shra; DW_OP_lit1;
DW_OP_minus)
...

I suppose the following happens.  The DW_OP_GNU_entry_value needs to be
evaluated, and gdb looks for a call site matching this pc:
...
(gdb) up
#1  0x0000000010000690 in main () at
gdb/testsuite/gdb.base/vla-optimized-out.c:42
42        j = f1 (i);
(gdb)
...

There is a call site here:
...
 <2><f6>: Abbrev Number: 5 (DW_TAG_GNU_call_site)
    <f7>   DW_AT_low_pc      : 0x10000694
    <ff>   DW_AT_abstract_origin: <0x110>
...
which is not matched because it's 0x4 off.

Looking at the .s file:
...
        bl f1    # 11   *call_value_nonlocal_aixdi      [length = 8]
        nop
.LVL4:
...
it becomes clear what happened.

The pc label for the call site:
...
        .uleb128 0x5     # (DIE (0x67) DW_TAG_GNU_call_site)
        .8byte  .LVL4    # DW_AT_low_pc
        .4byte  0x81     # DW_AT_abstract_origin
        .byte   0        # end of children of DIE 0x2d
...
comes after the nop, and it should come before.

FWIW, in principle, gdb could do better, because it could look at the pc:
...
(gdb) p /x $pc
$1 = 0x1000065c
...
and conclude that it's the start of the function:
...
(gdb) disassemble f1
Dump of assembler code for function f1:
=> 0x000000001000065c <+0>:     li      r3,5
   0x0000000010000660 <+4>:     blr
   0x0000000010000664 <+8>:     .long 0x0
   0x0000000010000668 <+12>:    .long 0x0
   0x000000001000066c <+16>:    .long 0x0
End of assembler dump.
...
and therefore DW_OP_GNU_entry_value: (DW_OP_reg3 (r3)) == DW_OP_reg3:
...
(gdb) p $r3
$2 = 5
...
which indeed has the correct value.

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[Bug testsuite/29813] [gdb/testsuite, powerpc64le] FAIL: gdb.base/vla-optimized-out.exp: o1: printed size of optimized out vla

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29813

--- Comment #1 from Tom de Vries <vries at gcc dot gnu.org> ---
(In reply to Tom de Vries from comment #0)
> I suppose the following happens.  The DW_OP_GNU_entry_value needs to be
> evaluated, and gdb looks for a call site matching this pc:
> ...
> (gdb) up
> #1  0x0000000010000690 in main () at
> gdb/testsuite/gdb.base/vla-optimized-out.c:42
> 42        j = f1 (i);
> (gdb)
> ...
> 
> There is a call site here:
> ...
>  <2><f6>: Abbrev Number: 5 (DW_TAG_GNU_call_site)
>     <f7>   DW_AT_low_pc      : 0x10000694
>     <ff>   DW_AT_abstract_origin: <0x110>
> ...
> which is not matched because it's 0x4 off.

That seems to be indeed the case:
...
(gdb) up
#1  0x00000000114d2d28 in throw_it (reason=RETURN_ERROR,
error=NO_ENTRY_VALUE_ERROR, 
    fmt=0x11597848 "DW_OP_entry_value resolving cannot find DW_TAG_call_site %s
in %s", 
    ap=0x7fffffffc6a0 "\244\006m\022")
    at /suse/tdevries/gdb/src/gdbsupport/common-exceptions.cc:200
...

BTW, looking at the gcc sources, the bl;nop in call_value_nonlocal_aix<mode>
disappears in gcc-9-branch.

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[Bug testsuite/29813] [gdb/testsuite, powerpc64le] FAIL: gdb.base/vla-optimized-out.exp: o1: printed size of optimized out vla

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29813

--- Comment #2 from Tom de Vries <vries at gcc dot gnu.org> ---
(In reply to Tom de Vries from comment #1)
> BTW, looking at the gcc sources, the bl;nop in call_value_nonlocal_aix<mode>
> disappears in gcc-9-branch.

Hmm, looking into that a bit more, I suspect that that was not the case, the
nop was just better hidden.

So, I've filed a gcc PR: PR107909 - "[powerpc64le, debug] Incorrect call site
location due to nop after call insn" ( 
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107909 ).

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[Bug testsuite/29813] [gdb/testsuite, powerpc64le] FAIL: gdb.base/vla-optimized-out.exp: o1: printed size of optimized out vla

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29813

--- Comment #3 from Tom de Vries <vries at gcc dot gnu.org> ---
Fixing the .s code manually gets us:
...
$ gdb -q -batch ./a.out -ex "break f1" -ex run -ex "set debug entry-values 1"
-ex "print sizeof (a)"
Breakpoint 1 at 0x1000065c: file vla-optimized-out.c, line 8.

