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Subject[PATCH 1/5] arm64/alternative_cb: move callback reference into replacements section
Date
In preparation of permitting callback type alternatives patching
routines to use any number of alternative instructions, move the
relative reference to the callback routine out of the primary
'struct alt_instr' data structure, where we are currently overloading
the 'alt_offset' member depending on the feature id. Instead, put
a relative reference to the callback at the start of the alternative
sequence.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
arch/arm64/include/asm/alternative.h | 39 +++++++++-----------
arch/arm64/kernel/alternative.c | 11 ++++--
2 files changed, 25 insertions(+), 25 deletions(-)

diff --git a/arch/arm64/include/asm/alternative.h b/arch/arm64/include/asm/alternative.h
index 4b650ec1d7dd..77da798e888b 100644
--- a/arch/arm64/include/asm/alternative.h
+++ b/arch/arm64/include/asm/alternative.h
@@ -24,6 +24,11 @@ struct alt_instr {
u8 alt_len; /* size of new instruction(s), <= orig_len */
};

+struct alt_instr_cb {
+ s32 cb_offset; /* offset to callback handler */
+ __le32 insn[]; /* sequence of alternative instructions */
+};
+
typedef void (*alternative_cb_t)(struct alt_instr *alt,
__le32 *origptr, __le32 *updptr, int nr_inst);

@@ -35,13 +40,9 @@ 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" \
- " .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 */
@@ -59,36 +60,29 @@ static inline void apply_alternatives_module(void *start, size_t length) { }
* but most assemblers die if insn1 or insn2 have a .inst. This should
* be fixed in a binutils release posterior to 2.25.51.0.2 (anything
* containing commit 4e4d08cf7399b606 or c1baaddf8861).
- *
- * Alternatives with callbacks do not generate replacement instructions.
*/
-#define __ALTERNATIVE_CFG(oldinstr, newinstr, feature, cfg_enabled, cb) \
- ".if "__stringify(cfg_enabled)" == 1\n" \
+#define __ALTERNATIVE_CFG(oldinstr, newinstr, feature) \
"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" \
"664:\n\t" \
- ".popsection\n\t" \
+ ".popsection\n\t"
+
+#define _ALTERNATIVE_CFG(oldinstr, newinstr, feature, cfg, ...) \
+ ".if "__stringify(IS_ENABLED(cfg))" == 1\n" \
+ __ALTERNATIVE_CFG(oldinstr, newinstr, feature) \
".org . - (664b-663b) + (662b-661b)\n\t" \
".org . - (662b-661b) + (664b-663b)\n" \
- ".else\n\t" \
- "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)
-
#define ALTERNATIVE_CB(oldinstr, cb) \
- __ALTERNATIVE_CFG(oldinstr, "NOT_AN_INSTRUCTION", ARM64_CB_PATCH, 1, cb)
+ __ALTERNATIVE_CFG(oldinstr, ".word " __stringify(cb) " - .\n", ARM64_CB_PATCH)
#else

#include <asm/assembler.h>
@@ -158,8 +152,11 @@ static inline void apply_alternatives_module(void *start, size_t length) { }
.macro alternative_cb cb
.set .Lasm_alt_mode, 0
.pushsection .altinstructions, "a"
- altinstruction_entry 661f, \cb, ARM64_CB_PATCH, 662f-661f, 0
+ altinstruction_entry 661f, 663f, ARM64_CB_PATCH, 662f-661f, 664f-663f
.popsection
+ .pushsection .altinstr_replacement, "ax"
+663: .word \cb - .
+664: .popsection
661:
.endm

diff --git a/arch/arm64/kernel/alternative.c b/arch/arm64/kernel/alternative.c
index b5d603992d40..a49930843784 100644
--- a/arch/arm64/kernel/alternative.c
+++ b/arch/arm64/kernel/alternative.c
@@ -151,6 +151,7 @@ static void __apply_alternatives(void *alt_region, bool is_module)
struct alt_region *region = alt_region;
__le32 *origptr, *updptr;
alternative_cb_t alt_cb;
+ struct alt_instr_cb *alt_cb_insn;

for (alt = region->begin; alt < region->end; alt++) {
int nr_inst;
@@ -161,7 +162,7 @@ static void __apply_alternatives(void *alt_region, bool is_module)
continue;

if (alt->cpufeature == ARM64_CB_PATCH)
- BUG_ON(alt->alt_len != 0);
+ BUG_ON(alt->alt_len < sizeof(*alt_cb_insn));
else
BUG_ON(alt->alt_len != alt->orig_len);

@@ -171,10 +172,12 @@ static void __apply_alternatives(void *alt_region, bool is_module)
updptr = is_module ? origptr : lm_alias(origptr);
nr_inst = alt->orig_len / AARCH64_INSN_SIZE;

- if (alt->cpufeature < ARM64_CB_PATCH)
+ if (alt->cpufeature < ARM64_CB_PATCH) {
alt_cb = patch_alternative;
- else
- alt_cb = ALT_REPL_PTR(alt);
+ } else {
+ alt_cb_insn = ALT_REPL_PTR(alt);
+ alt_cb = offset_to_ptr(&alt_cb_insn->cb_offset);
+ }

alt_cb(alt, origptr, updptr, nr_inst);

--
2.19.2
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