* [PATCH] warn-access: Prevent -Wuse-after-free on ARM [PR104213]
@ 2022-01-25 23:33 Marek Polacek
2022-01-26 0:35 ` Martin Sebor
2022-01-26 15:24 ` Jason Merrill
0 siblings, 2 replies; 6+ messages in thread
From: Marek Polacek @ 2022-01-25 23:33 UTC (permalink / raw)
To: GCC Patches; +Cc: Jason Merrill, Martin Sebor
Here, -Wuse-after-free warns about using 'this' which, on ARM, cdtors
return, as mandated by the EABI. To be entirely correct, it only
requires it for C1 and C2 ctors and D2 and D1 dtors, but I don't feel
like changing that now and possibly running into issues later on.
This patch uses suppress_warning on 'this' for certain cdtor_returns_this
cases in the C++ FE, and then warn_invalid_pointer makes use of this
information and doesn't warn.
In my first attempt I tried suppress_warning the MODIFY_EXPR or RETURN_EXPR
we build in build_delete_destructor_body, but the complication is that
the suppress_warning bits don't always survive gimplification; see e.g.
gimplify_modify_expr where we do
6130 if (COMPARISON_CLASS_P (*from_p))
6131 copy_warning (assign, *from_p);
but here we're not dealing with a comparison. Removing that check
regresses uninit-pr74762.C. Adding copy_warning (assign, *expr_p)
regresses c-c++-common/uninit-17.c.
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
PR target/104213
gcc/cp/ChangeLog:
* decl.cc (finish_constructor_body): Suppress -Wuse-after-free.
(finish_destructor_body): Likewise.
* optimize.cc (build_delete_destructor_body): Likewise.
gcc/ChangeLog:
* gimple-ssa-warn-access.cc (pass_waccess::warn_invalid_pointer): Don't
warn when the SSA_NAME_VAR of REF has supressed -Wuse-after-free.
gcc/testsuite/ChangeLog:
* g++.dg/warn/Wuse-after-free2.C: New test.
---
gcc/cp/decl.cc | 2 ++
gcc/cp/optimize.cc | 1 +
gcc/gimple-ssa-warn-access.cc | 14 +++++++++++---
gcc/testsuite/g++.dg/warn/Wuse-after-free2.C | 10 ++++++++++
4 files changed, 24 insertions(+), 3 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/warn/Wuse-after-free2.C
diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index 22d3dd1e2ad..6534a7fd320 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -17315,6 +17315,7 @@ finish_constructor_body (void)
add_stmt (build_stmt (input_location, LABEL_EXPR, cdtor_label));
val = DECL_ARGUMENTS (current_function_decl);
+ suppress_warning (val, OPT_Wuse_after_free);
val = build2 (MODIFY_EXPR, TREE_TYPE (val),
DECL_RESULT (current_function_decl), val);
/* Return the address of the object. */
@@ -17408,6 +17409,7 @@ finish_destructor_body (void)
tree val;
val = DECL_ARGUMENTS (current_function_decl);
+ suppress_warning (val, OPT_Wuse_after_free);
val = build2 (MODIFY_EXPR, TREE_TYPE (val),
DECL_RESULT (current_function_decl), val);
/* Return the address of the object. */
diff --git a/gcc/cp/optimize.cc b/gcc/cp/optimize.cc
index 4ad3f1dc9aa..13ab8b7361e 100644
--- a/gcc/cp/optimize.cc
+++ b/gcc/cp/optimize.cc
@@ -166,6 +166,7 @@ build_delete_destructor_body (tree delete_dtor, tree complete_dtor)
if (targetm.cxx.cdtor_returns_this ())
{
tree val = DECL_ARGUMENTS (delete_dtor);
+ suppress_warning (val, OPT_Wuse_after_free);
val = build2 (MODIFY_EXPR, TREE_TYPE (val),
DECL_RESULT (delete_dtor), val);
add_stmt (build_stmt (0, RETURN_EXPR, val));
diff --git a/gcc/gimple-ssa-warn-access.cc b/gcc/gimple-ssa-warn-access.cc
index 8bc33eeb6fa..484bcd34c25 100644
--- a/gcc/gimple-ssa-warn-access.cc
+++ b/gcc/gimple-ssa-warn-access.cc
@@ -3880,9 +3880,17 @@ pass_waccess::warn_invalid_pointer (tree ref, gimple *use_stmt,
bool maybe, bool equality /* = false */)
{
/* Avoid printing the unhelpful "<unknown>" in the diagnostics. */
- if (ref && TREE_CODE (ref) == SSA_NAME
- && (!SSA_NAME_VAR (ref) || DECL_ARTIFICIAL (SSA_NAME_VAR (ref))))
- ref = NULL_TREE;
+ if (ref && TREE_CODE (ref) == SSA_NAME)
+ {
+ tree var = SSA_NAME_VAR (ref);
+ if (!var)
+ ref = NULL_TREE;
+ /* Don't warn for cases like when a cdtor returns 'this' on ARM. */
+ else if (warning_suppressed_p (var, OPT_Wuse_after_free))
+ return;
+ else if (DECL_ARTIFICIAL (var))
+ ref = NULL_TREE;
+ }
location_t use_loc = gimple_location (use_stmt);
if (use_loc == UNKNOWN_LOCATION)
diff --git a/gcc/testsuite/g++.dg/warn/Wuse-after-free2.C b/gcc/testsuite/g++.dg/warn/Wuse-after-free2.C
new file mode 100644
index 00000000000..6d5f2bf01b5
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wuse-after-free2.C
@@ -0,0 +1,10 @@
+// PR target/104213
+// { dg-do compile }
+// { dg-options "-Wuse-after-free" }
+
+class C
+{
+ virtual ~C();
+};
+
+C::~C() {} // { dg-bogus "used after" }
base-commit: aeac414923aa1e87986c7fc6f9b921d89a9b86cf
--
2.34.1
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] warn-access: Prevent -Wuse-after-free on ARM [PR104213]
2022-01-25 23:33 [PATCH] warn-access: Prevent -Wuse-after-free on ARM [PR104213] Marek Polacek
@ 2022-01-26 0:35 ` Martin Sebor
2022-01-26 0:49 ` Marek Polacek
2022-01-26 15:24 ` Jason Merrill
1 sibling, 1 reply; 6+ messages in thread
From: Martin Sebor @ 2022-01-26 0:35 UTC (permalink / raw)
To: Marek Polacek, GCC Patches; +Cc: Martin Sebor
On 1/25/22 16:33, Marek Polacek via Gcc-patches wrote:
> Here, -Wuse-after-free warns about using 'this' which, on ARM, cdtors
> return, as mandated by the EABI. To be entirely correct, it only
> requires it for C1 and C2 ctors and D2 and D1 dtors, but I don't feel
> like changing that now and possibly running into issues later on.
