Updating to new OTS repo from https://github.com/khaledhosny/ots.git

src/gpos.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "gpos.h"
 
 #include <limits>
 #include <vector>
 
-#include "gdef.h"
-#include "gsub.h"
 #include "layout.h"
 #include "maxp.h"
 
 // GPOS - The Glyph Positioning Table
 // http://www.microsoft.com/typography/otspec/gpos.htm
 
+#define TABLE_NAME "GPOS"
+
 namespace {
 
 enum GPOS_TYPE {
   GPOS_TYPE_SINGLE_ADJUSTMENT = 1,
   GPOS_TYPE_PAIR_ADJUSTMENT = 2,
   GPOS_TYPE_CURSIVE_ATTACHMENT = 3,
   GPOS_TYPE_MARK_TO_BASE_ATTACHMENT = 4,
   GPOS_TYPE_MARK_TO_LIGATURE_ATTACHMENT = 5,
   GPOS_TYPE_MARK_TO_MARK_ATTACHMENT = 6,
   GPOS_TYPE_CONTEXT_POSITIONING = 7,
@@ skipping 41 matching lines @@
   {GPOS_TYPE_EXTENSION_POSITIONING, ParseExtensionPositioning}
 };
 
 const ots::LookupSubtableParser kGposLookupSubtableParser = {
   arraysize(kGposTypeParsers),
   GPOS_TYPE_EXTENSION_POSITIONING, kGposTypeParsers
 };
 
 // Shared Tables: ValueRecord, Anchor Table, and MarkArray
 
-bool ParseValueRecord(ots::Buffer* subtable, const uint8_t *data,
+bool ParseValueRecord(const ots::OpenTypeFile *file,
+                      ots::Buffer* subtable, const uint8_t *data,
                       const size_t length, const uint16_t value_format) {
   // Check existence of adjustment fields.
   for (unsigned i = 0; i < 4; ++i) {
     if ((value_format >> i) & 0x1) {
       // Just read the field since these fileds could take an arbitrary values.
       if (!subtable->Skip(2)) {
-        return OTS_FAILURE();
+        return OTS_FAILURE_MSG("Failed to read value reacord component");
       }
     }
   }
 
   // Check existence of offsets to device table.
   for (unsigned i = 0; i < 4; ++i) {
     if ((value_format >> (i + 4)) & 0x1) {
       uint16_t offset = 0;
       if (!subtable->ReadU16(&offset)) {
-        return OTS_FAILURE();
+        return OTS_FAILURE_MSG("Failed to read value record offset");
       }
       if (offset) {
         // TODO(bashi): Is it possible that device tables locate before
         // this record? No fonts contain such offset AKAIF.
         if (offset >= length) {
-          return OTS_FAILURE();
+          return OTS_FAILURE_MSG("Value record offset too high %d >= %ld", offset, length);
         }
-        if (!ots::ParseDeviceTable(data + offset, length - offset)) {
-          return OTS_FAILURE();
+        if (!ots::ParseDeviceTable(file, data + offset, length - offset)) {
+          return OTS_FAILURE_MSG("Failed to parse device table in value record");
         }
       }
     }
   }
   return true;
 }
 
-bool ParseAnchorTable(const uint8_t *data, const size_t length) {
+bool ParseAnchorTable(const ots::OpenTypeFile *file,
+                      const uint8_t *data, const size_t length) {
   ots::Buffer subtable(data, length);
 
   uint16_t format = 0;
   // Read format and skip 2 2-byte fields that could be arbitrary values.
   if (!subtable.ReadU16(&format) ||
       !subtable.Skip(4)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Faled to read anchor table");
   }
 
   if (format == 0 || format > kMaxAnchorFormat) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Bad Anchor table format %d", format);
   }
 
