[PATCH 1/4] module: Add module_subinit{_noexit} and module_subeixt helper macros

Youling Tang
2024-07-23T08:33:05Z

From: Youling Tang <tangyouling@kylinos.cn>

In theory init/exit should match their sequence, thus normally they should
look like this:
-------------------------+------------------------
init_A(); |
init_B(); |
init_C(); |
| exit_C();
| exit_B();
| exit_A();

Providing module_subinit{_noexit} and module_subeixt helps macros ensure
that modules init/exit match their order, while also simplifying the code.

The three macros are defined as follows:
- module_subinit(initfn, exitfn,rollback)
- module_subinit_noexit(initfn, rollback)
- module_subexit(rollback)

`initfn` is the initialization function and `exitfn` is the corresponding
exit function.

Signed-off-by: Youling Tang <tangyouling@kylinos.cn>
---
include/asm-generic/vmlinux.lds.h | 5 +++
include/linux/init.h | 62 ++++++++++++++++++++++++++++++-
include/linux/module.h | 22 +++++++++++
3 files changed, 88 insertions(+), 1 deletion(-)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 677315e51e54..48ccac7c6448 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -927,6 +927,10 @@
INIT_CALLS_LEVEL(7) \
__initcall_end = .;

+#define SUBINIT_CALL \
+ *(.subinitcall.init) \
+ *(.subexitcall.exit)
+
#define CON_INITCALL \
BOUNDED_SECTION_POST_LABEL(.con_initcall.init, __con_initcall, _start, _end)

@@ -1155,6 +1159,7 @@
INIT_DATA \
INIT_SETUP(initsetup_align) \
INIT_CALLS \
+ SUBINIT_CALL \
CON_INITCALL \
INIT_RAM_FS \
}
diff --git a/include/linux/init.h b/include/linux/init.h
index ee1309473bc6..e8689ff2cb6c 100644
--- a/include/linux/init.h
+++ b/include/linux/init.h
@@ -55,6 +55,9 @@
#define __exitdata __section(".exit.data")
#define __exit_call __used __section(".exitcall.exit")

+#define __subinit_call __used __section(".subinitcall.init")
+#define __subexit_call __used __section(".subexitcall.exit")
+
/*
* modpost check for section mismatches during the kernel build.
* A section mismatch happens when there are references from a
@@ -115,6 +118,9 @@
typedef int (*initcall_t)(void);
typedef void (*exitcall_t)(void);

+typedef int (*subinitcall_t)(void);
+typedef void (*subexitcall_t)(void);
+
#ifdef CONFIG_HAVE_ARCH_PREL32_RELOCATIONS
typedef int initcall_entry_t;

@@ -183,7 +189,61 @@ extern struct module __this_module;
#endif

#endif
-
+
+#ifndef __ASSEMBLY__
+struct subexitcall_rollback {
+ /*
+ * Records the address of the first sub-initialization function in the
+ * ".subexitcall.exit" section
+ */
+ unsigned long first_addr;
+ int ncalls;
+};
+
+static inline void __subexitcall_rollback(struct subexitcall_rollback *r)
+{
+ unsigned long addr = r->first_addr - sizeof(r->first_addr) * (r->ncalls - 1);
+
+ for (; r->ncalls--; addr += sizeof(r->first_addr)) {
+ unsigned long *tmp = (void *)addr;
+ subexitcall_t fn = (subexitcall_t)*tmp;
+ fn();
+ }
+}
+
+static inline void set_rollback_ncalls(struct subexitcall_rollback *r)
+{
+ r->ncalls++;
+}
+
+static inline void set_rollback_first_addr(struct subexitcall_rollback *rollback,
+ unsigned long addr)
+{
+ if (!rollback->first_addr)
+ rollback->first_addr = addr;
+}
+
+#define __subinitcall_noexit(initfn, rollback) \
+do { \
+ static subinitcall_t __subinitcall_##initfn __subinit_call = initfn; \
+ int _ret; \
+ _ret = initfn(); \
+ if (_ret < 0) { \
+ __subexitcall_rollback(rollback); \
+ return _ret; \
+ } \
+} while (0)
+
+#define __subinitcall(initfn, exitfn, rollback) \
+do { \
+ static subexitcall_t __subexitcall_##exitfn __subexit_call = exitfn; \
+ set_rollback_first_addr(rollback, (unsigned long)&__subexitcall_##exitfn); \
+ __subinitcall_noexit(initfn, rollback); \
+ set_rollback_ncalls(rollback); \
+} while (0)
+
+#endif /* !__ASSEMBLY__ */
+
#ifndef MODULE

#ifndef __ASSEMBLY__
diff --git a/include/linux/module.h b/include/linux/module.h
index 4213d8993cd8..95f7c60dede9 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -76,6 +76,28 @@ extern struct module_attribute module_uevent;
extern int init_module(void);
extern void cleanup_module(void);

+/*
+ * module_subinit() - Called when the driver is subinitialized
+ * @initfn: The subinitialization function that is called
+ * @exitfn: Corresponding exit function
+ * @rollback: Record information when the subinitialization failed
+ * or the driver was removed
+ *
+ * Use module_subinit_noexit() when there is only an subinitialization
+ * function but no corresponding exit function.
+ */
+#define module_subinit(initfn, exitfn, rollback) \
+ __subinitcall(initfn, exitfn, rollback);
+
+#define module_subinit_noexit(initfn, rollback) \
+ __subinitcall_noexit(initfn, rollback);
+
+/*
+ * module_subexit() - Called when the driver exits
+ */
+#define module_subexit(rollback) \
+ __subexitcall_rollback(rollback);
+
#ifndef MODULE
/**
* module_init() - driver initialization entry point
--
2.34.1