lkml.org 
[lkml]   [2021]   [Feb]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[tip: sched/core] static_call/x86: Add __static_call_return0()
The following commit has been merged into the sched/core branch of tip:

Commit-ID: 2f44200d3f3d6e6abab4e5529335f7852936f3a1
Gitweb: https://git.kernel.org/tip/2f44200d3f3d6e6abab4e5529335f7852936f3a1
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Mon, 18 Jan 2021 15:12:16 +01:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Fri, 05 Feb 2021 17:19:55 +01:00

static_call/x86: Add __static_call_return0()

Provide a stub function that return 0 and wire up the static call site
patching to replace the CALL with a single 5 byte instruction that
clears %RAX, the return value register.

The function can be cast to any function pointer type that has a
single %RAX return (including pointers). Also provide a version that
returns an int for convenience. We are clearing the entire %RAX register
in any case, whether the return value is 32 or 64 bits, since %RAX is
always a scratch register anyway.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210118141223.123667-2-frederic@kernel.org
---
arch/x86/kernel/static_call.c | 17 +++++++++++++++--
include/linux/static_call.h | 12 ++++++++++++
kernel/static_call.c | 5 +++++
3 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/static_call.c b/arch/x86/kernel/static_call.c
index ca9a380..9442c41 100644
--- a/arch/x86/kernel/static_call.c
+++ b/arch/x86/kernel/static_call.c
@@ -11,14 +11,26 @@ enum insn_type {
RET = 3, /* tramp / site cond-tail-call */
};

+/*
+ * data16 data16 xorq %rax, %rax - a single 5 byte instruction that clears %rax
+ * The REX.W cancels the effect of any data16.
+ */
+static const u8 xor5rax[] = { 0x66, 0x66, 0x48, 0x31, 0xc0 };
+
static void __ref __static_call_transform(void *insn, enum insn_type type, void *func)
{
+ const void *emulate = NULL;
int size = CALL_INSN_SIZE;
const void *code;

switch (type) {
case CALL:
code = text_gen_insn(CALL_INSN_OPCODE, insn, func);
+ if (func == &__static_call_return0) {
+ emulate = code;
+ code = &xor5rax;
+ }
+
break;

case NOP:
@@ -41,7 +53,7 @@ static void __ref __static_call_transform(void *insn, enum insn_type type, void
if (unlikely(system_state == SYSTEM_BOOTING))
return text_poke_early(insn, code, size);

- text_poke_bp(insn, code, size, NULL);
+ text_poke_bp(insn, code, size, emulate);
}

static void __static_call_validate(void *insn, bool tail)
@@ -54,7 +66,8 @@ static void __static_call_validate(void *insn, bool tail)
return;
} else {
if (opcode == CALL_INSN_OPCODE ||
- !memcmp(insn, ideal_nops[NOP_ATOMIC5], 5))
+ !memcmp(insn, ideal_nops[NOP_ATOMIC5], 5) ||
+ !memcmp(insn, xor5rax, 5))
return;
}

diff --git a/include/linux/static_call.h b/include/linux/static_call.h
index a2c0645..bd6735d 100644
--- a/include/linux/static_call.h
+++ b/include/linux/static_call.h
@@ -142,6 +142,8 @@ extern void __static_call_update(struct static_call_key *key, void *tramp, void
extern int static_call_mod_init(struct module *mod);
extern int static_call_text_reserved(void *start, void *end);

+extern long __static_call_return0(void);
+
#define DEFINE_STATIC_CALL(name, _func) \
DECLARE_STATIC_CALL(name, _func); \
struct static_call_key STATIC_CALL_KEY(name) = { \
@@ -206,6 +208,11 @@ static inline int static_call_text_reserved(void *start, void *end)
return 0;
}

+static inline long __static_call_return0(void)
+{
+ return 0;
+}
+
#define EXPORT_STATIC_CALL(name) \
EXPORT_SYMBOL(STATIC_CALL_KEY(name)); \
EXPORT_SYMBOL(STATIC_CALL_TRAMP(name))
@@ -222,6 +229,11 @@ struct static_call_key {
void *func;
};

+static inline long __static_call_return0(void)
+{
+ return 0;
+}
+
#define DEFINE_STATIC_CALL(name, _func) \
DECLARE_STATIC_CALL(name, _func); \
struct static_call_key STATIC_CALL_KEY(name) = { \
diff --git a/kernel/static_call.c b/kernel/static_call.c
index 84565c2..0bc11b5 100644
--- a/kernel/static_call.c
+++ b/kernel/static_call.c
@@ -438,6 +438,11 @@ int __init static_call_init(void)
}
early_initcall(static_call_init);

+long __static_call_return0(void)
+{
+ return 0;
+}
+
#ifdef CONFIG_STATIC_CALL_SELFTEST

static int func_a(int x)
\
 
 \ /
  Last update: 2021-02-08 13:42    [W:0.605 / U:0.400 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site