>
> This patch uses suppress_warning on 'this' for certain cdtor_returns_this
> cases in the C++ FE, and then warn_invalid_pointer makes use of this
> information and doesn't warn.
>
> In my first attempt I tried suppress_warning the MODIFY_EXPR or RETURN_EXPR
> we build in build_delete_destructor_body, but the complication is that
> the suppress_warning bits don't always survive gimplification; see e.g.
> gimplify_modify_expr where we do
>
> 6130 if (COMPARISON_CLASS_P (*from_p))
> 6131 copy_warning (assign, *from_p);
>
> but here we're not dealing with a comparison. Removing that check
> regresses uninit-pr74762.C. Adding copy_warning (assign, *expr_p)
> regresses c-c++-common/uninit-17.c.
>
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
Thanks for picking this up!
My only concern with suppressing the warning for the pointer rather
than just for the return statement is that it not lead to false
negatives. I played with the patch a little, trying to trigger one
but couldn't so it might be unfounded. Still, I'd expect targeting
the statement to be a simpler change (the warning already checks
for the suppression bit on the statement). Did you try it?
For reference, one of the test cases I tried is below. It would
be good to add it to the test suite to make sure the bug is caught
(there's a duplicate warning there that should at some point get
squashed).
struct A
{
virtual ~A ();
void f ();
};
A::~A ()
{
operator delete (this);
f ();
}
Martin
>
> PR target/104213
>
> gcc/cp/ChangeLog:
>
> * decl.cc (finish_constructor_body): Suppress -Wuse-after-free.
> (finish_destructor_body): Likewise.
> * optimize.cc (build_delete_destructor_body): Likewise.
>
> gcc/ChangeLog:
>
> * gimple-ssa-warn-access.cc (pass_waccess::warn_invalid_pointer): Don't
> warn when the SSA_NAME_VAR of REF has supressed -Wuse-after-free.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/warn/Wuse-after-free2.C: New test.
> ---
> gcc/cp/decl.cc | 2 ++
> gcc/cp/optimize.cc | 1 +
> gcc/gimple-ssa-warn-access.cc | 14 +++++++++++---
> gcc/testsuite/g++.dg/warn/Wuse-after-free2.C | 10 ++++++++++
> 4 files changed, 24 insertions(+), 3 deletions(-)
> create mode 100644 gcc/testsuite/g++.dg/warn/Wuse-after-free2.C
>
> diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
> index 22d3dd1e2ad..6534a7fd320 100644
> --- a/gcc/cp/decl.cc
> +++ b/gcc/cp/decl.cc
> @@ -17315,6 +17315,7 @@ finish_constructor_body (void)
> add_stmt (build_stmt (input_location, LABEL_EXPR, cdtor_label));
>
> val = DECL_ARGUMENTS (current_function_decl);
> + suppress_warning (val, OPT_Wuse_after_free);
> val = build2 (MODIFY_EXPR, TREE_TYPE (val),
> DECL_RESULT (current_function_decl), val);
> /* Return the address of the object. */
> @@ -17408,6 +17409,7 @@ finish_destructor_body (void)
> tree val;
>
> val = DECL_ARGUMENTS (current_function_decl);
> + suppress_warning (val, OPT_Wuse_after_free);
> val = build2 (MODIFY_EXPR, TREE_TYPE (val),
> DECL_RESULT (current_function_decl), val);
> /* Return the address of the object. */
> diff --git a/gcc/cp/optimize.cc b/gcc/cp/optimize.cc
> index 4ad3f1dc9aa..13ab8b7361e 100644
> --- a/gcc/cp/optimize.cc
> +++ b/gcc/cp/optimize.cc
> @@ -166,6 +166,7 @@ build_delete_destructor_body (tree delete_dtor, tree complete_dtor)
> if (targetm.cxx.cdtor_returns_this ())
> {
> tree val = DECL_ARGUMENTS (delete_dtor);
> + suppress_warning (val, OPT_Wuse_after_free);
> val = build2 (MODIFY_EXPR, TREE_TYPE (val),
> DECL_RESULT (delete_dtor), val);
> add_stmt (build_stmt (0, RETURN_EXPR, val));
> diff --git a/gcc/gimple-ssa-warn-access.cc b/gcc/gimple-ssa-warn-access.cc
> index 8bc33eeb6fa..484bcd34c25 100644
> --- a/gcc/gimple-ssa-warn-access.cc
> +++ b/gcc/gimple-ssa-warn-access.cc
> @@ -3880,9 +3880,17 @@ pass_waccess::warn_invalid_pointer (tree ref, gimple *use_stmt,
> bool maybe, bool equality /* = false */)
> {
> /* Avoid printing the unhelpful "<unknown>" in the diagnostics. */
> - if (ref && TREE_CODE (ref) == SSA_NAME
