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Sean Christopherson b616c2e284 Kconfig: Add option for asm goto w/ tied outputs to workaround clang-13 bug 
commit 1aa0e8b144 upstream.

Add a config option to guard (future) usage of asm_volatile_goto() that
includes "tied outputs", i.e. "+" constraints that specify both an input
and output parameter.  clang-13 has a bug[1] that causes compilation of
such inline asm to fail, and KVM wants to use a "+m" constraint to
implement a uaccess form of CMPXCHG[2].  E.g. the test code fails with

  <stdin>:1:29: error: invalid operand in inline asm: '.long (${1:l}) - .'
  int foo(int *x) { asm goto (".long (%l[bar]) - .\n": "+m"(*x) ::: bar); return *x; bar: return 0; }
                            ^
  <stdin>:1:29: error: unknown token in expression
  <inline asm>:1:9: note: instantiated into assembly here
          .long () - .
                 ^
  2 errors generated.

on clang-13, but passes on gcc (with appropriate asm goto support).  The
bug is fixed in clang-14, but won't be backported to clang-13 as the
changes are too invasive/risky.

gcc also had a similar bug[3], fixed in gcc-11, where gcc failed to
account for its behavior of assigning two numbers to tied outputs (one
for input, one for output) when evaluating symbolic references.

[1] https://github.com/ClangBuiltLinux/linux/issues/1512
[2] https://lore.kernel.org/all/YfMruK8%2F1izZ2VHS@google.com
[3] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98096

Suggested-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220202004945.2540433-2-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
 		2022-06-09 10:26:25 +02:00
..
Kconfig Kconfig: Add option for asm goto w/ tied outputs to workaround clang-13 bug 2022-06-09 10:26:25 +02:00
Makefile kbuild: do not quote string values in include/config/auto.conf 2022-01-08 18:03:57 +09:00
calibrate.c
…
do_mounts.c init: don't panic if mount_nodev_root failed 2021-09-19 22:24:52 -04:00
do_mounts.h init: add an init_mknod helper 2020-07-31 08:17:54 +02:00
do_mounts_initrd.c Merge branch 'hch.init_path' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2020-08-07 09:40:34 -07:00
do_mounts_rd.c init: add an init_unlink helper 2020-07-31 08:17:52 +02:00
init_task.c kcsan: Remove redundant zero-initialization of globals 2021-12-09 16:42:26 -08:00
initramfs.c memblock: use memblock_free for freeing virtual pointers 2021-11-06 13:30:41 -07:00
main.c kthread: Don't allocate kthread_struct for init and umh 2022-06-09 10:25:16 +02:00
noinitramfs.c init: move usermodehelper_enable() to populate_rootfs() 2021-09-08 11:50:27 -07:00
version.c kbuild: add an elfnote for whether vmlinux is built with lto 2021-04-25 05:25:42 +09:00