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Nick Desaulniers 1499054da8 mips: avoid explicit UB in assignment of mips_io_port_base 
[ Upstream commit 12051b318b ]

The code in question is modifying a variable declared const through
pointer manipulation.  Such code is explicitly undefined behavior, and
is the lone issue preventing malta_defconfig from booting when built
with Clang:

If an attempt is made to modify an object defined with a const-qualified
type through use of an lvalue with non-const-qualified type, the
behavior is undefined.

LLVM is removing such assignments. A simple fix is to not declare
variables const that you plan on modifying.  Limiting the scope would be
a better method of preventing unwanted writes to such a variable.

Further, the code in question mentions "compiler bugs" without any links
to bug reports, so it is difficult to know if the issue is resolved in
GCC. The patch was authored in 2006, which would have been GCC 4.0.3 or
4.1.1. The minimal supported version of GCC in the Linux kernel is
currently 4.6.

For what its worth, there was UB before the commit in question, it just
added a barrier and got lucky IRT codegen. I don't think there's any
actual compiler bugs related, just runtime bugs due to UB.

Link: https://github.com/ClangBuiltLinux/linux/issues/610
Fixes: 966f4406d9 ("[MIPS] Work around bad code generation for <asm/io.h>.")
Reported-by: Nathan Chancellor <natechancellor@gmail.com>
Debugged-by: Nathan Chancellor <natechancellor@gmail.com>
Suggested-by: Eli Friedman <efriedma@quicinc.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Tested-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: ralf@linux-mips.org
Cc: jhogan@kernel.org
Cc: Maciej W. Rozycki <macro@linux-mips.org>
Cc: Hassan Naveed <hnaveed@wavecomp.com>
Cc: Stephen Kitt <steve@sk2.org>
Cc: Serge Semin <fancer.lancer@gmail.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: linux-mips@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: clang-built-linux@googlegroups.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
2020-01-27 14:51:07 +01:00
..
.gitignore
8250-platform.c
asm-offsets.c Kbuild: rename CC_STACKPROTECTOR[_STRONG] config variables 2018-06-14 12:21:18 +09:00
binfmt_elfn32.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
binfmt_elfo32.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
bmips_5xxx_init.S
bmips_vec.S
branch.c MIPS: Use proper kernel-doc Return keyword 2018-01-18 22:29:02 +00:00
cacheinfo.c mips: cacheinfo: report shared CPU map 2020-01-17 19:47:15 +01:00
cevt-bcm1480.c MIPS: clockevent drivers: Set ->min_delta_ticks and ->max_delta_ticks 2017-04-14 13:11:16 -07:00
cevt-ds1287.c MIPS: clockevent drivers: Set ->min_delta_ticks and ->max_delta_ticks 2017-04-14 13:11:16 -07:00
cevt-gt641xx.c MIPS: clockevent drivers: Set ->min_delta_ticks and ->max_delta_ticks 2017-04-14 13:11:16 -07:00
cevt-r4k.c MIPS: cevt-r4k: Fix out-of-bounds array access 2017-04-10 13:31:12 +02:00
cevt-sb1250.c MIPS: clockevent drivers: Set ->min_delta_ticks and ->max_delta_ticks 2017-04-14 13:11:16 -07:00
cevt-txx9.c MIPS: clockevent drivers: Set ->min_delta_ticks and ->max_delta_ticks 2017-04-14 13:11:16 -07:00
cmpxchg.c MIPS: fix truncation in __cmpxchg_small for short values 2019-03-05 17:58:53 +01:00
cps-vec-ns16550.S Update MIPS email addresses 2017-11-03 09:02:30 -07:00
cps-vec.S MIPS: CPS: Fix MIPS_ISA_LEVEL_RAW fallout 2018-02-05 11:53:06 +00:00