> - && (!SSA_NAME_VAR (ref) || DECL_ARTIFICIAL (SSA_NAME_VAR (ref))))
> - ref = NULL_TREE;
> + if (ref && TREE_CODE (ref) == SSA_NAME)
> + {
> + tree var = SSA_NAME_VAR (ref);
> + if (!var)
> + ref = NULL_TREE;
> + /* Don't warn for cases like when a cdtor returns 'this' on ARM. */
> + else if (warning_suppressed_p (var, OPT_Wuse_after_free))
> + return;
> + else if (DECL_ARTIFICIAL (var))
> + ref = NULL_TREE;
> + }
>
> location_t use_loc = gimple_location (use_stmt);
> if (use_loc == UNKNOWN_LOCATION)
> diff --git a/gcc/testsuite/g++.dg/warn/Wuse-after-free2.C b/gcc/testsuite/g++.dg/warn/Wuse-after-free2.C
> new file mode 100644
> index 00000000000..6d5f2bf01b5
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/warn/Wuse-after-free2.C
> @@ -0,0 +1,10 @@
> +// PR target/104213
> +// { dg-do compile }
> +// { dg-options "-Wuse-after-free" }
> +
> +class C
> +{
> + virtual ~C();
> +};
> +
> +C::~C() {} // { dg-bogus "used after" }
>
> base-commit: aeac414923aa1e87986c7fc6f9b921d89a9b86cf
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] warn-access: Prevent -Wuse-after-free on ARM [PR104213]
2022-01-26 0:35 ` Martin Sebor
@ 2022-01-26 0:49 ` Marek Polacek
0 siblings, 0 replies; 6+ messages in thread
From: Marek Polacek @ 2022-01-26 0:49 UTC (permalink / raw)
To: Martin Sebor; +Cc: GCC Patches, Martin Sebor
On Tue, Jan 25, 2022 at 05:35:20PM -0700, Martin Sebor wrote:
> On 1/25/22 16:33, Marek Polacek via Gcc-patches wrote:
> > Here, -Wuse-after-free warns about using 'this' which, on ARM, cdtors
> > return, as mandated by the EABI. To be entirely correct, it only
> > requires it for C1 and C2 ctors and D2 and D1 dtors, but I don't feel
> > like changing that now and possibly running into issues later on.
> >
> > This patch uses suppress_warning on 'this' for certain cdtor_returns_this
> > cases in the C++ FE, and then warn_invalid_pointer makes use of this
> > information and doesn't warn.
> >
> > In my first attempt I tried suppress_warning the MODIFY_EXPR or RETURN_EXPR
> > we build in build_delete_destructor_body, but the complication is that
> > the suppress_warning bits don't always survive gimplification; see e.g.
> > gimplify_modify_expr where we do
> >
> > 6130 if (COMPARISON_CLASS_P (*from_p))
> > 6131 copy_warning (assign, *from_p);
> >
> > but here we're not dealing with a comparison. Removing that check
> > regresses uninit-pr74762.C. Adding copy_warning (assign, *expr_p)
> > regresses c-c++-common/uninit-17.c.
> >
> > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
>
> Thanks for picking this up!
>
> My only concern with suppressing the warning for the pointer rather
> than just for the return statement is that it not lead to false
> negatives. I played with the patch a little, trying to trigger one
> but couldn't so it might be unfounded. Still, I'd expect targeting
> the statement to be a simpler change (the warning already checks
> for the suppression bit on the statement). Did you try it?
I did -- that is the "In my first attempt..." paragraph in my patch
(we don't use copy_warning to propagate the suppress_warning bits).
Maybe it'd be a more correct way to approach this, that is, somehow
tweak gimplify_modify_expr to copy_warning for this special case.
> For reference, one of the test cases I tried is below. It would
> be good to add it to the test suite to make sure the bug is caught
> (there's a duplicate warning there that should at some point get
> squashed).
>
> struct A
> {
> virtual ~A ();
> void f ();
> };
>
> A::~A ()
> {
> operator delete (this);
> f ();
> }
Sure, happy to add it.
> Martin
>
> >
> > PR target/104213
> >
> > gcc/cp/ChangeLog:
> >
> > * decl.cc (finish_constructor_body): Suppress -Wuse-after-free.
> > (finish_destructor_body): Likewise.
> > * optimize.cc (build_delete_destructor_body): Likewise.
> >
> > gcc/ChangeLog:
> >
> > * gimple-ssa-warn-access.cc (pass_waccess::warn_invalid_pointer): Don't
> > warn when the SSA_NAME_VAR of REF has supressed -Wuse-after-free.
