[committed] analyzer: stop -ftrivial-auto-var-init from suppressing uninit warnings [PR104270]

[committed] analyzer: stop -ftrivial-auto-var-init from suppressing uninit warnings [PR104270]

[David Malcolm]

GCC 12 has gained two features for dealing with uninitialized variables:

(a) a new -Wanalyzer-use-of-uninitialized-value warning within -fanalyzer
for interprocedural path-sensitive detection of ununit uses, and

(b) a new -ftrivial-auto-var-init option for mitigating some uses of
uninit variables

It turns out that using (b) was thwarting (a), as it led to -fanalyzer
seeing calls to IFN_DEFERRED_INIT, which -fanalyzer wasn't
special-casing, thus treating it as initializing the variables in
question, and thus silencing -Wanalyzer-use-of-uninitialized-value on
them.

invoke.texi says:

"GCC still considers an automatic variable that doesn't have an explicit
initializer as uninitialized, @option{-Wuninitialized} will still report
warning messages on such automatic variables."

and thus -Wanalyzer-use-of-uninitialized-value ought to as well.

This patch adds special-case handling to -fanalyzer for
IFN_DEFERRED_INIT,  so that -fanalyzer will warn on uninit uses of
variables that are mitigated by -ftrivial-auto-var-init.

Successfully bootstrapped & regrtested on x86_64-pc-linux-gnu.

Not strictly a regression, but as this affects two new GCC 12 features
it seems appropriate to fix in stage 4.

Pushed to trunk as r12-6997-g9b4eee5fd158c4ee75d1f1000debbf5082fb9b56.

gcc/analyzer/ChangeLog:
	PR analyzer/104270
	* region-model.cc (region_model::on_call_pre): Handle
	IFN_DEFERRED_INIT.

gcc/testsuite/ChangeLog:
	PR analyzer/104270
	* gcc.dg/analyzer/uninit-trivial-auto-var-init-pattern.c: New
	test.
	* gcc.dg/analyzer/uninit-trivial-auto-var-init-uninitialized.c:
	New test.
	* gcc.dg/analyzer/uninit-trivial-auto-var-init-zero.c: New test.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>
---
 gcc/analyzer/region-model.cc                           | 10 ++++++++++
 .../analyzer/uninit-trivial-auto-var-init-pattern.c    |  7 +++++++
 .../uninit-trivial-auto-var-init-uninitialized.c       |  7 +++++++
 .../analyzer/uninit-trivial-auto-var-init-zero.c       |  7 +++++++
 4 files changed, 31 insertions(+)
 create mode 100644 gcc/testsuite/gcc.dg/analyzer/uninit-trivial-auto-var-init-pattern.c
 create mode 100644 gcc/testsuite/gcc.dg/analyzer/uninit-trivial-auto-var-init-uninitialized.c
 create mode 100644 gcc/testsuite/gcc.dg/analyzer/uninit-trivial-auto-var-init-zero.c

diff --git a/gcc/analyzer/region-model.cc b/gcc/analyzer/region-model.cc
index 6810cf508d9..4c312b053f8 100644
--- a/gcc/analyzer/region-model.cc
+++ b/gcc/analyzer/region-model.cc
@@ -1109,6 +1109,16 @@ region_model::on_call_pre (const gcall *call, region_model_context *ctxt,
 
   bool unknown_side_effects = false;
 
+  /* Special-case for IFN_DEFERRED_INIT.
+     We want to report uninitialized variables with -fanalyzer (treating
+     -ftrivial-auto-var-init= as purely a mitigation feature).
+     Handle IFN_DEFERRED_INIT by treating it as no-op: don't touch the
+     lhs of the call, so that it is still uninitialized from the point of
+     view of the analyzer.  */
+  if (gimple_call_internal_p (call)
+      && gimple_call_internal_fn (call) == IFN_DEFERRED_INIT)
+    return false;
+
   /* Some of the cases below update the lhs of the call based on the
      return value, but not all.  Provide a default value, which may
      get overwritten below.  */
diff --git a/gcc/testsuite/gcc.dg/analyzer/uninit-trivial-auto-var-init-pattern.c b/gcc/testsuite/gcc.dg/analyzer/uninit-trivial-auto-var-init-pattern.c
new file mode 100644
index 00000000000..0b78dc65267
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/analyzer/uninit-trivial-auto-var-init-pattern.c
@@ -0,0 +1,7 @@
+/* { dg-additional-options "-ftrivial-auto-var-init=pattern" } */
+
+int test_1 (void)
+{
+  int i; /* { dg-message "region created on stack here" } */
+  return i; /* { dg-warning "use of uninitialized value 'i'" } */
+}
diff --git a/gcc/testsuite/gcc.dg/analyzer/uninit-trivial-auto-var-init-uninitialized.c b/gcc/testsuite/gcc.dg/analyzer/uninit-trivial-auto-var-init-uninitialized.c
new file mode 100644
index 00000000000..124d3a327b8
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/analyzer/uninit-trivial-auto-var-init-uninitialized.c
@@ -0,0 +1,7 @@
+/* { dg-additional-options "-ftrivial-auto-var-init=uninitialized" } */
+
+int test_1 (void)
+{
+  int i; /* { dg-message "region created on stack here" } */
+  return i; /* { dg-warning "use of uninitialized value 'i'" } */
+}
diff --git a/gcc/testsuite/gcc.dg/analyzer/uninit-trivial-auto-var-init-zero.c b/gcc/testsuite/gcc.dg/analyzer/uninit-trivial-auto-var-init-zero.c
new file mode 100644
index 00000000000..ef7dc674867
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/analyzer/uninit-trivial-auto-var-init-zero.c
@@ -0,0 +1,7 @@
+/* { dg-additional-options "-ftrivial-auto-var-init=zero" } */
+
+int test_1 (void)
+{
+  int i; /* { dg-message "region created on stack here" } */
+  return i; /* { dg-warning "use of uninitialized value 'i'" } */
+}
-- 
2.26.3

