[Bug target/107032] New: ARM: libgcc2.c:2174:1: error: r7 cannot be used in 'asm' here

[Bug target/107032] New: ARM: libgcc2.c:2174:1: error: r7 cannot be used in 'asm' here

[thomas.petazzoni@free-electrons.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107032

            Bug ID: 107032
           Summary: ARM: libgcc2.c:2174:1: error: r7 cannot be used in
                    'asm' here
           Product: gcc
           Version: 11.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: thomas.petazzoni@free-electrons.com
  Target Milestone: ---

When building gcc 10.4.0 or 11.3.0 for Cortex-M3 or M7, the build fails with:

../../../libgcc/libgcc2.c: In function '__clear_cache':
../../../libgcc/libgcc2.c:2174:1: error: r7 cannot be used in 'asm' here
 2174 | }
      | ^
Makefile:501: recipe for target '_clear_cache.o' failed

GCC was configured like this:


(cd
/home/buildroot/autobuild/instance-0/output-1/build/host-gcc-initial-10.4.0/build
&& rm -rf config.cache;
PATH="/home/buildroot/autobuild/instance-0/output-1/host/bin:/home/buildroot/autobuild/instance-0/output-1/host/sbin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
PKG_CONFIG="/home/buildroot/autobuild/instance-0/output-1/host/bin/pkg-config"
PKG_CONFIG_SYSROOT_DIR="/" PKG_CONFIG_ALLOW_SYSTEM_CFLAGS=1
PKG_CONFIG_ALLOW_SYSTEM_LIBS=1
PKG_CONFIG_LIBDIR="/home/buildroot/autobuild/instance-0/output-1/host/lib/pkgconfig:/home/buildroot/autobuild/instance-0/output-1/host/share/pkgconfig"
AR="/usr/bin/ar" AS="/usr/bin/as" LD="/usr/bin/ld" NM="/usr/bin/nm"
CC="/usr/bin/gcc" GCC="/usr/bin/gcc" CXX="/usr/bin/g++" CPP="/usr/bin/cpp"
OBJCOPY="/usr/bin/objcopy" RANLIB="/usr/bin/ranlib"
CPPFLAGS="-I/home/buildroot/autobuild/instance-0/output-1/host/include"
CFLAGS="-O2 -I/home/buildroot/autobuild/instance-0/output-1/host/include"
CXXFLAGS="-O2 -I/home/buildroot/autobuild/instance-0/output-1/host/include"
LDFLAGS="-L/home/buildroot/autobuild/instance-0/output-1/host/lib
-Wl,-rpath,/home/buildroot/autobuild/instance-0/output-1/host/lib"
INTLTOOL_PERL=/usr/bin/perl CFLAGS="-O2
-I/home/buildroot/autobuild/instance-0/output-1/host/include"
LDFLAGS="-L/home/buildroot/autobuild/instance-0/output-1/host/lib
-Wl,-rpath,/home/buildroot/autobuild/instance-0/output-1/host/lib"
MAKEINFO=missing CFLAGS_FOR_TARGET="-D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE
-D_FILE_OFFSET_BITS=64  -O0 -g0   -Wl,-elf2flt=-r -static"
CXXFLAGS_FOR_TARGET="-D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE
-D_FILE_OFFSET_BITS=64  -O0 -g0   -Wl,-elf2flt=-r -static  -Wl,-elf2flt=-r
-static" AR_FOR_TARGET=gcc-ar NM_FOR_TARGET=gcc-nm RANLIB_FOR_TARGET=gcc-ranlib
CONFIG_SITE=/dev/null ./configure
--prefix="/home/buildroot/autobuild/instance-0/output-1/host"
--sysconfdir="/home/buildroot/autobuild/instance-0/output-1/host/etc"
--localstatedir="/home/buildroot/autobuild/instance-0/output-1/host/var"
--enable-shared --disable-static --disable-gtk-doc --disable-gtk-doc-html
--disable-doc --disable-docs --disable-documentation --disable-debug
--with-xmlto=no --with-fop=no --disable-nls --disable-dependency-tracking 
--target=arm-buildroot-uclinux-uclibcgnueabi
--with-sysroot=/home/buildroot/autobuild/instance-0/output-1/host/arm-buildroot-uclinux-uclibcgnueabi/sysroot
--enable-__cxa_atexit --with-gnu-ld --disable-libssp --disable-multilib
--disable-decimal-float
--with-gmp=/home/buildroot/autobuild/instance-0/output-1/host
--with-mpc=/home/buildroot/autobuild/instance-0/output-1/host
--with-mpfr=/home/buildroot/autobuild/instance-0/output-1/host
--with-pkgversion="Buildroot 2022.05-439-g18f6e4bf70"
--with-bugurl="http://bugs.buildroot.net/" --without-zstd --disable-libquadmath
--disable-libquadmath-support --disable-libsanitizer --disable-tls
--enable-threads --without-isl --without-cloog --with-float=soft
--with-abi="aapcs-linux" --with-cpu=cortex-m3 --with-float=soft
--with-mode=thumb --enable-languages=c --disable-shared --without-headers
--disable-threads --with-newlib --disable-largefile  )