> >
> > gcc/testsuite/ChangeLog:
> >
> > * g++.dg/warn/Wuse-after-free2.C: New test.
> > ---
> > gcc/cp/decl.cc | 2 ++
> > gcc/cp/optimize.cc | 1 +
> > gcc/gimple-ssa-warn-access.cc | 14 +++++++++++---
> > gcc/testsuite/g++.dg/warn/Wuse-after-free2.C | 10 ++++++++++
> > 4 files changed, 24 insertions(+), 3 deletions(-)
> > create mode 100644 gcc/testsuite/g++.dg/warn/Wuse-after-free2.C
> >
> > diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
> > index 22d3dd1e2ad..6534a7fd320 100644
> > --- a/gcc/cp/decl.cc
> > +++ b/gcc/cp/decl.cc
> > @@ -17315,6 +17315,7 @@ finish_constructor_body (void)
> > add_stmt (build_stmt (input_location, LABEL_EXPR, cdtor_label));
> > val = DECL_ARGUMENTS (current_function_decl);
> > + suppress_warning (val, OPT_Wuse_after_free);
> > val = build2 (MODIFY_EXPR, TREE_TYPE (val),
> > DECL_RESULT (current_function_decl), val);
> > /* Return the address of the object. */
> > @@ -17408,6 +17409,7 @@ finish_destructor_body (void)
> > tree val;
> > val = DECL_ARGUMENTS (current_function_decl);
> > + suppress_warning (val, OPT_Wuse_after_free);
> > val = build2 (MODIFY_EXPR, TREE_TYPE (val),
> > DECL_RESULT (current_function_decl), val);
> > /* Return the address of the object. */
> > diff --git a/gcc/cp/optimize.cc b/gcc/cp/optimize.cc
> > index 4ad3f1dc9aa..13ab8b7361e 100644
> > --- a/gcc/cp/optimize.cc
> > +++ b/gcc/cp/optimize.cc
> > @@ -166,6 +166,7 @@ build_delete_destructor_body (tree delete_dtor, tree complete_dtor)
> > if (targetm.cxx.cdtor_returns_this ())
> > {
> > tree val = DECL_ARGUMENTS (delete_dtor);
> > + suppress_warning (val, OPT_Wuse_after_free);
> > val = build2 (MODIFY_EXPR, TREE_TYPE (val),
> > DECL_RESULT (delete_dtor), val);
> > add_stmt (build_stmt (0, RETURN_EXPR, val));
> > diff --git a/gcc/gimple-ssa-warn-access.cc b/gcc/gimple-ssa-warn-access.cc
> > index 8bc33eeb6fa..484bcd34c25 100644
> > --- a/gcc/gimple-ssa-warn-access.cc
> > +++ b/gcc/gimple-ssa-warn-access.cc
> > @@ -3880,9 +3880,17 @@ pass_waccess::warn_invalid_pointer (tree ref, gimple *use_stmt,
> > bool maybe, bool equality /* = false */)
> > {
> > /* Avoid printing the unhelpful "<unknown>" in the diagnostics. */
> > - if (ref && TREE_CODE (ref) == SSA_NAME
> > - && (!SSA_NAME_VAR (ref) || DECL_ARTIFICIAL (SSA_NAME_VAR (ref))))
> > - ref = NULL_TREE;
> > + if (ref && TREE_CODE (ref) == SSA_NAME)
> > + {
> > + tree var = SSA_NAME_VAR (ref);
> > + if (!var)
> > + ref = NULL_TREE;
> > + /* Don't warn for cases like when a cdtor returns 'this' on ARM. */
> > + else if (warning_suppressed_p (var, OPT_Wuse_after_free))
> > + return;
> > + else if (DECL_ARTIFICIAL (var))
> > + ref = NULL_TREE;
> > + }
> > location_t use_loc = gimple_location (use_stmt);
> > if (use_loc == UNKNOWN_LOCATION)
> > diff --git a/gcc/testsuite/g++.dg/warn/Wuse-after-free2.C b/gcc/testsuite/g++.dg/warn/Wuse-after-free2.C
> > new file mode 100644
> > index 00000000000..6d5f2bf01b5
> > --- /dev/null
> > +++ b/gcc/testsuite/g++.dg/warn/Wuse-after-free2.C
> > @@ -0,0 +1,10 @@
> > +// PR target/104213
> > +// { dg-do compile }
> > +// { dg-options "-Wuse-after-free" }
> > +
> > +class C
> > +{
> > + virtual ~C();
> > +};
> > +
> > +C::~C() {} // { dg-bogus "used after" }
> >
> > base-commit: aeac414923aa1e87986c7fc6f9b921d89a9b86cf
>
Marek
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] warn-access: Prevent -Wuse-after-free on ARM [PR104213]
2022-01-25 23:33 [PATCH] warn-access: Prevent -Wuse-after-free on ARM [PR104213] Marek Polacek
2022-01-26 0:35 ` Martin Sebor
@ 2022-01-26 15:24 ` Jason Merrill
2022-01-26 16:39 ` Martin Sebor
1 sibling, 1 reply; 6+ messages in thread
From: Jason Merrill @ 2022-01-26 15:24 UTC (permalink / raw)
To: Marek Polacek, GCC Patches; +Cc: Martin Sebor
On 1/25/22 18:33, Marek Polacek wrote:
> Here, -Wuse-after-free warns about using 'this' which, on ARM, cdtors
> return, as mandated by the EABI. To be entirely correct, it only
> requires it for C1 and C2 ctors and D2 and D1 dtors, but I don't feel
> like changing that now and possibly running into issues later on.
