[PATCH 4.14 124/237] arm64: fix alternatives with LLVMs integrated assembler

Greg Kroah-Hartman
2020-02-27T13:57:28Z

From: Sami Tolvanen <samitolvanen@google.com>

[ 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>
---
arch/arm64/include/asm/alternative.h | 32 ++++++++++++++++++----------
1 file changed, 21 insertions(+), 11 deletions(-)

diff --git a/arch/arm64/include/asm/alternative.h b/arch/arm64/include/asm/alternative.h
index a91933b1e2e62..4cd4a793dc328 100644
--- a/arch/arm64/include/asm/alternative.h
+++ b/arch/arm64/include/asm/alternative.h
@@ -30,13 +30,16 @@ typedef void (*alternative_cb_t)(struct alt_instr *alt,
void __init apply_alternatives_all(void);
void apply_alternatives(void *start, size_t length);

-#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 */
@@ -57,15 +60,14 @@ void apply_alternatives(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" \
@@ -73,17 +75,25 @@ void apply_alternatives(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>
--
2.20.1