Full build log of GCC 10.4.0 for Cortex-M3:
 
http://autobuild.buildroot.net/results/e91/e91fa76142cf50e514d5fe4791a06f3c3c014b5a/build-end.log

Full build log of GCC 11.3.0 for Cortex-M7:
 
http://autobuild.buildroot.net/results/9f7/9f7a43a375d476f47702cd7848eba53b76fcd386/build-end.log

[Bug target/107032] ARM: libgcc2.c:2174:1: error: r7 cannot be used in 'asm' here

[clyon at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107032

Christophe Lyon <clyon at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |clyon at gcc dot gnu.org

--- Comment #1 from Christophe Lyon <clyon at gcc dot gnu.org> ---
At quick glance, I think this is caused by the definition of CLEAR_INSN_CACHE
in gcc/config/arm/uclinux-eabi.h:

/* Clear the instruction cache from `beg' to `end'.  This makes an
   inline system call to SYS_cacheflush.  */
#undef CLEAR_INSN_CACHE
#define CLEAR_INSN_CACHE(BEG, END)                                      \
{                                                                       \
  register unsigned long _beg __asm ("a1") = (unsigned long) (BEG);     \
  register unsigned long _end __asm ("a2") = (unsigned long) (END);     \
  register unsigned long _flg __asm ("a3") = 0;                         \
  register unsigned long _scno __asm ("r7") = 0xf0002;                  \
  __asm __volatile ("swi 0x0            @ sys_cacheflush"               \
                    : "=r" (_beg)                                       \
                    : "0" (_beg), "r" (_end), "r" (_flg), "r" (_scno)); \
}

which makes explicit use of r7.

This code has been like that since it was committed in 2007....
So I suspect nobody ever tried to build this configuration.

[Bug target/107032] ARM: libgcc2.c:2174:1: error: r7 cannot be used in 'asm' here

[thomas.petazzoni@free-electrons.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107032

--- Comment #2 from Thomas Petazzoni <thomas.petazzoni@free-electrons.com> ---
Thanks for the feedback. There must be something special in those
configurations, because I did build a Cortex-M4 configuration with gcc 11.3.0
just a few days ago, and it built fine.

[Bug target/107032] ARM: libgcc2.c:2174:1: error: r7 cannot be used in 'asm' here

[clyon at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107032

--- Comment #3 from Christophe Lyon <clyon at gcc dot gnu.org> ---
Interesting....

Did you use the same target triplet?

arm*-*-uclinuxfdpiceabi is handled differently from
arm-buildroot-uclinux-uclibcgnueabi

[Bug target/107032] ARM: libgcc2.c:2174:1: error: r7 cannot be used in 'asm' here

[thomas.petazzoni@free-electrons.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107032

--- Comment #4 from Thomas Petazzoni <thomas.petazzoni@free-electrons.com> ---
Yes, same triplet. We do not (yet) have FDPIC support for ARM in Buildroot (we
have a patch series pending for that).

[Bug target/107032] ARM: libgcc2.c:2174:1: error: r7 cannot be used in 'asm' here

[clyon at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107032

--- Comment #5 from Christophe Lyon <clyon at gcc dot gnu.org> ---
Could you share the preprocessed source file in the M3 and M4 cases along with
the full command line used to compile it?

[Bug target/107032] ARM: libgcc2.c:2174:1: error: r7 cannot be used in 'asm' here

[rearnsha at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107032

Richard Earnshaw <rearnsha at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2022-09-27
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1

--- Comment #6 from Richard Earnshaw <rearnsha at gcc dot gnu.org> ---
In Thumb code r7 is the frame pointer, so can't be used in inline assembler
without a dance whenever the frame pointer might be needed.  I'm surprised this
hasn't shown up before.

We're going to need a separate definition of this macro when compiling for
Thumb as you can't easily rewrite this.  The code will need to do something
like

mov scratch, r7
mov r7, #<syscall-value>
svc 0
mov r7, scratch

[Bug target/107032] ARM: libgcc2.c:2174:1: error: r7 cannot be used in 'asm' here

[clyon at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107032

--- Comment #7 from Christophe Lyon <clyon at gcc dot gnu.org> ---
Indeed, but I am surprised it seems to compile for cortex-m4?

[Bug target/107032] ARM: libgcc2.c:2174:1: error: r7 cannot be used in 'asm' here

[rearnsha at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107032

--- Comment #8 from Richard Earnshaw <rearnsha at gcc dot gnu.org> ---
Perhaps something is changing the decision on the use of the frame pointer.