On Sat, Jul 23, 2016 at 4:30 PM, Alexandre Oliva <aol...@redhat.com> wrote:
> We used to emit, in debug information, the values bound to pointer to
> member function template parameters only when they were NULL or
> virtual member functions, because those can be represented with
> DW_AT_const_value.
>
> In order to represent the symbolic pointer to member function
> constants for non-virtual member functions, we'd need to be able to
> emit relocations for part of DW_AT_const_value, which we don't. The
> more viable alternative is to use DW_AT_location to represent such
> values, as slated for inclusion in DWARFv5, according to
> <URL:http://www.dwarfstd.org/ShowIssue.php?issue=130412.1>.
>
> With this patch, when we can't emit a DW_AT_const_value, we emit each
> "member" of the pointer to member function "record" as a
> DW_OP_stack_value DW_OP_piece, as long as the referenced member
> function is output in the same translation unit, otherwise we'd get
> relocations to external symbols, something to avoid in debug sections.
>
> Regstrapped on x86_64-linux-gnu and i686-pc-linux-gnu, and manually
> cross-tested with both endiannesses (just to be sure ;-) with a
> mips64-elf target. Ok to install?
>
> for gcc/ChangeLog
>
> PR debug/49366
> * dwarf2out.c (loc_list_from_tree_1): Expand some CONSTRUCTORs
> in DW_OP_pieces, just enough to handle pointers to member
> functions.
> (gen_remaining_tmpl_value_param_die_attribute): Use a location
> expression on DWARFv5 if a constant value doesn't work.
This change broke early LTO debug by emitting locations during early finish.
A simplistic fix is to do
@@ -24410,7 +24794,8 @@ gen_remaining_tmpl_value_param_die_attri
if (!tree_add_const_value_attribute (e->die, e->arg))
{
dw_loc_descr_ref loc = NULL;
- if (dwarf_version >= 5 || !dwarf_strict)
+ if (! early_dwarf
+ && (dwarf_version >= 5 || !dwarf_strict))
loc = loc_descriptor_from_tree (e->arg, 2, NULL);
if (loc)
add_AT_loc (e->die, DW_AT_location, loc);
but in reality the issue is (again) that we can't refer to a DIE here. Thus
it doesn't seem to be possible in dwarf to have debug info for
void func ();
do <func> ();
with func being optimized out.
The issue with LTO / early debug is that we can't prune DIEs that refer
to optimized out entities from early debug output thus we have to create
those DIEs late only (in the above case, as tmpl_value_param_die_table
is not streamed, not at all for LTO). Without LTO the issue is avoided
by resolve_addr pruning such references to optimized out entities from
location lists.
It would be nice to enhance dwarf to allow debug info for do <func>
so that printing the template parameter value is still possible even
if 'func' itself is optimized out.
Richard.
> for gcc/testsuite/ChangeLog
>
> PR debug/49366
> * g++.dg/debug/dwarf2/template-params-12.H: New.
> * g++.dg/debug/dwarf2/template-params-12f.C: New.
> * g++.dg/debug/dwarf2/template-params-12g.C: New.
> * g++.dg/debug/dwarf2/template-params-12n.C: New.
> * g++.dg/debug/dwarf2/template-params-12s.C: New.
> * g++.dg/debug/dwarf2/template-params-12u.C: New.
> * g++.dg/debug/dwarf2/template-params-12v.C: New.
> * g++.dg/debug/dwarf2/template-params-12w.C: New.
