[PATCH] riscv: Fix _movi_p loading incorrect value

[Kim Kuparinen]

Signed-off-by: Kim Kuparinen <kimi.h.kuparinen@gmail.com>
---

Hi, I recently sent out a misleading version of this patch. There is an
issue with how _movi_p handles 64bit addresses whose low 32bits would be
sign-extended, essentially following the logic in the previous email:

https://lists.gnu.org/archive/html/lightning/2021-11/msg00005.html

> movi_p a0, 0b0010 1001
> 
> is expanded to
> 
> // lo
> lui r0, 0b10    // r0 => 0b1111 1000
> addiw r0, 0b01  // r0 => 0b1111 1001
> // hi
> lui a0, 0b00    // a0 => 0b0000 0000
> addiw a0, b10   // a0 => 0b0000 0010
> slli a0, 4      // a0 => 0b0010 0000
> add a0, a0, r0  // a0 => 0b0001 1001

Previously I incorrectly assumed this also related to movi, which it doesn't, 
sorry
about that. The errors I encountered were segmentation faults from incorrect 
addresses
on qemu-system-riscv64 v7.0.0 with kernel 5.16.0-6-riscv64, and this was a 
minimal
example I could come up with:

> #include <lightning.h>
> 
> static jit_state_t *_jit;
> 
> typedef int (*f_t)();
> 
> int main()
> {
>       init_jit(0);
>       _jit = jit_new_state();
> 
>       jit_prolog();
>       jit_node_t *addr = jit_movi(JIT_R0, 0);
>       jit_jmpr(JIT_R0);
>       jit_patch(addr); // addr = 0x3ff7fdc02c
> 
>       jit_reti(0);
> 
>       f_t f = (f_t)jit_emit();
>       jit_clear_state();
> 
>       f();
> }

In my case, the jit'ed code seems to generally be placed around 0x3ffxxxxxxx, 
which
triggers this bug, but I wouldn't be surprised if some other system place the
code somewhere else and don't trigger it.

The testsuite was also failing on almost all tests until I applied this patch, 
now
all tests pass on my machine.

If you still consider this patch incorrect, please at least take this as a bug
report :)

 lib/jit_riscv-cpu.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/lib/jit_riscv-cpu.c b/lib/jit_riscv-cpu.c
index 388489f..821c922 100644
--- a/lib/jit_riscv-cpu.c
+++ b/lib/jit_riscv-cpu.c
@@ -1363,6 +1363,10 @@ _movi_p(jit_state_t *_jit, jit_int32_t r0, jit_word_t i0)
     LUI(r0, hi >> 12);
     ADDIW(r0, r0, lo);
     ww = i0 >> 32;
+
+    if(hi < 0)
+           ww++;
+
     lo = ww << 20 >> 20;
     hi = ww - lo;
     LUI(rn(t0), hi >> 12);
@@ -2331,6 +2335,10 @@ _patch_at(jit_state_t *_jit, jit_word_t instr, 
jit_word_t label)
            i.w = u.i[2];
            if (i.U.opcode == 55) {                             /* LUI */
                ww = label >> 32;
+
+               if(hi < 0)
+                       ww++;
+
                lo = ww << 20 >> 20;
                hi = ww - lo;
                i.U.imm12_31 = hi >> 12;
-- 
2.35.1