[PATCH v3] RISC-V: Enable dead code elimination

[Jisheng Zhang]

On Sun, May 21, 2023 at 04:51:14PM +0800, Jisheng Zhang wrote:
> On Sun, May 21, 2023 at 04:48:47PM +0800, Jisheng Zhang wrote:
> > On Wed, May 17, 2023 at 04:29:36PM +0800, Zhangjin Wu wrote:
> > > Select CONFIG_HAVE_LD_DEAD_CODE_DATA_ELIMINATION for RISC-V, allowing
> > > the user to enable dead code elimination. In order for this to work,
> > > ensure that we keep the alternative table by annotating them with KEEP.
> > > 
> > > This boots well on qemu with both rv32_defconfig & rv64 defconfig, but
> > > it only shrinks their builds by ~1%, a smaller config is thereforce
> > > customized to test this feature:
> > 
> > OOPS, I didn't noticed that you have sent out the patch and you are now
> > in v3. I may read your patch sevral months ago, but I forget it.
> > But your version missed an important preparation patch which is
> > to fix the typo in commom vmlinux.lds.h in asm-generic, thus LD_ORPHAN_WARN
> > will warn loudly. See[1] for more details.
> > 
> > Another missing point is we need to keep the .init.pi* and .init.bss*
> > sections. See[1] for more details.
> > 
> > Since you are the first person to send out the patch of
> > HAVE_LD_DEAD_CODE_DATA_ELIMINATION for riscv, do you mind if I update
> > my series and take your patch in my series v2, make you as the commmit
> > author, use your commit msg, and add my co-developped tag etc?

Another option is: I remove patch4 from my series and you send out an
updated version to fix the missing .init.pi* and .init.bss* KEEP.
> 
> forget to add Link reference:
> 
> [1] Link: https://lore.kernel.org/linux-riscv/20230511141211.2418-1-jszhang@kernel.org/
> 
> > 
> > Thanks
> > 
> > > 
> > >           | rv32                   | rv64
> > >   --------|------------------------|---------------------
> > >    No DCE | 4460684                | 4893488
> > >       DCE | 3986716                | 4376400
> > >    Shrink |  473968 (~10.6%)       |  517088 (~10.5%)
> > > 
> > > The config used above only reserves necessary options to boot on qemu
> > > with serial console, more like the size-critical embedded scenes:
> > > 
> > >   - rv64 config: https://pastebin.com/crz82T0s
> > >   - rv32 config: rv64 config + 32-bit.config
> > > 
> > > Signed-off-by: Zhangjin Wu <falcon at tinylab.org>
> > > ---
> > >  arch/riscv/Kconfig              | 1 +
> > >  arch/riscv/kernel/vmlinux.lds.S | 2 +-
> > >  2 files changed, 2 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > > index 348c0fa1fc8c..d2eb1a862ea8 100644
> > > --- a/arch/riscv/Kconfig
> > > +++ b/arch/riscv/Kconfig
> > > @@ -111,6 +111,7 @@ config RISCV
> > >  	select HAVE_KPROBES_ON_FTRACE if !XIP_KERNEL
> > >  	select HAVE_KRETPROBES if !XIP_KERNEL
> > >  	select HAVE_RETHOOK if !XIP_KERNEL
> > > +	select HAVE_LD_DEAD_CODE_DATA_ELIMINATION
> > >  	select HAVE_MOVE_PMD
> > >  	select HAVE_MOVE_PUD
> > >  	select HAVE_PCI
> > > diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S
> > > index e5f9f4677bbf..0f5dfbc113d4 100644
> > > --- a/arch/riscv/kernel/vmlinux.lds.S
> > > +++ b/arch/riscv/kernel/vmlinux.lds.S
> > > @@ -112,7 +112,7 @@ SECTIONS
> > >  	. = ALIGN(8);
> > >  	.alternative : {
> > >  		__alt_start = .;
> > > -		*(.alternative)
> > > +		KEEP(*(.alternative))
> > >  		__alt_end = .;
> > >  	}
> > >  	__init_end = .;
> > > -- 
> > > 2.25.1
> > > 
> > > 
> > > _______________________________________________
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> > > linux-riscv at lists.infradead.org
> > > http://lists.infradead.org/mailman/listinfo/linux-riscv