[PATCH v4 2/2] bug: introduce ASSERT_VAR_CAN_HOLD()

Petr Tesarik
2024-03-25T08:31:47Z

From: Petr Tesarik <petr.tesarik1@huawei-partners.com>

Introduce an ASSERT_VAR_CAN_HOLD() macro to check at build time that a
variable can hold the given value.

Use this macro in swiotlb to make sure that the list and pad_slots fields
of struct io_tlb_slot are big enough to hold the maximum possible value of
IO_TLB_SEGSIZE.

Signed-off-by: Petr Tesarik <petr.tesarik1@huawei-partners.com>
---
include/linux/build_bug.h | 10 ++++++++++
kernel/dma/swiotlb.c | 2 ++
2 files changed, 12 insertions(+)

diff --git a/include/linux/build_bug.h b/include/linux/build_bug.h
index 3aa3640f8c18..6e2486508af0 100644
--- a/include/linux/build_bug.h
+++ b/include/linux/build_bug.h
@@ -86,4 +86,14 @@
"Offset of " #field " in " #type " has changed.")

+/*
+ * Compile time check that a variable can hold the given value
+ */
+#define ASSERT_VAR_CAN_HOLD(var, value) ({ \
+ typeof(value) __val = (value); \
+ typeof(var) __tmp = __val; \
+ BUILD_BUG_ON_MSG(__tmp != __val, \
+ #var " cannot hold " #value "."); \
+})
+
#endif /* _LINUX_BUILD_BUG_H */
diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index d7a8cb93ef2d..a34ea2c35446 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -285,6 +285,8 @@ static void swiotlb_init_io_tlb_pool(struct io_tlb_pool *mem, phys_addr_t start,
mem->areas[i].used = 0;
}

+ ASSERT_VAR_CAN_HOLD(mem->slots[0].list, IO_TLB_SEGSIZE);
+ ASSERT_VAR_CAN_HOLD(mem->slots[0].pad_slots, IO_TLB_SEGSIZE);
for (i = 0; i < mem->nslabs; i++) {
mem->slots[i].list = min(IO_TLB_SEGSIZE - io_tlb_offset(i),
mem->nslabs - i);
--
2.34.1