Re: [PATCH] Add no_sanitize_coverage attribute.

["Martin Liška" <mliska@suse.cz>]

On 5/20/21 10:45 AM, Marco Elver wrote:
> On Thu, 20 May 2021 at 10:33, Martin Liška <mliska@suse.cz> wrote:
>> Hello.
>>
>> The patch implements one missing attribute which can be used for per-function
>> disabling of coverage sanitization.
>>
>> Patch can bootstrap on x86_64-linux-gnu and survives regression tests.
> 
> Thanks for implementing this so quickly. One thing I just have to
> double check, is if this works with always_inline (not instrumented if
> inlined into no_sanitize),

No, in this case it's instrumented (if caller has not set the attribute).

> and inline (not inlined if inline fn is
> no_sanitize_coverage).

No again, it's not blocking inlining.

> Just like the other no_sanitize* do. The test doesn't mention them.

It's aligned with similar issue that was discussed some time ago:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94722#c9

Martin

> 
> Thanks,
> -- Marco
> 
>> Ready to be installed?
>> Thanks,
>> Martin
>>
>> gcc/ChangeLog:
>>
>>          * asan.h (sanitize_coverage_p): New function.
>>          * doc/extend.texi: Document it.
>>          * fold-const.c (fold_range_test): Use sanitize_flags_p
>>          instead of flag_sanitize_coverage.
>>          (fold_truth_andor): Likewise.
>>          * sancov.c: Likewise.
>>          * tree-ssa-ifcombine.c (ifcombine_ifandif): Likewise.
>>
>> gcc/c-family/ChangeLog:
>>
>>          * c-attribs.c (handle_no_sanitize_coverage_attribute): New.
>>
>> gcc/testsuite/ChangeLog:
>>
>>          * gcc.dg/sancov/attribute.c: New test.
>> ---
>>    gcc/asan.h                              | 10 ++++++++++
>>    gcc/c-family/c-attribs.c                | 20 ++++++++++++++++++++
>>    gcc/doc/extend.texi                     |  6 ++++++
>>    gcc/fold-const.c                        |  4 ++--
>>    gcc/sancov.c                            |  4 ++--
>>    gcc/testsuite/gcc.dg/sancov/attribute.c | 15 +++++++++++++++
>>    gcc/tree-ssa-ifcombine.c                |  4 +++-
>>    7 files changed, 58 insertions(+), 5 deletions(-)
>>    create mode 100644 gcc/testsuite/gcc.dg/sancov/attribute.c
>>
>> diff --git a/gcc/asan.h b/gcc/asan.h
>> index f110f1db563..8c0b2baf170 100644
>> --- a/gcc/asan.h
>> +++ b/gcc/asan.h
>> @@ -249,4 +249,14 @@ sanitize_flags_p (unsigned int flag, const_tree fn = current_function_decl)
>>      return result_flags;
>>    }
>>
>> +/* Return true when coverage sanitization should happend for FN function.  */
>> +
>> +static inline bool
>> +sanitize_coverage_p (const_tree fn = current_function_decl)
>> +{
>> +  return (flag_sanitize_coverage
>> +         && lookup_attribute ("no_sanitize_coverage",
>> +                              DECL_ATTRIBUTES (fn)) == NULL_TREE);
>> +}
>> +
>>    #endif /* TREE_ASAN */
>> diff --git a/gcc/c-family/c-attribs.c b/gcc/c-family/c-attribs.c
>> index ccf9e4ccf0b..671b27c3200 100644
>> --- a/gcc/c-family/c-attribs.c
>> +++ b/gcc/c-family/c-attribs.c
>> @@ -62,6 +62,8 @@ static tree handle_no_address_safety_analysis_attribute (tree *, tree, tree,
>>                                                           int, bool *);
>>    static tree handle_no_sanitize_undefined_attribute (tree *, tree, tree, int,
>>                                                      bool *);
>> +static tree handle_no_sanitize_coverage_attribute (tree *, tree, tree, int,
>> +                                                  bool *);
>>    static tree handle_asan_odr_indicator_attribute (tree *, tree, tree, int,
>>                                                   bool *);
>>    static tree handle_stack_protect_attribute (tree *, tree, tree, int, bool *);
>> @@ -449,6 +451,8 @@ const struct attribute_spec c_common_attribute_table[] =
>>                                handle_no_sanitize_thread_attribute, NULL },
>>      { "no_sanitize_undefined",  0, 0, true, false, false, false,
>>                                handle_no_sanitize_undefined_attribute, NULL },
>> +  { "no_sanitize_coverage",   0, 0, true, false, false, false,
>> +                             handle_no_sanitize_coverage_attribute, NULL },
>>      { "asan odr indicator",     0, 0, true, false, false, false,
>>                                handle_asan_odr_indicator_attribute, NULL },
>>      { "warning",                      1, 1, true,  false, false, false,
>> @@ -1211,6 +1215,22 @@ handle_no_sanitize_undefined_attribute (tree *node, tree name, tree, int,
>>      return NULL_TREE;
>>    }
>>
>> +/* Handle a "no_sanitize_coverage" attribute; arguments as in
