Hi,
On 2024/5/18 15:52, Zhang Boyang wrote:
Hi,
On 2024/5/17 20:56, Gao Xiang wrote:
The following EROFS patch will use this helper to handle overflow
ALIGN_UP() cases.
Signed-off-by: Gao Xiang <hsiang...@linux.alibaba.com>
---
include/grub/safemath.h | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
diff --git a/include/grub/safemath.h b/include/grub/safemath.h
index fbd9b5925..baaea0ef4 100644
--- a/include/grub/safemath.h
+++ b/include/grub/safemath.h
@@ -32,6 +32,22 @@
#define grub_cast(a, res) grub_add ((a), 0, (res))
+#define ALIGN_UP_OVF(v, align, res) \
+({ \
+ bool __failed; \
+ typeof(v) a; \
I think "a" should be changed to some unique name like "__a", because
variable shadowing might occur:
int a = 10, b = 4;
if (!ALIGN_UP_OVF(a, b, &a)) { // "a" is shadowed
printf("a=%d\n", a);
}
The uniqueness of variable name can reduce the possibility of variable
shadowing, but it will not eliminate the pitfall.
https://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html
The ultimate solution would be a macro-like "static inline" function,
but I'm not sure whether a inline function is appropriate in grub headers.
Oh, sorry, I'm wrong. This marco can't be a inline function because
function signature requires specific types to be given to a variable,
which will eliminate the efforts of overflow macros.
By the way, I think it would be better to write a comment about "align
should not equal to 0 and it must be a power of 2"
Zhang Boyang
+ \
+ __failed = grub_sub ((typeof(v))(align), 1, &a); \
The cast "(typeof(v))" is unnecessary and it will silently ignore
overflow/underflow.
Zhang Boyang
+ if (__failed == false) \
+ { \
+ __failed = grub_add (v, a, res); \
+ if (__failed == false) \
+ { \
+ *(res) &= ~a; \
+ } \
+ } \
+__failed;})
+
#else
#error gcc 5.1 or newer or clang 8.0 or newer is required
#endif
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