On Tue, 30 Apr 2019 11:33:21 -0700 Linus Torvalds torvalds@linux-foundation.org wrote:
On Tue, Apr 30, 2019 at 10:49 AM Steven Rostedt rostedt@goodmis.org wrote:
+asm(
".text\n"/* Trampoline for function update with interrupts enabled */".global ftrace_emulate_call_irqoff\n"".type ftrace_emulate_call_irqoff, @function\n""ftrace_emulate_call_irqoff:\n\t""push %gs:ftrace_bp_call_return\n\t"Well, as mentioned in my original suggestion, this won't work on 32-bit, or on UP. They have different models for per-cpu data (32-bti uses %fs, and UP doesn't use a segment override at all).
Ah, yeah, I forgot about 32-bit. I could easily make this use fs as well, and for UP, just use a static variable.
Maybe we just don't care about UP at all for this code, of course.
And maybe we can make the decision to also make 32-bit just not use this either - so maybe the code is ok per se, just needs to make sure it never triggers for the cases that it's not written for..
"ftrace_emulate_call_update_irqoff:\n\t""push %gs:ftrace_bp_call_return\n\t""sti\n\t""jmp *ftrace_update_func_call\n".. and this should then use the "push push sti ret" model instead.
Plus get updated for objtool complaints.
Yeah, I see that now. Somehow it disappeared when I looked for it after making some other changes. I can update it.
Anyway, since Andy really likes the entry code change, can we have that patch in parallel and judge the difference that way? Iirc, that was x86-64 specific too.
Note, I don't think live kernel patching supports 32 bit anyway, so that may not be an issue.
Josh,
When you come back to the office, can you look into that method?
-- Steve