> ---
> gcc/dwarf2out.c | 93
> +++++++++++++++++++++-
> .../g++.dg/debug/dwarf2/template-params-12.H | 17 ++++
> .../g++.dg/debug/dwarf2/template-params-12f.C | 7 ++
> .../g++.dg/debug/dwarf2/template-params-12g.C | 7 ++
> .../g++.dg/debug/dwarf2/template-params-12n.C | 10 +++
> .../g++.dg/debug/dwarf2/template-params-12s.C | 8 ++
> .../g++.dg/debug/dwarf2/template-params-12u.C | 7 ++
> .../g++.dg/debug/dwarf2/template-params-12v.C | 6 ++
> .../g++.dg/debug/dwarf2/template-params-12w.C | 6 ++
> 9 files changed, 160 insertions(+), 1 deletion(-)
> create mode 100644 gcc/testsuite/g++.dg/debug/dwarf2/template-params-12.H
> create mode 100644 gcc/testsuite/g++.dg/debug/dwarf2/template-params-12f.C
> create mode 100644 gcc/testsuite/g++.dg/debug/dwarf2/template-params-12g.C
> create mode 100644 gcc/testsuite/g++.dg/debug/dwarf2/template-params-12n.C
> create mode 100644 gcc/testsuite/g++.dg/debug/dwarf2/template-params-12s.C
> create mode 100644 gcc/testsuite/g++.dg/debug/dwarf2/template-params-12u.C
> create mode 100644 gcc/testsuite/g++.dg/debug/dwarf2/template-params-12v.C
> create mode 100644 gcc/testsuite/g++.dg/debug/dwarf2/template-params-12w.C
>
> diff --git a/gcc/dwarf2out.c b/gcc/dwarf2out.c
> index e3cb586..c658220 100644
> --- a/gcc/dwarf2out.c
> +++ b/gcc/dwarf2out.c
> @@ -16142,6 +16142,89 @@ loc_list_from_tree_1 (tree loc, int want_address,
> case COMPLEX_CST:
> if ((ret = cst_pool_loc_descr (loc)))
> have_address = 1;
> + else if (TREE_CODE (loc) == CONSTRUCTOR)
> + {
> + tree type = TREE_TYPE (loc);
> + unsigned HOST_WIDE_INT size = int_size_in_bytes (type);
> + unsigned HOST_WIDE_INT offset = 0;
> + unsigned HOST_WIDE_INT cnt;
> + constructor_elt *ce;
> +
> + if (TREE_CODE (type) == RECORD_TYPE)
> + {
> + /* This is very limited, but it's enough to output
> + pointers to member functions, as long as the
> + referenced function is defined in the current
> + translation unit. */
> + FOR_EACH_VEC_SAFE_ELT (CONSTRUCTOR_ELTS (loc), cnt, ce)
> + {
> + tree val = ce->value;
> +
> + tree field = ce->index;
> +
> + if (val)
> + STRIP_NOPS (val);
> +
> + if (!field || DECL_BIT_FIELD (field))
> + {
> + expansion_failed (loc, NULL_RTX,
> + "bitfield in record type
> constructor");
> + size = offset = (unsigned HOST_WIDE_INT)-1;
> + ret = NULL;
> + break;
> + }
> +
> + HOST_WIDE_INT fieldsize = tree_to_shwi (DECL_SIZE_UNIT
> (field));
> + unsigned HOST_WIDE_INT pos = int_byte_position (field);
> + gcc_assert (pos + fieldsize <= size);
> + if (pos < offset)
> + {
> + expansion_failed (loc, NULL_RTX,
> + "out-of-order fields in record
> constructor");
> + size = offset = (unsigned HOST_WIDE_INT)-1;
> + ret = NULL;
> + break;
> + }
> + if (pos > offset)
> + {
> + ret1 = new_loc_descr (DW_OP_piece, pos - offset, 0);
> + add_loc_descr (&ret, ret1);
> + offset = pos;
> + }
> + if (val && fieldsize != 0)
> + {
> + ret1 = loc_descriptor_from_tree (val, want_address,
> context);
> + if (!ret1)
> + {
> + expansion_failed (loc, NULL_RTX,
> + "unsupported expression in
> field");
> + size = offset = (unsigned HOST_WIDE_INT)-1;
> + ret = NULL;
> + break;
> + }
> + add_loc_descr (&ret, ret1);
> + }
> + if (fieldsize)
> + {
> + ret1 = new_loc_descr (DW_OP_piece, fieldsize, 0);
> + add_loc_descr (&ret, ret1);
> + offset = pos + fieldsize;
> + }
> + }
> +
> + if (offset != size)
> + {
> + ret1 = new_loc_descr (DW_OP_piece, size - offset, 0);
> + add_loc_descr (&ret, ret1);
> + offset = size;
> + }
> +
> + have_address = !!want_address;
> + }
> + else
> + expansion_failed (loc, NULL_RTX,
> + "constructor of non-record type");
> + }
> else
> /* We can construct small constants here using int_loc_descriptor. */
> expansion_failed (loc, NULL_RTX,
> @@ -24177,7 +24260,15 @@ gen_remaining_tmpl_value_param_die_attribute (void)
> FOR_EACH_VEC_ELT (*tmpl_value_parm_die_table, i, e)
> {
> if (!tree_add_const_value_attribute (e->die, e->arg))
> - (*tmpl_value_parm_die_table)[j++] = *e;
> + {
> + dw_loc_descr_ref loc = NULL;
> + if (dwarf_version >= 5 || !dwarf_strict)
> + loc = loc_descriptor_from_tree (e->arg, 2, NULL);
> + if (loc)
> + add_AT_loc (e->die, DW_AT_location, loc);
> + else
> + (*tmpl_value_parm_die_table)[j++] = *e;
> + }
> }
> tmpl_value_parm_die_table->truncate (j);
> }
> diff --git a/gcc/testsuite/g++.dg/debug/dwarf2/template-params-12.H
> b/gcc/testsuite/g++.dg/debug/dwarf2/template-params-12.H
> new file mode 100644
> index 0000000..24c26e7
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/debug/dwarf2/template-params-12.H
> @@ -0,0 +1,17 @@
> +// Tests for the fix for PR debug/49366.
