Re: [all pushed] Re: [PATCH 00/36] Support building GDB as a C++ program

Pedro Alves
2015-05-15T15:04:52Z

On 05/15/2015 09:21 AM, asmwarrior wrote:
> Hi, Pedro, I just found another build issue when building gdb under g++.

Thanks!

>
> Building mingw GDB with --enable-build-with-cxx shows:
>
> ../../binutils-gdb/gdb/python/py-unwind.c:500:45: error: cannot convert 'cached_frame_info::reg_info*' to 'pyuw_prev_register(frame_info*, void**, int)::reg_info*' in initialization
> struct reg_info *reg_info = cached_frame->reg;
> ^
> ../../binutils-gdb/gdb/python/py-unwind.c:501:60: error: invalid use of incomplete type 'struct pyuw_prev_register(frame_info*, void**, int)::reg_info'
> struct reg_info *reg_info_end = reg_info + cached_frame->reg_count;
> ^
> ../../binutils-gdb/gdb/python/py-unwind.c:500:10: error: forward declaration of 'struct pyuw_prev_register(frame_info*, void**, int)::reg_info'
> struct reg_info *reg_info = cached_frame->reg;
> ^
> ../../binutils-gdb/gdb/python/py-unwind.c:505:37: error: cannot increment a pointer to incomplete type 'pyuw_prev_register(frame_info*, void**, int)::reg_info'
> for (; reg_info < reg_info_end; ++reg_info)
> ^
> ../../binutils-gdb/gdb/python/py-unwind.c:507:29: error: invalid use of incomplete type 'struct pyuw_prev_register(frame_info*, void**, int)::reg_info'
> if (regnum == reg_info->number)
> ^
> ../../binutils-gdb/gdb/python/py-unwind.c:500:10: error: forward declaration of 'struct pyuw_prev_register(frame_info*, void**, int)::reg_info'
> struct reg_info *reg_info = cached_frame->reg;
> ^
> ../../binutils-gdb/gdb/python/py-unwind.c:508:68: error: invalid use of incomplete type 'struct pyuw_prev_register(frame_info*, void**, int)::reg_info'
> return frame_unwind_got_bytes (this_frame, regnum, reg_info->data);
> ^
> ../../binutils-gdb/gdb/python/py-unwind.c:500:10: error: forward declaration of 'struct pyuw_prev_register(frame_info*, void**, int)::reg_info'
> struct reg_info *reg_info = cached_frame->reg;
> ^
> ../../binutils-gdb/gdb/python/py-unwind.c: In function 'int pyuw_sniffer(const frame_unwind*, frame_info*, void**)':
> ../../binutils-gdb/gdb/python/py-unwind.c:574:70: warning: invalid conversion from 'void*' to 'cached_frame_info*' [-fpermissive]
> reg_count * sizeof (cached_frame->reg[0]));
> ^
> ../../binutils-gdb/gdb/python/py-unwind.c: In function 'void pyuw_on_new_gdbarch(gdbarch*)':
> ../../binutils-gdb/gdb/python/py-unwind.c:636:47: warning: invalid conversion from 'void*' to 'pyuw_gdbarch_data_type*' [-fpermissive]
> gdbarch_data (newarch, pyuw_gdbarch_data);
> ^
> ../../binutils-gdb/gdb/python/py-unwind.c:647:29: warning: invalid conversion from 'void*' to 'const frame_data*' [-fpermissive]
> unwinder->unwind_data = (void *) newarch;
> ^
> ../../binutils-gdb/gdb/python/py-unwind.c: At global scope:
> ../../binutils-gdb/gdb/python/py-unwind.c:699:21: error: redefinition of 'PyTypeObject pending_frame_object_type'
> static PyTypeObject pending_frame_object_type =
> ^
> ../../binutils-gdb/gdb/python/py-unwind.c:96:21: error: 'PyTypeObject pending_frame_object_type' previously declared here
> static PyTypeObject pending_frame_object_type
> ^
> ../../binutils-gdb/gdb/python/py-unwind.c:749:21: error: redefinition of 'PyTypeObject unwind_info_object_type'
> static PyTypeObject unwind_info_object_type =
> ^
> ../../binutils-gdb/gdb/python/py-unwind.c:99:21: error: 'PyTypeObject unwind_info_object_type' previously declared here
> static PyTypeObject unwind_info_object_type
> ^
>
>
> The first kind of error is caused by embedded struct definition, so I moved it out of the parent struct.

