https://gcc.gnu.org/bugzilla/show_bug.cgi?id=48200
--- Comment #38 from Jan Hubicka <hubicka at ucw dot cz> ---
Hi,
I am attaching prototype patch. It implements "symver" attribute which
can be attached to a definition such as:
hubicka@lomikamen-jh:/aux/hubicka/trunk5/build4/gcc$ cat t.c
__attribute__ ((symver("bar@2.2")))
int t()
{
}
hubicka@lomikamen-jh:/aux/hubicka/trunk5/build4/gcc$ ./xgcc -B ./ -O2 t.c -S
hubicka@lomikamen-jh:/aux/hubicka/trunk5/build4/gcc$ cat t.s
.file "t.c"
.text
.p2align 4
.globl t
.type t, @function
t:
.LFB0:
.cfi_startproc
ret
.cfi_endproc
.LFE0:
.size t, .-t
.symver t, bar@2.2
.ident "GCC: (GNU) 10.0.0 20191114 (experimental)"
.section .note.GNU-stack,"",@progbits
Internally it defines a new kind of alias (symver alias) with assembler
name "bar@2.2" so LTO symbol table match ELF symbol table for the unit:
hubicka@lomikamen-jh:/aux/hubicka/trunk5/build4/gcc$ nm t.o
0000000000000000 T bar@2.2
0000000000000000 T t
hubicka@lomikamen-jh:/aux/hubicka/trunk5/build4/gcc$ ./xgcc -B ./ -O2
t.c -c -flto
hubicka@lomikamen-jh:/aux/hubicka/trunk5/build4/gcc$ gcc-nm t.o
00000000 T bar@2.2
00000000 T t
Internally in GCC the symver is handled just as normal alias only output
differntly. I think GCC, just like static linker, does not really need
to understand the versions because there are no direct ways to bind to
those symbols.
I wonder if someone sees limitations to this design (in particular
attaching the symver directly to the definition).
In PR66825 Carlos proposed "version_def" attribute which can be
implemented too (I suppose all I need is to concatenate the strings into
the actual name). I wonder what would be preferred and easier for
users?
Also Carlos proposes "version_ref" that can be used for external
definitions. I am not quite sure how to do that with existing GAS and
LTO since different translation units can reffer to different versions.
But my understnading is that for LTO it is critical to implement the def
part.
Hopefully I can turn this into a patch proposal tomorrow to meet the
stage1 deadline, so comments are welcome especially if they come really
soon :)
Honza