> +struct B {
> + void g();
> + virtual void v() = 0;
> + virtual void w();
> +};
> +void B::g() {}
> +void B::w() {}
> +struct S : B {
> + void f();
> + void v();
> + void u();
> +};
> +void S::f() {}
> +void S::v() {}
> +template <void (B::*MF)()> void t() {}
> +template <void (S::*MF)()> void t() {}
> diff --git a/gcc/testsuite/g++.dg/debug/dwarf2/template-params-12f.C
> b/gcc/testsuite/g++.dg/debug/dwarf2/template-params-12f.C
> new file mode 100644
> index 0000000..e2da829
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/debug/dwarf2/template-params-12f.C
> @@ -0,0 +1,7 @@
> +// { dg-options "-gdwarf-2 -dA" }
> +// { dg-final { scan-assembler-times "DIE \\(\[^\n\]*\\)
> DW_TAG_template_value_param" 1 } }
> +// { dg-final { scan-assembler-times "DIE \\(\[^\n\]*\\)
> DW_TAG_template_value_param\[^\n\]*\n\[^\n\]* DW_AT_name\n\[^\n\]*
> DW_AT_type\n\[^\n\]*\[^\n\]* DW_AT_location\n\[^\n\]*
> DW_OP_addr\n\[^\n\]*_ZN1S1fEv\[^\n\]*\n\[^\n\]* DW_OP_stack_value\n\[^\n\]*
> DW_OP_piece\n\[^\n\]*\n\[^\n\]* DW_OP_lit0\n\[^\n\]*
> DW_OP_stack_value\n\[^\n\]* DW_OP_piece" 1 } }
> +#include "template-params-12.H"
> +/* We get a location list with a pair of DW_OP_pieces for pointers to
> + non-virtual member functions. */
> +template void t<&S::f>();
> diff --git a/gcc/testsuite/g++.dg/debug/dwarf2/template-params-12g.C
> b/gcc/testsuite/g++.dg/debug/dwarf2/template-params-12g.C
> new file mode 100644
> index 0000000..813f71d
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/debug/dwarf2/template-params-12g.C
> @@ -0,0 +1,7 @@
> +// { dg-options "-gdwarf-2 -dA" }
> +// { dg-final { scan-assembler-times "DIE \\(\[^\n\]*\\)
> DW_TAG_template_value_param" 1 } }
> +// { dg-final { scan-assembler-times "DIE \\(\[^\n\]*\\)
> DW_TAG_template_value_param\[^\n\]*\n\[^\n\]* DW_AT_name\n\[^\n\]*
> DW_AT_type\n\[^\n\]*\[^\n\]* DW_AT_location\n\[^\n\]*
> DW_OP_addr\n\[^\n\]*_ZN1B1gEv\[^\n\]*\n\[^\n\]* DW_OP_stack_value\n\[^\n\]*
> DW_OP_piece\n\[^\n\]*\n\[^\n\]* DW_OP_lit0\n\[^\n\]*
> DW_OP_stack_value\n\[^\n\]* DW_OP_piece" 1 } }
> +#include "template-params-12.H"
> +/* We get a location list with a pair of DW_OP_pieces for pointers to
> + non-virtual member functions. */
> +template void t<&S::g>();
> diff --git a/gcc/testsuite/g++.dg/debug/dwarf2/template-params-12n.C
> b/gcc/testsuite/g++.dg/debug/dwarf2/template-params-12n.C
> new file mode 100644
> index 0000000..d3c1f58
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/debug/dwarf2/template-params-12n.C
> @@ -0,0 +1,10 @@
> +// { dg-options "-gdwarf-2 -dA" }
> +// { dg-final { scan-assembler-times "DIE \\(\[^\n\]*\\)
> DW_TAG_template_value_param" 1 } }
> +// { dg-final { scan-assembler-times "DIE \\(\[^\n\]*\\)
> DW_TAG_template_value_param\[^\n\]*\n\[^\n\]* DW_AT_name\n\[^\n\]*
> DW_AT_type\n\[^\n\]* DW_AT_const_value" 1 } }
> +#include "template-params-12.H"
> +/* We get const_value for NULL pointers to member functions. */
> +#if __cplusplus > 199711L // Ugh, C++98 barfs at both the cast and the
> overload.
