linux/samples
Linus Torvalds 4356e9f841 work around gcc bugs with 'asm goto' with outputs
We've had issues with gcc and 'asm goto' before, and we created a
'asm_volatile_goto()' macro for that in the past: see commits
3f0116c323 ("compiler/gcc4: Add quirk for 'asm goto' miscompilation
bug") and a9f180345f ("compiler/gcc4: Make quirk for
asm_volatile_goto() unconditional").

Then, much later, we ended up removing the workaround in commit
43c249ea0b ("compiler-gcc.h: remove ancient workaround for gcc PR
58670") because we no longer supported building the kernel with the
affected gcc versions, but we left the macro uses around.

Now, Sean Christopherson reports a new version of a very similar
problem, which is fixed by re-applying that ancient workaround.  But the
problem in question is limited to only the 'asm goto with outputs'
cases, so instead of re-introducing the old workaround as-is, let's
rename and limit the workaround to just that much less common case.

It looks like there are at least two separate issues that all hit in
this area:

 (a) some versions of gcc don't mark the asm goto as 'volatile' when it
     has outputs:

        https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98619
        https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110420

     which is easy to work around by just adding the 'volatile' by hand.

 (b) Internal compiler errors:

        https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110422

     which are worked around by adding the extra empty 'asm' as a
     barrier, as in the original workaround.

but the problem Sean sees may be a third thing since it involves bad
code generation (not an ICE) even with the manually added 'volatile'.

but the same old workaround works for this case, even if this feels a
bit like voodoo programming and may only be hiding the issue.

Reported-and-tested-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/all/20240208220604.140859-1-seanjc@google.com/
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Uros Bizjak <ubizjak@gmail.com>
Cc: Jakub Jelinek <jakub@redhat.com>
Cc: Andrew Pinski <quic_apinski@quicinc.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2024-02-09 15:57:48 -08:00
..
acrn virt: acrn: Replace obsolete memalign() with posix_memalign() 2023-04-20 14:20:51 +02:00
auxdisplay
binderfs
bpf work around gcc bugs with 'asm goto' with outputs 2024-02-09 15:57:48 -08:00
cgroup samples/cgroup: add .gitignore file for generated samples 2024-01-24 11:52:40 -08:00
configfs treewide: remove editor modelines and cruft 2021-05-07 00:26:34 -07:00
connector
coresight coresight: syscfg: Example CoreSight configuration loadable module 2021-11-26 11:34:07 -07:00
fanotify Add gitignore file for samples/fanotify/ subdirectory 2021-11-07 11:19:24 -08:00
fprobe fprobe: Pass return address to the handlers 2023-06-06 21:39:55 +09:00
ftrace RISC-V Patches for the 6.8 Merge Window, Part 4 2024-01-20 11:06:04 -08:00
hid bpf: Replace deprecated -target with --target= for Clang 2023-06-29 15:46:17 +02:00
hidraw
hw_breakpoint samples/hw_breakpoint: mark sample_hbp as static 2023-07-26 11:17:19 -07:00
kdb kdb: Rename members of struct kdbtab_t 2021-07-27 17:05:06 +01:00
kfifo samples/kfifo: Rename read_lock/write_lock 2021-10-13 14:36:48 +02:00
kmemleak kmemleak-test: drop __init to get better backtrace 2023-06-09 16:25:40 -07:00
kobject samples/kobject: make kobj_type structure constant 2023-02-08 13:34:41 +01:00
kprobes samples: kprobes: Fixes a typo 2023-10-10 01:00:50 +09:00
landlock samples/landlock: Support TCP restrictions 2023-10-26 21:07:17 +02:00
livepatch livepatch: Reorder to use before freeing a pointer 2022-03-23 13:51:11 +01:00
mei samples: mei: don't wait on read completion upon write. 2021-08-01 09:54:22 +02:00
nitro_enclaves nitro_enclaves: Add fixes for checkpatch blank line reports 2021-09-14 11:11:20 +02:00
pfsm samples: Add userspace example for TI TPS6594 PFSM 2023-06-15 13:41:53 +02:00
pidfd
pktgen samples: pktgen: fix append mode failed issue 2023-07-03 09:15:26 +01:00
qmi soc: qcom: qmi: use const for struct qmi_elem_info 2022-08-29 17:33:01 -05:00
rpmsg
rust samples: rust: print: Add sample code for Arc printing 2023-04-10 05:05:43 +02:00
seccomp samples/seccomp: Adjust sample to also provide kill option 2022-02-10 19:09:12 -08:00
timers
trace_events samples: Replace strlcpy() with strscpy() 2023-11-30 12:20:53 -08:00
trace_printk
uhid
user_events tracing/user_events: Use write ABI in example 2023-03-29 06:52:09 -04:00
v4l media updates for v6.8-rc1 2024-01-12 14:29:48 -08:00
vfio-mdev eventfd: simplify eventfd_signal() 2023-11-28 14:08:38 +01:00
vfs
watch_queue
watchdog
Kconfig samples: introduce new samples subdir for cgroup 2023-12-10 16:51:54 -08:00
Makefile samples: introduce new samples subdir for cgroup 2023-12-10 16:51:54 -08:00