Could you update to r109036 and post the output on this testcase?

Sure, the output is:

@​skel = global [1 x i8*] zeroinitializer ; <[1 x i8*]*> [#uses=0]

Unknown constant!
UNREACHABLE executed at /usr/local/google/home/espindola/llvm/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp:903!

Fixed in r109117.

I still get the same failure:

@​skel = global [1 x i8*] zeroinitializer ; <[1 x i8*]*> [#uses=0]

Unknown constant!
UNREACHABLE executed at /usr/local/google/home/espindola/llvm/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp:909!

I program that should allow you to reproduce without gold:

#include <assert.h>
#include "llvm-c/lto.h"
int main(int argc, char *argv[]) {
lto_module_t M = lto_module_create(argv[1]);
assert (M);
unsigned sym_count = lto_module_get_num_symbols(M);

lto_code_gen_t cg = lto_codegen_create();
lto_codegen_add_module(cg, M);
lto_codegen_model output_type = LTO_CODEGEN_PIC_MODEL_STATIC;
lto_codegen_set_pic_model(cg, output_type);
lto_codegen_set_debug_model(cg, LTO_DEBUG_MODEL_DWARF);
bool err = lto_codegen_write_merged_modules(cg, "foo.bc");
return 0;
}

Just pass the test.bc file to it and lto_codegen_write_merged_modules will abort with the same error message.

This is related to llvm/llvm-bugzilla-archive#7700 .

Fixed in r111949 and related commits.

Fixed in r111949 and related commits.

With those patches, the test case in the original description gave me these:

@​skel = global [1 x i8*] zeroinitializer ; <[1 x i8*]*> [#uses=0]

Unknown constant!
UNREACHABLE executed at /local.toadette/aliang/fixing/llvmsvn/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp:909!
Aborted

Does anyone else see the same result?

@​skel = global [1 x i8*] zeroinitializer ; <[1 x i8*]*> [#uses=0]

Unknown constant!
UNREACHABLE executed at
/local.toadette/aliang/fixing/llvmsvn/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp:909!

That UNREACHABLE is no longer at line 909 in BitcodeWriter.cpp on ToT; are your sources up to date?

@​skel = global [1 x i8*] zeroinitializer ; <[1 x i8*]*> [#uses=0]

Unknown constant!
UNREACHABLE executed at
/local.toadette/aliang/fixing/llvmsvn/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp:909!

That UNREACHABLE is no longer at line 909 in BitcodeWriter.cpp on ToT; are your
sources up to date?

This UNREACHABLE disappeared. Thanks. The reason is that I did not replace those old LLVMgold.so and libLTO.so.

But I got the following:
/local/llvm-gcc/lib/gcc/i686-pc-linux-gnu/4.2.1/../../../../i686-pc-linux-gnu/bin/ld: error: /local/llvm-gcc/libexec/gcc/i686-pc-linux-gnu/4.2.1/LLVMgold.so: could not load plugin library: /local/llvm-gcc/libexec/gcc/i686-pc-linux-gnu/4.2.1/LLVMgold.so: undefined symbol: lto_codegen_set_cpu

Missing lto_codegen_set_cpu is a separate gold plugin issue. Please use new PR.

Missing lto_codegen_set_cpu is a separate gold plugin issue. Please use new PR.

I fixed this by adding lto_codegen_set_cpu and lto_codegen_set_assembler_args to lto.exports

Then I still got the Unknown constant! by doing:
$ cat conftest.c
int
main ()
{
return 0;
}

$ llvm-gcc -use-gold-plugin -Wl,-plugin-opt=also-emit-llvm -O4 -g conftest.c
collect2: ld terminated with signal 6 [Aborted]

declare i32 @​main() nounwind readnone

Unknown constant!
UNREACHABLE executed at /local.toadette/aliang/fixing/llvmsvn/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp:910!

It turns out there was another bug in bitcode linking. This is now fixed in r112091. I updated lto.exports too.

It turns out there was another bug in bitcode linking. This is now fixed in
r112091. I updated lto.exports too.

I compiled httpd-2.2.9.tar.gz using the latest code. It compiles without problem, however, I got a lot of "BFD: Dwarf Error: Could not find abbrev number" when I do objdump.

It is configured with:
../configure --prefix=/local/install CFLAGS="-O4 -g" CC="llvm-gcc -use-gold-plugin -Wl,-plugin-opt=also-emit-llvm" CXX="llvm-g++ -use-gold-plugin -Wl,-plugin-opt=also-emit-llvm" RANLIB="/bin/true" --with-mpm=worker

then I make

then go to .libs and do
objdump -l -S httpd > httpd.S
and got:
"
BFD: Dwarf Error: Could not find abbrev number 116.
BFD: Dwarf Error: Could not find abbrev number 5864.
BFD: Dwarf Error: Could not find abbrev number 117.
BFD: Dwarf Error: Could not find abbrev number 110.
BFD: Dwarf Error: Could not find abbrev number 116.
BFD: Dwarf Error: Could not find abbrev number 116.
BFD: Dwarf Error: Could not find abbrev number 120.
BFD: Dwarf Error: Could not find abbrev number 116.
BFD: Dwarf Error: Could not find abbrev number 127.
BFD: Dwarf Error: Could not find abbrev number 127.
BFD: Dwarf Error: Could not find abbrev number 116.
BFD: Dwarf Error: Could not find abbrev number 116.
BFD: Dwarf Error: Could not find abbrev number 111.
BFD: Dwarf Error: Could not find abbrev number 267.
BFD: Dwarf Error: Could not find abbrev number 267.
BFD: Dwarf Error: Could not find abbrev number 5495.
BFD: Dwarf Error: Could not find abbrev number 12928.
...
...
"

I did get one httpd.S though.

Please file a new bug with an example of a bitcode file that produces a .o with broken debug info. Thanks!

Please file a new bug with an example of a bitcode file that produces a .o with
broken debug info. Thanks!

http://llvm.org/bugs/show_bug.cgi?id=8003

I haven't reduce it to a single bytecode file. Instead I uploaded a tarball of bytecode files that can be linked to get the final binary.