[PATCH u-boot 37/39] ARM: don't use -ffunction-sections/-fdata-sections with LTO build

[Tom Rini]

On Fri, Mar 12, 2021 at 08:29:05AM +0100, Marek Behun wrote:
> On Fri, 12 Mar 2021 15:19:26 +0800
> Bin Meng <bmeng.cn at gmail.com> wrote:
> 
> > On Fri, Mar 12, 2021 at 3:11 PM Marek Behun <marek.behun at nic.cz> wrote:
> > >
> > > On Fri, 12 Mar 2021 14:48:04 +0800
> > > Bin Meng <bmeng.cn at gmail.com> wrote:
> > >  
> > > > On Fri, Mar 12, 2021 at 2:45 PM Marek Behun <marek.behun at nic.cz> wrote:  
> > > > >
> > > > > On Wed, 10 Mar 2021 11:40:42 +0800
> > > > > Bin Meng <bmeng.cn at gmail.com> wrote:
> > > > >  
> > > > > > On Sun, Mar 7, 2021 at 12:26 PM Marek Behún <marek.behun at nic.cz> wrote:  
> > > > > > >
> > > > > > > When building with LTO, using -ffunction-sections/-fdata-sections is not
> > > > > > > useful anymore.
> > > > > > >
> > > > > > > Signed-off-by: Marek Behún <marek.behun at nic.cz>
> > > > > > > ---
> > > > > > >  arch/arm/config.mk | 8 ++++++--
> > > > > > >  1 file changed, 6 insertions(+), 2 deletions(-)
> > > > > > >  
> > > > > >
> > > > > > I believe we should also remove --gc-sections.  
> > > > >
> > > > > It seems that --gc-sections cannot be removed, otherwise some builds,
> > > > > for example turris_mox_defconfig, fail with
> > > > >
> > > > >   LTO     u-boot
> > > > > /usr/libexec/gcc/aarch64-unknown-linux-gnu/ld: /usr/lib/gcc/aarch64-unknown-linux-gnu/10.2.0/libgcc.a(lse-init.o): in function `init_have_lse_atomics':
> > > > > /var/tmp/portage/cross-aarch64-unknown-linux-gnu/gcc-10.2.0-r5/work/gcc-10.2.0/libgcc/config/aarch64/lse-init.c:44: undefined reference to `__getauxval'
> > > > > /usr/libexec/gcc/aarch64-unknown-linux-gnu/ld: /usr/lib/gcc/aarch64-unknown-linux-gnu/10.2.0/libgcc.a(_absvsi2.o): in function `__absvdi2':
> > > > > /var/tmp/portage/cross-aarch64-unknown-linux-gnu/gcc-10.2.0-r5/work/gcc-10.2.0/libgcc/libgcc2.c:228: undefined reference to `abort'
> > > > > /usr/libexec/gcc/aarch64-unknown-linux-gnu/ld: /usr/lib/gcc/aarch64-unknown-linux-gnu/10.2.0/libgcc.a(_absvsi2.o): in function `__absvsi2':
> > > > > /var/tmp/portage/cross-aarch64-unknown-linux-gnu/gcc-10.2.0-r5/work/gcc-10.2.0/libgcc/libgcc2.c:246: undefined reference to `abort'
> > > > > /usr/libexec/gcc/aarch64-unknown-linux-gnu/ld: /usr/lib/gcc/aarch64-unknown-linux-gnu/10.2.0/libgcc.a(_absvdi2.o): in function `__absvti2':
> > > > > /var/tmp/portage/cross-aarch64-unknown-linux-gnu/gcc-10.2.0-r5/work/gcc-10.2.0/libgcc/libgcc2.c:267: undefined reference to `abort'
> > > > > /usr/libexec/gcc/aarch64-unknown-linux-gnu/ld: /usr/lib/gcc/aarch64-unknown-linux-gnu/10.2.0/libgcc.a(_addvsi3.o): in function `__addvdi3':
> > > > > /var/tmp/portage/cross-aarch64-unknown-linux-gnu/gcc-10.2.0-r5/work/gcc-10.2.0/libgcc/libgcc2.c:81: undefined reference to `abort'
> > > > > /usr/libexec/gcc/aarch64-unknown-linux-gnu/ld: /usr/lib/gcc/aarch64-unknown-linux-gnu/10.2.0/libgcc.a(_addvsi3.o): in function `__addvsi3':
