[PATCH v2 1/4] target/mips: fix JALS32/J32 instruction handling for microMIPS

[Marcin Nowakowski]

microMIPS J & JAL instructions perform a jump in a 128MB region and 5
top bits of the address need to be preserved. This is different behavior
compared to standard mips systems, where the jump is executed within a
256MB region.
Note that microMIPS32 instruction set documentation appears to have
inconsistent information regarding JALX32 instruction - it is written in
the doc that:

"To execute a procedure call within the current 256 MB-aligned region
(...)
The low 26 bits of the target address is the target field shifted left
2 bits."

But the target address is already 26 bits. Moreover, the operation
description indicates that 28 bits are copied, so the statement about
use of 26 bits is _most likely_ incorrect and the corresponding code
remains the same as for standard mips instruction set.

Signed-off-by: Marcin Nowakowski <marcin.nowakowski@fungible.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
---
 target/mips/tcg/translate.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/target/mips/tcg/translate.c b/target/mips/tcg/translate.c
index 624e6b7786..567ca11ccf 100644
--- a/target/mips/tcg/translate.c
+++ b/target/mips/tcg/translate.c
@@ -4917,6 +4917,13 @@ static void gen_compute_branch(DisasContext *ctx, 
uint32_t opc,
         break;
     case OPC_J:
     case OPC_JAL:
+        {
+            /* Jump to immediate */
+            int jal_mask = ctx->hflags & MIPS_HFLAG_M16 ? 0xF8000000 : 
0xF0000000;
+            btgt = ((ctx->base.pc_next + insn_bytes) & jal_mask) |
+                (uint32_t)offset;
+            break;
+        }
     case OPC_JALX:
         /* Jump to immediate */
         btgt = ((ctx->base.pc_next + insn_bytes) & (int32_t)0xF0000000) |
-- 
2.25.1