[Bug lto/61526] relocation R_X86_64_PC32 in shared object with static and extern

["ubizjak at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61526

--- Comment #4 from Uroš Bizjak <ubizjak at gmail dot com> ---
(In reply to Sandra Loosemore from comment #3)
> The testcase added for this bug in GCC 4.9.1 is failing with a link error on
> an arm-none-eabi target that doesn't support -shared.  Should it be
> restricted to linux targets?

Probably the best way is to add check_effective_target_shared to
lib/target-supports.exp (similar to existing c_e_t_static) procedure and use it
through the testsuite.
>From gcc-bugs-return-456873-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Mon Jul 21 17:33:09 2014
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From: "coleb at eyesopen dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/61872] New: Assigning to "long double" causes memset to be improperly elided
Date: Mon, 21 Jul 2014 17:33:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?ida872

            Bug ID: 61872
           Summary: Assigning to "long double" causes memset to be
                    improperly elided
           Product: gcc
           Version: 4.8.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: coleb at eyesopen dot com

Created attachment 33169
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id3169&actioníit
Intermediate file generated by the compiler for the above test case

The following code zeros out memory being used as a "long double" in order to
be able to memcmp the memory later. However, assigning to the long double later
causes the optimizer to omit the preceding memset of zero.

The following code boils this down to a simple test case:


#include <assert.h>
#include <string.h>
#include <iomanip>
#include <iostream>

void Dump( const void * mem, size_t n )
{
  const unsigned char * p = reinterpret_cast< const unsigned char *>( mem );
  for ( size_t i = 0; i < n; i++ )
  {
    std::cout << std::hex << std::setw(2) << std::setfill( std::cout.widen('0')
) << int(p[i]) << " ";
  }
  std::cout << std::endl;
}

int main()
{
  long double a;
  memset(&a, '\0', sizeof(long double));
  //Dump(&a, sizeof(long double)); // Uncomment me to make the test pass
  a = 1.0;

  long double b;
    memset(&b, '\0', sizeof(long double));
  //Dump(&b, sizeof(long double)); // Uncomment me to make the test pass
  b = 1.0;

  std::cout << memcmp(&a, &b, sizeof(long double)) << std::endl;

  Dump(&a, sizeof(long double));
  Dump(&b, sizeof(long double));

  assert(memcmp(&a, &b, sizeof(long double)) == 0);
}


Uncommenting the "Dump" function calls causing the test to pass, presumably
because the optimizer notices the zero'd out memory is now being used by Dump
before the assignment.

Note, this only occurs with -O1 or higher.

I've attached the associated .ii files from the following command:

coleb@rhel7:~> g++ -v -save-temps -O1 ./LongDoubleMemSetElided.cpp && ./a.out
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/4.8.2/lto-wrapper
Target: x86_64-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
--infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla
--enable-bootstrap --enable-shared --enable-threads=posix
--enable-checking=release --with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions --enable-gnu-unique-object
--enable-linker-build-id --with-linker-hash-style=gnu
--enable-languages=c,c++,objc,obj-c++,java,fortran,ada,go,lto --enable-plugin
--enable-initfini-array --disable-libgcj
--with-isl=/builddir/build/BUILD/gcc-4.8.2-20131106/obj-x86_64-redhat-linux/isl-install
--with-cloog=/builddir/build/BUILD/gcc-4.8.2-20131106/obj-x86_64-redhat-linux/cloog-install
--with-tune=generic --with-arch_32=x86-64 --build=x86_64-redhat-linux
Thread model: posix
gcc version 4.8.2 20131106 (Red Hat 4.8.2-3) (GCC)
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-O1' '-shared-libgcc' '-mtune=generic'
'-march=x86-64'
 /usr/libexec/gcc/x86_64-redhat-linux/4.8.2/cc1plus -E -quiet -v -D_GNU_SOURCE
./LongDoubleMemSetElided.cpp -mtune=generic -march=x86-64 -O1 -fpch-preprocess
-o LongDoubleMemSetElided.ii
ignoring nonexistent directory
"/usr/lib/gcc/x86_64-redhat-linux/4.8.2/include-fixed"
ignoring nonexistent directory
"/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../x86_64-redhat-linux/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../include/c++/4.8.2

