Gas: Any pseudo instruction to disable a single RELOC?

Gas: Any pseudo instruction to disable a single RELOC?

[YunQiang Su]

Is there a way to disable generating RELOC for a single instruction?
One example is

     .set noreorder
xx:
      .reloc 0,R_MIPS_NONE,0  # append a new reloc.
      bal 4
      nop
      sll $2,$2,0
      sll $2,$2,0


In this example, I wish `bal 4` would be keeped as is.
Is there a way to disable generating any RELOC?

Re: Gas: Any pseudo instruction to disable a single RELOC?

[Jan Beulich]

On 12.01.2024 11:08, YunQiang Su wrote:
> Is there a way to disable generating RELOC for a single instruction?
> One example is
> 
>      .set noreorder
> xx:
>       .reloc 0,R_MIPS_NONE,0  # append a new reloc.
>       bal 4
>       nop
>       sll $2,$2,0
>       sll $2,$2,0
> 
> 
> In this example, I wish `bal 4` would be keeped as is.
> Is there a way to disable generating any RELOC?

I don't think there is, and I don't think there should be. People using
.reloc absolutely need to know what they are doing.

Jan

Re: Gas: Any pseudo instruction to disable a single RELOC?

[YunQiang Su]

> I don't think there is, and I don't think there should be. People using
> .reloc absolutely need to know what they are doing.
>

Thank you, I find a solution.
BAL  . + 4
won't emit any relocs.

Background:
MIPS pre-R6 has no instructions that can read PC directly, thus we
have to use an branch and link instruction to do so.

I am working on GCC to support it. I don' want to emit an label for this
simple branch.

Re: Gas: Any pseudo instruction to disable a single RELOC?

[Xi Ruoyao]

在 2024-01-12星期五的 22:41 +0800，YunQiang Su写道：
> > I don't think there is, and I don't think there should be. People using
> > .reloc absolutely need to know what they are doing.
> > 
> 
> Thank you, I find a solution.
> BAL  . + 4
> won't emit any relocs.
> 
> Background:
> MIPS pre-R6 has no instructions that can read PC directly, thus we
> have to use an branch and link instruction to do so.

For this purpose GAS already supports the nal alias for bltzal $r0, 0.

> I am working on GCC to support it. I don' want to emit an label for this
> simple branch.

-- 
Xi Ruoyao <xry111@xry111.site>
School of Aerospace Science and Technology, Xidian University

Re: Gas: Any pseudo instruction to disable a single RELOC?

[YunQiang Su]

[-- Attachment #1: Type: text/plain, Size: 305 bytes --]

>
> For this purpose GAS already supports the nal alias for bltzal $r0, 0.
>

Yes. I tried it first, and the performance of it is soooo bad.
The attached test case on Loongson 3A:

classic-MIPS-PIC          NAL-PIC                    BAL-PIC
1.5s                               18s (eighteen)           5s

[-- Attachment #2: xx.c --]
[-- Type: application/octet-stream, Size: 934 bytes --]

#include <stdio.h>

volatile int g1 = 1;
volatile int g2 = 2;
volatile int g3 = 3;
volatile int g4 = 4;
volatile int g5 = 5;
volatile int g6 = 6;
volatile int g7 = 7;
volatile int g8 = 8;

volatile int g9 = 9;
volatile int g10 = 10;
volatile int g11 = 11;
volatile int g12 = 12;
volatile int g13 = 13;
volatile int g14 = 14;
volatile int g15 = 15;
volatile int g16 = 16;

volatile int g17 = 17;
volatile int g18 = 18;
volatile int g19 = 19;
volatile int g20 = 20;
volatile int g21 = 21;
volatile int g22 = 22;
volatile int g23 = 23;
volatile int g24 = 24;

__attribute__ ((noinline))
volatile int f () {
        return g1 + g2 + g3 + g4 + g5 + g6 + g7 + g8 +
                g9 + g10 + g11 + g12 + g13 + g14 + g15 + g16 +
                g17 + g18 + g19 + g20 + g21 + g22 + g23 + g24;
}

int main () {
        int x;
        for (int i = 0; i< 1e8; i++) {
                x += f ();
        }
	printf ("%d\n", x);
        return x;
}