[Bug c/29171] New: forgotten memcpy with -ffreestanding -fwhole-program --combine

[acahalan at gmail dot com]

Unlike Bug #29159 and Bug #17402, this one involves -ffreestanding. The results
are not really different. Basically, gcc is unable to correctly compile
anything significant with -fwhole-program. With or without the -ffreestanding
option, gcc will leave undefined references to various string.h things. It does
not matter if the program provides these functions in *.c files.

Note that -ffreestanding is illogical. I do have a C library, even including
the various libgcc things. I added -ffreestanding just now because a comment in
Bug #17402 incorrectly suggests this as a fix for the problem. Note that
-ffreestanding is probably undesirable even if would work, because I provide a
runtime and I expect gcc to take advantage of that runtime.

So anyway...

I have a number of *.c files, including a bit of inline assembly, which form
the entire program. ("program" being a shared object which gets executed via
the _init function) There are no other source libraries. I have a memset.c
containing the obvious function. This is based on klibc (bare-bones Linux C
library) with the assembly files replaced with *.c files.

No matter what attributes I place on the functions, either in the *.c or *.h
files, the compiler produces an undefined reference to memset. Though gcc
certainly compiles the function, it seems to forget this. I don't think an
undefined reference should even be possible with the -fwhole-program option;
this supposedly tells the compiler that I'm giving the WHOLE program.

The gcc version:

$ gcc -v
Using built-in specs.
Target: x86_64-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
--infodir=/usr/share/info --enable-shared --enable-threads=posix
--enable-checking=release --with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions --enable-libgcj-multifile
--enable-languages=c,c++,objc,obj-c++,java,fortran,ada --enable-java-awt=gtk
--disable-dssi --enable-plugin
--with-java-home=/usr/lib/jvm/java-1.4.2-gcj-1.4.2.0/jre --with-cpu=generic
--host=x86_64-redhat-linux
Thread model: posix
gcc version 4.1.1 20060828 (Red Hat 4.1.1-20)

The compile command line, with numerous unrelated *.c files
chopped out of the middle:

gcc -m32 -std=gnu99 -nostdinc -isystem
/usr/lib/gcc/x86_64-redhat-linux/4.1.1/include -D__KLIBC__ -Iinclude
-Iinclude/bits32 -Iinclude/arch/i386 -mregparm=3 -D_REGPARM=3
-Wstrict-prototypes -Wmissing-prototypes -msoft-float -fPIC
-fomit-frame-pointer -march=pentium2 -Os -fno-defer-pop -fno-common
-mtune=nocona -Wstrict-aliasing=2 -fvisibility=hidden -W -Wall -Wshadow -g3
-ffreestanding -fwhole-program --combine -c buffer.c testlib.c klibc/strcmp.c
klibc/strcpy.c klibc/strncpy.c klibc/memcpy.c klibc/memset.c klibc/strlen.c
klibc/strspn.c klibc/strxspn.c klibc/malloc.c klibc/mmap.c klibc/pause.c
klibc/raise.c klibc/sleep.c klibc/sigaction.c klibc/libgcc/__udivdi3.c
klibc/libgcc/__umoddi3.c klibc/libgcc/__udivmoddi4.c -o bigblob.pic


The link command line:

gcc -m32 -shared -Wl,-O9 -Wl,-warn-common -Wl,-soname,libfoo.so.1
-Wl,-z,initfirst -nostartfiles -nodefaultlibs -nostdlib -o tmp.so
bigblob.pic

Examining the result:

nm tmp.so | grep -i ' u ' 
        U memcpy

I have tried the memcpy function with and without various attributes including:
externally_visible, unused, noinline, regparm(0)

Last of all, here is the memcpy function itself.

/////////////////////////////////////////////////////////
#include <string.h>
#include <stdint.h>

void *memcpy(void *restrict dst, const void *restrict src, size_t n)
{
       const char *p = src;
       char *q = dst;
#if defined(__i386__)
       size_t nl = n >> 2;
       asm volatile ("cld ; rep ; movsl ; movl %3,%0 ; rep ; movsb":"+c" (nl),
                     "+S"(p), "+D"(q)
                     :"r"(n & 3));
#elif defined(__x86_64__)
       size_t nq = n >> 3;
       asm volatile ("cld ; rep ; movsq ; movl %3,%%ecx ; rep ; movsb":"+c"
                     (nq), "+S"(p), "+D"(q)
                     :"r"((uint32_t) (n & 7)));
#else
       while (n--) {
               *q++ = *p++;
       }
#endif

       return dst;
}


-- 
           Summary: forgotten memcpy with -ffreestanding -fwhole-program --
                    combine
           Product: gcc
           Version: 4.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: acahalan at gmail dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29171