[Bug c/62287] New: gcc generates near call for extern weak function

["breiten at lexmark dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62287

            Bug ID: 62287
           Summary: gcc generates near call for extern weak function
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: breiten at lexmark dot com

The following code, from a linux driver, attempts to call a weak function, if
the  address of that function is non-zero (i.e. defined in an earlier-loaded
module).

However, when configured for arm-eabi, a normal "bl" instruction is issued. 
While it generates the logic to test and avoid the call if bar is NULL, we get
a relocation error when the driver is loaded, because 0 is too far away from
0xbf7xxxx.  Verified this on 4.7.2, 4,8.3, and 4.9.0.  gcc-4.2 generates the bx
opcode that I expect.

The current documentation for -mlong-calls" under "ARM options" states:

The exceptions to this rule are that weak function definitions, functions with
the ‘long-call’ attribute or the ‘section’ attribute, and functions that are
within the scope of a ‘ #pragma long_calls’ directive are always turned into
long calls.

I did see PR51643, which addresses this sort of problem for tail calls, and I
see it behave correctly if I modify the code below to allow a tail-call.

extern void bar(void)__attribute__((weak));

int foo()
{
   if( bar)
     bar();

  return 0;
}

Here's my configuration/version info:
Target: arm-poky-linux-gnueabi
Configured with:
/bonus/scratch/gcc49/poky/gg-debug/tmp/work-shared/gcc-4.9.0-r0/gcc-4.9.0/configure
--build=x86_64-linux --host=x86_64-linux --target=arm-poky-linux-gnueabi
--prefix=/bonus/scratch/gcc49/poky/gg-debug/tmp/sysroots/x86_64-linux/usr
--exec_prefix=/bonus/scratch/gcc49/poky/gg-debug/tmp/sysroots/x86_64-linux/usr
--bindir=/bonus/scratch/gcc49/poky/gg-debug/tmp/sysroots/x86_64-linux/usr/bin/cortexa53-vfp-neon-poky-linux-gnueabi
--sbindir=/bonus/scratch/gcc49/poky/gg-debug/tmp/sysroots/x86_64-linux/usr/bin/cortexa53-vfp-neon-poky-linux-gnueabi
--libexecdir=/bonus/scratch/gcc49/poky/gg-debug/tmp/sysroots/x86_64-linux/usr/libexec/cortexa53-vfp-neon-poky-linux-gnueabi
--datadir=/bonus/scratch/gcc49/poky/gg-debug/tmp/sysroots/x86_64-linux/usr/share
--sysconfdir=/bonus/scratch/gcc49/poky/gg-debug/tmp/sysroots/x86_64-linux/etc
--sharedstatedir=/bonus/scratch/gcc49/poky/gg-debug/tmp/sysroots/x86_64-linux/com
--localstatedir=/bonus/scratch/gcc49/poky/gg-debug/tmp/sysroots/x86_64-linux/var
--libdir=/bonus/scratch/gcc49/poky/gg-debug/tmp/sysroots/x86_64-linux/usr/lib/cortexa53-vfp-neon-poky-linux-gnueabi
--includedir=/bonus/scratch/gcc49/poky/gg-debug/tmp/sysroots/x86_64-linux/usr/include
--oldincludedir=/bonus/scratch/gcc49/poky/gg-debug/tmp/sysroots/x86_64-linux/usr/include
--infodir=/bonus/scratch/gcc49/poky/gg-debug/tmp/sysroots/x86_64-linux/usr/share/info
--mandir=/bonus/scratch/gcc49/poky/gg-debug/tmp/sysroots/x86_64-linux/usr/share/man
--disable-silent-rules --disable-dependency-tracking
--with-libtool-sysroot=/bonus/scratch/gcc49/poky/gg-debug/tmp/sysroots/x86_64-linux
--enable-clocale=generic --with-gnu-ld --enable-shared --enable-languages=c,c++
--enable-threads=posix --disable-multilib --enable-c99 --enable-long-long
--enable-symvers=gnu --enable-libstdcxx-pch
--program-prefix=arm-poky-linux-gnueabi- --without-local-prefix
--enable-target-optspace --enable-lto --enable-libssp --disable-bootstrap
--disable-libmudflap --with-system-zlib --with-linker-hash-style=gnu
--enable-linker-build-id --with-ppl=no --with-cloog=no
--enable-checking=release --enable-cheaders=c_global
--with-gxx-include-dir=/bonus/scratch/gcc49/poky/gg-debug/tmp/sysroots/gg/usr/include/c++
--with-sysroot=/bonus/scratch/gcc49/poky/gg-debug/tmp/sysroots/gg
--with-build-sysroot=/bonus/scratch/gcc49/poky/gg-debug/tmp/sysroots/gg
--enable-poison-system-directories --disable-libunwind-exceptions
--with-mpfr=/bonus/scratch/gcc49/poky/gg-debug/tmp/sysroots/x86_64-linux/usr
--with-system-zlib --disable-nls
Thread model: posix
gcc version 4.9.0 (GCC)