cpu-bugs64.c MIPS: Fix printk continuations in cpu-bugs64.c 2017-01-24 18:30:34 +01:00
cpu-probe.c MIPS: elf_hwcap: Export userspace ASEs 2019-10-17 13:45:32 -07:00
crash.c MIPS: kexec: Mark CPU offline before disabling local IRQ 2018-11-21 09:19:10 +01:00
crash_dump.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
csrc-bcm1480.c clocksource: Use a plain u64 instead of cycle_t 2016-12-25 11:04:12 +01:00
csrc-ioasic.c clocksource: Use a plain u64 instead of cycle_t 2016-12-25 11:04:12 +01:00
csrc-r4k.c clocksource: Use a plain u64 instead of cycle_t 2016-12-25 11:04:12 +01:00
csrc-sb1250.c clocksource: Use a plain u64 instead of cycle_t 2016-12-25 11:04:12 +01:00
early_printk.c mips: unify prom_putchar() declarations 2018-07-17 09:40:17 -07:00
early_printk_8250.c mips: unify prom_putchar() declarations 2018-07-17 09:40:17 -07:00
elf.c Update MIPS email addresses 2017-11-03 09:02:30 -07:00
entry.S MIPS: Add syscall detection for restartable sequences 2018-06-19 21:13:56 -07:00
ftrace.c MIPS: function_graph: Simplify with function_graph_enter() 2018-12-05 19:32:10 +01:00
genex.S MIPS: Fix ejtag handler on SMP 2018-06-24 09:27:27 -07:00
gpio_txx9.c
head.S MIPS: head: Reorder instructions missing a delay slot 2017-06-27 23:35:21 +02:00
i8253.c MIPS: kernel: only use i8253 clocksource with periodic clockevent 2019-08-29 08:28:27 +02:00
idle.c MIPS: Annotate cpu_wait implementations with __cpuidle 2018-06-28 14:18:54 -07:00
irq-gt641xx.c
irq-msc01.c
irq-rm7000.c
irq.c MIPS: irq: Allocate accurate order pages for irq stack 2019-03-10 07:17:20 +01:00
irq_txx9.c
jump_label.c jump_label: move 'asm goto' support test to Kconfig 2019-06-04 08:02:34 +02:00
kgdb.c MIPS: KGDB: fix kgdb support for SMP platforms. 2019-05-10 17:54:07 +02:00
kprobes.c bpf/error-inject/kprobes: Clear current_kprobe and enable preempt in kprobe 2018-06-21 12:33:19 +02:00
linux32.c MIPS: Delete unused code in linux32.c 2018-08-01 13:20:27 -07:00
machine_kexec.c MIPS: kexec: Mark CPU offline before disabling local IRQ 2018-11-21 09:19:10 +01:00
Makefile License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
mcount.S mips: ftrace: fix static function graph tracing 2018-06-19 15:00:12 -07:00
mips-cm.c mips: cm: reprime error cause 2019-02-15 08:10:11 +01:00
mips-cpc.c MIPS: CPC: Map registers using DT in mips_cpc_default_phys_base() 2018-02-08 14:02:01 +00:00
mips-mt-fpaff.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
mips-mt.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
mips-r2-to-r6-emul.c MIPS: Declare various variables & functions static 2017-08-29 15:21:55 +02:00
mips_machine.c
module.c Merge branch 'upstream' of git://git.linux-mips.org/pub/scm/ralf/upstream-linus 2017-07-15 10:59:54 -07:00
octeon_switch.S Kbuild: rename CC_STACKPROTECTOR[_STRONG] config variables 2018-06-14 12:21:18 +09:00
perf_event.c sched/headers: Prepare for new header dependencies before moving code to <linux/sched/task_stack.h> 2017-03-02 08:42:36 +01:00
perf_event_mipsxx.c MIPS: perf: Fix build with CONFIG_CPU_BMIPS5000 enabled 2019-05-25 18:23:33 +02:00
pm-cps.c MIPS: pm-cps: Block system suspend when a JTAG probe is present 2018-03-09 13:53:26 +00:00
pm.c
probes-common.h MIPS: Update email address for Marcin Nowakowski 2017-11-02 10:58:43 +00:00
proc.c MIPS: Treat Loongson Extensions as ASEs 2019-10-11 18:20:55 +02:00
process.c MIPS: Remove function size check in get_frame_info() 2019-03-13 14:02:37 -07:00
