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Building a kernel with CONFIG_CC_OPTIMISE_FOR_SIZE leads to the following functions being copied several times in vmlinux: 31 times __ilog2_u32() 34 times fls() Disassembly follows: c00f476c <fls>: c00f476c: 7c 63 00 34 cntlzw r3,r3 c00f4770: 20 63 00 20 subfic r3,r3,32 c00f4774: 4e 80 00 20 blr c00f4778 <__ilog2_u32>: c00f4778: 94 21 ff f0 stwu r1,-16(r1) c00f477c: 7c 08 02 a6 mflr r0 c00f4780: 90 01 00 14 stw r0,20(r1) c00f4784: 4b ff ff e9 bl c00f476c <fls> c00f4788: 80 01 00 14 lwz r0,20(r1) c00f478c: 38 63 ff ff addi r3,r3,-1 c00f4790: 7c 08 03 a6 mtlr r0 c00f4794: 38 21 00 10 addi r1,r1,16 c00f4798: 4e 80 00 20 blr When forcing inlining of fls(), we get c0008b80 <__ilog2_u32>: c0008b80: 7c 63 00 34 cntlzw r3,r3 c0008b84: 20 63 00 1f subfic r3,r3,31 c0008b88: 4e 80 00 20 blr vmlinux size gets reduced by 1 kbyte with that change. Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/adc9c9d6378f6b5008246ca717993d7870188efb.1644569473.git.christophe.leroy@csgroup.eu
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.