Re: [PATCH 1/4] module: Add module_subinit{_noexit} and module_subeixt helper macros
From: Youling Tang
Date: Tue Jul 23 2024 - 21:20:47 EST
Hi, Mika
On 23/07/2024 17:58, Mika Penttilä wrote:
On 7/23/24 11:32, Youling Tang wrote:
From: Youling Tang <tangyouling@xxxxxxxxxx>
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@xxxxxxxxxx>
---
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();
+ }
+}
How does this guarantee the exit calls match sequence? Are you assuming
linker puts exit functions in reverse order?
Take btrfs for example:
Initialize the function sequentially in init_btrfs_fs() using
module_subinit{_noexit}, storing the corresponding function addresses
in the specified ".subinitcall.init" and ".subexitcall.exit" sections.
Using gcc to compile btrfs to.ko, the view section contains the following:
```
$ objdump -d -j ".subinitcall.init" fs/btrfs/super.o
fs/btrfs/super.o: file format elf64-x86-64
Disassembly of section .subinitcall.init:
0000000000000000 <__subinitcall_register_btrfs.0>:
...
0000000000000008 <__subinitcall_btrfs_run_sanity_tests.2>:
...
0000000000000010 <__subinitcall_btrfs_print_mod_info.3>:
...
0000000000000018 <__subinitcall_btrfs_interface_init.4>:
...
0000000000000020 <__subinitcall_btrfs_prelim_ref_init.6>:
...
0000000000000028 <__subinitcall_btrfs_delayed_ref_init.8>:
...
0000000000000030 <__subinitcall_btrfs_auto_defrag_init.10>:
...
0000000000000038 <__subinitcall_btrfs_delayed_inode_init.12>:
...
0000000000000040 <__subinitcall_ordered_data_init.14>:
...
0000000000000048 <__subinitcall_extent_map_init.16>:
...
0000000000000050 <__subinitcall_btrfs_bioset_init.18>:
...
0000000000000058 <__subinitcall_extent_buffer_init_cachep.20>:
...
0000000000000060 <__subinitcall_extent_state_init_cachep.22>:
...
0000000000000068 <__subinitcall_btrfs_free_space_init.24>:
...
0000000000000070 <__subinitcall_btrfs_ctree_init.26>:
...
0000000000000078 <__subinitcall_btrfs_transaction_init.28>:
...
0000000000000080 <__subinitcall_btrfs_init_dio.30>:
...
0000000000000088 <__subinitcall_btrfs_init_cachep.32>:
...
0000000000000090 <__subinitcall_btrfs_init_compress.34>:
...
0000000000000098 <__subinitcall_btrfs_init_sysfs.36>:
...
00000000000000a0 <__subinitcall_btrfs_props_init.38>:
...
```
```
$ objdump -d -j ".subexitcall.exit" fs/btrfs/super.o
fs/btrfs/super.o: file format elf64-x86-64
Disassembly of section .subexitcall.exit:
0000000000000000 <__subexitcall_unregister_btrfs.1>:
...
0000000000000008 <__subexitcall_btrfs_interface_exit.5>:
...
0000000000000010 <__subexitcall_btrfs_prelim_ref_exit.7>:
...
0000000000000018 <__subexitcall_btrfs_delayed_ref_exit.9>:
...
0000000000000020 <__subexitcall_btrfs_auto_defrag_exit.11>:
...
0000000000000028 <__subexitcall_btrfs_delayed_inode_exit.13>:
...
0000000000000030 <__subexitcall_ordered_data_exit.15>:
...
0000000000000038 <__subexitcall_extent_map_exit.17>:
...
0000000000000040 <__subexitcall_btrfs_bioset_exit.19>:
...
0000000000000048 <__subexitcall_extent_buffer_free_cachep.21>:
...
0000000000000050 <__subexitcall_extent_state_free_cachep.23>:
...
0000000000000058 <__subexitcall_btrfs_free_space_exit.25>:
...
0000000000000060 <__subexitcall_btrfs_ctree_exit.27>:
...
0000000000000068 <__subexitcall_btrfs_transaction_exit.29>:
...
0000000000000070 <__subexitcall_btrfs_destroy_dio.31>:
...
0000000000000078 <__subexitcall_btrfs_destroy_cachep.33>:
...
0000000000000080 <__subexitcall_btrfs_exit_compress.35>:
...
0000000000000088 <__subexitcall_btrfs_exit_sysfs.37>:
...
```
From the above, we can see that the compiler stores the init/exit function
in reverse order.
Thanks,
Youling.