prom.c mips: Make sure dt memory regions are valid 2019-06-15 11:54:05 +02:00
ptrace.c MIPS: Add FP_MODE regset support 2018-07-19 13:58:44 -07:00
ptrace32.c MIPS: Correct the 64-bit DSP accumulator register size 2018-07-19 13:47:21 -07:00
r4k_fpu.S MIPS: Fix MIPS64 FP save/restore on 32-bit kernels 2017-11-09 14:13:40 +00:00
r4k_switch.S Kbuild: rename CC_STACKPROTECTOR[_STRONG] config variables 2018-06-14 12:21:18 +09:00
r2300_fpu.S MIPS: Move r2300 FP code from r2300_switch.S to r2300_fpu.S 2017-08-29 15:21:51 +02:00
r2300_switch.S Kbuild: rename CC_STACKPROTECTOR[_STRONG] config variables 2018-06-14 12:21:18 +09:00
relocate.c Update MIPS email addresses 2017-11-03 09:02:30 -07:00
relocate_kernel.S MIPS: kexec: fix typos 2018-06-24 09:26:01 -07:00
reset.c MIPS: Hang more efficiently on halt/powerdown/restart 2018-03-09 11:22:43 +00:00
rtlx-cmp.c
rtlx-mt.c
rtlx.c vfs: do bulk POLL* -> EPOLL* replacement 2018-02-11 14:34:03 -08:00
scall32-o32.S MIPS: Wire up io_pgetevents syscall 2018-06-19 21:14:29 -07:00
scall64-64.S MIPS: Wire up io_pgetevents syscall 2018-06-19 21:14:29 -07:00
scall64-n32.S MIPS: Wire up io_pgetevents syscall 2018-06-19 21:14:29 -07:00
scall64-o32.S MIPS: scall64-o32: Fix indirect syscall number load 2019-05-02 09:58:53 +02:00
segment.c
setup.c mips: avoid explicit UB in assignment of mips_io_port_base 2020-01-27 14:51:07 +01:00
signal-common.h
signal.c Here are the main MIPS changes for 4.19. 2018-08-13 19:24:32 -07:00
signal32.c compat: Move compat_timespec/ timeval to compat_time.h 2018-04-19 13:29:54 +02:00
signal_n32.c MIPS: Remove nabi_no_regargs 2018-08-01 13:20:15 -07:00
signal_o32.c MIPS: Remove nabi_no_regargs 2018-08-01 13:20:15 -07:00
smp-bmips.c MIPS: bmips: mark exception vectors as char arrays 2019-11-10 11:27:31 +01:00
smp-cmp.c MIPS: smp-cmp: Fix vpe_id build error 2017-11-01 23:23:00 +00:00
smp-cps.c MIPS: SMP-CPS: Remove duplicate assignment of core in play_dead 2018-02-05 14:36:06 +00:00
smp-mt.c MIPS: Use mips_gic_present() in place of gic_present 2017-09-04 13:53:14 +02:00
smp-up.c MIPS: SMP: Allow boot_secondary SMP op to return errors 2017-08-30 00:57:27 +02:00
smp.c MIPS changes for 4.15 2017-11-15 11:36:08 -08:00
spinlock_test.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
spram.c
stacktrace.c sched/headers: Prepare for new header dependencies before moving code to <linux/sched/task_stack.h> 2017-03-02 08:42:36 +01:00
sync-r4k.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
syscall.c mm: add ksys_mmap_pgoff() helper; remove in-kernel calls to sys_mmap_pgoff() 2018-04-02 20:16:11 +02:00
sysrq.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
time.c MIPS: Convert update_persistent_clock() to update_persistent_clock64() 2018-05-14 23:58:23 +01:00
topology.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
traps.c A few MIPS fixes for 4.19: 2018-08-23 14:23:08 -07:00
unaligned.c MIPS: Declare various variables & functions static 2017-08-29 15:21:55 +02:00
uprobes.c MIPS: uprobes: remove set but not used variable 'epc' 2019-06-25 11:35:56 +08:00
vdso.c MIPS: math-emu: Write-protect delay slot emulation pages 2019-01-09 17:38:47 +01:00
vmlinux.lds.S MIPS: Ensure ELF appended dtb is relocated 2019-03-27 14:14:39 +09:00
vpe-cmp.c
vpe-mt.c
vpe.c MIPS: VPE: Fix spelling mistake: "uneeded" -> "unneeded" 2018-05-14 23:58:23 +01:00
watch.c MIPS: Watch: Avoid duplication of bits in mips_read_watch_registers 2018-01-23 15:46:01 +00:00