[PATCH 2/2] arch/{sparc,sparc64}/Makefile: define ARCH_FPIC

[Denys Vlasenko]

On Tue, Jul 18, 2017 at 11:40 PM, Thomas Petazzoni
<thomas.petazzoni at free-electrons.com> wrote:
> Hello,
>
> On Sat, 15 Jul 2017 14:44:21 +0200, Denys Vlasenko wrote:
>
>> Can you investigate this further?
>> LIBBUSYBOX build results in entire busybox code being put into a library.
>>
>> nm -D libbusybox.so.1.28.0.git
>>
>> shows that there are only defined entry points to each applet's main():
>>
>> 0007b159 T bunzip2_main
>> 0007c8db T bzip2_main
>> 000677bb T cal_main
>> 0008e08e T cat_main
>>
>> (so, at max less than 350 entry points), and references to libc functions:
>>
>>          U asprintf
>>          U atof
>>          U atoi
>>
>> No internal libbb functions or variables are exposed.
>>
>> I don't understand the error messages you are seeing. bb_errno should
>> have hidden visibility,
>> meaning that it is an internal (to libbusybox.so) label, and all
>> references to it
>> should be resolved without any shared linker magic. .LCn labels are
>> similar, they are
>> referring to text strings (messages and such).
>>
>> What is going on? Why your linker has relocations between individual
>> .o files which go
>> to the same library?
>
> I'm not really sure what's going on. But the problem can very easily be
> reproduced:
>
> $ git clone git://git.buildroot.org/buildroot
> $ cd buildroot/
> $ cat > .config <<EOF
> BR2_sparc=y
> BR2_TOOLCHAIN_EXTERNAL=y
> BR2_TOOLCHAIN_EXTERNAL_DOWNLOAD=y
> BR2_TOOLCHAIN_EXTERNAL_URL="http://autobuild.buildroot.org/toolchains/tarballs/br-sparc-uclibc-2017.05-1078-g95b1dae.tar.bz2"
> BR2_TOOLCHAIN_EXTERNAL_GCC_6=y
> BR2_TOOLCHAIN_EXTERNAL_HEADERS_4_1=y
> BR2_TOOLCHAIN_EXTERNAL_LOCALE=y
> # BR2_TOOLCHAIN_EXTERNAL_HAS_THREADS_DEBUG is not set
> BR2_TOOLCHAIN_EXTERNAL_CXX=y
> BR2_INIT_NONE=y
> BR2_SYSTEM_BIN_SH_NONE=y
> BR2_PACKAGE_BUSYBOX_INDIVIDUAL_BINARIES=y
> # BR2_TARGET_ROOTFS_TAR is not set
> EOF
> $ make olddefconfig
> $ make
>
> It builds only Busybox, so it's very quick to reach the build failure.
> This time, I got:
>
> libbb/lib.a(appletlib.o): In function `find_applet_by_name':
> appletlib.c:(.text.find_applet_by_name+0x14): relocation truncated to fit: R_SPARC_GOT13 against symbol `applet_nameofs' defined in .rodata.applet_nameofs section in libbb/lib.a(appletlib.o)
> appletlib.c:(.text.find_applet_by_name+0x18): relocation truncated to fit: R_SPARC_GOT13 against symbol `applet_names' defined in .rodata.applet_names section in libbb/lib.a(appletlib.o)
> libbb/lib.a(appletlib.o): In function `bb_show_usage':
> appletlib.c:(.text.bb_show_usage+0x10): relocation truncated to fit: R_SPARC_GOT13 against symbol `applet_name' defined in COMMON section in libbb/lib.a(appletlib.o)
> appletlib.c:(.text.bb_show_usage+0x54): relocation truncated to fit: R_SPARC_GOT13 against symbol `bb_banner' defined in .rodata.bb_banner section in libbb/lib.a(messages.o)
> libbb/lib.a(appletlib.o): In function `lbb_prepare':
> appletlib.c:(.text.lbb_prepare+0x18): relocation truncated to fit: R_SPARC_GOT13 against symbol `bb_errno' defined in COMMON section in libbb/lib.a(ptr_to_globals.o)
> appletlib.c:(.text.lbb_prepare+0x20): relocation truncated to fit: R_SPARC_GOT13 against symbol `applet_name' defined in COMMON section in libbb/lib.a(appletlib.o)
> libbb/lib.a(appletlib.o): In function `run_applet_no_and_exit':
> appletlib.c:(.text.run_applet_no_and_exit+0x28): relocation truncated to fit: R_SPARC_GOT13 against symbol `xfunc_error_retval' defined in .data.xfunc_error_retval section in libbb/lib.a(default_error_retval.o)
> appletlib.c:(.text.run_applet_no_and_exit+0x38): relocation truncated to fit: R_SPARC_GOT13 against symbol `applet_name' defined in COMMON section in libbb/lib.a(appletlib.o)
> appletlib.c:(.text.run_applet_no_and_exit+0xb0): relocation truncated to fit: R_SPARC_GOT13 against symbol `applet_main' defined in .data.rel.ro.applet_main section in libbb/lib.a(appletlib.o)
> appletlib.c:(.text.run_applet_no_and_exit+0xcc): relocation truncated to fit: R_SPARC_GOT13 against symbol `applet_suid' defined in .rodata.applet_suid section in libbb/lib.a(appletlib.o)
> appletlib.c:(.text.run_applet_no_and_exit+0x11c): additional relocation overflows omitted from the output
> collect2: error: ld returned 1 exit status
>
> When I build with my patches (the build is successful), and then look
> at libbbusybox.so with readelf, the .got section is indeed very small,
> much smaller than the 8 KB limit detailed in gcc's documentation about
> -fpic vs. -fPIC:
>
> $ ./output/host/usr/bin/sparc-linux-readelf -a output/target/lib/libbusybox.so.1.26.2 | grep "\.got"
>   [17] .got              PROGBITS        000dc000 0cc000 00021c 04  WA  0   0  4
>
> So the size is only 0x21c.
>
> Any idea on how to investigate this further?

I think what happens is compiler does not know where applet_names[] are,
assumes it's in another library and generates a reloc.
Then, the "short" fpic reloc does not work at link time.