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static_call: Handle tail-calls

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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) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20200818135805.101186767@infradead.org
This commit is contained in:
Peter Zijlstra 2020-08-18 15:57:49 +02:00 committed by Ingo Molnar
parent 452cddbff7
commit 5b06fd3bb9
6 changed files with 60 additions and 18 deletions
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21
arch/x86/kernel/static_call.c
View File

@ -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);
}

4
include/linux/static_call.h
View File

@ -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();
}

7
include/linux/static_call_types.h
View File

@ -16,6 +16,13 @@
#define STATIC_CALL_TRAMP(name) __PASTE(STATIC_CALL_TRAMP_PREFIX, name)
#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).

21
kernel/static_call.c
View File

@ -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;

7
tools/include/linux/static_call_types.h
View File

@ -16,6 +16,13 @@
#define STATIC_CALL_TRAMP(name) __PASTE(STATIC_CALL_TRAMP_PREFIX, name)
#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).

18
tools/objtool/check.c
View File

@ -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;
}