llvm dev - Mar 2018 - Using Xray compilation with C programs

Hi all,

I was interested in trying out the Xray profiling component in LLVM and was
trying to compile a C program with Clang with Xray flags. Unfortunately, I
keep getting a linker error everytime I try to compile the C program with
Clang. However, the error goes away when I try to compile the same C
program with Clang++ with -xc++ flag.

Searching around for this issue, looks like somebody has already filed a
bug for this issue:
https://bugs.llvm.org/show_bug.cgi?id=34904

Is there any way to get around this bug or to solve this issue?

Issue description from the filed bug:

According to documentation it should be possible to use xray
instrumentation on C program by specifying the flags
-fxray-instrument.

Linking fails when compiling the following program:

----8<----- (minimal.c)
int main ()
{
  return 0;
}
----8<-----
$ clang --version
clang version 6.0.0 (trunk 315272)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/jonasbu/local/bin

$ clang -fxray-instrument minimal.c
/home/jonasbu/local/lib/clang/6.0.0/lib/linux/libclang_rt.xray-x86_64.a(xray_inmemory_log.cc.o):
In function `getGlobalFd()':
/home/jonasbu/llvm-clang/llvm/projects/compiler-rt/lib/xray/xray_inmemory_log.cc:123:
undefined reference to `__cxa_guard_acquire'
/home/jonasbu/llvm-clang/llvm/projects/compiler-rt/lib/xray/xray_inmemory_log.cc:123:
undefined reference to `__cxa_guard_release'
/home/jonasbu/local/lib/clang/6.0.0/lib/linux/libclang_rt.xray-x86_64.a(xray_inmemory_log.cc.o):
In function `__xray_InMemoryRawLog<__xray_InMemoryEmulateTSC(int32_t,
XRayEntryType)::<lambda(uint8_t&)> >':
/home/jonasbu/llvm-clang/llvm/projects/compiler-rt/lib/xray/xray_inmemory_log.cc:136:
undefined reference to `__cxa_thread_atexit'
/home/jonasbu/local/lib/clang/6.0.0/lib/linux/libclang_rt.xray-x86_64.a(xray_inmemory_log.cc.o):
In function `__xray_OpenLogFile':
/home/jonasbu/llvm-clang/llvm/projects/compiler-rt/lib/xray/xray_inmemory_log.cc:85:
undefined reference to `__cxa_guard_acquire'
/home/jonasbu/llvm-clang/llvm/projects/compiler-rt/lib/xray/xray_inmemory_log.cc:85:
undefined reference to `__cxa_guard_release'
/home/jonasbu/llvm-clang/llvm/projects/compiler-rt/lib/xray/xray_inmemory_log.cc:87:
undefined reference to `__cxa_guard_acquire'
/home/jonasbu/llvm-clang/llvm/projects/compiler-rt/lib/xray/xray_inmemory_log.cc:87:
undefined reference to `__cxa_guard_release'
...
...
...

As expected, the same program compiles and links fine as a C++ program:

$ clang++ -xc++ -fxray-instrument minimal.c
<no output>
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Dean - any ideas if this is/should be supported? (I think the last time we
discussed this with Kostya the answer was sanitizer-like runtime libraries
shouldn't use any C++ features? (for reasons like this, and others) so
maybe this case is another to add to the list of motivations to
continue/complete that work?)

On Sun, Mar 11, 2018 at 12:05 PM Harsh 00 via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> Hi all,
>
> I was interested in trying out the Xray profiling component in LLVM and
> was trying to compile a C program with Clang with Xray flags.
> Unfortunately, I keep getting a linker error everytime I try to compile the
> C program with Clang. However, the error goes away when I try to compile
> the same C program with Clang++ with -xc++ flag.
>
> Searching around for this issue, looks like somebody has already filed a
> bug for this issue:
> https://bugs.llvm.org/show_bug.cgi?id=34904
>
> Is there any way to get around this bug or to solve this issue?
>
> Issue description from the filed bug:
>
> According to documentation it should be possible to use xray
instrumentation on C program by specifying the flags -fxray-instrument.
>
> Linking fails when compiling the following program:
>
> ----8<----- (minimal.c)
> int main ()
> {
>   return 0;
> }
> ----8<-----
> $ clang --version
> clang version 6.0.0 (trunk 315272)
> Target: x86_64-unknown-linux-gnu
> Thread model: posix
> InstalledDir: /home/jonasbu/local/bin
>
> $ clang -fxray-instrument minimal.c
>
/home/jonasbu/local/lib/clang/6.0.0/lib/linux/libclang_rt.xray-x86_64.a(xray_inmemory_log.cc.o):
In function `getGlobalFd()':
>
/home/jonasbu/llvm-clang/llvm/projects/compiler-rt/lib/xray/xray_inmemory_log.cc:123:
undefined reference to `__cxa_guard_acquire'
>
/home/jonasbu/llvm-clang/llvm/projects/compiler-rt/lib/xray/xray_inmemory_log.cc:123:
undefined reference to `__cxa_guard_release'
>
/home/jonasbu/local/lib/clang/6.0.0/lib/linux/libclang_rt.xray-x86_64.a(xray_inmemory_log.cc.o):
In function `__xray_InMemoryRawLog<__xray_InMemoryEmulateTSC(int32_t,
XRayEntryType)::<lambda(uint8_t&)> >':
>
/home/jonasbu/llvm-clang/llvm/projects/compiler-rt/lib/xray/xray_inmemory_log.cc:136:
undefined reference to `__cxa_thread_atexit'
>
/home/jonasbu/local/lib/clang/6.0.0/lib/linux/libclang_rt.xray-x86_64.a(xray_inmemory_log.cc.o):
In function `__xray_OpenLogFile':
>
/home/jonasbu/llvm-clang/llvm/projects/compiler-rt/lib/xray/xray_inmemory_log.cc:85:
undefined reference to `__cxa_guard_acquire'
>
/home/jonasbu/llvm-clang/llvm/projects/compiler-rt/lib/xray/xray_inmemory_log.cc:85:
undefined reference to `__cxa_guard_release'
>
/home/jonasbu/llvm-clang/llvm/projects/compiler-rt/lib/xray/xray_inmemory_log.cc:87:
undefined reference to `__cxa_guard_acquire'
>
/home/jonasbu/llvm-clang/llvm/projects/compiler-rt/lib/xray/xray_inmemory_log.cc:87:
undefined reference to `__cxa_guard_release'
> ...
> ...
> ...
>
> As expected, the same program compiles and links fine as a C++ program:
>
> $ clang++ -xc++ -fxray-instrument minimal.c
> <no output>
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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