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Can't understand the difference between armv7e-m and armv7e-m-pic?

Hello people. I'm trying to do libgcc extraction for hard FPU's for k70 tower board. However, when I look at the libgcc library for arm targets, I find armv7-m, armv7e-m and armv7e-m-pic. I'm able to deduce from the armv7-m reference manual that the difference between armv7-m and armv7e-m is of the DSP chip i.e. armv7e-m will have a DSP chip. As the k70 has a DSP chip, therefore I'm able to conclude that I have the armv7e-m architecture. However, I'm unable to figure out the difference between armv7e-m and armv7e-m-pic? There is no reference about it in the armv7-m reference manual. Can someone help me out here?

Thanks,
Bilal

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0 Yasuhiko Koumoto over 7 years ago

Hi Bilal,

I think that 'pic' means the position independent code.
In the pic mode, all load and store instruction would be PC relative or a certain base register relative.
For example of GCC, GCC generates r3 relative codes for load or store in the pic mode.
1) source

volatile int a,b,c;
int main()
{
 c = a+b;
}

2) option: -march=armv7e-m -mthumb

main:
        ldr    r2, .L2
        ldr    r3, .L2+4
        ldr    r1, [r2]
        ldr    r3, [r3]
        ldr    r2, .L2+8
        add    r3, r3, r1
        str    r3, [r2]
        movs    r0, #0
        bx      lr
.L3:
        .align  2
.L2:
        .word  a
        .word  b
        .word  c

3) option: -march=armv7e-m -fpic -mthumb

main:
        ldr    r3, .L2
        ldr    r1, .L2+4
        ldr    r2, .L2+8
.LPIC0:
        add    r3, pc
        ldr    r0, [r3, r1]
        ldr    r2, [r3, r2]
        ldr    r1, .L2+12
        ldr    r0, [r0]
        ldr    r2, [r2]
        ldr    r1, [r3, r1]
        adds    r3, r0, r2
        str    r3, [r1]
        movs    r0, #0
        bx      lr
.L3:
        .align  2
.L2:
        .word  _GLOBAL_OFFSET_TABLE_-(.LPIC0+4)
        .word  a(GOT)
        .word  b(GOT)
        .word  c(GOT)

As the results, armv7e-m and armv7e-m-pic would be indentical other than the addressing mode.

Best Regards,
Yasuhiko Koumoto.

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