Breakpoint 1, f1 (i=5) at vla-optimized-out.c:8
8       }
Cannot find matching parameter at DW_TAG_call_site 0x10000690 at main
$1 = <optimized out>
...
and indeed there are no call site parameters in the call site, so now
"<optimized out>" is accurate.

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[Bug testsuite/29813] [gdb/testsuite, powerpc64le] FAIL: gdb.base/vla-optimized-out.exp: o1: printed size of optimized out vla

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29813

--- Comment #4 from Tom de Vries <vries at gcc dot gnu.org> ---
https://sourceware.org/pipermail/gdb-patches/2022-November/194326.html

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[Bug testsuite/29813] [gdb/testsuite, powerpc64le] FAIL: gdb.base/vla-optimized-out.exp: o1: printed size of optimized out vla

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29813

--- Comment #5 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Tom de Vries <vries@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=f3e033f32a0db3e81266a62b05f867b932a5995b

commit f3e033f32a0db3e81266a62b05f867b932a5995b
Author: Tom de Vries <tdevries@suse.de>
Date:   Tue Nov 29 22:47:31 2022 +0100

    [gdb/testsuite] Fix gdb.base/vla-optimized-out.exp for ppc64le

    On powerpc64le-linux, I run into:
    ...
    (gdb) PASS: gdb.base/vla-optimized-out.exp: o1: printed optimized out vla
    p sizeof (a)^M
    $2 = <optimized out>^M
    (gdb) FAIL: gdb.base/vla-optimized-out.exp: o1: \
      printed size of optimized out vla
    ...

    The problem happens as follows.

    In order to find the size of the optimized out vla, gdb needs to evaluate:
    ...
    <155> DW_AT_upper_bound : 13 byte block: f3 1 53 23 1 8 20 24 8 20 26 31 1c
\
      (DW_OP_GNU_entry_value: (DW_OP_reg3 (r3)); DW_OP_plus_uconst: 1;
       DW_OP_const1u: 32; DW_OP_shl; DW_OP_const1u: 32; DW_OP_shra; DW_OP_lit1;
       DW_OP_minus)
    ...

    When trying to evaluate DW_OP_GNU_entry_value, it looks for a call site
    matching the pc, but doesn't find it:
    ...
    $ gdb -q -batch outputs/gdb.base/vla-optimized-out/vla-optimized-out-o1 \
      -ex "break f1" -ex run -ex "set debug entry-values 1" -ex "print sizeof
(a)"
    Breakpoint 1 at 0x1000067c: file vla-optimized-out.c, line 34.

    Breakpoint 1, f1 (i=5) at vla-optimized-out.c:34
    34      }
    DW_OP_entry_value resolving cannot find DW_TAG_call_site 0x100006b0 in main
    $1 = <optimized out>
    ....

    The call site lookup fails because the call site label .LVL4:
    ...
            bl f1    # 11   *call_value_nonlocal_aixdi      [length = 8]
            nop
    .LVL4:
    ...
    is not placed directly after the bl insn.  This is gcc PR target/107909.

    However, after manually fixing the .s file we have instead:
    ...
    Cannot find matching parameter at DW_TAG_call_site 0x10000690 at main
    $1 = <optimized out>
    ...
    due to the fact that the call site has no call site parameters.

    The call site does have a reference to the corresponding function f1, with
    parameter i, for which we find location list entries:
    ...
      0037 1000067c 10000680 (DW_OP_reg3 (r3))
      004a 10000680 10000690 (DW_OP_GNU_entry_value: (DW_OP_reg3 (r3));
                              DW_OP_stack_value)
    ...
    and we could use the fact that the current pc is in the 1000067c-10000680
    range, and that that the range starts at the start of the function, to
deduce
    that DW_OP_GNU_entry_value: (DW_OP_reg3 (r3)) == DW_OP_reg3 (r3).
    But that's a non-trivial enhancement, filed as enhancement PR symtab/29836.

    Fix this by allowing <optimized out> for target powerpc and the gcc
compiler.

    Reviewed-By: Carl Love <cel@us.ibm.com>
    Tested-By: Carl Love <cel@us.ibm.com>
    PR testsuite/29813
    Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29813

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[Bug testsuite/29813] [gdb/testsuite, powerpc64le] FAIL: gdb.base/vla-optimized-out.exp: o1: printed size of optimized out vla

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29813

Tom de Vries <vries at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED
   Target Milestone|---                         |13.1

--- Comment #6 from Tom de Vries <vries at gcc dot gnu.org> ---
Fixed by commit above.

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