[Bug tdep/32152] New: [gdb/tdep, riscv64] FAIL: gdb.cp/non-trivial-retval.exp: finish from f1

[Bug tdep/32152] New: [gdb/tdep, riscv64] FAIL: gdb.cp/non-trivial-retval.exp: finish from f1

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=32152

            Bug ID: 32152
           Summary: [gdb/tdep, riscv64] FAIL:
                    gdb.cp/non-trivial-retval.exp: finish from f1
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: tdep
          Assignee: unassigned at sourceware dot org
          Reporter: vries at gcc dot gnu.org
  Target Milestone: ---

On riscv64-linux, I ran into:
...
(gdb) finish^M
Run till exit from #0  f1 (i1=i1@entry=23, i2=i2@entry=100) at
non-trivial-retval.cc:34^M
main () at non-trivial-retval.cc:163^M
163       B b = f2 (i1, i2);^M
Value returned is $6 = {a = -5856}^M
(gdb) FAIL: gdb.cp/non-trivial-retval.exp: finish from f1
...

The problem is that gdb thinks that the return value is in $a0:
...
$ gdb -q -batch non-trivial-retval \
  -ex "b f1" \
  -ex run \
  -ex "set debug riscv infcall on" \
  -ex finish
Breakpoint 1 at 0x80a: file non-trivial-retval.cc, line 34.
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/riscv64-linux-gnu/libthread_db.so.1".

Breakpoint 1, f1 (i1=i1@entry=23, i2=i2@entry=100) at non-trivial-retval.cc:34
34      {
[riscv-infcall] riscv_return_value: [R] type: 'A', length: 0x4, alignment: 0x4,
register a0
[riscv-infcall] riscv_return_value: [R] type: 'A', length: 0x4, alignment: 0x4,
register a0
[riscv-infcall] riscv_return_value: [R] type: 'A', length: 0x4, alignment: 0x4,
register a0
main () at non-trivial-retval.cc:163
163       B b = f2 (i1, i2);
Value returned is $1 = {a = -3568}
...
while $a0 actually contains a pointer to the returned value 123:
...
(gdb) p /x $a0
$3 = 0x3ffffff210
(gdb) p  *((unsigned int *)$a0)
$5 = 123
...
which is instead interpreted as an int:
...
(gdb) p (int) $a0
$6 = -3568
...

The system gcc compiler is configured with --with-abi=lp64d.

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[Bug tdep/32152] [gdb/tdep, riscv64] FAIL: gdb.cp/non-trivial-retval.exp: finish from f1

[schwab@linux-m68k.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=32152

--- Comment #1 from Andreas Schwab <schwab@linux-m68k.org> ---
I don't understand why the values are returned through memory, they are all
word-sized aggregates.

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[Bug tdep/32152] [gdb/tdep, riscv64] FAIL: gdb.cp/non-trivial-retval.exp: finish from f1

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=32152

--- Comment #2 from Tom de Vries <vries at gcc dot gnu.org> ---
(In reply to Andreas Schwab from comment #1)
> I don't understand why the values are returned through memory, they are all
> word-sized aggregates.

Here (
https://github.com/riscv-non-isa/riscv-elf-psabi-doc/blob/master/riscv-cc.adoc
) I found:
...
Aggregates larger than 2×XLEN bits are passed by reference and are replaced in
the argument list with the address, as are C++ aggregates with nontrivial copy
constructors, destructors, or vtables.
...

So, I think it's the case of "C++ aggregates with nontrivial copy constructors,
destructors, or vtables".

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[Bug tdep/32152] [gdb/tdep, riscv64] FAIL: gdb.cp/non-trivial-retval.exp: finish from f1

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=32152

--- Comment #3 from Tom de Vries <vries at gcc dot gnu.org> ---
Fixed by:
...
diff --git a/gdb/riscv-tdep.c b/gdb/riscv-tdep.c
index 932708ca4e9..bfb3b350b1d 100644
--- a/gdb/riscv-tdep.c
+++ b/gdb/riscv-tdep.c
@@ -2857,8 +2857,11 @@ static void
 riscv_call_arg_scalar_int (struct riscv_arg_info *ainfo,
                           struct riscv_call_info *cinfo)
 {
+  auto lang_req = language_pass_by_reference (ainfo->type);
   if (TYPE_HAS_DYNAMIC_LENGTH (ainfo->type)
-      || ainfo->length > (2 * cinfo->xlen))
+      || ainfo->length > (2 * cinfo->xlen)
+      || !lang_req.trivially_copy_constructible
+      || !lang_req.trivially_destructible)
     {
       /* Argument is going to be passed by reference.  */
       ainfo->argloc[0].loc_type
...

