On Sat, May 30, 2020 at 10:35:47AM -0700, Eric Biggers wrote:
On Sat, May 30, 2020 at 10:18:14AM -0700, Matthew Wilcox wrote:
On Fri, May 29, 2020 at 11:02:16PM -0700, Eric Biggers wrote:
- if (len <= DNAME_INLINE_LEN - 1) {
unsigned int i;for (i = 0; i < len; i++)strbuf[i] = READ_ONCE(str[i]);strbuf[len] = 0;This READ_ONCE is going to force the compiler to use byte accesses. What's wrong with using a plain memcpy()?
It's undefined behavior when the source can be concurrently modified.
Compilers can assume that it's not, and remove the memcpy() (instead just using the source data directly) if they can prove that the destination array is never modified again before it goes out of scope.
Do you have any suggestions that don't involve undefined behavior?
void *memcpy_unsafe(void *dst, volatile void *src, __kernel_size_t);
It can just call memcpy() of course, but the compiler can't reason about this function because it's not a stdlib function.