Use a direct per-cpu reference for the GDT instead of using a scratch
register.
Signed-off-by: NBrian Gerst <brgerst@gmail.com>
LKML-Reference: <1280594903-6341-2-git-send-email-brgerst@gmail.com>
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

Set the callback to receive evtchns from Xen, using the
callback vector delivery mechanism.

The traditional way for receiving event channel notifications from Xen
is via the interrupts from the platform PCI device.
The callback vector is a newer alternative that allow us to receive
notifications on any vcpu and doesn't need any PCI support: we allocate
a vector exclusively to receive events, in the vector handler we don't
need to interact with the vlapic, therefore we avoid a VMEXIT.
Signed-off-by: NStefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: NSheng Yang <sheng@linux.intel.com>
Signed-off-by: NJeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

The cache flush denied error is an erratum on some AMD 486 clones.  If an invd
instruction is executed in userspace, the processor calls exception 19 (13 hex)
instead of #GP (13 decimal).  On cpus where XMM is not supported, redirect
exception 19 to do_general_protection().  Also, remove die_if_kernel(), since
this was the last user.
Signed-off-by: NBrian Gerst <brgerst@gmail.com>
LKML-Reference: <1269176446-2489-2-git-send-email-brgerst@gmail.com>
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

The arg should be in %eax, but that is clobbered by the return value
of clone.  The function pointer can be in any register.  Also, don't
push args onto the stack, since regparm(3) is the normal calling
convention now.
Signed-off-by: NBrian Gerst <brgerst@gmail.com>
LKML-Reference: <1260380084-3707-4-git-send-email-brgerst@gmail.com>
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

In the PTREGSCALL1 and 2 macros, we can trivially avoid an unnecessary
pipeline serialization, so do so.

In PTREGSCALLS3 this is much less clear-cut since we have to push a
new value to the stack.  Leave it alone for now assuming it is as good
as it is going to be; may want to check on Atom or another in-order
x86 to see if we can do better.
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>
Cc: Brian Gerst <brgerst@gmail.com>
LKML-Reference: <1260403316-5679-2-git-send-email-brgerst@gmail.com>

Change 32-bit sys_clone to new PTREGSCALL stub, and merge with 64-bit.
Signed-off-by: NBrian Gerst <brgerst@gmail.com>
LKML-Reference: <1260403316-5679-7-git-send-email-brgerst@gmail.com>
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

Convert these to new PTREGSCALL stubs.
Signed-off-by: NBrian Gerst <brgerst@gmail.com>
LKML-Reference: <1260403316-5679-6-git-send-email-brgerst@gmail.com>
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

Change 32-bit sys_sigaltstack to PTREGSCALL2, and merge with 64-bit.
Signed-off-by: NBrian Gerst <brgerst@gmail.com>
LKML-Reference: <1260403316-5679-5-git-send-email-brgerst@gmail.com>
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

Change 32-bit sys_execve to PTREGSCALL3, and merge with 64-bit.
Signed-off-by: NBrian Gerst <brgerst@gmail.com>
LKML-Reference: <1260403316-5679-4-git-send-email-brgerst@gmail.com>
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

Change 32-bit sys_iopl to PTREGSCALL1, and merge with 64-bit.
Signed-off-by: NBrian Gerst <brgerst@gmail.com>
LKML-Reference: <1260403316-5679-3-git-send-email-brgerst@gmail.com>
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

Add new stubs which add the pt_regs pointer as the last arg, matching
64-bit.  This will allow these syscalls to be easily merged.
Signed-off-by: NBrian Gerst <brgerst@gmail.com>
LKML-Reference: <1260403316-5679-2-git-send-email-brgerst@gmail.com>
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

The function graph tracer replaces the return address with a hook
to trace the exit of the function call. This hook will finish by
returning to the real location the function should return to.

But the current implementation uses a ret to jump to the real
return location. This causes a imbalance between calls and ret.
That is the original function does a call, the ret goes to the
handler and then the handler does a ret without a matching call.

Although the function graph tracer itself still breaks the branch
predictor by replacing the original ret, by using a second ret and
causing an imbalance, it breaks the predictor even more.

This patch replaces the ret with a jmp to keep the calls and ret
balanced. I tested this on one box and it showed a 1.7% increase in
performance. Another box only showed a small 0.3% increase. But no
box that I tested this on showed a decrease in performance by
making this change.
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>
Acked-by: NMathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <20091013203425.042034383@goodmis.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Move irq-exit functions to .kprobes.text section to protect against
kprobes recursion.

