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digitalmars.D - controling callgrind intrumentation from D

reply Stefan Koch <uplink.coder googlemail.com> writes:
Hi I've found myself in need of controlling when the profiler 
callgrind  which is part of valgrind starts and stops 
instrumentation.
Both for performance reasons and to be able to actually read the 
part of the profile I am interested in, as otherwise it easily 
gets lost in the noise.

After a bit of digging I found that the callgrind header export 
macros with which to start and stop the instrumentation as well 
as telling it to dump the stats out.

But those use inline asm and the preprocessor so cannot be easily 
translated to D.
So just write extern wrapper functions and create a file that 
looks like

```d
#include <valgrind/callgrind.h>
extern void callgrind_start(void)
{
   CALLGRIND_START_INSTRUMENTATION;
}

extern void callgrind_stop(void)
{
   CALLGRIND_STOP_INSTRUMENTATION;
}

extern void callgrind_dumpstats(void)
{
   CALLGRIND_DUMP_STATS;
}
```

after compiling that with gcc and looking at the assembly you 
will see some useless preamble in those functions.

stack-overflow helpfully revealed that those are part of stack 
protection.
which `-fno-stack-protector` disables.
but then you are still left with the `eh_frame` section that 
isn't used.

`-fno-asynchronous-unwind-tables` gets rid of that.


the full commandline looks like
`gcc -Os callgrind_instr.c -c -fno-asynchronous-unwind-tables 
-fno-stack-protector`

now just add callgrind_instr.o to your build and use a d header 
such as

```d
extern (c) void callgrind_start();
extern (c) void callgrind_stop();
extern (c) void callgrind_dumpstats();
```

And there we go.
Pretty nice to be able to do that.
Sep 10
parent reply Stefan Koch <uplink.coder googlemail.com> writes:
On Friday, 10 September 2021 at 14:34:35 UTC, Stefan Koch wrote:
 ```d
 extern (c) void callgrind_start();
 extern (c) void callgrind_stop();
 extern (c) void callgrind_dumpstats();
 ```
Correction that's supposed to be: ```d extern (C) void callgrind_start(); extern (C) void callgrind_stop(); extern (C) void callgrind_dumpstats(); ```
Sep 10
parent bauss <jj_1337 live.dk> writes:
On Friday, 10 September 2021 at 15:13:06 UTC, Stefan Koch wrote:
 On Friday, 10 September 2021 at 14:34:35 UTC, Stefan Koch wrote:
 ```d
 extern (c) void callgrind_start();
 extern (c) void callgrind_stop();
 extern (c) void callgrind_dumpstats();
 ```
Correction that's supposed to be: ```d extern (C) void callgrind_start(); extern (C) void callgrind_stop(); extern (C) void callgrind_dumpstats(); ```
Wow it took me a long time to figure out the differences and that it was just the capitalization from c to C.
Sep 13