>
> This patch uses suppress_warning on 'this' for certain cdtor_returns_this
> cases in the C++ FE, and then warn_invalid_pointer makes use of this
> information and doesn't warn.
>
> In my first attempt I tried suppress_warning the MODIFY_EXPR or RETURN_EXPR
> we build in build_delete_destructor_body, but the complication is that
> the suppress_warning bits don't always survive gimplification; see e.g.
> gimplify_modify_expr where we do
>
> 6130 if (COMPARISON_CLASS_P (*from_p))
> 6131 copy_warning (assign, *from_p);
>
> but here we're not dealing with a comparison. Removing that check
> regresses uninit-pr74762.C. Adding copy_warning (assign, *expr_p)
> regresses c-c++-common/uninit-17.c.
>
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
OK if Martin doesn't have any suggestions.
> PR target/104213
>
> gcc/cp/ChangeLog:
>
> * decl.cc (finish_constructor_body): Suppress -Wuse-after-free.
> (finish_destructor_body): Likewise.
> * optimize.cc (build_delete_destructor_body): Likewise.
>
> gcc/ChangeLog:
>
> * gimple-ssa-warn-access.cc (pass_waccess::warn_invalid_pointer): Don't
> warn when the SSA_NAME_VAR of REF has supressed -Wuse-after-free.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/warn/Wuse-after-free2.C: New test.
> ---
> gcc/cp/decl.cc | 2 ++
> gcc/cp/optimize.cc | 1 +
> gcc/gimple-ssa-warn-access.cc | 14 +++++++++++---
> gcc/testsuite/g++.dg/warn/Wuse-after-free2.C | 10 ++++++++++
> 4 files changed, 24 insertions(+), 3 deletions(-)
> create mode 100644 gcc/testsuite/g++.dg/warn/Wuse-after-free2.C
>
> diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
> index 22d3dd1e2ad..6534a7fd320 100644
> --- a/gcc/cp/decl.cc
> +++ b/gcc/cp/decl.cc
> @@ -17315,6 +17315,7 @@ finish_constructor_body (void)
> add_stmt (build_stmt (input_location, LABEL_EXPR, cdtor_label));
>
> val = DECL_ARGUMENTS (current_function_decl);
> + suppress_warning (val, OPT_Wuse_after_free);
> val = build2 (MODIFY_EXPR, TREE_TYPE (val),
> DECL_RESULT (current_function_decl), val);
> /* Return the address of the object. */
> @@ -17408,6 +17409,7 @@ finish_destructor_body (void)
> tree val;
>
> val = DECL_ARGUMENTS (current_function_decl);
> + suppress_warning (val, OPT_Wuse_after_free);
> val = build2 (MODIFY_EXPR, TREE_TYPE (val),
> DECL_RESULT (current_function_decl), val);
> /* Return the address of the object. */
> diff --git a/gcc/cp/optimize.cc b/gcc/cp/optimize.cc
> index 4ad3f1dc9aa..13ab8b7361e 100644
> --- a/gcc/cp/optimize.cc
> +++ b/gcc/cp/optimize.cc
> @@ -166,6 +166,7 @@ build_delete_destructor_body (tree delete_dtor, tree complete_dtor)
> if (targetm.cxx.cdtor_returns_this ())
> {
> tree val = DECL_ARGUMENTS (delete_dtor);
> + suppress_warning (val, OPT_Wuse_after_free);
> val = build2 (MODIFY_EXPR, TREE_TYPE (val),
> DECL_RESULT (delete_dtor), val);
> add_stmt (build_stmt (0, RETURN_EXPR, val));
> diff --git a/gcc/gimple-ssa-warn-access.cc b/gcc/gimple-ssa-warn-access.cc
> index 8bc33eeb6fa..484bcd34c25 100644
> --- a/gcc/gimple-ssa-warn-access.cc
> +++ b/gcc/gimple-ssa-warn-access.cc
> @@ -3880,9 +3880,17 @@ pass_waccess::warn_invalid_pointer (tree ref, gimple *use_stmt,
> bool maybe, bool equality /* = false */)
> {
> /* Avoid printing the unhelpful "<unknown>" in the diagnostics. */
> - if (ref && TREE_CODE (ref) == SSA_NAME
> - && (!SSA_NAME_VAR (ref) || DECL_ARTIFICIAL (SSA_NAME_VAR (ref))))
> - ref = NULL_TREE;
> + if (ref && TREE_CODE (ref) == SSA_NAME)
> + {
> + tree var = SSA_NAME_VAR (ref);
> + if (!var)
> + ref = NULL_TREE;
> + /* Don't warn for cases like when a cdtor returns 'this' on ARM. */
> + else if (warning_suppressed_p (var, OPT_Wuse_after_free))
> + return;
> + else if (DECL_ARTIFICIAL (var))
> + ref = NULL_TREE;
> + }
>
> location_t use_loc = gimple_location (use_stmt);
> if (use_loc == UNKNOWN_LOCATION)
> diff --git a/gcc/testsuite/g++.dg/warn/Wuse-after-free2.C b/gcc/testsuite/g++.dg/warn/Wuse-after-free2.C
> new file mode 100644
> index 00000000000..6d5f2bf01b5
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/warn/Wuse-after-free2.C
> @@ -0,0 +1,10 @@
> +// PR target/104213
> +// { dg-do compile }
> +// { dg-options "-Wuse-after-free" }
> +
> +class C
> +{
> + virtual ~C();
> +};
> +
> +C::~C() {} // { dg-bogus "used after" }
>
> base-commit: aeac414923aa1e87986c7fc6f9b921d89a9b86cf
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] warn-access: Prevent -Wuse-after-free on ARM [PR104213]
2022-01-26 15:24 ` Jason Merrill
@ 2022-01-26 16:39 ` Martin Sebor
2022-01-26 17:21 ` [PATCH v2] " Marek Polacek
0 siblings, 1 reply; 6+ messages in thread
From: Martin Sebor @ 2022-01-26 16:39 UTC (permalink / raw)
To: Jason Merrill, Marek Polacek, GCC Patches; +Cc: Martin Sebor
On 1/26/22 08:24, Jason Merrill via Gcc-patches wrote:
> On 1/25/22 18:33, Marek Polacek wrote:
>> Here, -Wuse-after-free warns about using 'this' which, on ARM, cdtors
>> return, as mandated by the EABI. To be entirely correct, it only
>> requires it for C1 and C2 ctors and D2 and D1 dtors, but I don't feel
>> like changing that now and possibly running into issues later on.