When I ran kprobe stress test on x86-32, I found below symbols
cause unrecoverable recursive probing:

	ret_from_exception
	ret_from_intr
	check_userspace
	restore_all
	restore_all_notrace
	restore_nocheck
	irq_return

And also, I found some interrupt/exception entry points that
cause similar problems.

This patch moves those symbols (including their container functions)
to .kprobes.text section to prevent any kprobes probing.
Signed-off-by: NMasami Hiramatsu <mhiramat@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Jim Keniston <jkenisto@us.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
LKML-Reference: <20090908164755.24050.81182.stgit@dhcp-100-2-132.bos.redhat.com>
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>

In case gcc does something funny with the stack frames, or the return
from function code, we would like to detect that.

An arch may implement passing of a variable that is unique to the
function and can be saved on entering a function and can be tested
when exiting the function. Usually the frame pointer can be used for
this purpose.

This patch also implements this for x86. Where it passes in the stack
frame of the parent function, and will test that frame on exit.

There was a case in x86_32 with optimize for size (-Os) where, for a
few functions, gcc would align the stack frame and place a copy of the
return address into it. The function graph tracer modified the copy and
not the actual return address. On return from the funtion, it did not go
to the tracer hook, but returned to the parent. This broke the function
graph tracer, because the return of the parent (where gcc did not do
this funky manipulation) returned to the location that the child function
was suppose to. This caused strange kernel crashes.

This test detected the problem and pointed out where the issue was.

This modifies the parameters of one of the functions that the arch
specific code calls, so it includes changes to arch code to accommodate
the new prototype.

Note, I notice that the parsic arch implements its own push_return_trace.
This is now a generic function and the ftrace_push_return_trace should be
used instead. This patch does not touch that code.

Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Helge Deller <deller@gmx.de>
Cc: Kyle McMartin <kyle@mcmartin.ca>
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>

asm/desc.h is included in three assembly files, but the only macro
it defines, GET_DESC_BASE, is never used. This patch removes the
includes, removes the macro GET_DESC_BASE and the ASSEMBLY guard
from asm/desc.h.
Signed-off-by: NAlexander van Heukelum <heukelum@fastmail.fm>
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

The espfix code triggers if we have a protected mode userspace
application with a 16-bit stack. On returning to userspace, with iret,
the CPU doesn't restore the high word of the stack pointer. This is an
"official" bug, and the work-around used in the kernel is to temporarily
switch to a 32-bit stack segment/pointer pair where the high word of the
pointer is equal to the high word of the userspace stackpointer.

The current implementation uses THREAD_SIZE to determine the cut-off,
but there is no good reason not to use the more natural 64kb... However,
implementing this by simply substituting THREAD_SIZE with 65536 in
patch_espfix_desc crashed the test application. patch_espfix_desc tries
to do what is described above, but gets it subtly wrong if the userspace
stack pointer is just below a multiple of THREAD_SIZE: an overflow
occurs to bit 13... With a bit of luck, when the kernelspace
stackpointer is just below a 64kb-boundary, the overflow then ripples
trough to bit 16 and userspace will see its stack pointer changed by
65536.

This patch moves all espfix code into entry_32.S. Selecting a 16-bit
cut-off simplifies the code. The game with changing the limit dynamically
is removed too. It complicates matters and I see no value in it. Changing
only the top 16-bit word of ESP is one instruction and it also implies
that only two bytes of the ESPFIX GDT entry need to be changed and this
can be implemented in just a handful simple to understand instructions.
As a side effect, the operation to compute the original ESP from the
ESPFIX ESP and the GDT entry simplifies a bit too, and the remaining
three instructions have been expanded inline in entry_32.S.

impact: can now reliably run userspace with ESP=xxxxfffc on 16-bit
stack segment
Signed-off-by: NAlexander van Heukelum <heukelum@fastmail.fm>
Acked-by: NStas Sergeev <stsp@aknet.ru>
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

Returning to a task with a 16-bit stack requires special care: the iret
instruction does not restore the high word of esp in that case. The
espfix code fixes this, but currently is not invoked on NMIs. This means
that a running task gets the upper word of esp clobbered due intervening
NMIs. To reproduce, compile and run the following program with the nmi
watchdog enabled (nmi_watchdog=2 on the command line). Using gdb you can
see that the high bits of esp contain garbage, while the low bits are
still correct.

