> On Oct 28, 2015, at 11:03 AM, Justin Bogner via cfe-commits
> <cfe-commits@lists.llvm.org> wrote:
>
> Xinliang David Li via cfe-commits <cfe-commits@lists.llvm.org> writes:
>> Author: davidxl
>> Date: Tue Oct 27 00:15:35 2015
>> New Revision: 251385
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=251385&view=rev
>> Log:
>> Create undef reference to profile hook symbol
>>
>> Create undef reference to profile hook symbol when
>> PGO instrumentation is turned on. This allows
>> LLVM to omit emission of hook variable use method
>> for every single module instrumented.
>
> Nick: This approach should work for ld64 as well, right?
Hm, I tried this out with a dummy file:
liba.a(a.o):
0000000000000004 C ___llvm_profile_runtime
0000000000000000 T _foo
I compiled with:
$ cc -L. -la liba.a -Wl,-u -Wl,__llvm_profile_runtime b.c -o b
The hook symbol doesn't appear in the final executable:
b:
0000000100000000 T __mh_execute_header
0000000100000f90 T _main
U dyld_stub_binder
If I instead link with "-force_load liba.a", I get the expected result. I could
just be doing this incorrectly, so I'll defer to Nick.
>
> David: This seems like a good idea, but it's buggy as implemented.
> Details below.
>
>>
>> Modified:
>> cfe/trunk/lib/Driver/ToolChains.cpp
>> cfe/trunk/lib/Driver/ToolChains.h
>>
>> Modified: cfe/trunk/lib/Driver/ToolChains.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Driver/ToolChains.cpp?rev=251385&r1=251384&r2=251385&view=diff
>> ==============================================================================
>> --- cfe/trunk/lib/Driver/ToolChains.cpp (original)
>> +++ cfe/trunk/lib/Driver/ToolChains.cpp Tue Oct 27 00:15:35 2015
>> @@ -25,6 +25,7 @@
>> #include "llvm/Option/ArgList.h"
>> #include "llvm/Option/OptTable.h"
>> #include "llvm/Option/Option.h"
>> +#include "llvm/ProfileData/InstrProf.h"
>> #include "llvm/Support/ErrorHandling.h"
>> #include "llvm/Support/FileSystem.h"
>> #include "llvm/Support/MemoryBuffer.h"
>> @@ -3811,6 +3812,18 @@ SanitizerMask Linux::getSupportedSanitiz
>> return Res;
>> }
>>
>> +void Linux::addProfileRTLibs(const llvm::opt::ArgList &Args,
>> + llvm::opt::ArgStringList &CmdArgs) const {
>> + if (!needsProfileRT(Args)) return;
>> +
>> + // Add linker option -u__llvm_runtime_variable to cause runtime
>> + // initialization module to be linked in.
>> + if (!Args.hasArg(options::OPT_coverage))
>
> This check isn't right. What about the other gcov-style flags like
> -fprofile-args? What if both kinds of coverage are on for some strange
> reason? It's also a maintenance burden, since the logic needs to be
> duplicated from needsProfileRT. I think we need finer grained helpers -
> maybe something like needsGCOVRT and needsInstrProfRT, either of which
> will pull in the profileRTLibs.
Sorry I missed this.
vedant
>> + CmdArgs.push_back(Args.MakeArgString(
>> + Twine("-u", llvm::getInstrProfRuntimeHookVarName())));
>> + ToolChain::addProfileRTLibs(Args, CmdArgs);
>> +}
>> +
>> /// DragonFly - DragonFly tool chain which can call as(1) and ld(1) directly.
>>
>> DragonFly::DragonFly(const Driver &D, const llvm::Triple &Triple,
>>
>> Modified: cfe/trunk/lib/Driver/ToolChains.h
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Driver/ToolChains.h?rev=251385&r1=251384&r2=251385&view=diff
>> ==============================================================================
>> --- cfe/trunk/lib/Driver/ToolChains.h (original)
>> +++ cfe/trunk/lib/Driver/ToolChains.h Tue Oct 27 00:15:35 2015
>> @@ -744,6 +744,8 @@ public:
>> llvm::opt::ArgStringList &CC1Args) const override;
>> bool isPIEDefault() const override;
>> SanitizerMask getSupportedSanitizers() const override;
>> + void addProfileRTLibs(const llvm::opt::ArgList &Args,
>> + llvm::opt::ArgStringList &CmdArgs) const override;
>>
>> std::string Linker;
>> std::vector<std::string> ExtraOpts;
>>
>>
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