Re: [PATCH v5][makedumpfile 6/9] Add makedumpfile extensions support

[Tao Liu <ltao@redhat.com>]

Hi Kazu,

On Tue, Jun 16, 2026 at 07:51:47AM +0000, HAGIO KAZUHITO(萩尾 一仁) wrote:
> On 2026/06/16 11:17, Tao Liu wrote:
> > On Tue, Jun 16, 2026 at 1:39 PM HAGIO KAZUHITO(萩尾　一仁)
> > <k-hagio-ab@nec.com> wrote:
> >>
> >> On 2026/06/16 8:03, Tao Liu wrote:
> >>> Hi Stephen & Kazu,
> >>>
> >>> On Tue, Jun 16, 2026 at 5:12 AM Stephen Brennan
> >>> <stephen.s.brennan@oracle.com> wrote:
> >>>>
> >>>> HAGIO KAZUHITO(萩尾　一仁)   <k-hagio-ab@nec.com> writes:
> >>>>> On 2026/04/14 19:26, Tao Liu wrote:
> >>>>>
> >>>>>> +static bool init_kallsyms_btf(void)
> >>>>>> +{
> >>>>>> +    int count;
> >>>>>> +    bool ret = false;
> >>>>>> +    /* We will load module's btf/kallsyms on demand */
> >>>>>> +    bool init_ksyms_module = false;
> >>>>>> +    bool init_ktypes_module = false;
> >>>>>> +
> >>>>>> +    if (check_ksyms_require_modname("vmlinux", &count)) {
> >>>>>
> >>>>> Thank you for the explanation [1].
> >>>>>
> >>>>> so which code path adds "vmlinux" to the mods array before this line?
> >>>>> I could not find it.
> >>>>
> >>>> Hello Kazu,
> >>>>
> >>>> In kallsyms.c from patch 2, there is the line:
> >>>>     INIT_MOD_SYM(vmlinux, _stext);
> >>>> This adds a struct ksym_info to the main makedumpfile executable's
> >>>> array, which requests symbol "_stext" from vmlinux.
> >>>>
> >>>> In kallsyms.c "init_kernel_kallsyms()", again from patch 2, the first
> >>>> step is to call:
> >>>>      register_ksym_section((char *)__start_init_ksyms,
> >>>>                            (char *)__stop_init_ksyms))
> >>>> Which is a function generated by the macro REGISTER_SECTION(). The
> >>>> implementation will use add_ksym_modname() whens it encounters this
> >>>> symbol, ensuring that "vmlinux" is part of the modname array.
> >>>
> >>> Thanks for the detailed info, yes, it is exactly how "vmlinux" is
> >>> added to the array.
> >>
> >> hmm, maybe I still misread it though..
> >>
> >> The init_kernel_kallsyms() is called _after_ check_ksyms_require_modname().
> >> so I've meant that if no extension adds "vmlinux" to the modname array,
> >> no one calls it.  is it ok?
> >>
> >>           if (check_ksyms_require_modname("vmlinux", &count)) {
> >>                   if (!init_kernel_kallsyms())
> > 
> > No, even if you create a extension which doesn't require symbols from
> > "vmlinux", once you load it, the check_ksyms_require_modname() will
> > still be true and init_kernel_kallsyms() is called.
> > 
> > The reason is, with the introduction of makedumpfile.ld, and the line
> > "INIT_MOD_SYM(vmlinux, _stext);" in kallsyms.c, makedumpfile and
> > extensions have a similar section structure, you can regard
> > makedumpfile itself as an extension:
> > 
> > $ readelf -S makedumpfile | grep -E 'ksyms|ktypes'
> >    [25] .init_ksyms       PROGBITS         000000000046ee90  0006de90
> >    [26] .init_ktypes      PROGBITS         000000000046eeb8  0006deb8
> > $ readelf -S extensions/sample.so | grep -E 'ksyms|ktypes'
> >    [24] .init_ksyms       PROGBITS         0000000000003108  00002108
> >    [25] .init_ktypes      PROGBITS         0000000000003110  00002110
> > 
> > If makedumpfile doesn't load any extensions, then makedumpfile doesn't
> > need to initialize its .init_ksyms/ktypes section, the behaviour stays
> > the same as before;
> > If makedumpfile load at least one extensions, then the extension
> > subsystem will register all .init_ksyms/ktypes sections, both
> > extenison's and makedumpfile's.
> > 
> > This is like, extension say "I need sym1 & sym2 to be ready before I
> > can run", then makedumpfile say "OK, I got it, but before I can
> > resolve your sym1 & sym2, I need to resolve some symbol(e.g. vmlinux's
> > _stext) formyself first". So check_ksyms_require_modname("vmlinux",
> > &count) will be true.
> 
> hmm, but as far as I've tested with "extensions/sample.c" on RHEL10.2:
> 
> 1) add INIT_MOD_SYM(xfs, xfsstats) and GET_MOD_SYM(xfs, xfsstats)
> 
> ok
> 
> Loaded extension: /share/tmp/makedumpfile/extensions/sample.so
> sample.so: The address of xfsstats is: ffffffffc0c0b540   <<--- ok
> sample.so: The address of init_task is: ffffffffb4412940
> sample.so: The size of task_struct is: 10240 bytes
> sample.so: The offset of member mm within task_struct is: 2704 bytes
> sample.so: The size of member mm within task_struct is: 8 bytes
> sample.so: Your kernel is using maple tree in mm_struct
> 
> 2) remove all "vmlinux" entries (only INIT_MOD_SYM(xfs, xfsstats))
> 
> skipped
> 
> Loaded extension: /share/tmp/makedumpfile/extensions/sample.so
> check_required_ksyms_all_resolved: Symbol xfsstats in xfs not found
> init_extensions: Skip 1th extension
> 