>>
>> This patch uses suppress_warning on 'this' for certain cdtor_returns_this
>> cases in the C++ FE, and then warn_invalid_pointer makes use of this
>> information and doesn't warn.
>>
>> In my first attempt I tried suppress_warning the MODIFY_EXPR or
>> RETURN_EXPR
>> we build in build_delete_destructor_body, but the complication is that
>> the suppress_warning bits don't always survive gimplification; see e.g.
>> gimplify_modify_expr where we do
>>
>> 6130 if (COMPARISON_CLASS_P (*from_p))
>> 6131 copy_warning (assign, *from_p);
>>
>> but here we're not dealing with a comparison. Removing that check
>> regresses uninit-pr74762.C. Adding copy_warning (assign, *expr_p)
>> regresses c-c++-common/uninit-17.c.
>>
>> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
>
> OK if Martin doesn't have any suggestions.
Nothing further from me.
Thanks
Martin
>
>> PR target/104213
>>
>> gcc/cp/ChangeLog:
>>
>> * decl.cc (finish_constructor_body): Suppress -Wuse-after-free.
>> (finish_destructor_body): Likewise.
>> * optimize.cc (build_delete_destructor_body): Likewise.
>>
>> gcc/ChangeLog:
>>
>> * gimple-ssa-warn-access.cc (pass_waccess::warn_invalid_pointer):
>> Don't
>> warn when the SSA_NAME_VAR of REF has supressed -Wuse-after-free.
>>
>> gcc/testsuite/ChangeLog:
>>
>> * g++.dg/warn/Wuse-after-free2.C: New test.
>> ---
>> gcc/cp/decl.cc | 2 ++
>> gcc/cp/optimize.cc | 1 +
>> gcc/gimple-ssa-warn-access.cc | 14 +++++++++++---
>> gcc/testsuite/g++.dg/warn/Wuse-after-free2.C | 10 ++++++++++
>> 4 files changed, 24 insertions(+), 3 deletions(-)
>> create mode 100644 gcc/testsuite/g++.dg/warn/Wuse-after-free2.C
>>
>> diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
>> index 22d3dd1e2ad..6534a7fd320 100644
>> --- a/gcc/cp/decl.cc
>> +++ b/gcc/cp/decl.cc
>> @@ -17315,6 +17315,7 @@ finish_constructor_body (void)
>> add_stmt (build_stmt (input_location, LABEL_EXPR, cdtor_label));
>> val = DECL_ARGUMENTS (current_function_decl);
>> + suppress_warning (val, OPT_Wuse_after_free);
>> val = build2 (MODIFY_EXPR, TREE_TYPE (val),
>> DECL_RESULT (current_function_decl), val);
>> /* Return the address of the object. */
>> @@ -17408,6 +17409,7 @@ finish_destructor_body (void)
>> tree val;
>> val = DECL_ARGUMENTS (current_function_decl);
>> + suppress_warning (val, OPT_Wuse_after_free);
>> val = build2 (MODIFY_EXPR, TREE_TYPE (val),
>> DECL_RESULT (current_function_decl), val);
>> /* Return the address of the object. */
>> diff --git a/gcc/cp/optimize.cc b/gcc/cp/optimize.cc
>> index 4ad3f1dc9aa..13ab8b7361e 100644
>> --- a/gcc/cp/optimize.cc
>> +++ b/gcc/cp/optimize.cc
>> @@ -166,6 +166,7 @@ build_delete_destructor_body (tree delete_dtor,
>> tree complete_dtor)
>> if (targetm.cxx.cdtor_returns_this ())
>> {
>> tree val = DECL_ARGUMENTS (delete_dtor);
>> + suppress_warning (val, OPT_Wuse_after_free);
>> val = build2 (MODIFY_EXPR, TREE_TYPE (val),
>> DECL_RESULT (delete_dtor), val);
>> add_stmt (build_stmt (0, RETURN_EXPR, val));
>> diff --git a/gcc/gimple-ssa-warn-access.cc
>> b/gcc/gimple-ssa-warn-access.cc
>> index 8bc33eeb6fa..484bcd34c25 100644
>> --- a/gcc/gimple-ssa-warn-access.cc
>> +++ b/gcc/gimple-ssa-warn-access.cc
>> @@ -3880,9 +3880,17 @@ pass_waccess::warn_invalid_pointer (tree ref,
>> gimple *use_stmt,
>> bool maybe, bool equality /* = false */)
>> {
>> /* Avoid printing the unhelpful "<unknown>" in the diagnostics. */
>> - if (ref && TREE_CODE (ref) == SSA_NAME
>> - && (!SSA_NAME_VAR (ref) || DECL_ARTIFICIAL (SSA_NAME_VAR (ref))))
>> - ref = NULL_TREE;
>> + if (ref && TREE_CODE (ref) == SSA_NAME)
>> + {
>> + tree var = SSA_NAME_VAR (ref);
>> + if (!var)
>> + ref = NULL_TREE;
>> + /* Don't warn for cases like when a cdtor returns 'this' on
>> ARM. */
>> + else if (warning_suppressed_p (var, OPT_Wuse_after_free))
>> + return;
>> + else if (DECL_ARTIFICIAL (var))