This patch puts the espfix code back into the NMI code path.

The patch is slightly complicated due to the irqtrace infrastructure not
being NMI-safe. The NMI return path cannot call TRACE_IRQS_IRET.
Otherwise, the tail of the normal iret-code is correct for the nmi code
path too. To be able to share this code-path, the TRACE_IRQS_IRET was
move up a bit. The espfix code exists after the TRACE_IRQS_IRET, but
this code explicitly disables interrupts. This short interrupts-off
section is now not traced anymore. The return-to-kernel path now always
includes the preliminary test to decide if the espfix code should be
called. This is never the case, but doing it this way keeps the patch as
simple as possible and the few extra instructions should not affect
timing in any significant way.

 #define _GNU_SOURCE
 #include <stdio.h>
 #include <sys/types.h>
 #include <sys/mman.h>
 #include <unistd.h>
 #include <sys/syscall.h>
 #include <asm/ldt.h>

int modify_ldt(int func, void *ptr, unsigned long bytecount)
{
        return syscall(SYS_modify_ldt, func, ptr, bytecount);
}

/* this is assumed to be usable */
 #define SEGBASEADDR 0x10000
 #define SEGLIMIT 0x20000

/* 16-bit segment */
struct user_desc desc = {
        .entry_number = 0,
        .base_addr = SEGBASEADDR,
        .limit = SEGLIMIT,
        .seg_32bit = 0,
        .contents = 0, /* ??? */
        .read_exec_only = 0,
        .limit_in_pages = 0,
        .seg_not_present = 0,
        .useable = 1
};

int main(void)
{
        setvbuf(stdout, NULL, _IONBF, 0);

        /* map a 64 kb segment */
        char *pointer = mmap((void *)SEGBASEADDR, SEGLIMIT+1,
                        PROT_EXEC|PROT_READ|PROT_WRITE,
                        MAP_SHARED|MAP_ANONYMOUS, -1, 0);
        if (pointer == NULL) {
                printf("could not map space\n");
                return 0;
        }

        /* write ldt, new mode */
        int err = modify_ldt(0x11, &desc, sizeof(desc));
        if (err) {
                printf("error modifying ldt: %i\n", err);
                return 0;
        }

        for (int i=0; i<1000; i++) {
        asm volatile (
                "pusha\n\t"
                "mov %ss, %eax\n\t" /* preserve ss:esp */
                "mov %esp, %ebp\n\t"
                "push $7\n\t" /* index 0, ldt, user mode */
                "push $65536-4096\n\t" /* esp */
                "lss (%esp), %esp\n\t" /* switch to new stack */
                "push %eax\n\t" /* save old ss:esp on new stack */
                "push %ebp\n\t"
                "add $17*65536, %esp\n\t" /* set high bits */
                "mov %esp, %edx\n\t"

                "mov $10000000, %ecx\n\t" /* wait... */
                "1: loop 1b\n\t" /* ... a bit */

                "cmp %esp, %edx\n\t"
                "je 1f\n\t"
                "ud2\n\t" /* esp changed inexplicably! */
                "1:\n\t"
                "sub $17*65536, %esp\n\t" /* restore high bits */
                "lss (%esp), %esp\n\t" /* restore old ss:esp */
                "popa\n\t");

                printf("\rx%ix", i);
        }

        return 0;
}
Signed-off-by: NAlexander van Heukelum <heukelum@fastmail.fm>
Acked-by: NStas Sergeev <stsp@aknet.ru>
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

Fix:

 arch/x86/kernel/entry_32.S:446: Warning: 00000000080001d1 shortened to 00000000000001d1
 arch/x86/kernel/entry_32.S:457: Warning: 000000000800feff shortened to 000000000000feff
 arch/x86/kernel/entry_32.S:527: Warning: 00000000080001d1 shortened to 00000000000001d1
 arch/x86/kernel/entry_32.S:541: Warning: 000000000800feff shortened to 000000000000feff
 arch/x86/kernel/entry_32.S:676: Warning: 0000000008000091 shortened to 0000000000000091

TIF_SYSCALL_FTRACE is 0x08000000 and until now we checked the
first 16 bits of the work mask - bit 27 falls outside of that.

Update the entry_32.S code to check the full 32-bit mask.