>> +   struct attribute_spec.handler.  */
>> +
>> +static tree
>> +handle_no_sanitize_coverage_attribute (tree *node, tree name, tree, int,
>> +                                      bool *no_add_attrs)
>> +{
>> +  if (TREE_CODE (*node) != FUNCTION_DECL)
>> +    {
>> +      warning (OPT_Wattributes, "%qE attribute ignored", name);
>> +      *no_add_attrs = true;
>> +    }
>> +
>> +  return NULL_TREE;
>> +}
>> +
>>    /* Handle an "asan odr indicator" attribute; arguments as in
>>       struct attribute_spec.handler.  */
>>
>> diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
>> index 826804e6149..3ddeb0dee3a 100644
>> --- a/gcc/doc/extend.texi
>> +++ b/gcc/doc/extend.texi
>> @@ -3415,6 +3415,12 @@ The @code{no_sanitize_undefined} attribute on functions is used
>>    to inform the compiler that it should not check for undefined behavior
>>    in the function when compiling with the @option{-fsanitize=undefined} option.
>>
>> +@item no_sanitize_coverage
>> +@cindex @code{no_sanitize_coverage} function attribute
>> +The @code{no_sanitize_coverage} attribute on functions is used
>> +to inform the compiler that it should not do coverage-guided
>> +fuzzing code instrumentation (@option{-fsanitize-coverage}).
>> +
>>    @item no_split_stack
>>    @cindex @code{no_split_stack} function attribute
>>    @opindex fsplit-stack
>> diff --git a/gcc/fold-const.c b/gcc/fold-const.c
>> index 3be9c15e6b2..d088187a057 100644
>> --- a/gcc/fold-const.c
>> +++ b/gcc/fold-const.c
>> @@ -6016,7 +6016,7 @@ fold_range_test (location_t loc, enum tree_code code, tree type,
>>        logical_op_non_short_circuit
>>          = param_logical_op_non_short_circuit;
>>      if (logical_op_non_short_circuit
>> -      && !flag_sanitize_coverage
>> +      && !sanitize_coverage_p ()
>>          && lhs != 0 && rhs != 0
>>          && (code == TRUTH_ANDIF_EXPR || code == TRUTH_ORIF_EXPR)
>>          && operand_equal_p (lhs, rhs, 0))
>> @@ -9652,7 +9652,7 @@ fold_truth_andor (location_t loc, enum tree_code code, tree type,
>>        logical_op_non_short_circuit
>>          = param_logical_op_non_short_circuit;
>>      if (logical_op_non_short_circuit
>> -      && !flag_sanitize_coverage
>> +      && !sanitize_coverage_p ()
>>          && (code == TRUTH_AND_EXPR
>>              || code == TRUTH_ANDIF_EXPR
>>              || code == TRUTH_OR_EXPR
>> diff --git a/gcc/sancov.c b/gcc/sancov.c
>> index d656c37cae9..9cfbd425def 100644
>> --- a/gcc/sancov.c
>> +++ b/gcc/sancov.c
>> @@ -313,9 +313,9 @@ public:
>>        return new pass_sancov<O0> (m_ctxt);
>>      }
>>      virtual bool
>> -  gate (function *)
>> +  gate (function *fun)
>>      {
>> -    return flag_sanitize_coverage && (!O0 || !optimize);
>> +    return sanitize_coverage_p (fun->decl) && (!O0 || !optimize);
>>      }
>>      virtual unsigned int
>>      execute (function *fun)
>> diff --git a/gcc/testsuite/gcc.dg/sancov/attribute.c b/gcc/testsuite/gcc.dg/sancov/attribute.c
>> new file mode 100644
>> index 00000000000..bf6dbd4bae7
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.dg/sancov/attribute.c
>> @@ -0,0 +1,15 @@
>> +/* { dg-do compile } */
>> +/* { dg-options "-fsanitize-coverage=trace-pc -fdump-tree-optimized" } */
>> +
>> +void foo(void)
>> +{
>> +}
>> +
>> +void
>> +__attribute__((no_sanitize_coverage))
>> +bar(void)
>> +{
>> +}
>> +
>> +
>> +/* { dg-final { scan-tree-dump-times "__builtin___sanitizer_cov_trace_pc \\(\\)" 1 "optimized" } } */
>> diff --git a/gcc/tree-ssa-ifcombine.c b/gcc/tree-ssa-ifcombine.c
>> index 836a12d6b80..f93e04aa4df 100644
>> --- a/gcc/tree-ssa-ifcombine.c
>> +++ b/gcc/tree-ssa-ifcombine.c
>> @@ -40,6 +40,8 @@ along with GCC; see the file COPYING3.  If not see
>>    #include "gimplify-me.h"
>>    #include "tree-cfg.h"
>>    #include "tree-ssa.h"
>> +#include "attribs.h"
>> +#include "asan.h"
>>
>>    #ifndef LOGICAL_OP_NON_SHORT_CIRCUIT
>>    #define LOGICAL_OP_NON_SHORT_CIRCUIT \
>> @@ -567,7 +569,7 @@ ifcombine_ifandif (basic_block inner_cond_bb, bool inner_inv,
>>            if (param_logical_op_non_short_circuit != -1)
>>              logical_op_non_short_circuit
>>                = param_logical_op_non_short_circuit;
>> -         if (!logical_op_non_short_circuit || flag_sanitize_coverage)
>> +         if (!logical_op_non_short_circuit || sanitize_coverage_p ())
>>              return false;
>>            /* Only do this optimization if the inner bb contains only the conditional. */
>>            if (!gsi_one_before_end_p (gsi_start_nondebug_after_labels_bb (inner_cond_bb)))
>> --
>> 2.31.1
>>