Re: [PATCH 1/2] kallsyms: add symbol size for kallsyms symbols that can change size

[Geert Uytterhoeven]

Hi André,

On Mon, 24 Aug 2026 at 15:35, André Draszik <andre.draszik@xxxxxxxxxx> wrote:
> On Mon, 2026-08-24 at 14:26 +0200, Geert Uytterhoeven wrote:
> > On Tue, 28 Jul 2026 at 14:52, André Draszik <andre.draszik@xxxxxxxxxx> wrote:
> > > Add symbol size for kallsyms symbols that can change size so that sizes
> > > can be determined easily without having to manually calculate them
> > > when inspecting the object files (.tmp_vmlinux?.kallsyms.o or
> > > .tmp_vmlinux?). Without, the assembler records the symbol size as 0.
> > >
> > > This is primarily useful as a debugging aid in case of linker errors as
> > > part of link-vmlinux.sh, and because symbol size doesn't have to align
> > > with the offset to the next symbol due to padding/alignment.
> > >
> > > Signed-off-by: André Draszik <andre.draszik@xxxxxxxxxx>
> >
> > Thanks for your patch, which is now commit d6bf11a7e8a86135 ("kallsyms:
> > add symbol size for kallsyms symbols that can change size") upstream.
> >
> > FTR, this commit has a huge impact on kernel size, according to
> > bloat-o-meter:
> >
> >     $ bloat-o-meter vmlinux.{old,}
> >     add/remove: 4/0 grow/shrink: 0/0 up/down: 440264/0 (440264)
> >     Function                                     old     new   delta
> >     kallsyms_names                                 -  324543 +324543
> >     kallsyms_offsets                               -  114424 +114424
> >     kallsyms_token_table                           -     849    +849
> >     kallsyms_markers                               -     448    +448
> >     Total: Before=5085496, After=5525760, chg +8.66%
>
> I suppose the reason is that before the patch each of the above 4
> symbols' size was recorded as 0 in the ELF file by the assembler.
>
> With this patch, the assembler places the actual size for each
> symbol. Hence they appear to have grown, but in reality they
> haven't.
>
> Looking at the delta between each of the symbol's start address with
> and without the patch should confirm that, too.

Correct:

$ diff <(nm -S vmlinux.old | sort ) <(nm -S vmlinux | sort)
--- /dev/fd/63 2026-08-24 15:46:29.404049009 +0200
+++ /dev/fd/62 2026-08-24 15:46:29.404049009 +0200
@@ -34748,11 +34748,11 @@
 0045884a 000000c8 d decpair
 00458912 000000c7 D linux_banner
 004589dc D kallsyms_num_syms
-004589e0 D kallsyms_names
-004a7da0 D kallsyms_markers
-004a7f60 D kallsyms_token_table
+004589e0 0004f3bf D kallsyms_names
+004a7da0 000001c0 D kallsyms_markers
+004a7f60 00000351 D kallsyms_token_table
 004a82b4 D kallsyms_token_index
-004a84b4 D kallsyms_offsets
+004a84b4 0001bef8 D kallsyms_offsets
 004c43ac D kallsyms_seqs_of_names
 00520100 00000070 D stop_sched_class
 00520100 D __sched_class_highest

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds