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

Mika Penttilä
2024-07-23T09:58:17Z

On 7/23/24 11:32, Youling Tang wrote:
> 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();
> + }
> +}

How does this guarantee the exit calls match sequence? Are you assuming
linker puts exit functions in reverse order?

--Mika