/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../include/c++/4.8.2/x86_64-redhat-linux
 /usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../include/c++/4.8.2/backward
 /usr/lib/gcc/x86_64-redhat-linux/4.8.2/include
 /usr/local/include
 /usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-O1' '-shared-libgcc' '-mtune=generic'
'-march=x86-64'
 /usr/libexec/gcc/x86_64-redhat-linux/4.8.2/cc1plus -fpreprocessed
LongDoubleMemSetElided.ii -quiet -dumpbase LongDoubleMemSetElided.cpp
-mtune=generic -march=x86-64 -auxbase LongDoubleMemSetElided -O1 -version -o
LongDoubleMemSetElided.s
GNU C++ (GCC) version 4.8.2 20131106 (Red Hat 4.8.2-3) (x86_64-redhat-linux)
    compiled by GNU C version 4.8.2 20131106 (Red Hat 4.8.2-3), GMP version
5.1.1, MPFR version 3.1.1, MPC version 1.0.1
GGC heuristics: --param ggc-min-expand\x100 --param ggc-min-heapsize\x131072
GNU C++ (GCC) version 4.8.2 20131106 (Red Hat 4.8.2-3) (x86_64-redhat-linux)
    compiled by GNU C version 4.8.2 20131106 (Red Hat 4.8.2-3), GMP version
5.1.1, MPFR version 3.1.1, MPC version 1.0.1
GGC heuristics: --param ggc-min-expand\x100 --param ggc-min-heapsize\x131072
Compiler executable checksum: 854a658c8d093bd199c43bf0150da7d8
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-O1' '-shared-libgcc' '-mtune=generic'
'-march=x86-64'
 as -v --64 -o LongDoubleMemSetElided.o LongDoubleMemSetElided.s
GNU assembler version 2.23.52.0.1 (x86_64-redhat-linux) using BFD version
version 2.23.52.0.1-12.el7 20130226
COMPILER_PATH=/usr/libexec/gcc/x86_64-redhat-linux/4.8.2/:/usr/libexec/gcc/x86_64-redhat-linux/4.8.2/:/usr/libexec/gcc/x86_64-redhat-linux/:/usr/lib/gcc/x86_64-redhat-linux/4.8.2/:/usr/lib/gcc/x86_64-redhat-linux/
LIBRARY_PATH=/usr/lib/gcc/x86_64-redhat-linux/4.8.2/:/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../lib64/:/lib/../lib64/:/usr/lib/../lib64/:/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-O1' '-shared-libgcc' '-mtune=generic'
'-march=x86-64'
 /usr/libexec/gcc/x86_64-redhat-linux/4.8.2/collect2 --build-id --no-add-needed
--eh-frame-hdr --hash-style=gnu -m elf_x86_64 -dynamic-linker
/lib64/ld-linux-x86-64.so.2
/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../lib64/crt1.o
/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../lib64/crti.o
/usr/lib/gcc/x86_64-redhat-linux/4.8.2/crtbegin.o
-L/usr/lib/gcc/x86_64-redhat-linux/4.8.2
-L/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../lib64 -L/lib/../lib64
-L/usr/lib/../lib64 -L/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../..
LongDoubleMemSetElided.o -lstdc++ -lm -lgcc_s -lgcc -lc -lgcc_s -lgcc
/usr/lib/gcc/x86_64-redhat-linux/4.8.2/crtend.o
/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../lib64/crtn.o
64
00 00 00 00 00 00 00 80 ff 3f 40 00 00 00 00 00
00 00 00 00 00 00 00 80 ff 3f 00 00 00 00 00 00
a.out: ./LongDoubleMemSetElided.cpp:33: int main(): Assertion `memcmp(&a, &b,
sizeof(long double)) == 0' failed.
Aborted (core dumped)

Thank you!