Re: [committed] analyzer: stop -ftrivial-auto-var-init from suppressing uninit warnings [PR104270]

[Qing Zhao]

Hi, David,

Thank you for fixing this issue!

> On Feb 2, 2022, at 9:06 AM, David Malcolm via Gcc-patches <gcc-patches@gcc.gnu.org> wrote:
> 
> GCC 12 has gained two features for dealing with uninitialized variables:
> 
> (a) a new -Wanalyzer-use-of-uninitialized-value warning within -fanalyzer
> for interprocedural path-sensitive detection of ununit uses, and
> 
> (b) a new -ftrivial-auto-var-init option for mitigating some uses of
> uninit variables
> 
> It turns out that using (b) was thwarting (a), as it led to -fanalyzer
> seeing calls to IFN_DEFERRED_INIT, which -fanalyzer wasn't
> special-casing, thus treating it as initializing the variables in
> question, and thus silencing -Wanalyzer-use-of-uninitialized-value on
> them.
> 
> invoke.texi says:
> 
> "GCC still considers an automatic variable that doesn't have an explicit
> initializer as uninitialized, @option{-Wuninitialized} will still report
> warning messages on such automatic variables."
> 
> and thus -Wanalyzer-use-of-uninitialized-value ought to as well.

Then should we updated the invoke.texi to include this as well?

thanks.

Qing
> 
> This patch adds special-case handling to -fanalyzer for
> IFN_DEFERRED_INIT,  so that -fanalyzer will warn on uninit uses of
> variables that are mitigated by -ftrivial-auto-var-init.
> 
> Successfully bootstrapped & regrtested on x86_64-pc-linux-gnu.
> 
> Not strictly a regression, but as this affects two new GCC 12 features
> it seems appropriate to fix in stage 4.
> 
> Pushed to trunk as r12-6997-g9b4eee5fd158c4ee75d1f1000debbf5082fb9b56.
> 
> gcc/analyzer/ChangeLog:
> 	PR analyzer/104270
> 	* region-model.cc (region_model::on_call_pre): Handle
> 	IFN_DEFERRED_INIT.
> 
> gcc/testsuite/ChangeLog:
> 	PR analyzer/104270
> 	* gcc.dg/analyzer/uninit-trivial-auto-var-init-pattern.c: New
> 	test.
> 	* gcc.dg/analyzer/uninit-trivial-auto-var-init-uninitialized.c:
> 	New test.
> 	* gcc.dg/analyzer/uninit-trivial-auto-var-init-zero.c: New test.
> 
> Signed-off-by: David Malcolm <dmalcolm@redhat.com>
> ---
> gcc/analyzer/region-model.cc                           | 10 ++++++++++
> .../analyzer/uninit-trivial-auto-var-init-pattern.c    |  7 +++++++
> .../uninit-trivial-auto-var-init-uninitialized.c       |  7 +++++++
> .../analyzer/uninit-trivial-auto-var-init-zero.c       |  7 +++++++
> 4 files changed, 31 insertions(+)
> create mode 100644 gcc/testsuite/gcc.dg/analyzer/uninit-trivial-auto-var-init-pattern.c
> create mode 100644 gcc/testsuite/gcc.dg/analyzer/uninit-trivial-auto-var-init-uninitialized.c
> create mode 100644 gcc/testsuite/gcc.dg/analyzer/uninit-trivial-auto-var-init-zero.c
> 
> diff --git a/gcc/analyzer/region-model.cc b/gcc/analyzer/region-model.cc
> index 6810cf508d9..4c312b053f8 100644
> --- a/gcc/analyzer/region-model.cc
> +++ b/gcc/analyzer/region-model.cc
> @@ -1109,6 +1109,16 @@ region_model::on_call_pre (const gcall *call, region_model_context *ctxt,
> 
>   bool unknown_side_effects = false;
> 
> +  /* Special-case for IFN_DEFERRED_INIT.
> +     We want to report uninitialized variables with -fanalyzer (treating
> +     -ftrivial-auto-var-init= as purely a mitigation feature).
> +     Handle IFN_DEFERRED_INIT by treating it as no-op: don't touch the
> +     lhs of the call, so that it is still uninitialized from the point of
> +     view of the analyzer.  */
> +  if (gimple_call_internal_p (call)
> +      && gimple_call_internal_fn (call) == IFN_DEFERRED_INIT)
> +    return false;
> +
>   /* Some of the cases below update the lhs of the call based on the
>      return value, but not all.  Provide a default value, which may
>      get overwritten below.  */
> diff --git a/gcc/testsuite/gcc.dg/analyzer/uninit-trivial-auto-var-init-pattern.c b/gcc/testsuite/gcc.dg/analyzer/uninit-trivial-auto-var-init-pattern.c
> new file mode 100644
> index 00000000000..0b78dc65267
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/analyzer/uninit-trivial-auto-var-init-pattern.c
> @@ -0,0 +1,7 @@
> +/* { dg-additional-options "-ftrivial-auto-var-init=pattern" } */
> +
> +int test_1 (void)
> +{
> +  int i; /* { dg-message "region created on stack here" } */
> +  return i; /* { dg-warning "use of uninitialized value 'i'" } */
> +}
> diff --git a/gcc/testsuite/gcc.dg/analyzer/uninit-trivial-auto-var-init-uninitialized.c b/gcc/testsuite/gcc.dg/analyzer/uninit-trivial-auto-var-init-uninitialized.c
> new file mode 100644
> index 00000000000..124d3a327b8
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/analyzer/uninit-trivial-auto-var-init-uninitialized.c
> @@ -0,0 +1,7 @@
> +/* { dg-additional-options "-ftrivial-auto-var-init=uninitialized" } */
> +
> +int test_1 (void)
> +{
> +  int i; /* { dg-message "region created on stack here" } */
> +  return i; /* { dg-warning "use of uninitialized value 'i'" } */
> +}
> diff --git a/gcc/testsuite/gcc.dg/analyzer/uninit-trivial-auto-var-init-zero.c b/gcc/testsuite/gcc.dg/analyzer/uninit-trivial-auto-var-init-zero.c
> new file mode 100644
> index 00000000000..ef7dc674867
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/analyzer/uninit-trivial-auto-var-init-zero.c
> @@ -0,0 +1,7 @@
> +/* { dg-additional-options "-ftrivial-auto-var-init=zero" } */
> +
> +int test_1 (void)
> +{
> +  int i; /* { dg-message "region created on stack here" } */
> +  return i; /* { dg-warning "use of uninitialized value 'i'" } */
> +}
> -- 
> 2.26.3
> 

