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[PATCH 2/2] Support setting breakpoints on C++ method pointers
- From: Patrick Palka <patrick at parcs dot ath dot cx>
- To: gdb-patches at sourceware dot org
- Cc: Patrick Palka <patrick at parcs dot ath dot cx>
- Date: Mon, 22 Sep 2014 19:39:49 -0400
- Subject: [PATCH 2/2] Support setting breakpoints on C++ method pointers
- Authentication-results: sourceware.org; auth=none
- References: <1411355257-10861-1-git-send-email-patrick at parcs dot ath dot cx>
(Oops, I accidentally sent the older version of this patch a 2nd time.
Sorry for the noise.)
{ v2: I noticed that non-virtual method pointers are also affected by
this commit. That is, breaking on non-virtual method pointers now also
works whereas previously it didn't. So I rewrote the commit message and
augmented the testcase to also test non-virtual method pointers. I also
tweaked the documentation for the function cplus_method_ptr_to_value(). }
-- >8 --
This patch adds support for setting breakpoints on C++ method pointers,
both virtual and non-virtual. For example:
struct x
{
virtual void f ();
void g ();
}
void x::f () { }
void x::g () { }
struct y : x
{
}
(gdb) break *&y::f
Value can't be converted to integer.
(gdb) break *&y::g
Value can't be converted to integer.
Breaking on these expressions doesn't currently work because GDB doesn't
know how to convert a METHODPTR to an address in the function
value_as_address(). We have to teach value_as_address() how to extract
a symbolic address out from a METHODPTR in order for the above example
to work.
This patch tweaks value_as_address() to call cplus_method_ptr_to_value()
in order to extract a pointer value out of a METHODPTR. The latter
function does most of the work, but it needs a few tweaks. Firstly,
this patch makes the first argument of gnuv3_method_ptr_to_value(), i.e.
the argument corresponding to a "this" object pointer, optional.
Secondly, when the "this" pointer is omitted and a virtual method
pointer is passed in then we attempt to extract a pointer value by doing
a lookup of the virtual method pointer's symbolic name in the symbol
table.
Tested on x86_64-unknown-linux-gnu.
gdb/ChangeLog
* cp-abi.h (cplus_method_ptr_to_value): Document behavior for a
THIS_P that's NULL.
* gnu-v3-abi.c (gnuv3_method_ptr_to_value): Support method
resolution without a given "this" object.
* value.c (value_as_address): Handle TYPE_CODE_METHODPTR values.
gdb/testsuite/ChangeLog
* gdb.cp/method-ptr.exp: Add tests for breaking on non-virtual
method pointers.
(check_virtual_method_ptr_resolution): New parameter VIRTUAL.
Also test that setting a breakpoint on the given method pointer
works correctly.
* gdb.cp/method-ptr.cc: Introduce a few non-virtual methods
to test.
---
gdb/cp-abi.h | 4 ++-
gdb/gnu-v3-abi.c | 65 +++++++++++++++++++++++++------------
gdb/testsuite/gdb.cp/method-ptr.cc | 6 ++++
gdb/testsuite/gdb.cp/method-ptr.exp | 23 +++++++++++--
gdb/value.c | 8 +++++
5 files changed, 81 insertions(+), 25 deletions(-)
diff --git a/gdb/cp-abi.h b/gdb/cp-abi.h
index 7d4b7f3..1f38605 100644
--- a/gdb/cp-abi.h
+++ b/gdb/cp-abi.h
@@ -162,7 +162,9 @@ void cplus_print_method_ptr (const gdb_byte *contents,
int cplus_method_ptr_size (struct type *to_type);
/* Return the method which should be called by applying METHOD_PTR to
- *THIS_P, and adjust *THIS_P if necessary. */
+ *THIS_P, and adjust *THIS_P if necessary. If THIS_P is NULL then
+ return the method that would be called if METHOD_PTR was applied
+ to an object of METHOD_PTR's domain type (e.g. the type X in &X::f). */
struct value *cplus_method_ptr_to_value (struct value **this_p,
struct value *method_ptr);
diff --git a/gdb/gnu-v3-abi.c b/gdb/gnu-v3-abi.c
index ccb0be6..718694b 100644
--- a/gdb/gnu-v3-abi.c
+++ b/gdb/gnu-v3-abi.c
@@ -719,36 +719,59 @@ gnuv3_method_ptr_to_value (struct value **this_p, struct value *method_ptr)
gdbarch = get_type_arch (domain_type);
vbit = gnuv3_decode_method_ptr (gdbarch, contents, &ptr_value, &adjustment);
- /* First convert THIS to match the containing type of the pointer to
- member. This cast may adjust the value of THIS. */
- *this_p = value_cast (final_type, *this_p);
+ if (this_p != NULL)
+ {
+ /* First convert THIS to match the containing type of the pointer to
+ member. This cast may adjust the value of THIS. */
+ *this_p = value_cast (final_type, *this_p);
- /* Then apply whatever adjustment is necessary. This creates a somewhat
- strange pointer: it claims to have type FINAL_TYPE, but in fact it
- might not be a valid FINAL_TYPE. For instance, it might be a
- base class of FINAL_TYPE. And if it's not the primary base class,
- then printing it out as a FINAL_TYPE object would produce some pretty
- garbage.
