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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
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
connector
coresight
fanotify
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
kfifo
kmemleak kmemleak-test: drop __init to get better backtrace 2023-06-09 16:25:40 -07:00
kobject
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
mei
nitro_enclaves
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
rpmsg
rust
seccomp
timers
trace_events samples: Replace strlcpy() with strscpy() 2023-11-30 12:20:53 -08:00
trace_printk
uhid
user_events
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