GCC can turn our static_call(name)(args...) into a tail call, in which case we get a JMP.d32 into the trampoline (which then does a further tail-call).
Teach objtool to recognise and mark these in .static_call_sites and adjust the code patching to deal with this. Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org> --- arch/x86/kernel/static_call.c | 4 ++-- include/linux/static_call.h | 4 ++-- include/linux/static_call_types.h | 7 +++++++ kernel/static_call.c | 21 +++++++++++++-------- tools/include/linux/static_call_types.h | 7 +++++++ tools/objtool/check.c | 18 +++++++++++++----- 6 files changed, 44 insertions(+), 17 deletions(-) --- a/arch/x86/kernel/static_call.c +++ b/arch/x86/kernel/static_call.c @@ -41,7 +41,7 @@ static void __static_call_transform(void text_poke_bp(insn, code, size, NULL); } -void arch_static_call_transform(void *site, void *tramp, void *func) +void arch_static_call_transform(void *site, void *tramp, void *func, bool tail) { mutex_lock(&text_mutex); @@ -49,7 +49,7 @@ void arch_static_call_transform(void *si __static_call_transform(tramp, jmp + !func, func); if (IS_ENABLED(CONFIG_HAVE_STATIC_CALL_INLINE) && site) - __static_call_transform(site, !func, func); + __static_call_transform(site, 2*tail + !func, func); mutex_unlock(&text_mutex); } --- a/include/linux/static_call.h +++ b/include/linux/static_call.h @@ -64,7 +64,7 @@ /* * Either @site or @tramp can be NULL. */ -extern void arch_static_call_transform(void *site, void *tramp, void *func); +extern void arch_static_call_transform(void *site, void *tramp, void *func, bool tail); #endif @@ -137,7 +137,7 @@ void __static_call_update(struct static_ { cpus_read_lock(); WRITE_ONCE(key->func, func); - arch_static_call_transform(NULL, tramp, func); + arch_static_call_transform(NULL, tramp, func, false); cpus_read_unlock(); } --- a/include/linux/static_call_types.h +++ b/include/linux/static_call_types.h @@ -13,6 +13,13 @@ #define STATIC_CALL_TRAMP_STR(name) __stringify(STATIC_CALL_TRAMP(name)) /* + * Flags in the low bits of static_call_site::key. + */ +#define STATIC_CALL_SITE_TAIL 1UL /* tail call */ +#define STATIC_CALL_SITE_INIT 2UL /* init section */ +#define STATIC_CALL_SITE_FLAGS 3UL + +/* * The static call site table needs to be created by external tooling (objtool * or a compiler plugin). */ --- a/kernel/static_call.c +++ b/kernel/static_call.c @@ -15,8 +15,6 @@ extern struct static_call_site __start_s static bool static_call_initialized; -#define STATIC_CALL_INIT 1UL - /* mutex to protect key modules/sites */ static DEFINE_MUTEX(static_call_mutex); @@ -39,18 +37,23 @@ static inline void *static_call_addr(str static inline struct static_call_key *static_call_key(const struct static_call_site *site) { return (struct static_call_key *) - (((long)site->key + (long)&site->key) & ~STATIC_CALL_INIT); + (((long)site->key + (long)&site->key) & ~STATIC_CALL_SITE_FLAGS); } /* These assume the key is word-aligned. */ static inline bool static_call_is_init(struct static_call_site *site) { - return ((long)site->key + (long)&site->key) & STATIC_CALL_INIT; + return ((long)site->key + (long)&site->key) & STATIC_CALL_SITE_INIT; +} + +static inline bool static_call_is_tail(struct static_call_site *site) +{ + return ((long)site->key + (long)&site->key) & STATIC_CALL_SITE_TAIL; } static inline void static_call_set_init(struct static_call_site *site) { - site->key = ((long)static_call_key(site) | STATIC_CALL_INIT) - + site->key = ((long)static_call_key(site) | STATIC_CALL_SITE_INIT) - (long)&site->key; } @@ -104,7 +107,7 @@ void __static_call_update(struct static_ key->func = func; - arch_static_call_transform(NULL, tramp, func); + arch_static_call_transform(NULL, tramp, func, false); /* * If uninitialized, we'll not update the callsites, but they still @@ -153,7 +156,8 @@ void __static_call_update(struct static_ continue; } - arch_static_call_transform(site_addr, NULL, func); + arch_static_call_transform(site_addr, NULL, func, + static_call_is_tail(site)); } } @@ -197,7 +201,8 @@ static int __static_call_init(struct mod key->next = site_mod; } - arch_static_call_transform(site_addr, NULL, key->func); + arch_static_call_transform(site_addr, NULL, key->func, + static_call_is_tail(site)); } return 0; --- a/tools/include/linux/static_call_types.h +++ b/tools/include/linux/static_call_types.h @@ -13,6 +13,13 @@ #define STATIC_CALL_TRAMP_STR(name) __stringify(STATIC_CALL_TRAMP(name)) /* + * Flags in the low bits of static_call_site::key. + */ +#define STATIC_CALL_SITE_TAIL 1UL /* tail call */ +#define STATIC_CALL_SITE_INIT 2UL /* init section */ +#define STATIC_CALL_SITE_FLAGS 3UL + +/* * The static call site table needs to be created by external tooling (objtool * or a compiler plugin). */ --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -585,6 +585,10 @@ static int add_jump_destinations(struct } else { /* external sibling call */ insn->call_dest = rela->sym; + if (insn->call_dest->static_call_tramp) { + list_add_tail(&insn->static_call_node, + &file->static_call_list); + } continue; } @@ -636,6 +640,10 @@ static int add_jump_destinations(struct /* internal sibling call */ insn->call_dest = insn->jump_dest->func; + if (insn->call_dest->static_call_tramp) { + list_add_tail(&insn->static_call_node, + &file->static_call_list); + } } } } @@ -1348,6 +1356,10 @@ static int decode_sections(struct objtoo if (ret) return ret; + ret = read_static_call_tramps(file); + if (ret) + return ret; + ret = add_jump_destinations(file); if (ret) return ret; @@ -1372,10 +1384,6 @@ static int decode_sections(struct objtoo if (ret) return ret; - ret = read_static_call_tramps(file); - if (ret) - return ret; - return 0; } @@ -2505,7 +2513,7 @@ static int create_static_call_sections(s } memset(rela, 0, sizeof(*rela)); rela->sym = key_sym; - rela->addend = 0; + rela->addend = is_sibling_call(insn) ? STATIC_CALL_SITE_TAIL : 0; rela->type = R_X86_64_PC32; rela->offset = idx * sizeof(struct static_call_site) + 4; list_add_tail(&rela->list, &rela_sec->rela_list);