arm64: fix alternatives with LLVM's integrated assembler

[ Upstream commit c54f90c2627cc316d365e3073614731e17dbc631 ]

LLVM's integrated assembler fails with the following error when
building KVM:

  <inline asm>:12:6: error: expected absolute expression
   .if kvm_update_va_mask == 0
       ^
  <inline asm>:21:6: error: expected absolute expression
   .if kvm_update_va_mask == 0
       ^
  <inline asm>:24:2: error: unrecognized instruction mnemonic
          NOT_AN_INSTRUCTION
          ^
  LLVM ERROR: Error parsing inline asm

These errors come from ALTERNATIVE_CB and __ALTERNATIVE_CFG,
which test for the existence of the callback parameter in inline
assembly using the following expression:

  " .if " __stringify(cb) " == 0\n"

This works with GNU as, but isn't supported by LLVM. This change
splits __ALTERNATIVE_CFG and ALTINSTR_ENTRY into separate macros
to fix the LLVM build.

Link: https://github.com/ClangBuiltLinux/linux/issues/472
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/arch/arm64/include/asm/alternative.h b/arch/arm64/include/asm/alternative.h
index 4b650ec..887a851 100644 (file)
--- a/arch/arm64/include/asm/alternative.h
+++ b/arch/arm64/include/asm/alternative.h
@@ -35,13 +35,16 @@ void apply_alternatives_module(void *start, size_t length);
 static inline void apply_alternatives_module(void *start, size_t length) { }
 #endif
 
-#define ALTINSTR_ENTRY(feature,cb)                                           \
+#define ALTINSTR_ENTRY(feature)                                                      \
        " .word 661b - .\n"                             /* label           */ \
-       " .if " __stringify(cb) " == 0\n"                                     \
        " .word 663f - .\n"                             /* new instruction */ \
-       " .else\n"                                                            \
+       " .hword " __stringify(feature) "\n"            /* feature bit     */ \
+       " .byte 662b-661b\n"                            /* source len      */ \
+       " .byte 664f-663f\n"                            /* replacement len */
+
+#define ALTINSTR_ENTRY_CB(feature, cb)                                       \
+       " .word 661b - .\n"                             /* label           */ \
        " .word " __stringify(cb) "- .\n"               /* callback */        \
-       " .endif\n"                                                           \
        " .hword " __stringify(feature) "\n"            /* feature bit     */ \
        " .byte 662b-661b\n"                            /* source len      */ \
        " .byte 664f-663f\n"                            /* replacement len */
@@ -62,15 +65,14 @@ static inline void apply_alternatives_module(void *start, size_t length) { }
  *
  * Alternatives with callbacks do not generate replacement instructions.
  */
-#define __ALTERNATIVE_CFG(oldinstr, newinstr, feature, cfg_enabled, cb)        \
+#define __ALTERNATIVE_CFG(oldinstr, newinstr, feature, cfg_enabled)    \
        ".if "__stringify(cfg_enabled)" == 1\n"                         \
        "661:\n\t"                                                      \
        oldinstr "\n"                                                   \
        "662:\n"                                                        \
        ".pushsection .altinstructions,\"a\"\n"                         \
-       ALTINSTR_ENTRY(feature,cb)                                      \
+       ALTINSTR_ENTRY(feature)                                         \
        ".popsection\n"                                                 \
-       " .if " __stringify(cb) " == 0\n"                               \
        ".pushsection .altinstr_replacement, \"a\"\n"                   \
        "663:\n\t"                                                      \
        newinstr "\n"                                                   \
@@ -78,17 +80,25 @@ static inline void apply_alternatives_module(void *start, size_t length) { }
        ".popsection\n\t"                                               \
        ".org   . - (664b-663b) + (662b-661b)\n\t"                      \
        ".org   . - (662b-661b) + (664b-663b)\n"                        \
-       ".else\n\t"                                                     \
+       ".endif\n"
+
+#define __ALTERNATIVE_CFG_CB(oldinstr, feature, cfg_enabled, cb)       \
+       ".if "__stringify(cfg_enabled)" == 1\n"                         \
+       "661:\n\t"                                                      \
+       oldinstr "\n"                                                   \
+       "662:\n"                                                        \
+       ".pushsection .altinstructions,\"a\"\n"                         \
+       ALTINSTR_ENTRY_CB(feature, cb)                                  \
+       ".popsection\n"                                                 \
        "663:\n\t"                                                      \
        "664:\n\t"                                                      \
-       ".endif\n"                                                      \
        ".endif\n"
 
 #define _ALTERNATIVE_CFG(oldinstr, newinstr, feature, cfg, ...)        \
-       __ALTERNATIVE_CFG(oldinstr, newinstr, feature, IS_ENABLED(cfg), 0)
+       __ALTERNATIVE_CFG(oldinstr, newinstr, feature, IS_ENABLED(cfg))
 
 #define ALTERNATIVE_CB(oldinstr, cb) \
-       __ALTERNATIVE_CFG(oldinstr, "NOT_AN_INSTRUCTION", ARM64_CB_PATCH, 1, cb)
+       __ALTERNATIVE_CFG_CB(oldinstr, ARM64_CB_PATCH, 1, cb)
 #else
 
 #include <asm/assembler.h>