The __ubsan_handle_shift_out_of_bounds handler would be called for code
shifting a one into the sign bit like (1 << 31), which is all too common
in barebox. It's technically UB, but it's so prevalent that it's highly
unlikely to be treated by a compiler as anything else than the
standard-compliant (1U << 31).
Check for this case here and ignore it selectively.
Signed-off-by: Ahmad Fatoum <ahmad@xxxxxx>
---
lib/ubsan.c | 20 ++++++++++++++++++++
1 file changed, 20 insertions(+)
diff --git a/lib/ubsan.c b/lib/ubsan.c
index 89ca6e580bce..41a5731dda66 100644
--- a/lib/ubsan.c
+++ b/lib/ubsan.c
@@ -382,6 +382,26 @@ void __ubsan_handle_shift_out_of_bounds(struct shift_out_of_bounds_data *data,
if (suppress_report(&data->location))
return;
+ /* This handler would be called for code shifting a one into the
+ * sign bit like (1 << 31), which is all too common in barebox.
+ * It's technically UB, but it's so prevalent that it's highly
+ * unlikely to be treated by a compiler as anything else than the
+ * standard-compliant (1U << 31). Thus check for this case here
+ * and ignore it selectively
+ */
+ if (type_is_signed(lhs_type)) {
+ s_max lhs_int, rhs_int;
+
+ lhs_int = get_signed_val(lhs_type, lhs);
+ rhs_int = get_signed_val(rhs_type, rhs);
+
+ if (fls(lhs_int) + rhs_int == type_bit_width(lhs_type)) {
+ pr_debug("signed left shift of %lld by %lld ignored.\n",
+ (s64)lhs_int, (s64)rhs_int);
+ return;
+ }
+ }
+
ubsan_prologue(&data->location, &flags);
val_to_string(rhs_str, sizeof(rhs_str), rhs_type, rhs);
--
2.20.1
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