The following commit has been merged into the core/static_call branch of tip:
Commit-ID: 5b06fd3bb9cdce4f3e731c48eb5b74c4acc47997 Gitweb: https://git.kernel.org/tip/5b06fd3bb9cdce4f3e731c48eb5b74c4acc47997 Author: Peter Zijlstra <pet...@infradead.org> AuthorDate: Tue, 18 Aug 2020 15:57:49 +02:00 Committer: Ingo Molnar <mi...@kernel.org> CommitterDate: Tue, 01 Sep 2020 09:58:06 +02:00 static_call: Handle tail-calls 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> Signed-off-by: Ingo Molnar <mi...@kernel.org> Cc: Linus Torvalds <torva...@linux-foundation.org> Link: https://lore.kernel.org/r/20200818135805.101186...@infradead.org --- arch/x86/kernel/static_call.c | 21 ++++++++++++++++++--- 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, 60 insertions(+), 18 deletions(-) diff --git a/arch/x86/kernel/static_call.c b/arch/x86/kernel/static_call.c index ead6726..60a325c 100644 --- a/arch/x86/kernel/static_call.c +++ b/arch/x86/kernel/static_call.c @@ -41,15 +41,30 @@ static void __static_call_transform(void *insn, enum insn_type type, void *func) text_poke_bp(insn, code, size, NULL); } -void arch_static_call_transform(void *site, void *tramp, void *func) +static inline enum insn_type __sc_insn(bool null, bool tail) +{ + /* + * Encode the following table without branches: + * + * tail null insn + * -----+-------+------ + * 0 | 0 | CALL + * 0 | 1 | NOP + * 1 | 0 | JMP + * 1 | 1 | RET + */ + return 2*tail + null; +} + +void arch_static_call_transform(void *site, void *tramp, void *func, bool tail) { mutex_lock(&text_mutex); if (tramp) - __static_call_transform(tramp, func ? JMP : RET, func); + __static_call_transform(tramp, __sc_insn(!func, true), func); if (IS_ENABLED(CONFIG_HAVE_STATIC_CALL_INLINE) && site) - __static_call_transform(site, func ? CALL : NOP, func); + __static_call_transform(site, __sc_insn(!func, tail), func); mutex_unlock(&text_mutex); } diff --git a/include/linux/static_call.h b/include/linux/static_call.h index 0f74581..519bd66 100644 --- a/include/linux/static_call.h +++ b/include/linux/static_call.h @@ -103,7 +103,7 @@ /* * 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); #define STATIC_CALL_TRAMP_ADDR(name) &STATIC_CALL_TRAMP(name) @@ -206,7 +206,7 @@ void __static_call_update(struct static_call_key *key, void *tramp, void *func) { 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(); } diff --git a/include/linux/static_call_types.h b/include/linux/static_call_types.h index 408d345..89135bb 100644 --- a/include/linux/static_call_types.h +++ b/include/linux/static_call_types.h @@ -17,6 +17,13 @@ #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). */ diff --git a/kernel/static_call.c b/kernel/static_call.c index 97142cb..d98e0e4 100644 --- a/kernel/static_call.c +++ b/kernel/static_call.c @@ -15,8 +15,6 @@ extern struct static_call_site __start_static_call_sites[], 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(struct static_call_site *site) 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_call_key *key, void *tramp, void *func) 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 @@ -154,7 +157,8 @@ void __static_call_update(struct static_call_key *key, void *tramp, void *func) continue; } - arch_static_call_transform(site_addr, NULL, func); + arch_static_call_transform(site_addr, NULL, func, + static_call_is_tail(site)); } } @@ -198,7 +202,8 @@ static int __static_call_init(struct module *mod, key->mods = 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; diff --git a/tools/include/linux/static_call_types.h b/tools/include/linux/static_call_types.h index 408d345..89135bb 100644 --- a/tools/include/linux/static_call_types.h +++ b/tools/include/linux/static_call_types.h @@ -17,6 +17,13 @@ #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). */ diff --git a/tools/objtool/check.c b/tools/objtool/check.c index f8f7a40..75d0cd2 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -516,7 +516,7 @@ static int create_static_call_sections(struct objtool_file *file) } memset(reloc, 0, sizeof(*reloc)); reloc->sym = key_sym; - reloc->addend = 0; + reloc->addend = is_sibling_call(insn) ? STATIC_CALL_SITE_TAIL : 0; reloc->type = R_X86_64_PC32; reloc->offset = idx * sizeof(struct static_call_site) + 4; reloc->sec = reloc_sec; @@ -747,6 +747,10 @@ static int add_jump_destinations(struct objtool_file *file) } else { /* external sibling call */ insn->call_dest = reloc->sym; + if (insn->call_dest->static_call_tramp) { + list_add_tail(&insn->static_call_node, + &file->static_call_list); + } continue; } @@ -798,6 +802,10 @@ static int add_jump_destinations(struct objtool_file *file) /* 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); + } } } } @@ -1684,6 +1692,10 @@ static int decode_sections(struct objtool_file *file) if (ret) return ret; + ret = read_static_call_tramps(file); + if (ret) + return ret; + ret = add_jump_destinations(file); if (ret) return ret; @@ -1716,10 +1728,6 @@ static int decode_sections(struct objtool_file *file) if (ret) return ret; - ret = read_static_call_tramps(file); - if (ret) - return ret; - return 0; }
