/*
* thunks.S - assembly helpers for mixed-bitness code
* Copyright (c) 2015 Andrew Lutomirski
*
* This program is free software; you can redistribute it and/or modify
* it under the terms and conditions of the GNU General Public License,
* version 2, as published by the Free Software Foundation.
*
* This program is distributed in the hope it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* These are little helpers that make it easier to switch bitness on
* the fly.
*/
.text
.global call32_from_64
.type call32_from_64, @function
call32_from_64:
// rdi: stack to use
// esi: function to call
// Save registers
pushq %rbx
pushq %rbp
pushq %r12
pushq %r13
pushq %r14
pushq %r15
pushfq
// Switch stacks
mov %rsp,(%rdi)
mov %rdi,%rsp
// Switch to compatibility mode
pushq $0x23 /* USER32_CS */
pushq $1f
lretq
1:
.code32
// Call the function
call *%esi
// Switch back to long mode
jmp $0x33,$1f
.code64
1:
// Restore the stack
mov (%rsp),%rsp
// Restore registers
popfq
popq %r15
popq %r14
popq %r13
popq %r12
popq %rbp
popq %rbx
ret
.size call32_from_64, .-call32_from_64
op-back
The hwlat tracer creates a kernel thread at start of the tracer. It is
pinned to a single CPU and will move to the next CPU after each period of
running. If the user modifies the migration thread's affinity, it will not
change after that happens.
The original code created the thread at the first instance it was called,
but later was changed to destroy the thread after the tracer was finished,
and would not be created until the next instance of the tracer was
established. The code that initialized the affinity was only called on the
initial instantiation of the tracer. After that, it was not initialized, and
the previous affinity did not match the current newly created one, making
it appear that the user modified the thread's affinity when it did not, and
the thread failed to migrate again.
Cc: stable@vger.kernel.org
Fixes: 0330f7aa8ee6 ("tracing: Have hwlat trace migrate across tracing_cpumask CPUs")
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>