On 2019-12-17 18:47 +0100, Jan Hubicka wrote:
> > Would it be equivalent to:
> > 1) output foo_v2 local
> > 2) producing static alias with local name (.L1)
> > 3) do .symver .L1,foo@@@VERS_2
> > That is somewhat more systematic and would not lead to false
> > visibilities.
>
> I spent some time playing with this. An in order to
> 1) be able to handle foo_v2 according to the resolution info
> (so it behaves like a regular symbol and can be called dirrectly,
> localized and optimized)
> 2) get intended objdump -T relocations
> 3) do not polute global symbol tables
>
> I ended up with the following codegen:
>
> .type foo_v2, @function
> foo_v2:
> .LFB1:
> .cfi_startproc
> movl $2, %eax
> ret
> .cfi_endproc
> .LFE1:
> .size foo_v2, .-foo_v2
> .globl .LSYMVER0
> .set .LSYMVER0,foo_v2
> .symver .LSYMVER0, foo@@@VERS_2
>
> This uses @@@ symver version of gas which seems to have odd semantics of
> requiring to be passed global symbol name which it then tkes away and
> produces foo@@VERS_2.
>
> So the nm outoutp of the ltrans unit is:
> 0000000000000000 T foo_v1
> 0000000000000010 t foo_v2
> 0000000000000000 T foo@VERS_1
> 0000000000000010 T foo@@VERS_2
>
> So the difference to your patch is that foo_v2 is static which enables
> normal optimizations.
>
> Since additional symbol alias is produced this would also make it
> possible to attach multiple symver attributes with @@ string.
>
> Does somehting like this make sense to you? Modulo the obvious buffer
> overflow issue?
> Honza
Unfortunately, I got an ICE with my testcase with the patch applied to trunk.
lto1: internal compiler error: tree check: expected tree that contains ‘decl
minimal’ structure, have ‘identifier_node’ in do_assemble_symver, at
varasm.c:5986
0x6fa648 tree_contains_struct_check_failed(tree_node const*,
tree_node_structure_enum, char const*, int, char const*)
../../gcc/gcc/tree.c:9859
0x71466e contains_struct_check(tree_node*, tree_node_structure_enum, char
const*, int, char const*)
../../gcc/gcc/tree.h:3387
0x71466e do_assemble_symver(tree_node*, tree_node*)
../../gcc/gcc/varasm.c:5986
0x89e409 cgraph_node::assemble_thunks_and_aliases()
../../gcc/gcc/cgraphunit.c:2225
0x89e698 cgraph_node::expand()
../../gcc/gcc/cgraphunit.c:2351
0x89f62f expand_all_functions
../../gcc/gcc/cgraphunit.c:2456
0x89f62f symbol_table::compile()
../../gcc/gcc/cgraphunit.c:2806
0x7fb589 lto_main()
../../gcc/gcc/lto/lto.c:658
Please submit a full bug report,
with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.
See <https://gcc.gnu.org/bugs/> for instructions.
lto-wrapper: fatal error: /home/xry111/gcc-test/bin/gcc returned 1 exit status
compilation terminated.
/usr/bin/ld: error: lto-wrapper failed
collect2: error: ld returned 1 exit status
make: *** [Makefile:4: obj/test.so] Error 1
The change to lto/lto-common.c makes sense. I tried it instead of my change to
cgraph.h and everything is OK. I'll investigate the change to varasm.c a
little.
--
Xi Ruoyao <xry...@mengyan1223.wang>
School of Aerospace Science and Technology, Xidian University
