llvm dev - Apr 2015 - [LLVMdev] [lld] Linker cannot handle sections with non-unique names

Hi,

FYI

LLD cannot handle ELF sections with non-unique names. An object file
with such sections can be generated by the Clang since r234143. I am
not sure that Clang works absolutely correct but bfd linker works
fine.

Right now I do not have a time to investigate this problem. If nobody
take, I will try to solve it later.

Here is the reproduction script for x86_64 host:

$ cat test.cc
template <class T>
void foo(T) {}

int main() {
  foo(0);
  foo(1.0);
}

$ clang++ -c test.cc -fno-unique-section-names
$ lld -flavor gnu -target x86_64 --hash-style=both --build-id \
  --eh-frame-hdr -m elf_x86_64 \
  -dynamic-linker /lib64/ld-linux-x86-64.so.2 -o a.out \
  <bunch of regular linker arguments here>
$ ./a.out
Illegal instruction

$ clang++ -c test.cc -funique-section-names
$ lld -flavor gnu -target x86_64 --hash-style=both --build-id \
  --eh-frame-hdr -m elf_x86_64 \
  -dynamic-linker /lib64/ld-linux-x86-64.so.2 -o a.out \
  <bunch of regular linker arguments here>
$ ./a.out

-- 
Simon Atanasyan

Thanks Simon fir the test. I may be able to get  to this issue later too. The
bug is mostly in the elf reader where it's skipping real sections with the
same name.


> On Apr 18, 2015, at 06:52, Simon Atanasyan <simon at atanasyan.com>
wrote:
> 
> Hi,
> 
> FYI
> 
> LLD cannot handle ELF sections with non-unique names. An object file
> with such sections can be generated by the Clang since r234143. I am
> not sure that Clang works absolutely correct but bfd linker works
> fine.
> 
> Right now I do not have a time to investigate this problem. If nobody
> take, I will try to solve it later.
> 
> Here is the reproduction script for x86_64 host:
> 
> $ cat test.cc
> template <class T>
> void foo(T) {}
> 
> int main() {
>  foo(0);
>  foo(1.0);
> }
> 
> $ clang++ -c test.cc -fno-unique-section-names
> $ lld -flavor gnu -target x86_64 --hash-style=both --build-id \
>  --eh-frame-hdr -m elf_x86_64 \
>  -dynamic-linker /lib64/ld-linux-x86-64.so.2 -o a.out \
>  <bunch of regular linker arguments here>
> $ ./a.out
> Illegal instruction
> 
> $ clang++ -c test.cc -funique-section-names
> $ lld -flavor gnu -target x86_64 --hash-style=both --build-id \
>  --eh-frame-hdr -m elf_x86_64 \
>  -dynamic-linker /lib64/ld-linux-x86-64.so.2 -o a.out \
>  <bunch of regular linker arguments here>
> $ ./a.out
> 
> -- 
> Simon Atanasyan

Attached patch fixes the issue.

On Sat, Apr 18, 2015 at 6:52 AM, Simon Atanasyan <simon at atanasyan.com>
wrote:
> Hi,
>
> FYI
>
> LLD cannot handle ELF sections with non-unique names. An object file
> with such sections can be generated by the Clang since r234143. I am
> not sure that Clang works absolutely correct but bfd linker works
> fine.
>
> Right now I do not have a time to investigate this problem. If nobody
> take, I will try to solve it later.
>
> Here is the reproduction script for x86_64 host:
>
> $ cat test.cc
> template <class T>
> void foo(T) {}
>
> int main() {
>   foo(0);
>   foo(1.0);
> }
>
> $ clang++ -c test.cc -fno-unique-section-names
> $ lld -flavor gnu -target x86_64 --hash-style=both --build-id \
>   --eh-frame-hdr -m elf_x86_64 \
>   -dynamic-linker /lib64/ld-linux-x86-64.so.2 -o a.out \
>   <bunch of regular linker arguments here>
> $ ./a.out
> Illegal instruction
>
> $ clang++ -c test.cc -funique-section-names
> $ lld -flavor gnu -target x86_64 --hash-style=both --build-id \
>   --eh-frame-hdr -m elf_x86_64 \
>   -dynamic-linker /lib64/ld-linux-x86-64.so.2 -o a.out \
>   <bunch of regular linker arguments here>
> $ ./a.out
>
> --
> Simon Atanasyan
>
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On Sun, Apr 19, 2015 at 3:44 PM, Shankar Easwaran <shankarke at gmail.com>
wrote:
> Attached patch fixes the issue.
>
This seems OK to me but please add a testcase.

On Mon, Apr 20, 2015 at 1:44 AM, Shankar Easwaran <shankarke at gmail.com>
wrote:
> Attached patch fixes the issue.
Thanks for the quick fix. The patch LGTM if you add a test case.
Unfortunately yaml2obj does not support duplicated section names but
we can use a binary input file.

-- 
Simon Atanasyan