On Fri, 9 Jan 2009, Matthew Wilcox wrote: > > That seems like valuable feedback to give to the GCC developers. Well, one thing we should remember is that the kernel really _is_ special. The kernel not only does things no other program tends to do (inline asms are unusual in the first place - many of them are literally due to system issues like atomic accesses and interrupts that simply aren't an issue in user space, or that need so much abstraction that they aren't inlinable anyway). But the kernel also has totally different requirements in other ways. When was the last time you did user space programming and needed to get a backtrace from a user with register info because you simply don't have the hardware that he has? IOW, debugging in user space tends to be much more about trying to reproduce the bug - in a way that we often cannot in the kernel. User space in general is much more reproducible, since it's seldom as hardware- or timing-dependent (threading does change the latter, but usually user space threading is not _nearly_ as aggressive as the kernel has to be). So the thing is, even if gcc was "perfect", it would likely be perfect for a different audience than the kernel. Do you think _any_ user space programmer worries about the stack space being a few hundred bytes larger because the compiler inlined two functions, and caused stack usage to be sum of them instead of just the maximum of the two? So we do have special issues. And exactly _because_ we have special issues we should also expect that some compiler defaults simply won't ever really be appropriate for us. Linus -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
