[llvm-dev] How to pass the current function name at runtime without additional Global variables?

[Alberto Barbaro via llvm-dev]

Thanks David and Phoebe,
In the end I think the best solution is just to declare a global pointer
with the function name and pass it as a parameter.

Thanks again for your suggestions and help.

Alberto

On Mon, Jan 10, 2022, 02:58 Wang, Phoebe <phoebe.wang at intel.com> wrote:

> Some wild thoughts. Even release built binaries contain the information of
> function name (unless you stripe them), we always see them in a crash
> backtrace. So we may be able to get the function name by the function
> address with the aid of debug API. Or write one ourselves. Then we can
> insert the call to this function before the external call in a pass. For
> example:
>
>
>
> extern int bar(char *, int);
>
>
>
> int foo(int a) {
>
>     char *name = __get_name(bar); // This is what we are inserting
>
>     return bar(name, a);
>
> }
>
>
>
> Ps: Just realize the calling functions are external. Not sure how to do
> with SOs, static link library should be workable.
>
>
>
> Thanks
>
> Phoebe
>
>
>
> *From:* llvm-dev <llvm-dev-bounces at lists.llvm.org> *On Behalf Of *David
> Blaikie via llvm-dev
> *Sent:* Monday, January 10, 2022 10:22 AM
> *To:* Alberto Barbaro <barbaro.alberto at gmail.com>
> *Cc:* llvm-dev <llvm-dev at lists.llvm.org>
> *Subject:* Re: [llvm-dev] How to pass the current function name at
> runtime without additional Global variables?
>
>
>
> On Sun, Jan 9, 2022 at 12:42 AM Alberto Barbaro via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
> Hi all,
>
> I'm working on a little LLVM pass that should add a call to an external
> function ( C++ project ) and pass as a parameter the name of the function
> that is about to be called. I have a problem finding a nice way to pass the
> current function name. In fact, so far,  Unfortunately the only solution
> that I have found for passing the name is to create a global for each
> function, store the name there and pass it as a parameter. I don't really
> like this solution because the size of the final binary increases and the
> overall approach feels not  optimal.
>
>
>
> Assuming that I have a variable `I` which is the CallInst instruction, is
> it possible to pass the function name at runtime to my external library in
> a nice way? I thought about passing the address of the instruction and
> casting it back to the CallInst instruction but I don't know how to do it.
>
>
>
> That doesn't quite line up to me - the "Instruction"/CallInst only exists
> at compile-time, not runtime. So if you embedded the pointer value into the
> program, casting that pointer back to a CallInst at runtime in the program
> would only give you a corrupt pointer/garbage.
>
>
>
> Any suggestions?
>
>
> Not much to it that I can think of - one way or another you'd have to have
> the string embedded in the program somewhere, or in a side-table (eg: your
> compiler could produce a little csv file or something that lets you lookup
> some ID number to the string value - then you just encode/pass around the
> ID in the program, and in some post-processing step you can lookup the
> string in the csv file given the ID). You could avoid a global variable by
> generating instructions in the caller that could write the string value
> into a buffer, then pass that buffer by-value to the function you're
> calling - but that's a ton of extra instructions compared to passing a
> pointer to a global/constant buffer.
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20220110/f3e785a2/attachment.html>