llvm dev - Apr 2017 - How to pass a StringRef to a function call inserted as instrumentation?

I am wriitng an LLVM pass to insert instrumentation at certain points of
the program. I want to pass the `StringRef` obtained from `getName()` as a
parameter to a function `func(char* s)`. I can allocate some space on stack
using `AllocaInst` to generate an `alloca` instruction. But, how can I copy
the `StringRef` to the stack space?

-- 

Thanks & Regards,
Dipanjan
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StringRef::str().c_str() or StringRef::data()?

2017-04-29 7:32 GMT+08:00 Dipanjan Das via llvm-dev <llvm-dev at
lists.llvm.org
>:
>
> I am wriitng an LLVM pass to insert instrumentation at certain points of
> the program. I want to pass the `StringRef` obtained from `getName()` as a
> parameter to a function `func(char* s)`. I can allocate some space on stack
> using `AllocaInst` to generate an `alloca` instruction. But, how can I copy
> the `StringRef` to the stack space?
>
> --
>
> Thanks & Regards,
> Dipanjan
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>

-- 
Wei-Ren Chen (陳韋任)
Homepage: https://people.cs.nctu.edu.tw/~chenwj
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StringRef::data, basically char*

On 28 April 2017 at 16:37, 陳韋任 <chenwj.cs97g at g2.nctu.edu.tw> wrote:
> StringRef::str().c_str() or StringRef::data()?
>
> 2017-04-29 7:32 GMT+08:00 Dipanjan Das via llvm-dev <
> llvm-dev at lists.llvm.org>:
>
>>
>> I am wriitng an LLVM pass to insert instrumentation at certain points
of
>> the program. I want to pass the `StringRef` obtained from `getName()`
as a
>> parameter to a function `func(char* s)`. I can allocate some space on
stack
>> using `AllocaInst` to generate an `alloca` instruction. But, how can I
copy
>> the `StringRef` to the stack space?
>>
>> --
>>
>> Thanks & Regards,
>> Dipanjan
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>>
>
>
> --
> Wei-Ren Chen (陳韋任)
> Homepage: https://people.cs.nctu.edu.tw/~chenwj
>


-- 

Thanks & Regards,
Dipanjan
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Hi, Dipanjan,

On 28 April 2017 at 16:32, Dipanjan Das via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> I am wriitng an LLVM pass to insert instrumentation at certain points of
the
> program. I want to pass the `StringRef` obtained from `getName()` as a
> parameter to a function `func(char* s)`. I can allocate some space on stack
> using `AllocaInst` to generate an `alloca` instruction. But, how can I copy
> the `StringRef` to the stack space?
I think this is usually done via anonymous globals. For example if you
use Clang to compile this:

void note_store(char *LocName, void *Addr);
void foo(int *Ptr) {
  note_store("store in foo", (void *)Ptr);
  *Ptr = 42;
}

you get (essentially):

@.str = private unnamed_addr constant [13 x i8] c"store in foo\00",
align 1

define void @foo(i32* %Ptr) {
  %Ptr8 = bitcast i32* %Ptr to i8*
  call void @note_store(i8* getelementptr inbounds ([13 x i8], [13 x
i8]* @.str, i64 0, i64 0), i8* %Ptr8)
  store i32 42, i32* %Ptr, align 4
  ret void
}

So you'll create a new global i8 array that gets initialized to your
StringRef's data and then pass a pointer to its first element into
your instrumentation function.

Cheers.

Tim.

Hi Tim,

I think this is usually done via anonymous globals. For example if
you
> use Clang to compile this:
> .
> .
> .
> So you'll create a new global i8 array that gets initialized to your
> StringRef's data and then pass a pointer to its first element into
> your instrumentation function.
>

Sorry to reply late. It worked perfectly fine. For the sake of
completeness, this is what I did:

   Value* var_name = builder.CreateGlobalStringPtr(po->getName()); //
builder is an IRBuilder instance

Above created the following IR:

@0 = private unnamed_addr constant [2 x i8] c"a\00"

-- 

Thanks & Regards,
Dipanjan
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