[Bug driver/82834] New: Cross-compiler doesn't find correct multilib for target

[simon at pushface dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82834

            Bug ID: 82834
           Summary: Cross-compiler doesn't find correct multilib for
                    target
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: driver
          Assignee: unassigned at gcc dot gnu.org
          Reporter: simon at pushface dot org
  Target Milestone: ---

I have r254339, and built a cross-compiler on macOS 10.11.6 (darwin 15.6.0),
newlib 2.5.0:

$ arm-eabi-gcc -v
Using built-in specs.
COLLECT_GCC=arm-eabi-gcc
COLLECT_LTO_WRAPPER=/opt/gcc-8.0.0/bin/../libexec/gcc/arm-eabi/8.0.0/lto-wrapper
Target: arm-eabi
Configured with: /Volumes/Miscellaneous/tmp/gcc/configure
--build=x86_64-apple-darwin15 --disable-libada --disable-libcc1
--disable-libcilkrts --disable-libmudflap --disable-libsanitizer
--disable-libssp --disable-nls --disable-shared --disable-lto
--enable-languages=c,ada --enable-multilib
--prefix=/Volumes/Miscellaneous/arm/gcc-8.0.0 --target=arm-eabi
--with-bugurl=URL:mailto:simon@pushface.org --with-gnu-as --with-gnu-ld
--with-newlib --with-stage1-ldflags='-static-libstdc++ -static-libgcc
-Wl,-headerpad_max_install_names' --with-system-zlib --without-libiconv-prefix
--with-arch=armv7
Thread model: single
gcc version 8.0.0 20171102 (experimental) (GCC)

This was on macOS 10.11.6 (Darwin 15.6.0)

I compile my code with
 -mlittle-endian
 -mfloat-abi=hard
 -mcpu=cortex-m4
 -mfpu=fpv4-sp-d16
 -mthumb
and it looks as though the compiler has added
 -march=armv7e-m+fp

When I link (same options), the link fails because

/opt/gcc-8.0.0/bin/../lib/gcc/arm-eabi/8.0.0/../../../../arm-eabi/bin/ld:
error: /Users/simon/cortex-gnat-rts/test-stm32f4//testbed uses VFP register
arguments,
/opt/gcc-8.0.0/bin/../lib/gcc/arm-eabi/8.0.0/../../../../arm-eabi/lib/libm.a(lib_a-acosl.o)
does not
/opt/gcc-8.0.0/bin/../lib/gcc/arm-eabi/8.0.0/../../../../arm-eabi/bin/ld:
failed to merge target specific data of file
/opt/gcc-8.0.0/bin/../lib/gcc/arm-eabi/8.0.0/../../../../arm-eabi/lib/libm.a(lib_a-acosl.o)

etc etc.

I find that I get a successful link by adding

 -L/opt/gcc-8.0.0/arm-eabi/lib/thumb/autofp/v7/fpu 
 -L/opt/gcc-8.0.0/lib/gcc/arm-eabi/8.0.0/thumb/autofp/v7/fpu