> Am 12.10.2024 um 16:43 schrieb Martin Uecker <uec...@tugraz.at>:
>
>
> There is code which should not fail at run-time. For this,
> it is helpful to get a warning when a compiler inserts traps
> (e.g. sanitizers, hardbools, __builtin_trap(), etc.).
>
> Having a warning for this also has many other use cases, e.g.
> one can use it with some sanitizer to rule out that some
> piece of code has certain undefined behavior such as
> signed overflow or undefined behavior in left-shifts
> (one gets a warning if the optimizer does not prove the
> trap is dead and it is emitted).
>
> Another potential use case could be writing tests.
>
>
> Bootstrapped and regression tested on x64_84.
>
>
> Add warning option that warns when a trap is generated.
>
> This adds a warning option -Wtrap that is emitted in
> expand_builtin_trap. It can be used to verify that traps
> are generated or - more importantly - are not generated
> under various conditions, e.g. for UBSan with -fsanitize-trap,
> hardbools, etc.
Isn’t it better to diagnose with more context from the callers that insert the
trap?
> gcc/ChangeLog:
> * common.opt (Wtrap): Add warning.
> * builtins.cc (expand_builtin_trap): Add warning.
> * doc/invoke.texi (Wtrap): Document warning.
>
> gcc/testsuite/ChangeLog:
> * gcc.dg/Wtrap.c: New test.
>
> diff --git a/gcc/builtins.cc b/gcc/builtins.cc
> index 37c7c98e5c7..76268f62481 100644
> --- a/gcc/builtins.cc
> +++ b/gcc/builtins.cc
> @@ -5896,6 +5896,14 @@ expand_builtin_assume_aligned (tree exp, rtx target)
> void
> expand_builtin_trap (void)
> {
> + if (warn_trap)
> + {
> + location_t current_location =
> + linemap_unwind_to_first_non_reserved_loc (line_table, input_location,
> + NULL);
> + warning_at (current_location, OPT_Wtrap, "trap generated");
> + }
> +
> if (targetm.have_trap ())
> {
> rtx_insn *insn = emit_insn (targetm.gen_trap ());
> diff --git a/gcc/common.opt b/gcc/common.opt
> index 12b25ff486d..1cc4936ebbf 100644
> --- a/gcc/common.opt
> +++ b/gcc/common.opt
> @@ -812,6 +812,10 @@ Wsystem-headers
> Common Var(warn_system_headers) Warning
> Do not suppress warnings from system headers.
>
> +Wtrap
> +Common Var(warn_trap) Warning
> +Warn whenever a trap is generated.
> +
> Wtrampolines
> Common Var(warn_trampolines) Warning
> Warn whenever a trampoline is generated.
> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> index 575dffd2a2f..68833c4350f 100644
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -8784,6 +8784,14 @@ made up of data only and thus requires no special
> treatment. But, for
> most targets, it is made up of code and thus requires the stack to be
> made executable in order for the program to work properly.
>
> +@opindex Wtrap
> +@opindex Wno-trap
> +@item -Wtrap
> +Warn when explicit traps are generated. Traps may be generated for
> +a variety of reasons, e.g. when using the undefined behavior sanitizer
> +together with @option{-fsanitize-trap=undefined}.
> +
> +
> @opindex Wfloat-equal
> @opindex Wno-float-equal
> @item -Wfloat-equal
> diff --git a/gcc/testsuite/gcc.dg/Wtrap.c b/gcc/testsuite/gcc.dg/Wtrap.c
> new file mode 100644
> index 00000000000..2f2878f9d45
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/Wtrap.c
> @@ -0,0 +1,8 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -Wtrap" } */
> +
> +void foo(void)
> +{
> + __builtin_trap(); /* { dg-warning "trap generated" } */
> +}
> +
>
