On 2021/7/3 3:56, Matthew Wilcox wrote: > On Fri, Jul 02, 2021 at 05:21:09PM +0800, Zhen Lei wrote: >> Move the evaluation expression "size - offset" after the "if (offset < 0)" >> judgment statement to eliminate a false positive produced by the UBSAN. >> >> No functional changes. >> >> ========================================================================== >> UBSAN: Undefined behaviour in fs/iomap.c:1435:9 >> signed integer overflow: >> 0 - -9223372036854775808 cannot be represented in type 'long long int' > > I don't understand. I thought we defined the behaviour of signed > integer overflow in the kernel with whatever-the-gcc-flag-is? -9223372036854775808 ==> 0x8000000000000000 ==> -0 I don't fully understand what you mean. This is triggered by explicit error injection '-0' at runtime, which should not be detected by compilation options. lseek(r1, 0x8000000000000000, 0x3) > > > . >