+ /* Then apply whatever adjustment is necessary. This creates a somewhat
+ strange pointer: it claims to have type FINAL_TYPE, but in fact it
+ might not be a valid FINAL_TYPE. For instance, it might be a
+ base class of FINAL_TYPE. And if it's not the primary base class,
+ then printing it out as a FINAL_TYPE object would produce some pretty
+ garbage.
- But we don't really know the type of the first argument in
- METHOD_TYPE either, which is why this happens. We can't
- dereference this later as a FINAL_TYPE, but once we arrive in the
- called method we'll have debugging information for the type of
- "this" - and that'll match the value we produce here.
+ But we don't really know the type of the first argument in
+ METHOD_TYPE either, which is why this happens. We can't
+ dereference this later as a FINAL_TYPE, but once we arrive in the
+ called method we'll have debugging information for the type of
+ "this" - and that'll match the value we produce here.
- You can provoke this case by casting a Base::* to a Derived::*, for
- instance. */
- *this_p = value_cast (builtin_type (gdbarch)->builtin_data_ptr, *this_p);
- *this_p = value_ptradd (*this_p, adjustment);
- *this_p = value_cast (final_type, *this_p);
+ You can provoke this case by casting a Base::* to a Derived::*, for
+ instance. */
+ *this_p = value_cast (builtin_type (gdbarch)->builtin_data_ptr, *this_p);
+ *this_p = value_ptradd (*this_p, adjustment);
+ *this_p = value_cast (final_type, *this_p);
+ }
if (vbit)
{
LONGEST voffset;
voffset = ptr_value / TYPE_LENGTH (vtable_ptrdiff_type (gdbarch));
- return gnuv3_get_virtual_fn (gdbarch, value_ind (*this_p),
- method_type, voffset);
+
+ /* If we don't have a "this" object to apply the method pointer to,
+ then retrieve the value of the virtual method by looking up its
+ symbolic name within the symbol table. */
+ if (this_p == NULL)
+ {
+ const char *physname;
+ struct symbol *sym;
+
+ physname = gnuv3_find_method_in (domain_type, voffset, adjustment);
+ if (physname == NULL)
+ return NULL;
+
+ sym = lookup_symbol (physname, NULL, VAR_DOMAIN, NULL);
+ if (sym == NULL)
+ return NULL;
+
+ return value_of_variable (sym, NULL);
+ }
+ else
+ return gnuv3_get_virtual_fn (gdbarch, value_ind (*this_p),
+ method_type, voffset);
}
else
return value_from_pointer (lookup_pointer_type (method_type), ptr_value);
diff --git a/gdb/testsuite/gdb.cp/method-ptr.cc b/gdb/testsuite/gdb.cp/method-ptr.cc
index db47484..4e1524a 100644
--- a/gdb/testsuite/gdb.cp/method-ptr.cc
+++ b/gdb/testsuite/gdb.cp/method-ptr.cc
@@ -20,11 +20,14 @@ struct x
virtual void f ();
virtual void g ();
virtual void h ();
+
+ void a ();
};
void x::f () { }
void x::g () { }
void x::h () { }
+void x::a () { }
struct y : x
{
@@ -32,11 +35,14 @@ struct y : x
virtual void j ();
virtual void k ();
+
+ void b ();
};
void y::f () { }
void y::j () { }
void y::k () { }
+void y::b () { }
struct z : y
{
diff --git a/gdb/testsuite/gdb.cp/method-ptr.exp b/gdb/testsuite/gdb.cp/method-ptr.exp
index 732b861..ca6be4b 100644
--- a/gdb/testsuite/gdb.cp/method-ptr.exp
+++ b/gdb/testsuite/gdb.cp/method-ptr.exp
@@ -33,23 +33,38 @@ if ![test_debug_format "DWARF 2"] {
return 0
}
-# Check that the virtual method pointer NAME resolves to symbol SYMBOL.
