On Sun, 14 Nov 2021 at 02:07, David Malcolm via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> This patch adds two new attributes. The followup patch makes use of
> the attributes in -fanalyzer.
>
> gcc/c-family/ChangeLog:
> * c-attribs.c (attr_noreturn_exclusions): Add
> "returns_zero_on_failure" and "returns_zero_on_success".
> (attr_returns_twice_exclusions): Likewise.
> (attr_returns_zero_on_exclusions): New.
> (c_common_attribute_table): Add "returns_zero_on_failure" and
> "returns_zero_on_success".
> (handle_returns_zero_on_attributes): New.
>
> gcc/ChangeLog:
> * doc/extend.texi (Common Function Attributes): Document
> "returns_zero_on_failure" and "returns_zero_on_success".
>
> gcc/testsuite/ChangeLog:
> * c-c++-common/attr-returns-zero-on-1.c: New test.
>
> Signed-off-by: David Malcolm <dmalc...@redhat.com>
> ---
> gcc/c-family/c-attribs.c | 37 ++++++++++
> gcc/doc/extend.texi | 16 +++++
> .../c-c++-common/attr-returns-zero-on-1.c | 68 +++++++++++++++++++
> 3 files changed, 121 insertions(+)
> create mode 100644 gcc/testsuite/c-c++-common/attr-returns-zero-on-1.c
>
> diff --git a/gcc/c-family/c-attribs.c b/gcc/c-family/c-attribs.c
> index 100c2dabab2..9e03156de5e 100644
> --- a/gcc/c-family/c-attribs.c
> +++ b/gcc/c-family/c-attribs.c
> @@ -153,6 +153,7 @@ static tree handle_argspec_attribute (tree *, tree, tree,
> int, bool *);
> static tree handle_fnspec_attribute (tree *, tree, tree, int, bool *);
> static tree handle_warn_unused_attribute (tree *, tree, tree, int, bool *);
> static tree handle_returns_nonnull_attribute (tree *, tree, tree, int, bool
> *);
> +static tree handle_returns_zero_on_attributes (tree *, tree, tree, int, bool
> *);
> static tree handle_omp_declare_simd_attribute (tree *, tree, tree, int,
> bool *);
> static tree handle_omp_declare_variant_attribute (tree *, tree, tree, int,
> @@ -221,6 +222,8 @@ extern const struct attribute_spec::exclusions
> attr_noreturn_exclusions[] =
> ATTR_EXCL ("pure", true, true, true),
> ATTR_EXCL ("returns_twice", true, true, true),
> ATTR_EXCL ("warn_unused_result", true, true, true),
> + ATTR_EXCL ("returns_zero_on_failure", true, true, true),
> + ATTR_EXCL ("returns_zero_on_success", true, true, true),
> ATTR_EXCL (NULL, false, false, false),
> };
>
> @@ -235,6 +238,8 @@ attr_warn_unused_result_exclusions[] =
> static const struct attribute_spec::exclusions
> attr_returns_twice_exclusions[] =
> {
> ATTR_EXCL ("noreturn", true, true, true),
> + ATTR_EXCL ("returns_zero_on_failure", true, true, true),
> + ATTR_EXCL ("returns_zero_on_success", true, true, true),
> ATTR_EXCL (NULL, false, false, false),
> };
>
> @@ -275,6 +280,16 @@ static const struct attribute_spec::exclusions
> attr_stack_protect_exclusions[] =
> ATTR_EXCL (NULL, false, false, false),
> };
>
> +/* Exclusions that apply to the returns_zero_on_* attributes. */
> +static const struct attribute_spec::exclusions
> + attr_returns_zero_on_exclusions[] =
> +{
> + ATTR_EXCL ("noreturn", true, true, true),
> + ATTR_EXCL ("returns_twice", true, true, true),
> + ATTR_EXCL ("returns_zero_on_failure", true, true, true),
> + ATTR_EXCL ("returns_zero_on_success", true, true, true),
> + ATTR_EXCL (NULL, false, false, false),
> +};
>
> /* Table of machine-independent attributes common to all C-like languages.
