linux-kernel - Re: [PATCH v8] module: replace module_layout with module

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Date:   Thu, 2 Feb 2023 07:23:20 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Song Liu <song@...nel.org>,
        "linux-modules@...r.kernel.org" <linux-modules@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     "hch@....de" <hch@....de>,
        "kernel-team@...a.com" <kernel-team@...a.com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Guenter Roeck <linux@...ck-us.net>
Subject: Re: [PATCH v8] module: replace module_layout with module_memory



Le 01/02/2023 à 23:32, Song Liu a écrit :
> module_layout manages different types of memory (text, data, rodata, etc.)
> in one allocation, which is problematic for some reasons:
> 
> 1. It is hard to enable CONFIG_STRICT_MODULE_RWX.
> 2. It is hard to use huge pages in modules (and not break strict rwx).
> 3. Many archs uses module_layout for arch-specific data, but it is not
>     obvious how these data are used (are they RO, RX, or RW?)
> 
> Improve the scenario by replacing 2 (or 3) module_layout per module with
> up to 7 module_memory per module:
> 
>          MOD_TEXT,
>          MOD_DATA,
>          MOD_RODATA,
>          MOD_RO_AFTER_INIT,
>          MOD_INIT_TEXT,
>          MOD_INIT_DATA,
>          MOD_INIT_RODATA,
> 
> and allocating them separately. This adds slightly more entries to
> mod_tree (from up to 3 entries per module, to up to 7 entries per
> module). However, this at most adds a small constant overhead to
> __module_address(), which is expected to be fast.
> 
> Various archs use module_layout for different data. These data are put
> into different module_memory based on their location in module_layout.
> IOW, data that used to go with text is allocated with MOD_MEM_TYPE_TEXT;
> data that used to go with data is allocated with MOD_MEM_TYPE_DATA, etc.
> 
> module_memory simplifies quite some of the module code. For example,
> ARCH_WANTS_MODULES_DATA_IN_VMALLOC is a lot cleaner, as it just uses a
> different allocator for the data. kernel/module/strict_rwx.c is also
> much cleaner with module_memory.
> 
> Signed-off-by: Song Liu <song@...nel.org>
> Cc: Luis Chamberlain <mcgrof@...nel.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Guenter Roeck <linux@...ck-us.net>
> Cc: Christophe Leroy <christophe.leroy@...roup.eu>
> 

   CALL    scripts/checksyscalls.sh
   CC      kernel/module/main.o
kernel/module/main.c: In function 'mod_mem_use_vmalloc':
kernel/module/main.c:1175:16: error: implicit declaration of function 
'mod_mem_is_core_data'; did you mean 'mod_mem_type_is_core_data'? 
[-Werror=implicit-function-declaration]
  1175 |         return mod_mem_is_core_data(type);
       |                ^~~~~~~~~~~~~~~~~~~~
       |                mod_mem_type_is_core_data
cc1: some warnings being treated as errors
make[3]: *** [scripts/Makefile.build:252: kernel/module/main.o] Error 1
make[2]: *** [scripts/Makefile.build:504: kernel/module] Error 2
make[1]: *** [scripts/Makefile.build:504: kernel] Error 2
make: *** [Makefile:2024: .] Error 2