Re: [RFC PATCH] UBSan: run-time undefined behavior sanity checker

[Rasmus Villemoes <linux@rasmusvillemoes.dk>]

On Mon, Oct 20 2014, Andrey Ryabinin <a.ryabinin@samsung.com> wrote:

> UBSan uses compile-time instrumentation to catch undefined behavior (UB).
> Compiler inserts code that perform certain kinds of
> checks before operations that could cause UB.
> If check fails (i.e. UB detected) __ubsan_handle_* function called.
> to print error message.
>
> So the most of the work is done by compiler.
> This patch just implements ubsan handlers printing errors.
>
> GCC supports this since 4.9, however upcoming GCC 5.0 has
> more checkers implemented.

[...]

> +
> +#define REPORTED_BIT 31
> +#define COLUMN_MASK (~(1U << REPORTED_BIT))
> +
> +static bool is_disabled(struct source_location *location)
> +{
> +	return test_and_set_bit(REPORTED_BIT,
> +				(unsigned long *)&location->column);
> +}

[...]

> +struct source_location {
> +	const char *file_name;
> +	u32 line;
> +	u32 column;
> +};


AFAICT, this introduces UB and/or memory corruption on big-endian
systems with BITS_PER_LONG==64. (Also, on both LE and BE 64 bit systems,
there's the issue of the alignment of location->column, which is likely
to be 4-but-not-8 byte aligned).

Is the layout of struct source_location dictated by gcc? 

Rasmus