>
> @@ -493,6 +508,12 @@ const struct attribute_spec c_common_attribute_table[] =
> handle_warn_unused_attribute, NULL },
> { "returns_nonnull", 0, 0, false, true, true, false,
> handle_returns_nonnull_attribute, NULL },
> + { "returns_zero_on_failure",0, 0, false, true, true, false,
> + handle_returns_zero_on_attributes,
> + attr_returns_zero_on_exclusions },
> + { "returns_zero_on_success",0, 0, false, true, true, false,
> + handle_returns_zero_on_attributes,
> + attr_returns_zero_on_exclusions },
> { "omp declare simd", 0, -1, true, false, false, false,
> handle_omp_declare_simd_attribute, NULL },
> { "omp declare variant base", 0, -1, true, false, false, false,
> @@ -5660,6 +5681,22 @@ handle_returns_nonnull_attribute (tree *node, tree
> name, tree, int,
> return NULL_TREE;
> }
>
> +/* Handle "returns_zero_on_failure" and "returns_zero_on_success" attributes;
> + arguments as in struct attribute_spec.handler. */
> +
> +static tree
> +handle_returns_zero_on_attributes (tree *node, tree name, tree, int,
> + bool *no_add_attrs)
> +{
> + if (!INTEGRAL_TYPE_P (TREE_TYPE (*node)))
> + {
> + error ("%qE attribute on a function not returning an integral type",
> + name);
> + *no_add_attrs = true;
> + }
> + return NULL_TREE;
Hi David,
Just curious if a warning should be emitted if the function is marked
with the attribute but it's return value isn't actually 0 ?
There are other constants like -1 or 1 that are often used to indicate
error, so maybe tweak the attribute to
take the integer as an argument ?
Sth like returns_int_on_success(cst) / returns_int_on_failure(cst) ?
Also, would it make sense to extend it for pointers too for returning
NULL on success / failure ?
Thanks,
Prathamesh
> +}
> +
> /* Handle a "designated_init" attribute; arguments as in
> struct attribute_spec.handler. */
>
> diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
> index e9f47519df2..5a6ef464779 100644
> --- a/gcc/doc/extend.texi
> +++ b/gcc/doc/extend.texi
> @@ -3784,6 +3784,22 @@ function. Examples of such functions are
> @code{setjmp} and @code{vfork}.
> The @code{longjmp}-like counterpart of such function, if any, might need
> to be marked with the @code{noreturn} attribute.
>
> +@item returns_zero_on_failure
> +@cindex @code{returns_zero_on_failure} function attribute
> +The @code{returns_zero_on_failure} attribute hints that the function
> +can succeed or fail, returning non-zero on success and zero on failure.
> +This is used by the @option{-fanalyzer} option to consider both outcomes
> +separately, which may improve how it explores error-handling paths, and
> +how such outcomes are labelled in diagnostics. It is also a hint
> +to the human reader of the source code.
> +
> +@item returns_zero_on_success
> +@cindex @code{returns_zero_on_success} function attribute
> +The @code{returns_zero_on_success} attribute is identical to the
> +@code{returns_zero_on_failure} attribute, apart from having the
> +opposite interpretation of the return value: zero on success, non-zero
> +on failure.
> +
> @item section ("@var{section-name}")
> @cindex @code{section} function attribute
> @cindex functions in arbitrary sections
> diff --git a/gcc/testsuite/c-c++-common/attr-returns-zero-on-1.c
> b/gcc/testsuite/c-c++-common/attr-returns-zero-on-1.c
> new file mode 100644
> index 00000000000..5475dfe61db
> --- /dev/null
> +++ b/gcc/testsuite/c-c++-common/attr-returns-zero-on-1.c
> @@ -0,0 +1,68 @@
> +/* Verify the parsing of the "returns_zero_on_{sucess|failure}" attributes.
