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d8ad6d39c3
'jiffies' and 'jiffies_64' are meant to alias (two different symbols that
share the same address). Most architectures make the symbols alias to the
same address via a linker script assignment in their
arch/<arch>/kernel/vmlinux.lds.S:
jiffies = jiffies_64;
which is effectively a definition of jiffies.
jiffies and jiffies_64 are both forward declared for all architectures in
include/linux/jiffies.h. jiffies_64 is defined in kernel/time/timer.c.
x86_64 was peculiar in that it wasn't doing the above linker script
assignment, but rather was:
1. defining jiffies in arch/x86/kernel/time.c instead via the linker script.
2. overriding the symbol jiffies_64 from kernel/time/timer.c in
arch/x86/kernel/vmlinux.lds.s via 'jiffies_64 = jiffies;'.
As Fangrui notes:
In LLD, symbol assignments in linker scripts override definitions in
object files. GNU ld appears to have the same behavior. It would
probably make sense for LLD to error "duplicate symbol" but GNU ld
is unlikely to adopt for compatibility reasons.
This results in an ODR violation (UB), which seems to have survived
thus far. Where it becomes harmful is when;
1. -fno-semantic-interposition is used:
As Fangrui notes:
Clang after LLVM commit 5b22bcc2b70d
("[X86][ELF] Prefer to lower MC_GlobalAddress operands to .Lfoo$local")
defaults to -fno-semantic-interposition similar semantics which help
-fpic/-fPIC code avoid GOT/PLT when the referenced symbol is defined
within the same translation unit. Unlike GCC
-fno-semantic-interposition, Clang emits such relocations referencing
local symbols for non-pic code as well.
This causes references to jiffies to refer to '.Ljiffies$local' when
jiffies is defined in the same translation unit. Likewise, references to
jiffies_64 become references to '.Ljiffies_64$local' in translation units
that define jiffies_64. Because these differ from the names used in the
linker script, they will not be rewritten to alias one another.
2. Full LTO
Full LTO effectively treats all source files as one translation
unit, causing these local references to be produced everywhere. When
the linker processes the linker script, there are no longer any
references to jiffies_64' anywhere to replace with 'jiffies'. And
thus '.Ljiffies$local' and '.Ljiffies_64$local' no longer alias
at all.
In the process of porting patches enabling Full LTO from arm64 to x86_64,
spooky bugs have been observed where the kernel appeared to boot, but init
doesn't get scheduled.
Avoid the ODR violation by matching other architectures and define jiffies
only by linker script. For -fno-semantic-interposition + Full LTO, there
is no longer a global definition of jiffies for the compiler to produce a
local symbol which the linker script won't ensure aliases to jiffies_64.
Fixes: 40747ffa5a ("asmlinkage: Make jiffies visible")
Reported-by: Nathan Chancellor <natechancellor@gmail.com>
Reported-by: Alistair Delva <adelva@google.com>
Debugged-by: Nick Desaulniers <ndesaulniers@google.com>
Debugged-by: Sami Tolvanen <samitolvanen@google.com>
Suggested-by: Fangrui Song <maskray@google.com>
Signed-off-by: Bob Haarman <inglorion@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com> # build+boot on
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: stable@vger.kernel.org
Link: https://github.com/ClangBuiltLinux/linux/issues/852
Link: https://lkml.kernel.org/r/20200602193100.229287-1-inglorion@google.com
127 lines
2.9 KiB
C
127 lines
2.9 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Copyright (c) 1991,1992,1995 Linus Torvalds
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* Copyright (c) 1994 Alan Modra
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* Copyright (c) 1995 Markus Kuhn
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* Copyright (c) 1996 Ingo Molnar
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* Copyright (c) 1998 Andrea Arcangeli
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* Copyright (c) 2002,2006 Vojtech Pavlik
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* Copyright (c) 2003 Andi Kleen
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*
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*/
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#include <linux/clocksource.h>
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#include <linux/clockchips.h>
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#include <linux/interrupt.h>
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#include <linux/irq.h>
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#include <linux/i8253.h>
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#include <linux/time.h>
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#include <linux/export.h>
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#include <asm/vsyscall.h>
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#include <asm/x86_init.h>
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#include <asm/i8259.h>
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#include <asm/timer.h>
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#include <asm/hpet.h>
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#include <asm/time.h>
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unsigned long profile_pc(struct pt_regs *regs)
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{
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unsigned long pc = instruction_pointer(regs);
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if (!user_mode(regs) && in_lock_functions(pc)) {
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#ifdef CONFIG_FRAME_POINTER
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return *(unsigned long *)(regs->bp + sizeof(long));
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#else
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unsigned long *sp = (unsigned long *)regs->sp;
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/*
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* Return address is either directly at stack pointer
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* or above a saved flags. Eflags has bits 22-31 zero,
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* kernel addresses don't.
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*/
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if (sp[0] >> 22)
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return sp[0];
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if (sp[1] >> 22)
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return sp[1];
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#endif
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}
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return pc;
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}
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EXPORT_SYMBOL(profile_pc);
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/*
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* Default timer interrupt handler for PIT/HPET
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*/
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static irqreturn_t timer_interrupt(int irq, void *dev_id)
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{
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global_clock_event->event_handler(global_clock_event);
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return IRQ_HANDLED;
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}
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static void __init setup_default_timer_irq(void)
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{
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unsigned long flags = IRQF_NOBALANCING | IRQF_IRQPOLL | IRQF_TIMER;
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/*
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* Unconditionally register the legacy timer interrupt; even
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* without legacy PIC/PIT we need this for the HPET0 in legacy
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* replacement mode.
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*/
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if (request_irq(0, timer_interrupt, flags, "timer", NULL))
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pr_info("Failed to register legacy timer interrupt\n");
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}
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/* Default timer init function */
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void __init hpet_time_init(void)
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{
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if (!hpet_enable()) {
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if (!pit_timer_init())
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return;
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}
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setup_default_timer_irq();
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}
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static __init void x86_late_time_init(void)
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{
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/*
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* Before PIT/HPET init, select the interrupt mode. This is required
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* to make the decision whether PIT should be initialized correct.
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*/
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x86_init.irqs.intr_mode_select();
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/* Setup the legacy timers */
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x86_init.timers.timer_init();
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/*
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* After PIT/HPET timers init, set up the final interrupt mode for
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* delivering IRQs.
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*/
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x86_init.irqs.intr_mode_init();
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tsc_init();
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}
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/*
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* Initialize TSC and delay the periodic timer init to
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* late x86_late_time_init() so ioremap works.
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*/
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void __init time_init(void)
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{
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late_time_init = x86_late_time_init;
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}
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/*
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* Sanity check the vdso related archdata content.
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*/
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void clocksource_arch_init(struct clocksource *cs)
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{
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if (cs->vdso_clock_mode == VDSO_CLOCKMODE_NONE)
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return;
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if (cs->mask != CLOCKSOURCE_MASK(64)) {
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pr_warn("clocksource %s registered with invalid mask %016llx for VDSO. Disabling VDSO support.\n",
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cs->name, cs->mask);
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cs->vdso_clock_mode = VDSO_CLOCKMODE_NONE;
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}
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}
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