Re: Differences between builtins and modules

On Tue, Feb 24, 2015 at 10:02:55PM -0300, Lucas De Marchi wrote:

quoted

On Mon, Feb 23, 2015 at 12:51 PM, Michal Marek [off-list ref] wrote:

quoted

On 2015-02-23 15:30, Lucas De Marchi wrote:

quoted

My questions are:
1) should we put *all* the "modules" in the builtin index?

You mean all *.o files that do not end up in some *.ko? That won't work,
because unlike module names, the names of object files are not global.

I was actually meaning anything that can have a directory under
/sys/module/. I figure we can't easily know this.

I see. Well, we could generate the .modinfo section also for builtin
object files and discard it from vmlinux later, like this:

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index ac78910..efe1798 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h

@@ -683,6 +683,7 @@
        EXIT_CALL                                                       \
        *(.discard)                                                     \
        *(.discard.*)                                                   \
+       *(.modinfo)                                                     \
        }

 /**

diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h
index 1c9effa..f38abfa 100644
--- a/include/linux/moduleparam.h
+++ b/include/linux/moduleparam.h

@@ -16,23 +16,17 @@
 /* Chosen so that structs with an unsigned long line up. */
 #define MAX_PARAM_PREFIX_LEN (64 - sizeof(unsigned long))

-#ifdef MODULE
 #define __MODULE_INFO(tag, name, info)                                   \
 static const char __UNIQUE_ID(name)[]                                    \
   __used __attribute__((section(".modinfo"), unused, aligned(1)))        \
   = __stringify(tag) "=" info
-#else  /* !MODULE */
-/* This struct is here for syntactic coherency, it is not used */
-#define __MODULE_INFO(tag, name, info)                                   \
-  struct __UNIQUE_ID(name) {}
-#endif
 #define __MODULE_PARM_TYPE(name, _type)                                          \
-  __MODULE_INFO(parmtype, name##type, #name ":" _type)
+  __MODULE_INFO(parmtype, name##type, MODULE_PARAM_PREFIX #name ":" _type)

 /* One for each parameter, describing how to use it.  Some files do
    multiple of these per line, so can't just use MODULE_INFO. */
 #define MODULE_PARM_DESC(_parm, desc) \
-       __MODULE_INFO(parm, _parm, #_parm ":" desc)
+       __MODULE_INFO(parm, _parm, MODULE_PARAM_PREFIX #_parm ":" desc)

 struct kernel_param;

Then some script would look at the parmtype= fields in the built-in.o
files and complement the list of builtin modules. However, the question
is whether this is worth it. As far as I understand, the problem is just
the discrepancy between modules.builtin and /sys/module. In practice, no
sane tool is going to need to modprobe 'vt' or 'printk', because there
is no configuration in which these modules would exist.