Sun ld comdat group support

Question

While this may be a little OT, given that it discusses gcc/binutils, the underlying topic is the solaris linker in /usr/ccs/bin/ld, and this seemed like the most likely forum for linker expertise.
The following discussion concludes that the sun linker does not support COMDAT groups adequetly to build gcc 4 with the gnu assembler and the sun linker (as is recommmended by the gcc folks, and as is done by sun for /usr/sfw/bin/gcc in solaris 10)
http://gcc.gnu.org/ml/gcc/2005-04/msg01332.html
But the documentation for the linker seems to suggest otherwise:
http://docs.sun.com/app/docs/doc/817-1983/6mhm6r4fj?a=view#chapter7-11598
In the most recent binutils ld testsuite, there is a test for comdat support:
-------- group1a.s ---------
.section .text,"axG",%progbits,foo_group,comdat
.weak foo
foo:
.word 0
-------- group1b.s ---------
.section .text,"axG",%progbits,foo_group,comdat
.global foo
.global bar
foo:
.word 0
bar:
Run these through the gnu assembler:
/usr/local/binutils-2.16.1/bin/as --gdwarf2 group1a.s -o group1a.o
/usr/local/binutils-2.16.1/bin/as --gdwarf2 group1b.s -o group1b.o
And then link them, once with the sun linker, and once with the gnu linker:
/usr/local/binutils-2.16.1/bin/ld group1a.o group1b.o -o linked.gnu
/usr/ccs/bin/ld group1a.o group1b.o -o linked.sun
Now, if we look at foo and bar in the generated images
elfdump -s -N .symtab linked.gnu | egrep "foo|bar"
[8] 0x08048074 0x00000000 NOTY WEAK D 0 .text foo
[11] 0x00000000 0x00000000 NOTY GLOB D 0 UNDEF bar
elfdump -s -N .symtab linked.sun | egrep "foo|bar"
[15] 0x080501ef 0x00000000 NOTY GLOB D 0 .text bar
[21] 0x080501ed 0x00000000 NOTY GLOB D 0 .text foo
we can see that the gnu linker generated foo as a weak symbol, and left bar undefined, while the sun linker emitted foo as a global, and defined bar.
ok. so now try without the comdat flags:
----- nogroup1a.s -----
.section .text,"ax",%progbits
.weak foo
foo:
.word 0
----- nogroup1b.s -----
.section .text,"ax",%progbits
.global foo
.global bar
foo:
.word 0
bar:
and assemble and link as above. Now, if we look at the output from elfdump:
elfdump -s -N .symtab nogroup.linked.sun | egrep "foo|bar"
[15] 0x080501f2 0x00000000 NOTY GLOB D 0 .text bar
[21] 0x080501f0 0x00000000 NOTY GLOB D 0 .text foo
elfdump -s -N .symtab nogroup.linked.gnu | egrep "foo|bar"
[8] 0x08048078 0x00000000 NOTY GLOB D 0 .text foo
[11] 0x0804807a 0x00000000 NOTY GLOB D 0 .text bar
Now, we get identical results for foo and bar with the two linkers. Even more interesting is that for the sun linker, the results did not change when we removed the comdat flags. It is as if the sun linker happily absorbs and then ignores the fact that the sections are marked as COMDAT. So what is going on here? Does the sun linker really support COMDAT? Have I misinterpreted something? Which linker is right, according to the ELF spec?
Sorry for the long post, any insight would be appreciated.

Answer 1

Ok. That is a reasonable, if not very helpful answer.
In the meantime, here is a simpler example that shows the problem a little more clearly:
cat foobar.s.section .text,"axG",%progbits,foo_group,comdat
.global foo
foo:
.word 0
.section .text,"ax",%progbits
.global bar
bar:
.word 0
.section .text,"ax",%progbits
.global baz
baz:
.word 0
Now, assemble this twice into two different object files:
/usr/local/binutils-2.16.1/bin/as gdwarf2 foobar.s -o foobar2.o /usr/local//binutils-2.16.1/bin/as gdwarf2 foobar.s -o foobar1.o
If we link these two object files together, we should get two errors about undefined symbols: one for bar, and one for baz. foo should be ok because its COMDAT.
So:
/usr/local/binutils-2.16.1/bin/ld -shared foobar1.o foobar2.o foobar2.o: In function `bar':
: multiple definition of `bar'
foobar1.o:: first defined here
foobar2.o: In function `baz':
: multiple definition of `baz'
foobar1.o:: first defined here
Which is what we expect. But /usr/ccs/bin/ld gives:
/usr/ccs/bin/ld -G foobar1.o foobar2.o
ld: fatal: symbol `foo' is multiply-defined:
(file foobar1.o type=NOTY; file foobar2.o type=NOTY);
ld: fatal: symbol `bar' is multiply-defined:
(file foobar1.o type=NOTY; file foobar2.o type=NOTY);
ld: fatal: symbol `baz' is multiply-defined:
(file foobar1.o type=NOTY; file foobar2.o type=NOTY);
ld: fatal: File processing errors. No output written to a.out
which seems incorrect to me.