>> + ref = NULL_TREE;
>> + }
>> location_t use_loc = gimple_location (use_stmt);
>> if (use_loc == UNKNOWN_LOCATION)
>> diff --git a/gcc/testsuite/g++.dg/warn/Wuse-after-free2.C
>> b/gcc/testsuite/g++.dg/warn/Wuse-after-free2.C
>> new file mode 100644
>> index 00000000000..6d5f2bf01b5
>> --- /dev/null
>> +++ b/gcc/testsuite/g++.dg/warn/Wuse-after-free2.C
>> @@ -0,0 +1,10 @@
>> +// PR target/104213
>> +// { dg-do compile }
>> +// { dg-options "-Wuse-after-free" }
>> +
>> +class C
>> +{
>> + virtual ~C();
>> +};
>> +
>> +C::~C() {} // { dg-bogus "used after" }
>>
>> base-commit: aeac414923aa1e87986c7fc6f9b921d89a9b86cf
>
^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH v2] warn-access: Prevent -Wuse-after-free on ARM [PR104213]
2022-01-26 16:39 ` Martin Sebor
@ 2022-01-26 17:21 ` Marek Polacek
0 siblings, 0 replies; 6+ messages in thread
From: Marek Polacek @ 2022-01-26 17:21 UTC (permalink / raw)
To: Martin Sebor; +Cc: Jason Merrill, GCC Patches, Martin Sebor
On Wed, Jan 26, 2022 at 09:39:46AM -0700, Martin Sebor wrote:
> On 1/26/22 08:24, Jason Merrill via Gcc-patches wrote:
> > On 1/25/22 18:33, Marek Polacek wrote:
> > > Here, -Wuse-after-free warns about using 'this' which, on ARM, cdtors
> > > return, as mandated by the EABI. To be entirely correct, it only
> > > requires it for C1 and C2 ctors and D2 and D1 dtors, but I don't feel
> > > like changing that now and possibly running into issues later on.
> > >
> > > This patch uses suppress_warning on 'this' for certain cdtor_returns_this
> > > cases in the C++ FE, and then warn_invalid_pointer makes use of this
> > > information and doesn't warn.
> > >
> > > In my first attempt I tried suppress_warning the MODIFY_EXPR or
> > > RETURN_EXPR
> > > we build in build_delete_destructor_body, but the complication is that
> > > the suppress_warning bits don't always survive gimplification; see e.g.
> > > gimplify_modify_expr where we do
> > >
> > > 6130 if (COMPARISON_CLASS_P (*from_p))
> > > 6131 copy_warning (assign, *from_p);
> > >
> > > but here we're not dealing with a comparison. Removing that check
> > > regresses uninit-pr74762.C. Adding copy_warning (assign, *expr_p)
> > > regresses c-c++-common/uninit-17.c.
> > >
> > > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
> >
> > OK if Martin doesn't have any suggestions.
>
> Nothing further from me.
Here's what I've pushed then (it adds the testcase Martin mentioned earlier).
Thanks,
-- >8 --
Here, -Wuse-after-free warns about using 'this' which, on ARM, cdtors
return, as mandated by the EABI. To be entirely correct, it only
requires it for C1 and C2 ctors and D2 and D1 dtors, but I don't feel
like changing that now and possibly running into issues later on.
This patch uses suppress_warning on 'this' for certain cdtor_returns_this
cases in the C++ FE, and then warn_invalid_pointer makes use of this
information and doesn't warn.
In my first attempt I tried suppress_warning the MODIFY_EXPR or RETURN_EXPR
we build in build_delete_destructor_body, but the complication is that
the suppress_warning bits don't always survive gimplification; see e.g.
gimplify_modify_expr where we do
6130 if (COMPARISON_CLASS_P (*from_p))
6131 copy_warning (assign, *from_p);
but here we're not dealing with a comparison. Removing that check
regresses uninit-pr74762.C. Adding copy_warning (assign, *expr_p)
regresses c-c++-common/uninit-17.c.
PR target/104213
gcc/cp/ChangeLog:
* decl.cc (finish_constructor_body): Suppress -Wuse-after-free.
(finish_destructor_body): Likewise.
* optimize.cc (build_delete_destructor_body): Likewise.
gcc/ChangeLog:
* gimple-ssa-warn-access.cc (pass_waccess::warn_invalid_pointer): Don't
warn when the SSA_NAME_VAR of REF has supressed -Wuse-after-free.
gcc/testsuite/ChangeLog:
* g++.dg/warn/Wuse-after-free2.C: New test.
