[Bug c/98482] New: -mfentry creates invalid call for -mcmodel=large

[toiwoton at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98482

            Bug ID: 98482
           Summary: -mfentry creates invalid call for -mcmodel=large
           Product: gcc
           Version: 10.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: toiwoton at gmail dot com
  Target Milestone: ---

GCC on x86_64 with `-mfentry` generates invalid code for `-mcmodel=large`. The
call to `__fentry__` uses plain `call` instruction, but this can only address
locations within 32 bit range while the target may be anywhere in the 64 bit
range due to `-mcmodel=large`.

The expected code would be something which loads a 64 bit value to a register
and then uses register indirect call, so instead of
        call    __fentry__
there needs to be
        movabsq $__fentry__, %rax
        call    *%rax

$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/10/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none:amdgcn-amdhsa:hsa
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 10.2.1-3'
--with-bugurl=file:///usr/share/doc/gcc-10/README.Bugs
--enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++,m2 --prefix=/usr
--with-gcc-major-version-only --program-suffix=-10
--program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --enable-bootstrap --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes
--with-default-libstdcxx-abi=new --enable-gnu-unique-object
--disable-vtable-verify --enable-plugin --enable-default-pie --with-system-zlib
--enable-libphobos-checking=release --with-target-system-zlib=auto
--enable-objc-gc=auto --enable-multiarch --disable-werror --with-arch-32=i686
--with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib
--with-tune=generic
--enable-offload-targets=nvptx-none=/build/gcc-10-0py4jQ/gcc-10-10.2.1/debian/tmp-nvptx/usr,amdgcn-amdhsa=/build/gcc-10-0py4jQ/gcc-10-10.2.1/debian/tmp-gcn/usr,hsa
--without-cuda-driver --enable-checking=release --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=x86_64-linux-gnu
--with-build-config=bootstrap-lto-lean --enable-link-mutex
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 10.2.1 20201224 (Debian 10.2.1-3) 
$ cat mfentry.c
void func(void)
{
}
$ gcc -mfentry -pg -S mfentry.c -mcmodel=large -fno-pie -O2 -save-temps
$ cat mfentry.i
# 1 "mfentry.c"
# 1 "<built-in>"
# 1 "<command-line>"
# 31 "<command-line>"
# 1 "/usr/include/stdc-predef.h" 1 3 4
# 32 "<command-line>" 2
# 1 "mfentry.c"
void func(void)
{
}
$ cat mfentry.s
        .file   "mfentry.c"
        .text
        .p2align 4
        .globl  func
        .type   func, @function
func:
.LFB0:
        .cfi_startproc
1:      call    __fentry__
        ret
        .cfi_endproc
.LFE0:
        .size   func, .-func
        .ident  "GCC: (Debian 10.2.1-3) 10.2.1 20201224"
        .section        .note.GNU-stack,"",@progbits