From b424ae3130031f0420aaf9fb3193627883a0becd Mon Sep 17 00:00:00 2001
From: "H. Peter Anvin" <hpa@zytor.com>
Date: Mon, 10 Dec 2018 13:30:51 -0800
Subject: BR 3392534: error out on an inconsistently redefined label

If a label is redefined in the same pass, and the value is
inconsistent, then error out. While we are at it, give the source
location of the previous definition.

This explicitly rejects BR 3392535; there seems to be no reason to
reject duplicate definitions with the same value, as there is no
inconsistency involved.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
---
 asm/labels.c | 77 ++++++++++++++++++++++++++++++++++++++++++++++--------------
 1 file changed, 59 insertions(+), 18 deletions(-)

diff --git a/asm/labels.c b/asm/labels.c
index c00d6e5b..a073f798 100644
--- a/asm/labels.c
+++ b/asm/labels.c
@@ -109,9 +109,11 @@ union label {                   /* actual label structures */
         int32_t subsection;     /* Available for ofmt->herelabel() */
         int64_t offset;
         int64_t size;
+        int64_t defined;        /* 0 if undefined, passn+1 for when defn seen */
         char *label, *mangled, *special;
+        const char *def_file;   /* Where defined */
+        int32_t def_line;
         enum label_type type, mangled_type;
-        bool defined;
     } defn;
     struct {
         int32_t movingon;
@@ -369,7 +371,7 @@ handle_herelabel(union label *lptr, int32_t *segment, int64_t *offset)
             location.offset = *offset;
         } else {
             /* Keep a separate offset for the new segment */
-            *offset  = switch_segment(newseg);
+            *offset = switch_segment(newseg);
         }
     }
 }
@@ -434,6 +436,13 @@ void define_label(const char *label, int32_t segment,
     union label *lptr;
     bool created, changed;
     int64_t size;
+    int64_t lastdef;
+
+    /*
+     * The backend may invoke this before pass 1, so treat that as
+     * a special "pass".
+     */
+    const int64_t lpass = pass0 + 1;
 
     /*
      * Phase errors here can be one of two types: a new label appears,
@@ -442,17 +451,26 @@ void define_label(const char *label, int32_t segment,
      */
     lptr = find_label(label, true, &created);
 
+    lastdef = lptr->defn.defined;
+
     if (segment) {
         /* We are actually defining this label */
-        if (lptr->defn.type == LBL_EXTERN) /* auto-promote EXTERN to GLOBAL */
+        if (lptr->defn.type == LBL_EXTERN) {
+            /* auto-promote EXTERN to GLOBAL */
             lptr->defn.type = LBL_GLOBAL;
+            lastdef = 0; /* We are "re-creating" this label */
+        }
     } else {
         /* It's a pseudo-segment (extern, common) */
         segment = lptr->defn.segment ? lptr->defn.segment : seg_alloc();
     }
 
-    if (lptr->defn.defined || lptr->defn.type == LBL_BACKEND) {
-        /* We have seen this on at least one previous pass */
+    if (lastdef || lptr->defn.type == LBL_BACKEND) {
+        /*
+         * We have seen this on at least one previous pass, or
+         * potentially earlier in this same pass (in which case we
+         * will probably error out further down.)
+         */
         mangle_label_name(lptr);
         handle_herelabel(lptr, &segment, &offset);
     }
@@ -470,28 +488,51 @@ void define_label(const char *label, int32_t segment,
         size = 0;               /* This is a hack... */
     }
 
-    changed = created || !lptr->defn.defined ||
+    changed = created || !lastdef ||
         lptr->defn.segment != segment ||
-        lptr->defn.offset != offset || lptr->defn.size != size;
+        lptr->defn.offset != offset ||
+        lptr->defn.size != size;
     global_offset_changed += changed;
 
-    /*
-     * This probably should be ERR_NONFATAL, but not quite yet.  As a
-     * special case, LBL_SPECIAL symbols are allowed to be changed
-     * even during the last pass.
-     */
-    if (changed && pass0 > 1 && lptr->defn.type != LBL_SPECIAL) {
-        nasm_error(ERR_WARNING, "label `%s' %s during code generation",
-                   lptr->defn.label,
-                   created ? "defined" : "changed");
+    if (changed) {
+        if (lastdef == lpass) {
+            int32_t saved_line = 0;
+            const char *saved_fname = NULL;
+
+            /*
+             * Defined elsewhere in the program, seen in this pass.
+             */
+            nasm_error(ERR_NONFATAL,
+                       "label `%s' inconsistently redefined",
+                       lptr->defn.label);
+
+            src_get(&saved_line, &saved_fname);
+            src_set(lptr->defn.def_line, lptr->defn.def_file);
+            nasm_error(ERR_NOTE, "label `%s' originally defined here",
+                       lptr->defn.label);
+            src_set(saved_line, saved_fname);
+        } else if (pass0 > 1 && lptr->defn.type != LBL_SPECIAL) {
+            /*
+             * This probably should be ERR_NONFATAL, but not quite yet.  As a
+             * special case, LBL_SPECIAL symbols are allowed to be changed
+             * even during the last pass.
+             */
+            nasm_error(ERR_WARNING, "label `%s' %s during code generation",
+                       lptr->defn.label,
+                       created ? "defined" : "changed");
+        }
     }
 
     lptr->defn.segment = segment;
     lptr->defn.offset  = offset;
     lptr->defn.size    = size;
-    lptr->defn.defined = true;
+    lptr->defn.defined = lpass;
+
+    if (changed || lastdef != lpass)
+        src_get(&lptr->defn.def_line, &lptr->defn.def_file);
 
-    out_symdef(lptr);
+    if (lastdef != lpass)
+        out_symdef(lptr);
 }
 
 /*
-- 
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