* g++.dg/warn/Wuse-after-free3.C: New test.
---
gcc/cp/decl.cc | 2 ++
gcc/cp/optimize.cc | 1 +
gcc/gimple-ssa-warn-access.cc | 14 +++++++++++---
gcc/testsuite/g++.dg/warn/Wuse-after-free2.C | 10 ++++++++++
gcc/testsuite/g++.dg/warn/Wuse-after-free3.C | 16 ++++++++++++++++
5 files changed, 40 insertions(+), 3 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/warn/Wuse-after-free2.C
create mode 100644 gcc/testsuite/g++.dg/warn/Wuse-after-free3.C
diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index 22d3dd1e2ad..6534a7fd320 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -17315,6 +17315,7 @@ finish_constructor_body (void)
add_stmt (build_stmt (input_location, LABEL_EXPR, cdtor_label));
val = DECL_ARGUMENTS (current_function_decl);
+ suppress_warning (val, OPT_Wuse_after_free);
val = build2 (MODIFY_EXPR, TREE_TYPE (val),
DECL_RESULT (current_function_decl), val);
/* Return the address of the object. */
@@ -17408,6 +17409,7 @@ finish_destructor_body (void)
tree val;
val = DECL_ARGUMENTS (current_function_decl);
+ suppress_warning (val, OPT_Wuse_after_free);
val = build2 (MODIFY_EXPR, TREE_TYPE (val),
DECL_RESULT (current_function_decl), val);
/* Return the address of the object. */
diff --git a/gcc/cp/optimize.cc b/gcc/cp/optimize.cc
index 4ad3f1dc9aa..13ab8b7361e 100644
--- a/gcc/cp/optimize.cc
+++ b/gcc/cp/optimize.cc
@@ -166,6 +166,7 @@ build_delete_destructor_body (tree delete_dtor, tree complete_dtor)
if (targetm.cxx.cdtor_returns_this ())
{
tree val = DECL_ARGUMENTS (delete_dtor);
+ suppress_warning (val, OPT_Wuse_after_free);
val = build2 (MODIFY_EXPR, TREE_TYPE (val),
DECL_RESULT (delete_dtor), val);
add_stmt (build_stmt (0, RETURN_EXPR, val));
diff --git a/gcc/gimple-ssa-warn-access.cc b/gcc/gimple-ssa-warn-access.cc
index afcf0f71bec..3dcaf4230b8 100644
--- a/gcc/gimple-ssa-warn-access.cc
+++ b/gcc/gimple-ssa-warn-access.cc
@@ -3880,9 +3880,17 @@ pass_waccess::warn_invalid_pointer (tree ref, gimple *use_stmt,
bool maybe, bool equality /* = false */)
{
/* Avoid printing the unhelpful "<unknown>" in the diagnostics. */
- if (ref && TREE_CODE (ref) == SSA_NAME
- && (!SSA_NAME_VAR (ref) || DECL_ARTIFICIAL (SSA_NAME_VAR (ref))))
- ref = NULL_TREE;
+ if (ref && TREE_CODE (ref) == SSA_NAME)
+ {
+ tree var = SSA_NAME_VAR (ref);
+ if (!var)
+ ref = NULL_TREE;
+ /* Don't warn for cases like when a cdtor returns 'this' on ARM. */
+ else if (warning_suppressed_p (var, OPT_Wuse_after_free))
+ return;
+ else if (DECL_ARTIFICIAL (var))
+ ref = NULL_TREE;
+ }
location_t use_loc = gimple_location (use_stmt);
if (use_loc == UNKNOWN_LOCATION)
diff --git a/gcc/testsuite/g++.dg/warn/Wuse-after-free2.C b/gcc/testsuite/g++.dg/warn/Wuse-after-free2.C
new file mode 100644
index 00000000000..6d5f2bf01b5
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wuse-after-free2.C
@@ -0,0 +1,10 @@
+// PR target/104213
+// { dg-do compile }
+// { dg-options "-Wuse-after-free" }
+
+class C
+{
+ virtual ~C();
+};
+
+C::~C() {} // { dg-bogus "used after" }
diff --git a/gcc/testsuite/g++.dg/warn/Wuse-after-free3.C b/gcc/testsuite/g++.dg/warn/Wuse-after-free3.C
new file mode 100644
index 00000000000..1862ac8b09d
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wuse-after-free3.C
@@ -0,0 +1,16 @@
+// PR target/104213
+// { dg-do compile }
+// { dg-options "-Wuse-after-free" }
+// FIXME: We should not output the warning twice.
+
+struct A
+{
+ virtual ~A ();
+ void f ();
+};
+
+A::~A ()
+{
+ operator delete (this);
+ f (); // { dg-warning "used after" }
+} // { dg-warning "used after" }
base-commit: 00d8321124123daf41f7c51526355a5a610cdeb8
--
2.34.1
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2022-01-26 17:22 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
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2022-01-25 23:33 [PATCH] warn-access: Prevent -Wuse-after-free on ARM [PR104213] Marek Polacek
2022-01-26 0:35 ` Martin Sebor
2022-01-26 0:49 ` Marek Polacek
2022-01-26 15:24 ` Jason Merrill
2022-01-26 16:39 ` Martin Sebor
2022-01-26 17:21 ` [PATCH v2] " Marek Polacek
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