> > > > > /var/tmp/portage/cross-aarch64-unknown-linux-gnu/gcc-10.2.0-r5/work/gcc-10.2.0/libgcc/libgcc2.c:92: undefined reference to `abort'
> > > > > /usr/libexec/gcc/aarch64-unknown-linux-gnu/ld: /usr/lib/gcc/aarch64-unknown-linux-gnu/10.2.0/libgcc.a(_addvdi3.o):/var/tmp/portage/cross-aarch64-unknown-linux-gnu/gcc-10.2.0-r5/work/gcc-10.2.0/libgcc/libgcc2.c:106: more undefined references to `abort' follow
> > > > > /usr/libexec/gcc/aarch64-unknown-linux-gnu/ld: /usr/lib/gcc/aarch64-unknown-linux-gnu/10.2.0/libgcc.a(_eprintf.o): in function `__eprintf':
> > > > > /var/tmp/portage/cross-aarch64-unknown-linux-gnu/gcc-10.2.0-r5/work/gcc-10.2.0/libgcc/libgcc2.c:2152: undefined reference to `stderr'
> > > > > /usr/libexec/gcc/aarch64-unknown-linux-gnu/ld: /var/tmp/portage/cross-aarch64-unknown-linux-gnu/gcc-10.2.0-r5/work/gcc-10.2.0/libgcc/libgcc2.c:2152: undefined reference to `stderr'
> > > > > /usr/libexec/gcc/aarch64-unknown-linux-gnu/ld: /usr/lib/gcc/aarch64-unknown-linux-gnu/10.2.0/libgcc.a(_eprintf.o): in function `fprintf':
> > > > > /usr/aarch64-unknown-linux-gnu/sys-include/bits/stdio2.h:103: undefined reference to `__fprintf_chk'
> > > > > /usr/libexec/gcc/aarch64-unknown-linux-gnu/ld: /usr/lib/gcc/aarch64-unknown-linux-gnu/10.2.0/libgcc.a(_eprintf.o): in function `__eprintf':
> > > > > /var/tmp/portage/cross-aarch64-unknown-linux-gnu/gcc-10.2.0-r5/work/gcc-10.2.0/libgcc/libgcc2.c:2153: undefined reference to `fflush'
> > > > > /usr/libexec/gcc/aarch64-unknown-linux-gnu/ld: /var/tmp/portage/cross-aarch64-unknown-linux-gnu/gcc-10.2.0-r5/work/gcc-10.2.0/libgcc/libgcc2.c:2154: undefined reference to `abort'  
> > > >
> > > > Ouch! How compiler behaves when it comes to LTO and works with all
> > > > these compiler/linker options is really a mystery ...  
> > >
> > > OK, it seems that on aarch64 we are actually using system's libgcc :)  
> > 
> > Thanks.
> > 
> > > Not the internal one. So it seems we need --gc-sections to throw away
> > > garbade that is not used.  
> > 
> > Needed only when CONFIG_USE_PRIVATE_LIBGCC is off?
> 
> Seems that way.

Well, _and_ we need libgcc for anything too.  A quick set of hacks:
diff --git a/Makefile b/Makefile
index d6eda45385c3..af3e03ac9fa0 100644
--- a/Makefile
+++ b/Makefile
@@ -830,8 +830,6 @@ u-boot-main := $(libs-y)
 # Add GCC lib
 ifeq ($(CONFIG_USE_PRIVATE_LIBGCC),y)
 PLATFORM_LIBGCC = arch/$(ARCH)/lib/lib.a
-else
-PLATFORM_LIBGCC := -L $(shell dirname `$(CC) $(c_flags) -print-libgcc-file-name`) -lgcc
 endif
 PLATFORM_LIBS += $(PLATFORM_LIBGCC)
 
Shows that turris_mox links just fine without the main gcc, because I
probably misunderstood something a bit ages back when dealing with the
libgcc fun we have.  So I'm gonna see if that hack above is actually
just correct for all the other cases.

-- 
Tom
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