i'm playing with the blackfin target which defines USER_LABEL_PREFIX to "_" 
and i seem to be ending up with symbols with too many _ prefixes ... i traced 
it back to the libc_hidden_def() macro in libc-symbols.h

for example, this bit of code:
int __libc_close(int fd) { return fd; }
strong_alias(__libc_close,close)
libc_hidden_proto(close)
libc_hidden_def(close)

on a target where USER_LABEL_PREFIX is defined to "", we'd correctly end up 
with global symbols __libc_close and close, and an internal hidden __GI_close

however, on an a target where USER_LABEL_PREFIX is defined to "_", we'd end up 
with global symbols ___libc_close and _close, an internal hidden ___GI_close, 
and an undefined reference to ____GI_close

i'm thinking it's because __hidden_ver1() is incorrectly using 
__hidden_asmname() when defining the __EI_##name alias ... the alias name is 
processed by gcc itself which will insert USER_LABEL_PREFIX, so calling 
__hidden_asmname() which also inserts USER_LABEL_PREFIX for us generates an 
alias to a double prefixed asmname

if i change __hidden_ver1() to call __hidden_asmname1() with an empty prefix 
for the alias, my final object ends up with the correct prefixes ... sample 
file along with patch are attached, tested against x86_64 and bfin elf 
targets

current cvs:
$ gcc -c hidden-test.c && readelf -s hidden-test.o | grep close
     8: 0000000000000000    12 FUNC    GLOBAL DEFAULT    1 __libc_close
     9: 0000000000000000    12 FUNC    GLOBAL DEFAULT    1 close
    10: 0000000000000000    12 FUNC    GLOBAL HIDDEN    1 __GI_close
$ bfin-elf-gcc -c hidden-test.c && readelf -s hidden-test.o | grep close
     6: 00000000    14 FUNC    GLOBAL DEFAULT    1 ___libc_close
     7: 00000000    14 FUNC    GLOBAL HIDDEN    1 ___GI_close
     8: 00000000     0 NOTYPE  GLOBAL DEFAULT  UND ____GI_close
with my simple patch:
$ gcc -DFIX -c hidden-test.c && readelf -s hidden-test.o | grep close
     8: 0000000000000000    12 FUNC    GLOBAL DEFAULT    1 __libc_close
     9: 0000000000000000    12 FUNC    GLOBAL DEFAULT    1 close
    10: 0000000000000000    12 FUNC    GLOBAL HIDDEN    1 __GI_close
$ bfin-elf-gcc -DFIX -c hidden-test.c && readelf -s hidden-test.o | grep close
     6: 00000000    14 FUNC    GLOBAL DEFAULT    1 ___libc_close
     7: 00000000    14 FUNC    GLOBAL DEFAULT    1 _close
     8: 00000000    14 FUNC    GLOBAL HIDDEN    1 ___GI_close