That's the right fix.

> The second kind of error is caused by using static keyword on a CPYCHECKER_TYPE_OBJECT_FOR_TYPEDEF decoreated variable, I see that all other files use extern, so I changed to extern.

That too, is the right fix, though the problem isn't caused by
CPYCHECKER_TYPE_OBJECT_FOR_TYPEDEF. The problem is that with C we
can "forward declare" variables like this:

static int foo;

void
use_foo (void)
{
if (foo == 2)
bar ();
}

static int foo = 3;

But that's not valid C++ (and a link error with C and -fno-common).

So we need to fix the definition too, though, otherwise we have a
static / extern mismatch. G++ warns about it, but until we get rid
of -fpermissive and enable -Werror in C++ mode, it's easy to
miss. Building in C mode does catch that with an error though.

Here's what I pushed.

From 13fa0398d7dd8d2b468acf0aba5610ce014709a6 Mon Sep 17 00:00:00 2001
From: Yuanhui Zhang <asmwarrior@gmail.com>
Date: Fri, 15 May 2015 16:00:40 +0100
Subject: [PATCH] Fix a couple C++ build issues

Building mingw GDB with --enable-build-with-cxx shows:

../../binutils-gdb/gdb/python/py-unwind.c:500:45: error: cannot convert 'cached_frame_info::reg_info*' to 'pyuw_prev_register(frame_info*, void**, int)::reg_info*' in initialization
struct reg_info *reg_info = cached_frame->reg;
^
../../binutils-gdb/gdb/python/py-unwind.c:501:60: error: invalid use of incomplete type 'struct pyuw_prev_register(frame_info*, void**, int)::reg_info'
struct reg_info *reg_info_end = reg_info + cached_frame->reg_count;
^
../../binutils-gdb/gdb/python/py-unwind.c:500:10: error: forward declaration of 'struct pyuw_prev_register(frame_info*, void**, int)::reg_info'
struct reg_info *reg_info = cached_frame->reg;
^
../../binutils-gdb/gdb/python/py-unwind.c:505:37: error: cannot increment a pointer to incomplete type 'pyuw_prev_register(frame_info*, void**, int)::reg_info'
for (; reg_info < reg_info_end; ++reg_info)
^
../../binutils-gdb/gdb/python/py-unwind.c:507:29: error: invalid use of incomplete type 'struct pyuw_prev_register(frame_info*, void**, int)::reg_info'
if (regnum == reg_info->number)
^
../../binutils-gdb/gdb/python/py-unwind.c:500:10: error: forward declaration of 'struct pyuw_prev_register(frame_info*, void**, int)::reg_info'
struct reg_info *reg_info = cached_frame->reg;
^
../../binutils-gdb/gdb/python/py-unwind.c:508:68: error: invalid use of incomplete type 'struct pyuw_prev_register(frame_info*, void**, int)::reg_info'
return frame_unwind_got_bytes (this_frame, regnum, reg_info->data);
^
../../binutils-gdb/gdb/python/py-unwind.c:500:10: error: forward declaration of 'struct pyuw_prev_register(frame_info*, void**, int)::reg_info'
struct reg_info *reg_info = cached_frame->reg;
^
../../binutils-gdb/gdb/python/py-unwind.c: In function 'int pyuw_sniffer(const frame_unwind*, frame_info*, void**)':
../../binutils-gdb/gdb/python/py-unwind.c:574:70: warning: invalid conversion from 'void*' to 'cached_frame_info*' [-fpermissive]
reg_count * sizeof (cached_frame->reg[0]));
^
../../binutils-gdb/gdb/python/py-unwind.c: In function 'void pyuw_on_new_gdbarch(gdbarch*)':
../../binutils-gdb/gdb/python/py-unwind.c:636:47: warning: invalid conversion from 'void*' to 'pyuw_gdbarch_data_type*' [-fpermissive]
gdbarch_data (newarch, pyuw_gdbarch_data);
^
../../binutils-gdb/gdb/python/py-unwind.c:647:29: warning: invalid conversion from 'void*' to 'const frame_data*' [-fpermissive]
unwinder->unwind_data = (void *) newarch;
^
../../binutils-gdb/gdb/python/py-unwind.c: At global scope:
../../binutils-gdb/gdb/python/py-unwind.c:699:21: error: redefinition of 'PyTypeObject pending_frame_object_type'
static PyTypeObject pending_frame_object_type =
^
../../binutils-gdb/gdb/python/py-unwind.c:96:21: error: 'PyTypeObject pending_frame_object_type' previously declared here
static PyTypeObject pending_frame_object_type
^
../../binutils-gdb/gdb/python/py-unwind.c:749:21: error: redefinition of 'PyTypeObject unwind_info_object_type'
static PyTypeObject unwind_info_object_type =
^
../../binutils-gdb/gdb/python/py-unwind.c:99:21: error: 'PyTypeObject unwind_info_object_type' previously declared here
static PyTypeObject unwind_info_object_type
^