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[Bug tdep/32152] [gdb/tdep, riscv64] FAIL: gdb.cp/non-trivial-retval.exp: finish from f1

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=32152

--- Comment #4 from Tom de Vries <vries at gcc dot gnu.org> ---
https://sourceware.org/pipermail/gdb-patches/2025-January/214582.html

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[Bug tdep/32152] [gdb/tdep, riscv64] FAIL: gdb.cp/non-trivial-retval.exp: finish from f1

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=32152

--- Comment #5 from Sourceware Commits <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=84067a55fcbb15f903c7298adc3a708c6a431e12

commit 84067a55fcbb15f903c7298adc3a708c6a431e12
Author: Tom de Vries <tdevries@suse.de>
Date:   Fri Jan 10 10:32:00 2025 +0100

    [gdb/tdep] Fix gdb.cp/non-trivial-retval.exp on riscv64-linux

    With test-case gdb.cp/non-trivial-retval.exp on riscv64-linux, I ran into:
    ...
    (gdb) finish^M
    Run till exit from #0  f1 (i1=i1@entry=23, i2=i2@entry=100) \
      at non-trivial-retval.cc:34^M
    main () at non-trivial-retval.cc:163^M
    163       B b = f2 (i1, i2);^M
    Value returned is $6 = {a = -5856}^M
    (gdb) FAIL: $exp: finish from f1
    ...
    where "Value returned is $6 = {a = 123}" is expected.

    The problem is that gdb thinks that the return value is in $a0:
    ...
    $ gdb -q -batch non-trivial-retval \
      -ex "b f1" \
      -ex run \
      -ex "set debug riscv infcall on" \
      -ex finish
    Breakpoint 1 at 0x80a: file non-trivial-retval.cc, line 34.
    [Thread debugging using libthread_db enabled]
    Using host libthread_db library "/lib/riscv64-linux-gnu/libthread_db.so.1".

    Breakpoint 1, f1 (i1=i1@entry=23, i2=i2@entry=100) at
non-trivial-retval.cc:34
    34      {
    [riscv-infcall] riscv_return_value: \
      [R] type: 'A', length: 0x4, alignment: 0x4, register a0
    [riscv-infcall] riscv_return_value: \
      [R] type: 'A', length: 0x4, alignment: 0x4, register a0
    [riscv-infcall] riscv_return_value: \
      [R] type: 'A', length: 0x4, alignment: 0x4, register a0
    main () at non-trivial-retval.cc:163
    163       B b = f2 (i1, i2);
    Value returned is $1 = {a = -3568}
    ...
    while $a0 actually contains a pointer to the returned value 123:
    ...
    (gdb) p /x $a0
    $3 = 0x3ffffff210
    (gdb) p  *((unsigned int *)$a0)
    $5 = 123
    ...

    The returned type is:
    ...
    class A
    {
    public:
      A () {}
      A (A &obj);

      int a;
    };
    ...
    which is a C++ aggregate with a nontrivial (because it's user-defined) copy
    constructor:

    According to the ABI [1], indeed this is returned by reference:
    ...
    Values are returned in the same manner as a first named argument of the
same
    type would be passed.  If such an argument would have been passed by
    reference, the caller allocates memory for the return value, and passes the
    address as an implicit first parameter.
      ...
    Aggregates larger than 2×XLEN bits are passed by reference and are replaced
in
    the argument list with the address, as are C++ aggregates with nontrivial
copy
    constructors, destructors, or vtables.
    ...

    Fix this in riscv_call_arg_scalar_int by checking for
    language_pass_by_reference ().trivially_copy_constructible.

    The vtable case is explictly mentioned in the ABI, but AFAIU already
covered
    by the nontrivial copy constructor case.

    The nontrivial destructor case is also not supported, but the testsuite
    doesn't seem to trigger this.

    Fix this by:
    - extending the test-case to cover this scenario, and
    - fixing it in riscv_call_arg_scalar_int by checking for
      language_pass_by_reference ().trivially_destructible.

    Tested on riscv64-linux.

    PR tdep/32152
    Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=32152

    Approved-By: Andrew Burgess <aburgess@redhat.com>

    [1]
https://github.com/riscv-non-isa/riscv-elf-psabi-doc/blob/master/riscv-cc.adoc

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[Bug tdep/32152] [gdb/tdep, riscv64] FAIL: gdb.cp/non-trivial-retval.exp: finish from f1

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=32152

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
   Target Milestone|---                         |17.1
         Resolution|---                         |FIXED

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

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