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| author | Sean Christopherson <seanjc@google.com> | 2022-02-02 00:49:41 +0000 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2022-06-09 10:23:26 +0200 |
| commit | 64639d11186e208f371cbbff74115514ac53a606 (patch) | |
| tree | 8e94ec9bbbb067f6b67b73a331c0c9d018d543f5 /init/Kconfig | |
| parent | 3892794a18136452101fc86cebc5c6d69ac93683 (diff) | |
| download | linux-stable-64639d11186e208f371cbbff74115514ac53a606.tar.gz linux-stable-64639d11186e208f371cbbff74115514ac53a606.tar.bz2 linux-stable-64639d11186e208f371cbbff74115514ac53a606.zip | |
Kconfig: Add option for asm goto w/ tied outputs to workaround clang-13 bug
commit 1aa0e8b144b6474c4914439d232d15bfe883636b 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>
Diffstat (limited to 'init/Kconfig')
| -rw-r--r-- | init/Kconfig | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/init/Kconfig b/init/Kconfig index 11f8a845f259..d19ed66aba3b 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -77,6 +77,11 @@ config CC_HAS_ASM_GOTO_OUTPUT depends on CC_HAS_ASM_GOTO def_bool $(success,echo 'int foo(int x) { asm goto ("": "=r"(x) ::: bar); return x; bar: return 0; }' | $(CC) -x c - -c -o /dev/null) +config CC_HAS_ASM_GOTO_TIED_OUTPUT + depends on CC_HAS_ASM_GOTO_OUTPUT + # Detect buggy gcc and clang, fixed in gcc-11 clang-14. + def_bool $(success,echo 'int foo(int *x) { asm goto (".long (%l[bar]) - .\n": "+m"(*x) ::: bar); return *x; bar: return 0; }' | $CC -x c - -c -o /dev/null) + config TOOLS_SUPPORT_RELR def_bool $(success,env "CC=$(CC)" "LD=$(LD)" "NM=$(NM)" "OBJCOPY=$(OBJCOPY)" $(srctree)/scripts/tools-support-relr.sh) |