-proc check_virtual_method_ptr_resolution { name symbol } {
+# Check that the method pointer NAME resolves to symbol SYMBOL. Set VIRTUAL
+# to 1 if NAME is a virtual method pointer (default), 0 otherwise.
+proc check_virtual_method_ptr_resolution { name symbol {virtual 1} } {
global decimal
# Printing the expression &NAME should show the resolved symbol SYMBOL.
- gdb_test "print &$name" "\\$$decimal = &virtual $symbol\\(\\)\\s"
+ if {$virtual != 0} {
+ gdb_test "print &$name" "\\s&virtual $symbol\\(\\)\\s"
+ } else {
+ gdb_test "print &$name" "\\s<$symbol\\(\\)>\\s"
+ }
+
+ # Breaking on the expression &NAME should create a breakpoint on the symbol
+ # SYMBOL.
+ set breakpoint_line [gdb_get_line_number $symbol]
+ gdb_test "break *&$name" \
+ "Breakpoint $decimal at .*, line $breakpoint_line\\.\\s"
+ delete_breakpoints
}
check_virtual_method_ptr_resolution "x::f" "x::f"
check_virtual_method_ptr_resolution "x::g" "x::g"
check_virtual_method_ptr_resolution "x::h" "x::h"
+check_virtual_method_ptr_resolution "x::a" "x::a" 0
check_virtual_method_ptr_resolution "y::f" "y::f"
check_virtual_method_ptr_resolution "y::g" "x::g"
check_virtual_method_ptr_resolution "y::h" "x::h"
check_virtual_method_ptr_resolution "y::j" "y::j"
check_virtual_method_ptr_resolution "y::k" "y::k"
+check_virtual_method_ptr_resolution "y::a" "x::a" 0
+check_virtual_method_ptr_resolution "y::b" "y::b" 0
check_virtual_method_ptr_resolution "z::f" "y::f"
check_virtual_method_ptr_resolution "z::g" "z::g"
@@ -58,3 +73,5 @@ check_virtual_method_ptr_resolution "z::j" "z::j"
check_virtual_method_ptr_resolution "z::k" "y::k"
check_virtual_method_ptr_resolution "z::l" "z::l"
check_virtual_method_ptr_resolution "z::m" "z::m"
+check_virtual_method_ptr_resolution "z::a" "x::a" 0
+check_virtual_method_ptr_resolution "z::b" "y::b" 0
diff --git a/gdb/value.c b/gdb/value.c
index fdc8858d..63ff363 100644
--- a/gdb/value.c
+++ b/gdb/value.c
@@ -2639,6 +2639,14 @@ value_as_address (struct value *val)
return gdbarch_addr_bits_remove (gdbarch, value_as_long (val));
#else
+ if (TYPE_CODE (value_type (val)) == TYPE_CODE_METHODPTR)
+ {
+ val = cplus_method_ptr_to_value (NULL, val);
+ if (val == NULL)
+ error (_("Method pointer can't be converted to an address."));
+ }
+
+
/* There are several targets (IA-64, PowerPC, and others) which
don't represent pointers to functions as simply the address of
the function's entry point. For example, on the IA-64, a
--
2.1.1.273.g97b8860