[ %cx => %ecx fix from Cyrill Gorcunov <gorcunov@gmail.com> ]
Signed-off-by: NJaswinder Singh Rajput <jaswinderrajput@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: "H. Peter Anvin" <hpa@kernel.org>
LKML-Reference: <1237012693.18733.3.camel@ht.satnam>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Impact: Cleanup

Checkin be44d2aa eliminates the use of
a 16-bit stack for espfix.  However, at least one instruction remained
that only operated on the low 16 bits of %esp.

This is not a bug per se because the kernel stack is always an aligned
4K or 8K block.  Therefore it cannot cross 64K boundaries; this code,
in fact, relies strictly on that fact.

However, it's a lot cleaner (and, for that matter, smaller) to operate
on the entire 32-bit register.
Signed-off-by: NStas Sergeev <stsp@aknet.ru>
CC: Zachary Amsden <zach@vmware.com>
CC: Chuck Ebbert <cebbert@redhat.com>
Signed-off-by: NH. Peter Anvin <hpa@linux.intel.com>

In general, the only definitions that assembly files can use
are in _types.S headers (where available), so convert them.
Signed-off-by: NJeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

Some syscalls need to access the pt_regs structure, either to copy
user register state or to modifiy it.  This patch adds stubs to load
the address of the pt_regs struct into the %eax register, and changes
the syscalls to regparm(1) to receive the pt_regs pointer as the
first argument.
Signed-off-by: NBrian Gerst <brgerst@gmail.com>
Acked-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Impact: stack protector for x86_32

Implement stack protector for x86_32.  GDT entry 28 is used for it.
It's set to point to stack_canary-20 and have the length of 24 bytes.
CONFIG_CC_STACKPROTECTOR turns off CONFIG_X86_32_LAZY_GS and sets %gs
to the stack canary segment on entry.  As %gs is otherwise unused by
the kernel, the canary can be anywhere.  It's defined as a percpu
variable.

x86_32 exception handlers take register frame on stack directly as
struct pt_regs.  With -fstack-protector turned on, gcc copies the
whole structure after the stack canary and (of course) doesn't copy
back on return thus losing all changed.  For now, -fno-stack-protector
is added to all files which contain those functions.  We definitely
need something better.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Impact: pt_regs changed, lazy gs handling made optional, add slight
        overhead to SAVE_ALL, simplifies error_code path a bit

On x86_32, %gs hasn't been used by kernel and handled lazily.  pt_regs
doesn't have place for it and gs is saved/loaded only when necessary.
In preparation for stack protector support, this patch makes lazy %gs
handling optional by doing the followings.

* Add CONFIG_X86_32_LAZY_GS and place for gs in pt_regs.

* Save and restore %gs along with other registers in entry_32.S unless
  LAZY_GS.  Note that this unfortunately adds "pushl $0" on SAVE_ALL
  even when LAZY_GS.  However, it adds no overhead to common exit path
  and simplifies entry path with error code.

* Define different user_gs accessors depending on LAZY_GS and add
  lazy_save_gs() and lazy_load_gs() which are noop if !LAZY_GS.  The
  lazy_*_gs() ops are used to save, load and clear %gs lazily.

* Define ELF_CORE_COPY_KERNEL_REGS() which always read %gs directly.

xen and lguest changes need to be verified.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Jeremy Fitzhardinge <jeremy@xensource.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Impact: cleanup

Use .macro instead of cpp #define where approriate.  This cleans up
code and will ease future changes.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

We are getting rid of subarchitecture support - move the hook files
to asm/. (These are now stale and should be replaced with more explicit
runtime mechanisms - but the transition is simpler this way.)
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Impact: less contention when issuing invalidate IPI, cleanup

Make x86_32 use the same tlb code as 64bit.  The 64bit code uses
multiple IPI vectors for tlb shootdown to reduce contention.  This
patch makes x86_32 allocate the same 8 IPIs as x86_64 and share the
code paths.

Note that the usage of asmlinkage is inconsistent for x86_32 and 64
and calls for further cleanup.  This has been noted with a FIXME
comment in tlb_64.c.
Signed-off-by: NTejun Heo <tj@kernel.org>

This reverts commit e0c73175.

