Created
November 15, 2023 15:44
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#include <stdio.h> | |
#include <stdlib.h> | |
int | |
main (int argc, char *argv[]) | |
{ | |
long target; | |
long dest; | |
long pc; | |
long delta; | |
long pcala_hi20; | |
long pcala_lo12; | |
long pcala64_lo20; | |
long pcala64_hi12; | |
dest = strtoul (argv[1], NULL, 16); | |
pc = strtoul (argv[2], NULL, 16); | |
delta = dest - (pc & ~0xfffUL); | |
delta = delta + ((delta & 0x800UL) << 1); | |
delta = delta + ((delta & 0x80000000UL) << 1); | |
delta = delta - ((delta & 0x800UL) << 21); | |
pcala_hi20 = (delta >> 12) & 0xfffffUL; | |
pcala_lo12 = delta & 0xfffUL; | |
pcala64_lo20 = (delta >> 32) & 0xfffffUL; | |
pcala64_hi12 = (delta >> 52) & 0xfffUL; | |
printf ("R_LARCH_PCALA_HI20 = 0x%lx\n", pcala_hi20); | |
printf ("R_LARCH_PCALA_LO12 = 0x%lx\n", pcala_lo12); | |
printf ("R_LARCH_PCALA64_LO20 = 0x%lx\n", pcala64_lo20); | |
printf ("R_LARCH_PCALA64_HI12 = 0x%lx\n", pcala64_hi12); | |
target = (pc & ~0xfffUL) + ((pcala_hi20 << 44) >> 32) + | |
((pcala64_hi12 << 52) | (pcala64_lo20 << 32) | (((pcala_lo12 << 52) >> 52) & 0xffffffffUL)); | |
if (target != dest) { | |
printf ("%0lx != %0lx\n", dest, target); | |
return -1; | |
} | |
return 0; | |
} |
It is feasible if we find that way. But it seems difficult.
a),
Refer to RISC-V, we can use
.L1:
pcalau12i $xx, sym
addi.d $xx, $r0, .L1
lu32i $xx, .L1
lu52i $xx, $xx, .L1
They are not current abi.
b),
Mark they are always adjacent. Like call36.
c),
Set imm in instructions to indicate the bytes distance with pcalau12i.
.L1:
pcalau12i $xx, sym
addi.d $xx, $r0, (. - .L1), sym
lu32i $xx, (. - .L1), sym
lu52i $xx, $xx, (. - .L1), sym
It looks even more difficult to implement with linker relaxation enabling. They are not current abi, too.
Yes. The instruction's free encoding bit-field can be used to maintain the relationship before relocation. But this is no longer compatible with what it used to be.
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@MQ-mengqing Even after scheduling, if 4 instructions are still in the same 4k aligned space, there is actually only one
pc
. If they are in different 4k, then all 4 instructions have a way to calculate thepc
of thepcalau12i
instruction when relocating. Is this feasible?