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.nowakow...@fungible.com>
---
target/mips/tcg/translate.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/target/mips/tcg/translate.c b/target/mips/tcg/translate.c
index 624e6b7786..5d46f24141 100644
--- a/target/mips/tcg/translate.c
+++ b/target/mips/tcg/translate.c
@@ -4860,6 +4860,7 @@ static void gen_compute_branch(DisasContext *ctx,
uint32_t opc,
target_ulong btgt = -1;
int blink = 0;
int bcond_compute = 0;
+ int jal_mask = 0;
TCGv t0 = tcg_temp_new();
TCGv t1 = tcg_temp_new();
@@ -4917,6 +4918,11 @@ static void gen_compute_branch(DisasContext *ctx,
uint32_t opc,
break;
case OPC_J:
case OPC_JAL:
+ /* Jump to immediate */
+ 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