> */
> +
> +/* Correct usage. */
> +
> +extern int test_int_return_s ()
> + __attribute__((returns_zero_on_success));
> +extern long test_long_return_f ()
> + __attribute__((returns_zero_on_failure));
> +
> +/* Should complain if not a function. */
> +
> +extern int not_a_function_s
> + __attribute__((returns_zero_on_success)); /* { dg-warning
> "'returns_zero_on_success' attribute only applies to function types" } */
> +extern int not_a_function_f
> + __attribute__((returns_zero_on_failure)); /* { dg-warning
> "'returns_zero_on_failure' attribute only applies to function types" } */
> +
> +/* Should complain if return type is not integral. */
> +
> +extern void test_void_return_s ()
> + __attribute__((returns_zero_on_success)); /* { dg-error
> "'returns_zero_on_success' attribute on a function not returning an integral
> type" } */
> +extern void test_void_return_f ()
> + __attribute__((returns_zero_on_failure)); /* { dg-error
> "'returns_zero_on_failure' attribute on a function not returning an integral
> type" } */
> +
> +extern void *test_void_star_return_s ()
> + __attribute__((returns_zero_on_success)); /* { dg-error
> "'returns_zero_on_success' attribute on a function not returning an integral
> type" } */
> +extern void *test_void_star_return_f ()
> + __attribute__((returns_zero_on_failure)); /* { dg-error
> "'returns_zero_on_failure' attribute on a function not returning an integral
> type" } */
> +
> +/* (and this prevents mixing with returns_non_null, which requires a
> pointer). */
> +
> +/* Should complain if more than one returns_* attribute. */
> +
> +extern int test_void_returns_s_f ()
> + __attribute__((returns_zero_on_success))
> + __attribute__((returns_zero_on_failure)); /* { dg-warning "ignoring
> attribute 'returns_zero_on_failure' because it conflicts with attribute
> 'returns_zero_on_success'" } */
> +extern int test_void_returns_f_s ()
> + __attribute__((returns_zero_on_failure))
> + __attribute__((returns_zero_on_success)); /* { dg-warning "ignoring
> attribute 'returns_zero_on_success' because it conflicts with attribute
> 'returns_zero_on_failure'" } */
> +
> +/* Should complain if mixed with "noreturn". */
> +
> +extern int test_noreturn_returns_s ()
> + __attribute__((noreturn))
> + __attribute__((returns_zero_on_success)); /* { dg-warning "ignoring
> attribute 'returns_zero_on_success' because it conflicts with attribute
> 'noreturn'" } */
> +extern int test_returns_s_noreturn ()
> + __attribute__((returns_zero_on_success))
> + __attribute__((noreturn)); /* { dg-warning "ignoring attribute 'noreturn'
> because it conflicts with attribute 'returns_zero_on_success'" } */
> +extern int test_noreturn_returns_f ()
> + __attribute__((noreturn))
> + __attribute__((returns_zero_on_failure)); /* { dg-warning "ignoring
> attribute 'returns_zero_on_failure' because it conflicts with attribute
> 'noreturn'" } */
> +extern int test_returns_f_noreturn ()
> + __attribute__((returns_zero_on_failure))
> + __attribute__((noreturn)); /* { dg-warning "ignoring attribute 'noreturn'
> because it conflicts with attribute 'returns_zero_on_failure'" } */
> +
> +/* Should complain if mixed with "returns_twice". */
> +
> +extern int test_returns_twice_returns_s ()
> + __attribute__((returns_twice))
> + __attribute__((returns_zero_on_success)); /* { dg-warning "ignoring
> attribute 'returns_zero_on_success' because it conflicts with attribute
> 'returns_twice'" } */
> +extern int test_returns_s_returns_twice ()
> + __attribute__((returns_zero_on_success))
> + __attribute__((returns_twice)); /* { dg-warning "ignoring attribute
> 'returns_twice' because it conflicts with attribute
> 'returns_zero_on_success'" } */
> +extern int test_returns_twice_returns_f ()
> + __attribute__((returns_twice))
> + __attribute__((returns_zero_on_failure)); /* { dg-warning "ignoring
> attribute 'returns_zero_on_failure' because it conflicts with attribute
> 'returns_twice'" } */
> +extern int test_returns_f_returns_twice ()
> + __attribute__((returns_zero_on_failure))
> + __attribute__((returns_twice)); /* { dg-warning "ignoring attribute
> 'returns_twice' because it conflicts with attribute
> 'returns_zero_on_failure'" } */
> --
> 2.26.3
>
