Messages in this thread | | | Date | Fri, 17 Jun 2022 13:11:42 -0700 | From | Josh Poimboeuf <> | Subject | Re: [RFC][PATCH] ftrace,objtool: PC32 based __mcount_loc |
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On Fri, Jun 17, 2022 at 01:24:53PM +0200, Peter Zijlstra wrote: > > Hi, > > I recently noticed that __mcount_loc is 64bit wide, containing absolute > addresses. Since __mcount_loc is a permanent section (not one we drop > after boot), this bloats the kernel memory usage for no real purpose. > > The below patch adds __mcount_loc_32 and objtool support to generate it. > This saves, on an x86_64-defconfig + FTRACE, 23975*4 ~= 94K of permanent > storage. > > XXX hobbled sorttable for now > XXX compile tested only > > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Nice!
Some nits:
- No need for renaming the section, it can still be called '__mcount_loc' regardless?
- No need for a new FTRACE_MCOUNT32_USE_OBJTOOL config option or '--mcount32' cmdline option, just change the old ones to be pc32?
- change "32" to "PC32": CC_USING_MCOUNT_LOC_PC32
That will shrink this patch down quite a bit.
-- Josh
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