Re: alloca without runtime?

2017-05-10 Thread 岩倉 澪 via Digitalmars-d-learn

On Wednesday, 10 May 2017 at 20:25:45 UTC, aberba wrote:

On Thursday, 4 May 2017 at 14:54:58 UTC, 岩倉 澪 wrote:

On Thursday, 4 May 2017 at 12:50:02 UTC, Kagamin wrote:

You can try ldc and llvm intrinsics
http://llvm.org/docs/LangRef.html#alloca-instruction
http://llvm.org/docs/LangRef.html#llvm-stacksave-intrinsic


Ah, yep!

pragma(LDC_alloca) void* alloca(size_t);

This appears to work with ldc. It would be nice if there was a 
way to do this with dmd/other compilers as well though. If it 
were up to me I'd have alloca defined by the language standard 
and every compiler would have to provide an implementation 
like this. At the very least I'd like to have an alloca that 
works with dmd, as I want to do debug builds with dmd and 
release builds with ldc.


embedded platform?


An embedded platform would be a good use-case for this, but I'm 
just trying to do this on Linux x86_64 personally. It's a fun 
experiment to see how far I can push D to give me low-level 
control without dependencies


Re: alloca without runtime?

2017-05-10 Thread aberba via Digitalmars-d-learn

On Thursday, 4 May 2017 at 14:54:58 UTC, 岩倉 澪 wrote:

On Thursday, 4 May 2017 at 12:50:02 UTC, Kagamin wrote:

You can try ldc and llvm intrinsics
http://llvm.org/docs/LangRef.html#alloca-instruction
http://llvm.org/docs/LangRef.html#llvm-stacksave-intrinsic


Ah, yep!

pragma(LDC_alloca) void* alloca(size_t);

This appears to work with ldc. It would be nice if there was a 
way to do this with dmd/other compilers as well though. If it 
were up to me I'd have alloca defined by the language standard 
and every compiler would have to provide an implementation like 
this. At the very least I'd like to have an alloca that works 
with dmd, as I want to do debug builds with dmd and release 
builds with ldc.


embedded platform?


Re: alloca without runtime?

2017-05-04 Thread 岩倉 澪 via Digitalmars-d-learn

On Thursday, 4 May 2017 at 12:50:02 UTC, Kagamin wrote:

You can try ldc and llvm intrinsics
http://llvm.org/docs/LangRef.html#alloca-instruction
http://llvm.org/docs/LangRef.html#llvm-stacksave-intrinsic


Ah, yep!

pragma(LDC_alloca) void* alloca(size_t);

This appears to work with ldc. It would be nice if there was a 
way to do this with dmd/other compilers as well though. If it 
were up to me I'd have alloca defined by the language standard 
and every compiler would have to provide an implementation like 
this. At the very least I'd like to have an alloca that works 
with dmd, as I want to do debug builds with dmd and release 
builds with ldc.


Re: alloca without runtime?

2017-05-04 Thread Kagamin via Digitalmars-d-learn

You can try ldc and llvm intrinsics
http://llvm.org/docs/LangRef.html#alloca-instruction
http://llvm.org/docs/LangRef.html#llvm-stacksave-intrinsic


Re: alloca without runtime?

2017-05-04 Thread 岩倉 澪 via Digitalmars-d-learn

On Sunday, 30 April 2017 at 05:07:31 UTC, 岩倉 澪 wrote:
I've been playing around with using D with no runtime on Linux, 
but recently I was thinking it would be nice to have an alloca 
implementation. I was thinking I could just bump the stack 
pointer (with alignment considerations) but from what I 
understand compilers sometimes generate code that references 
variables relative to RSP instead of RBP? I've seen people 
saying that a proper alloca can't be implemented without help 
from the compiler...


I took a peek in druntime and found rt.alloca which has 
__alloca implemented with inline asm. I tried throwing that in 
my project and calling it but it segfaults on rep movsq. The 
comments in the code suggest it is trying to copy temps on the 
stack but I seem to get a really large garbage RCX, I don't 
fully follow what is going on yet.


Is there any way I can get a working alloca without using 
druntime, c runtime, etc?


As a follow-up, here is a simple example of what I mean:

first, let's create a main.d, we'll define our own entry point 
and make a call to alloca in main:


extern (C):
void _start()
{
asm nothrow @nogc
{
naked;
xor RBP, RBP;
pop RDI;
mov RSI, RSP;
and RSP, -16;
call main;
mov RDI, RAX;
mov RAX, 60;
syscall;
ret;
}
}
pragma(startaddress, _start);
int main(int argc, char** argv)
{
import rt.alloca;
void* a = __alloca(42);
return 0;
}

Next, let's make an rt directory and copy the source of 
druntime's rt.alloca into rt/alloca.d


Now let's compile these:

dmd -betterC -debuglib= -defaultlib= -boundscheck=off -vgc -vtls 
-c -gc main.d rt/alloca.d


Great, now we need to strip symbols out to make this work, like 
so:


objcopy -R '.data.*[0-9]TypeInfo_*' -R '.[cd]tors.*' -R .eh_frame 
-R minfo -R .group.d_dso -R .data.d_dso_rec -R .text.d_dso_init 
-R .dtors.d_dso_dtor -R .ctors.d_dso_ctor -N __start_minfo -N 
__stop_minfo main.o
objcopy -R '.data.*[0-9]TypeInfo_*' -R '.[cd]tors.*' -R .eh_frame 
-R minfo -R .group.d_dso -R .data.d_dso_rec -R .text.d_dso_init 
-R .dtors.d_dso_dtor -R .ctors.d_dso_ctor -N __start_minfo -N 
__stop_minfo alloca.o


With that out of the way, we are ready to link:

ld main.o alloca.o

And when we try to run ./a.out we get a segfault.

What I want is a way to allocate on the stack (size of allocation 
not necessarily known at compile-time) and for the compiler to be 
aware that it can't generate code that refers to variables on the 
stack relative to rsp, or anything else that might break the 
naive implementation of alloca as simply bumping rsp with inline 
asm. Apparently this "magic" __alloca can't be used outside of 
the compiler, or is there a way to make it work?


alloca without runtime?

2017-04-29 Thread 岩倉 澪 via Digitalmars-d-learn
I've been playing around with using D with no runtime on Linux, 
but recently I was thinking it would be nice to have an alloca 
implementation. I was thinking I could just bump the stack 
pointer (with alignment considerations) but from what I 
understand compilers sometimes generate code that references 
variables relative to RSP instead of RBP? I've seen people saying 
that a proper alloca can't be implemented without help from the 
compiler...


I took a peek in druntime and found rt.alloca which has __alloca 
implemented with inline asm. I tried throwing that in my project 
and calling it but it segfaults on rep movsq. The comments in the 
code suggest it is trying to copy temps on the stack but I seem 
to get a really large garbage RCX, I don't fully follow what is 
going on yet.


Is there any way I can get a working alloca without using 
druntime, c runtime, etc?