From f40385c959d01bf33a0e3c12ef0fdb402ad98a1c Mon Sep 17 00:00:00 2001
From: Max Filippov <jcmvbkbc@gmail.com>
Date: Fri, 27 Apr 2018 13:07:53 -0700
Subject: [PATCH] target/xtensa: check zero overhead loop alignment

ISA book documents that the first instruction of zero overhead loop
must fit completely into naturally aligned region of an instruction
fetch unit size. Check that condition and log a message if it's
violated.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
---
 target/xtensa/cpu.h          | 1 +
 target/xtensa/overlay_tool.h | 1 +
 target/xtensa/translate.c    | 7 +++++++
 3 files changed, 9 insertions(+)

diff --git a/target/xtensa/cpu.h b/target/xtensa/cpu.h
index e9d2e109f7..51b4551464 100644
--- a/target/xtensa/cpu.h
+++ b/target/xtensa/cpu.h
@@ -369,6 +369,7 @@ struct XtensaConfig {
     unsigned nareg;
     int excm_level;
     int ndepc;
+    unsigned inst_fetch_width;
     uint32_t vecbase;
     uint32_t exception_vector[EXC_MAX];
     unsigned ninterrupt;
diff --git a/target/xtensa/overlay_tool.h b/target/xtensa/overlay_tool.h
index b24ad11fec..ee37a04a17 100644
--- a/target/xtensa/overlay_tool.h
+++ b/target/xtensa/overlay_tool.h
@@ -456,6 +456,7 @@
     .options = XTENSA_OPTIONS, \
     .nareg = XCHAL_NUM_AREGS, \
     .ndepc = (XCHAL_XEA_VERSION >= 2), \
+    .inst_fetch_width = XCHAL_INST_FETCH_WIDTH, \
     EXCEPTIONS_SECTION, \
     INTERRUPTS_SECTION, \
     TLB_SECTION, \
diff --git a/target/xtensa/translate.c b/target/xtensa/translate.c
index a11162eebe..7dd8b55d4a 100644
--- a/target/xtensa/translate.c
+++ b/target/xtensa/translate.c
@@ -970,6 +970,13 @@ static void disas_xtensa_insn(CPUXtensaState *env, DisasContext *dc)
     }
 
     dc->next_pc = dc->pc + len;
+    if (xtensa_option_enabled(dc->config, XTENSA_OPTION_LOOP) &&
+        dc->lbeg == dc->pc &&
+        ((dc->pc ^ (dc->next_pc - 1)) & -dc->config->inst_fetch_width)) {
+        qemu_log_mask(LOG_GUEST_ERROR,
+                      "unaligned first instruction of a loop (pc = %08x)\n",
+                      dc->pc);
+    }
     for (i = 1; i < len; ++i) {
         b[i] = cpu_ldub_code(env, dc->pc + i);
     }