[committed] docs: mention analyzer interaction with -ftrivial-auto-var-init [PR104270]

[David Malcolm]

On Wed, 2022-02-02 at 17:14 +0000, Qing Zhao wrote:
> Hi, David,
> 
> Thank you for fixing this issue!
> 
> > On Feb 2, 2022, at 9:06 AM, David Malcolm via Gcc-patches <
> > gcc-patches@gcc.gnu.org> wrote:
> > 
> > GCC 12 has gained two features for dealing with uninitialized
> > variables:
> > 
> > (a) a new -Wanalyzer-use-of-uninitialized-value warning within
> > -fanalyzer
> > for interprocedural path-sensitive detection of ununit uses, and
> > 
> > (b) a new -ftrivial-auto-var-init option for mitigating some uses
> > of
> > uninit variables
> > 
> > It turns out that using (b) was thwarting (a), as it led to
> > -fanalyzer
> > seeing calls to IFN_DEFERRED_INIT, which -fanalyzer wasn't
> > special-casing, thus treating it as initializing the variables in
> > question, and thus silencing -Wanalyzer-use-of-uninitialized-value
> > on
> > them.
> > 
> > invoke.texi says:
> > 
> > "GCC still considers an automatic variable that doesn't have an
> > explicit
> > initializer as uninitialized, @option{-Wuninitialized} will still
> > report
> > warning messages on such automatic variables."
> > 
> > and thus -Wanalyzer-use-of-uninitialized-value ought to as well.
> 
> Then should we updated the invoke.texi to include this as well?

Good point; I've taken the liberty of pushing the following to trunk
as a followup (as r12-7007-gfb45d8e692d41d)

Thanks
Dave

gcc/ChangeLog:
	PR analyzer/104270
	* doc/invoke.texi (-ftrivial-auto-var-init=): Add reference to
	-Wanalyzer-use-of-uninitialized-value to paragraph documenting that
	-ftrivial-auto-var-init= doesn't suppress warnings.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>
---
 gcc/doc/invoke.texi | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index cfd415110cd..b1b8cc806c7 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -12304,7 +12304,8 @@ Initialize automatic variables with either a pattern or with zeroes to increase
 the security and predictability of a program by preventing uninitialized memory
 disclosure and use.
 GCC still considers an automatic variable that doesn't have an explicit
-initializer as uninitialized, @option{-Wuninitialized} will still report
+initializer as uninitialized, @option{-Wuninitialized} and
+@option{-Wanalyzer-use-of-uninitialized-value} will still report
 warning messages on such automatic variables.
 With this option, GCC will also initialize any padding of automatic variables
 that have structure or union types to zeroes.
-- 
2.26.3