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Author Topic: problems with the AArch64 inline Assembler  (Read 2306 times)

derMischka81

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  • Posts: 6
problems with the AArch64 inline Assembler
« on: February 16, 2021, 01:28:19 pm »
I use the inline Asssembler on my RPi3 with 64Bit OS.

I have problems with the following inline Assembler instruction

Code: Pascal  [Select][+][-]
  1. asm
  2.   add x1, x1, x7, lsl #3
  3. end;
  4.  

The Instruction should do the following thing:

x1 := x1 + (x7 shl 3)

but if I compile and check the results inklusive the assembly window I can see that the BarrelShift (lsl #3) is missing.


The Next Problem is a branch to a Object-function.

Code: Pascal  [Select][+][-]
  1. TTestObj1.testproc;
  2. begin
  3. end;
  4.  
  5. TTestObj2.asmprob;nostackframe;assembler;
  6. asm
  7.   stp x0, x30, [sp, #-16]!
  8.  
  9.   ldr x0, [x0, FTestObj1]
  10.   bl TTestObj1.testproc
  11.  
  12.   ldp x0, x30 [sp], #16
  13. end;
  14.  

The Branch-Value/Address is not correct --> jumps to the branch line self (infinite loop)
« Last Edit: February 16, 2021, 01:42:33 pm by derMischka81 »

Zvoni

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Re: problems with the AArch64 inline Assembler
« Reply #1 on: February 16, 2021, 03:33:55 pm »
I was under the impression, that the ADD in Assembly has three operands: Destination, Source1, Source2
You have 4 operands
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PascalDragon

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Re: problems with the AArch64 inline Assembler
« Reply #2 on: February 17, 2021, 09:43:35 am »
I use the inline Asssembler on my RPi3 with 64Bit OS.

I have problems with the following inline Assembler instruction

Code: Pascal  [Select][+][-]
  1. asm
  2.   add x1, x1, x7, lsl #3
  3. end;
  4.  

The Instruction should do the following thing:

x1 := x1 + (x7 shl 3)

but if I compile and check the results inklusive the assembly window I can see that the BarrelShift (lsl #3) is missing.

You are aware that I as a compiler developer had already replied to this in on your thread in German forum? And that you should report this on the bug tracker?

The Next Problem is a branch to a Object-function.

Code: Pascal  [Select][+][-]
  1. TTestObj1.testproc;
  2. begin
  3. end;
  4.  
  5. TTestObj2.asmprob;nostackframe;assembler;
  6. asm
  7.   stp x0, x30, [sp, #-16]!
  8.  
  9.   ldr x0, [x0, FTestObj1]
  10.   bl TTestObj1.testproc
  11.  
  12.   ldp x0, x30 [sp], #16
  13. end;
  14.  

The Branch-Value/Address is not correct --> jumps to the branch line self (infinite loop)

I think you better use a combination of ADRP and ADR to load the address into a register and branch to that. What exactly the assembler reader generates for your code I'd need to check.

I was under the impression, that the ADD in Assembly has three operands: Destination, Source1, Source2
You have 4 operands

The ADD instruction (among others) can also have an additional shift left as fourth parameter. See for example here.

Jonas Maebe

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Re: problems with the AArch64 inline Assembler
« Reply #3 on: February 17, 2021, 02:26:00 pm »
I use the inline Asssembler on my RPi3 with 64Bit OS.

I have problems with the following inline Assembler instruction

Code: Pascal  [Select][+][-]
  1. asm
  2.   add x1, x1, x7, lsl #3
  3. end;
  4.  
This bug is fixed in trunk and fixes_3_2.

Quote
Code: Pascal  [Select][+][-]
  1. TTestObj1.testproc;
  2. begin
  3. end;
  4.  
  5. TTestObj2.asmprob;nostackframe;assembler;
  6. asm
  7.   stp x0, x30, [sp, #-16]!
  8.  
  9.   ldr x0, [x0, FTestObj1]
  10.   bl TTestObj1.testproc
  11.  
  12.   ldp x0, x30 [sp], #16
  13. end;
  14.  
While not yet supported, for now this at least gives a compilation error rather than resulting in invalid code. The compiler does not yet parse "ldr x0, [x0, FTestObj1]" correctly either though (it seems to ignore the "FTestObj1"; even if it does not exist, no compilation error is printed).

The RTL uses very little AArch64 inline assembly and since it's a new architecture, existing inline assembly tests are not checked for it (they would have to be translated first). So there are probably quite a few more bugs in its assembler reader...

 

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