This is a bug which shouldn't happen, thanks for pointing it out.

> 3) restore INIT_MOD_SYM(vmlinux, init_task) and GET_MOD_SYM(vmlinux, init_task)
> 
> still skipped
> 
> Loaded extension: /share/tmp/makedumpfile/extensions/sample.so
> check_required_ksyms_all_resolved: Symbol xfsstats in xfs not found
> init_extensions: Skip 1th extension
> 

Also a bug. I made a code modification based on the v5 to fix, could you please
give a try? If no problem I will integrate it with v6.

diff --git a/btf_info.c b/btf_info.c
index 1506152..fbb487b 100644
--- a/btf_info.c
+++ b/btf_info.c
@@ -202,10 +202,6 @@ bool init_kernel_btf(void)
 		goto out;
 	}
 
-	if (!register_ktype_section((char *)__start_init_ktypes,
-				    (char *)__stop_init_ktypes))
-		return ret;
-
 	size = stop_btf - start_btf;
 	buf = (char *)malloc(size);
 	if (!buf) {
diff --git a/extension.c b/extension.c
index 190dd9e..276ffb1 100644
--- a/extension.c
+++ b/extension.c
@@ -153,7 +153,7 @@ static void load_extensions(void)
 	}
 }
 
-static bool register_extension_sections(void)
+static bool register_ksyms_ktypes_sections(void)
 {
 	char *start, *stop;
 	int i;
@@ -170,6 +170,18 @@ static bool register_extension_sections(void)
 		if (!register_ktype_section(start, stop))
 			goto out;
 	}
+	/* If no extensions, don't register makedumpfile's section */
+	if (handle_cbs_len > 0) {
+		start = dlsym(NULL, "__start_init_ksyms");
+		stop = dlsym(NULL, "__stop_init_ksyms");
+		if (!register_ksym_section(start, stop))
+			goto out;
+
+		start = dlsym(NULL, "__start_init_ktypes");
+		stop = dlsym(NULL, "__stop_init_ktypes");
+		if (!register_ktype_section(start, stop))
+			goto out;
+	}
 	ret = true;
 out:
 	return ret;
@@ -260,7 +272,7 @@ void init_extensions(void)
 	void (*init)(void);
 
 	load_extensions();
-	if (!register_extension_sections())
+	if (!register_ksyms_ktypes_sections())
 		goto fail;
 	if (!init_kallsyms_btf()) 
 		goto fail;
diff --git a/kallsyms.c b/kallsyms.c
index f231a06..0037600 100644
--- a/kallsyms.c
+++ b/kallsyms.c
@@ -276,10 +276,6 @@ bool init_kernel_kallsyms(void)
 		return ret;
 	}
 
-	if (!register_ksym_section((char *)__start_init_ksyms,
-				   (char *)__stop_init_ksyms))
-		return ret;
-
 	if (!readmem(VADDR, SYMBOL(kallsyms_num_syms), &kallsyms_num_syms,
 		sizeof(kallsyms_num_syms))) {
 		ERRMSG("Can't get kallsyms_num_syms!\n");


> 4) also restore INIT_MOD_STRUCT_MEMBER(vmlinux, task_struct, mm) and
>     GET_MOD_STRUCT_MEMBER_SSIZE(vmlinux, task_struct, mm)
> 
> ok
> 
> Loaded extension: /share/tmp/makedumpfile/extensions/sample.so
> sample.so: The address of xfsstats is: ffffffffc0c0b540
> sample.so: The address of init_task is: ffffffffb4412940
> sample.so: The size of task_struct is: 10240 bytes
> 
> 
> So, it looks like, with the current condition check in init_kallsyms_btf()
> (check_ksyms_require_modname and check_ktypes_require_modname),
> a module needs to use INIT_* for vmlinux's kallsyms and BTF.
> 
> I'm still missing something..?
> 
> Thanks,
> Kazu