On Tue, 7 May 2019 07:54:53 -0700 Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > And honestly, I absolutely despise PeterZ's patch. The notion that we > should suddenly say that "oh, the i386 kernel stack is odd" after 28 > years of having that standard i386 stack is just crazy. And this: > > arch/x86/entry/entry_32.S | 136 ++++++++++++++++++++++++++++------- > ... > 12 files changed, 323 insertions(+), 140 deletions(-) > > > vs this: > > arch/x86/entry/entry_32.S | 7 +++- > ... > 6 files changed, 120 insertions(+), 13 deletions(-) > > is still pretty damn conclusive. Not to mention that the simple > approach had a truly mindbogglingly simple solution with no actual > subtle changes anywhere else. > > So I still claim that we should do my patch. Because it is SIMPLE. > It's straightforward, and I can explain every single line in it. Even > if I spent *way* too long until I realized that the "trivial" > memmove() wasn't so trivial. Yes, band-aids are usually simpler than a proper fix. We have 28 years of hacks built on hacks. There's a lot of hacks in the C code to handle the differences between the crappy way x86_32 does pt_regs and the proper way x86_64 does them. If the goal was just to add another band-aid to this, we now have one more subtle work around caused by two different methods being handled by a single code base. I don't look at Peter's patch and think "this is the solution for int3 emulate calls". I see Peter's patch as "Thanks God, we are finally getting rid of the cause of all theses work around hacks all over the place! and oh by the way, we can easily implement int3 call emulation because of it". To implement your way, we need to change how the int3 handler works. It will be the only exception handler having to return regs, otherwise it will crash. Sure, it's an easily solution for the one off change of emulating calls, but it's just another complex work around that nobody is going to understand in 5 years. -- Steve