This patch was wrong, as lockdep (and thus the irq state tracer)
aren't nmi safe. People are already seeing lockdep warnings due
to this.
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Impact: feature, let entry function decide to trace or not

This patch lets the graph tracer entry function decide if the tracing
should be done at the end as well. This requires all function graph
entry functions return 1 if it should trace, or 0 if the return should
not be traced.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Impact: consistency change for function graph

This patch makes function graph record the mcount caller address
the same way the function tracer does.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

entry_32.S is now the only user of KPROBE_ENTRY / KPROBE_END,
treewide. This patch reorders entry_64.S and explicitly generates
a separate section for functions that need the protection. The
generated code before and after the patch is equal.

The KPROBE_ENTRY and KPROBE_END macro's are removed too.
Signed-off-by: NAlexander van Heukelum <heukelum@fastmail.fm>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Impact: more efficient code for ftrace graph tracer

This patch uses the dynamic patching, when available, to patch
the function graph code into the kernel.

This patch will ease the way for letting both function tracing
and function graph tracing run together.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

fix return-tracer => graph-tracer namespace rename fallout.
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Impact: cleanup

This patch changes the name of the "return function tracer" into
function-graph-tracer which is a more suitable name for a tracing
which makes one able to retrieve the ordered call stack during
the code flow.
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
Acked-by: NSteven Rostedt <rostedt@goodmis.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Impact: improve backtrace quality

avoid the confusion in call trace because of the lack of padding at the
tail of function.

When do_exit gets called, the return address behind call instruction is
pushed into stack. If something get wrong in do_exit, for x86_64, the
entry "kernel_execve +0x00/0xXX" rather than "child_rip +0xYY/0xZZ" is
in the call trace.

That looks confusing, so add a u2d to make the return address still part
of the original call site. (This also catches any instances of us returning
from that function somehow.)
Signed-off-by: Njia zhang <jia.zhang2008@gmail.com>
Acked-by: NAlexander van Heukelum <heukelum@fastmail.fm>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

This patch adds the support for dynamic tracing on the function return tracer.
The whole difference with normal dynamic function tracing is that we don't need
to hook on a particular callback. The only pro that we want is to nop or set
dynamically the calls to ftrace_caller (which is ftrace_return_caller here).

Some security checks ensure that we are not trying to launch dynamic tracing for
return tracing while normal function tracing is already running.

An example of trace with getnstimeofday set as a filter:

ktime_get_ts+0x22/0x50 -> getnstimeofday (2283 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1396 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1382 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1825 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1426 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1464 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1524 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1382 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1382 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1434 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1464 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1502 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1404 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1397 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1051 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1314 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1344 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1163 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1390 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1374 ns)
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Impact: Optimize a bit the function return tracer

This patch changes the calling convention of prepare_ftrace_return to
pass its arguments by register. This will optimize it a bit and
prepare it to support dynamic tracing.
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Older versions of gas don't implement the C-style != operator, they
instead want the Pascal-style <> operator.  Change != to <> so we
don't break compilation with those old versions of gas.
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

Shrink the IRQ stubs on 32 bits down to just over four bytes per (we
fit seven into a 32-byte chunk.)  This shrinks the total icache
consumption of the IRQ stubs down to an even kilobyte, if all of them
are in active use.

The downside is that we end up with a double jump, which could have a
negative effect on some pipelines.  The double jump is always inside
the same cacheline on any modern chips (the exception being
486/Elan/Geode which have only 16-byte cachelines, but are unlikely to
have too many interrupt sources.)

To get the most effect, cache-align the IRQ stubs.
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

Don't generate interrupt stubs for interrupt vectors below
FIRST_EXTERNAL_VECTOR, and make the table of interrupt vectors
(interrupt[]) __initconst.  Both of these changes both conserve memory
and improve consistency with 64 bits.
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

Impact: add infrastructure for function-return tracing

Add low level support for ftrace return tracing.

This plug-in stores return addresses on the thread_info structure of
the current task.

The index of the current return address is initialized when the task
is the first one (init) and when a process forks (the child). It is
not needed when a task does a sys_execve because after this syscall,
it still needs to return on the kernel functions it called.

Note that the code of return_to_handler has been suggested by Steven
Rostedt as almost all of the ideas of improvements in this V3.

For purpose of security, arch/x86/kernel/process_32.c is not traced
because __switch_to() changes the current task during its execution.
That could cause inconsistency in the stored return address of this
function even if I didn't have any crash after testing with tracing on
this function enabled.
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>