/bonus/scratch/gcc49/poky/gg-debug/tmp/sysroots/x86_64-linux/usr/bin/cortexa53-vfp-neon-poky-linux-gnueabi/arm-poky-linux-gnueabi-gcc
-Os -mabi=aapcs-linux -mcpu=cortex-a53 -S -o - p.c

    .cpu cortex-a53
    .fpu softvfp
    .eabi_attribute 20, 1
    .eabi_attribute 21, 1
    .eabi_attribute 23, 3
    .eabi_attribute 24, 1
    .eabi_attribute 25, 1
    .eabi_attribute 26, 2
    .eabi_attribute 30, 4
    .eabi_attribute 34, 1
    .eabi_attribute 18, 4
    .file    "p.c"
    .text
    .align    2
    .global    foo
    .type    foo, %function
foo:
    @ args = 0, pretend = 0, frame = 0
    @ frame_needed = 0, uses_anonymous_args = 0
    stmfd    sp!, {r3, lr}
    ldr    r3, .L8
    cmp    r3, #0
    beq    .L2
    bl    bar
.L2:
    mov    r0, #0
    ldmfd    sp!, {r3, pc}
.L9:
    .align    2
.L8:
    .word    bar
    .size    foo, .-foo
    .weak    bar
    .ident    "GCC: (GNU) 4.9.0"
    .section    .note.GNU-stack,"",%progbits
>From gcc-bugs-return-459376-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Wed Aug 27 21:40:20 2014
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From: "trippels at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/58678] [4.9 Regression] pykde4-4.11.2 link error (devirtualization too trigger happy)
Date: Wed, 27 Aug 2014 21:40:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idX678

--- Comment #58 from Markus Trippelsdorf <trippels at gcc dot gnu.org> ---
A gentoo user wrote me that pykde still fails with the same error
when build with -flto.
And indeed both the testcase from comment0 and from comment 13 still
fail with -flto:

markus@x4 /tmp % cat test.ii
class A {
 public:
    virtual ~A();
};
class B : A {
    virtual int m_fn1();
};
void fn1() {
    delete reinterpret_cast<B*>(1);
}

markus@x4 /tmp % cat test2.ii
class Part {
public:
  virtual ~Part();
};
class A : Part {};
void fn1() {
  A *a;
  delete a;
}

markus@x4 /tmp % g++ -Wl,--no-undefined -shared -fPIC -flto -O2 test.ii
/tmp/ccvkKVlc.ltrans0.ltrans.o:ccvkKVlc.ltrans0.o:function B::~B(): error:
undefined reference to 'vtable for B'
/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.2/../../../../x86_64-pc-linux-gnu/bin/ld:
the vtable symbol may be undefined because the class is missing its key
function
/tmp/ccvkKVlc.ltrans0.ltrans.o:ccvkKVlc.ltrans0.o:function B::~B(): error:
undefined reference to 'A::~A()'
/tmp/ccvkKVlc.ltrans0.ltrans.o:ccvkKVlc.ltrans0.o:function B::~B(): error:
undefined reference to 'vtable for B'
/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.2/../../../../x86_64-pc-linux-gnu/bin/ld:
the vtable symbol may be undefined because the class is missing its key
function
/tmp/ccvkKVlc.ltrans0.ltrans.o:ccvkKVlc.ltrans0.o:function fn1(): error:
undefined reference to 'vtable for B'
/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.2/../../../../x86_64-pc-linux-gnu/bin/ld:
the vtable symbol may be undefined because the class is missing its key
function
/tmp/ccvkKVlc.ltrans0.ltrans.o:ccvkKVlc.ltrans0.o:function fn1(): error:
undefined reference to 'A::~A()'
/tmp/ccvkKVlc.ltrans0.ltrans.o:ccvkKVlc.ltrans0.o:function B::~B(): error:
undefined reference to 'A::~A()'
collect2: error: ld returned 1 exit status

markus@x4 /tmp % g++ -Wl,--no-undefined -shared -fPIC -flto -O2 test2.ii
/tmp/ccY0KXU2.ltrans0.ltrans.o:ccY0KXU2.ltrans0.o:function A::~A(): error:
undefined reference to 'Part::~Part()'
/tmp/ccY0KXU2.ltrans0.ltrans.o:ccY0KXU2.ltrans0.o:function A::~A(): error:
undefined reference to 'Part::~Part()'
/tmp/ccY0KXU2.ltrans0.ltrans.o:ccY0KXU2.ltrans0.o:typeinfo for A: error:
undefined reference to 'typeinfo for Part'
collect2: error: ld returned 1 exit status

markus@x4 /tmp % g++ -Wl,--no-undefined -shared -fPIC -O2 test.ii
markus@x4 /tmp % g++ -Wl,--no-undefined -shared -fPIC -O2 test2.ii
markus@x4 /tmp %