> +template void t<static_cast<void (S::*)()>(0)>();
> +#else
> +template void t<&S::v>();
> +#endif
> diff --git a/gcc/testsuite/g++.dg/debug/dwarf2/template-params-12s.C
> b/gcc/testsuite/g++.dg/debug/dwarf2/template-params-12s.C
> new file mode 100644
> index 0000000..8940eaf
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/debug/dwarf2/template-params-12s.C
> @@ -0,0 +1,8 @@
> +// { dg-options "-gdwarf-4 -gstrict-dwarf -dA" }
> +// { dg-final { scan-assembler-times "DIE \\(\[^\n\]*\\)
> DW_TAG_template_value_param" 1 } }
> +// { dg-final { scan-assembler-times "DIE \\(\[^\n\]*\\)
> DW_TAG_template_value_param\[^\n\]*\n\[^\n\]* DW_AT_name\n\[^\n\]*
> DW_AT_type\n\[^\n\]* \[^\n\]*DIE" 1 } }
> +#include "template-params-12.H"
> +/* We do NOT get a value or location for this one, because we've
> + enabled strict DWARF 4, and it could only be emitted as a location,
> + which is DWARF 5 only for template value params. */
> +template void t<&S::f>();
> diff --git a/gcc/testsuite/g++.dg/debug/dwarf2/template-params-12u.C
> b/gcc/testsuite/g++.dg/debug/dwarf2/template-params-12u.C
> new file mode 100644
> index 0000000..f79fa84
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/debug/dwarf2/template-params-12u.C
> @@ -0,0 +1,7 @@
> +// { dg-options "-gdwarf-2 -dA" }
> +// { dg-final { scan-assembler-times "DIE \\(\[^\n\]*\\)
> DW_TAG_template_value_param" 1 } }
> +// { dg-final { scan-assembler-times "DIE \\(\[^\n\]*\\)
> DW_TAG_template_value_param\[^\n\]*\n\[^\n\]* DW_AT_name\n\[^\n\]*
> DW_AT_type\n\[^\n\]* \[^\n\]*DIE" 1 } }
> +#include "template-params-12.H"
> +/* We do NOT get a value or location for this one, because it would
> + require a relocation to an undefined symbol in a debug section. */
> +template void t<&S::u>();
> diff --git a/gcc/testsuite/g++.dg/debug/dwarf2/template-params-12v.C
> b/gcc/testsuite/g++.dg/debug/dwarf2/template-params-12v.C
> new file mode 100644
> index 0000000..11aabae
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/debug/dwarf2/template-params-12v.C
> @@ -0,0 +1,6 @@
> +// { dg-options "-gdwarf-2 -dA" }
> +// { dg-final { scan-assembler-times "DIE \\(\[^\n\]*\\)
> DW_TAG_template_value_param" 1 } }
> +// { dg-final { scan-assembler-times "DIE \\(\[^\n\]*\\)
> DW_TAG_template_value_param\[^\n\]*\n\[^\n\]* DW_AT_name\n\[^\n\]*
> DW_AT_type\n\[^\n\]* DW_AT_const_value" 1 } }
> +#include "template-params-12.H"
> +/* We get const_value for pointers to virtual member functions. */
> +template void t<&S::v>();
> diff --git a/gcc/testsuite/g++.dg/debug/dwarf2/template-params-12w.C
> b/gcc/testsuite/g++.dg/debug/dwarf2/template-params-12w.C
> new file mode 100644
> index 0000000..11aabae
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/debug/dwarf2/template-params-12w.C
> @@ -0,0 +1,6 @@
> +// { dg-options "-gdwarf-2 -dA" }
> +// { dg-final { scan-assembler-times "DIE \\(\[^\n\]*\\)
> DW_TAG_template_value_param" 1 } }
> +// { dg-final { scan-assembler-times "DIE \\(\[^\n\]*\\)
> DW_TAG_template_value_param\[^\n\]*\n\[^\n\]* DW_AT_name\n\[^\n\]*
> DW_AT_type\n\[^\n\]* DW_AT_const_value" 1 } }
> +#include "template-params-12.H"
> +/* We get const_value for pointers to virtual member functions. */
> +template void t<&S::v>();
> --
> 2.1.0
>
>
> --
> Alexandre Oliva, freedom fighter http://FSFLA.org/~lxoliva/
> You must be the change you wish to see in the world. -- Gandhi
> Be Free! -- http://FSFLA.org/ FSF Latin America board member
> Free Software Evangelist|Red Hat Brasil GNU Toolchain Engineer
