[Qemu-devel] [RFC PATCH] disable execution of SWP/SWPB

[Alexey Starikovskiy]

Hi,

I was wondering how to implement disabling of SWP/SWPB execution if
they are not enabled in SCTLR.SW bit.
One way to do this is to intercept writes to SCTLR, do tb_flush and
make SWP [un]defined for any following translations depending on the
c1_sys state
during the translation.
The other way would be to dynamically define/undefine these
instructions without tb_flush. In this particular case of deprecated
instruction which would be enabled once per OS boot, tb_flush will not
make any performance impact, but there may be other instructions,
which would benefit from the second approach...

Please comment,
Alex.


diff --git a/target-arm/translate.c b/target-arm/translate.c
index 7a3c7d6..a54b436 100644
--- a/target-arm/translate.c
+++ b/target-arm/translate.c
@@ -7415,7 +7415,12 @@ static void disas_arm_insn(CPUARMState * env, DisasContex
                         }
                         tcg_temp_free(addr);
                     } else {
-                        /* SWP instruction */
+                        /* SWP/SWPB instruction */
+                        TCGv sctlr = load_cpu_field(cp15.c1_sys);
+                        int fail_label = gen_new_label();
+                        int done_label = gen_new_label();
+                        tcg_gen_andi_i32(sctlr, sctlr, 1 << 10); /* Check if SW
+                        tcg_gen_brcondi_i32(TCG_COND_EQ, sctlr, 0, fail_label);
                         rm = (insn) & 0xf;

                         /* ??? This is not really atomic.  However we know
@@ -7432,6 +7437,11 @@ static void disas_arm_insn(CPUARMState * env, DisasContex
                         }
                         tcg_temp_free_i32(addr);
                         store_reg(s, rd, tmp2);
+                        tcg_gen_br(done_label);
+                        gen_set_label(fail_label);
+                        gen_exception(EXCP_UDEF);
+                        gen_set_label(done_label);
+                        tcg_temp_free_i32(sctlr);
                     }
                 }
             } else {