The first kind of error is caused by the embedded struct definition,
so move it out of the parent struct.

The second kind of error is caused by forward declaring a static
global variable, which works in C, but not in C++ (or C with
-fno-common). Make it using extern instead, like done in other
similar cases.

gdb/ChangeLog:
2015-05-15 Yuanhui Zhang <asmwarrior@gmail.com>

* python/py-unwind.c (struct reg_info): Move out of ...
(struct cached_frame_info): ... this scope.
(pending_frame_object_type, unwind_info_object_type): Make extern.
---
gdb/ChangeLog | 6 ++++++
gdb/python/py-unwind.c | 26 ++++++++++++++------------
2 files changed, 20 insertions(+), 12 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 1492981..1fdc4f4 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,9 @@
+2015-05-15 Yuanhui Zhang <asmwarrior@gmail.com>
+
+ * python/py-unwind.c (struct reg_info): Move out of ...
+ (struct cached_frame_info): ... this scope.
+ (pending_frame_object_type, unwind_info_object_type): Make extern.
+
2015-05-15 Joel Brobecker <brobecker@adacore.com>

* ada-lang.c (ada_value_primitive_packed_val): Make sure
diff --git a/gdb/python/py-unwind.c b/gdb/python/py-unwind.c
index bcfea4b..b6e8a75 100644
--- a/gdb/python/py-unwind.c
+++ b/gdb/python/py-unwind.c
@@ -72,6 +72,15 @@ typedef struct
/* The data we keep for a frame we can unwind: frame ID and an array of
(register_number, register_value) pairs. */

+struct reg_info
+{
+ /* Register number. */
+ int number;
+
+ /* Register data bytes pointer. */
+ gdb_byte data[MAX_REGISTER_SIZE];
+};
+
typedef struct
{
/* Frame ID. */
@@ -83,20 +92,13 @@ typedef struct
/* Length of the `reg' array below. */
int reg_count;

- struct reg_info
- {
- /* Register number. */
- int number;
-
- /* Register data bytes pointer. */
- gdb_byte data[MAX_REGISTER_SIZE];
- } reg[];
+ struct reg_info reg[];
} cached_frame_info;

-static PyTypeObject pending_frame_object_type
+extern PyTypeObject pending_frame_object_type
CPYCHECKER_TYPE_OBJECT_FOR_TYPEDEF ("pending_frame_object");

-static PyTypeObject unwind_info_object_type
+extern PyTypeObject unwind_info_object_type
CPYCHECKER_TYPE_OBJECT_FOR_TYPEDEF ("unwind_info_object");

static unsigned int pyuw_debug = 0;
@@ -696,7 +698,7 @@ static PyMethodDef pending_frame_object_methods[] =
{NULL} /* Sentinel */
};

-static PyTypeObject pending_frame_object_type =
+PyTypeObject pending_frame_object_type =
{
PyVarObject_HEAD_INIT (NULL, 0)
"gdb.PendingFrame", /* tp_name */
@@ -746,7 +748,7 @@ static PyMethodDef unwind_info_object_methods[] =
{ NULL } /* Sentinel */
};

-static PyTypeObject unwind_info_object_type =
+PyTypeObject unwind_info_object_type =
{
PyVarObject_HEAD_INIT (NULL, 0)
"gdb.UnwindInfo", /* tp_name */
--
1.9.3