   // Format 2 and 3 has additional fields.
   if (format == 2) {
     // Format 2 provides an index to a glyph contour point, which will take
     // arbitrary value.
     uint16_t anchor_point = 0;
     if (!subtable.ReadU16(&anchor_point)) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Failed to read anchor point in format 2 Anchor Table");
     }
   } else if (format == 3) {
     uint16_t offset_x_device = 0;
     uint16_t offset_y_device = 0;
     if (!subtable.ReadU16(&offset_x_device) ||
         !subtable.ReadU16(&offset_y_device)) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Failed to read device table offsets in format 3 anchor table");
     }
     const unsigned format_end = static_cast<unsigned>(10);
     if (offset_x_device) {
       if (offset_x_device < format_end || offset_x_device >= length) {
-        return OTS_FAILURE();
+        return OTS_FAILURE_MSG("Bad x device table offset %d", offset_x_device);
       }
-      if (!ots::ParseDeviceTable(data + offset_x_device,
+      if (!ots::ParseDeviceTable(file, data + offset_x_device,
                                  length - offset_x_device)) {
-        return OTS_FAILURE();
+        return OTS_FAILURE_MSG("Failed to parse device table in anchor table");
       }
     }
     if (offset_y_device) {
       if (offset_y_device < format_end || offset_y_device >= length) {
-        return OTS_FAILURE();
+        return OTS_FAILURE_MSG("Bad y device table offset %d", offset_y_device);
       }
-      if (!ots::ParseDeviceTable(data + offset_y_device,
+      if (!ots::ParseDeviceTable(file, data + offset_y_device,
                                  length - offset_y_device)) {
-        return OTS_FAILURE();
+        return OTS_FAILURE_MSG("Failed to parse device table in anchor table");
       }
     }
   }
   return true;
 }
 
-bool ParseMarkArrayTable(const uint8_t *data, const size_t length,
+bool ParseMarkArrayTable(const ots::OpenTypeFile *file,
+                         const uint8_t *data, const size_t length,
                          const uint16_t class_count) {
   ots::Buffer subtable(data, length);
 
   uint16_t mark_count = 0;
   if (!subtable.ReadU16(&mark_count)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Can't read mark table length");
   }
 
   // MarkRecord consists of 4-bytes.
   const unsigned mark_records_end = 4 * static_cast<unsigned>(mark_count) + 2;
   if (mark_records_end > std::numeric_limits<uint16_t>::max()) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Bad mark table length");
   }
   for (unsigned i = 0; i < mark_count; ++i) {
     uint16_t class_value = 0;
     uint16_t offset_mark_anchor = 0;
     if (!subtable.ReadU16(&class_value) ||
         !subtable.ReadU16(&offset_mark_anchor)) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Can't read mark table %d", i);
     }
     // |class_value| may take arbitrary values including 0 here so we don't
     // check the value.
     if (offset_mark_anchor < mark_records_end ||
         offset_mark_anchor >= length) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Bad mark anchor offset %d for mark table %d", offset_mark_anchor, i);
     }
-    if (!ParseAnchorTable(data + offset_mark_anchor,
+    if (!ParseAnchorTable(file, data + offset_mark_anchor,
                           length - offset_mark_anchor)) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Faled to parse anchor table for mark table %d", i);
     }
   }
 
   return true;
 }
 
 // Lookup Type 1:
 // Single Adjustment Positioning Subtable
 bool ParseSingleAdjustment(const ots::OpenTypeFile *file, const uint8_t *data,
                            const size_t length) {
   ots::Buffer subtable(data, length);
 
   uint16_t format = 0;
   uint16_t offset_coverage = 0;
   uint16_t value_format = 0;
   if (!subtable.ReadU16(&format) ||
       !subtable.ReadU16(&offset_coverage) ||
       !subtable.ReadU16(&value_format)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Can't read single adjustment information");
   }
 
   if (format == 1) {
     // Format 1 exactly one value record.
-    if (!ParseValueRecord(&subtable, data, length, value_format)) {
-      return OTS_FAILURE();
+    if (!ParseValueRecord(file, &subtable, data, length, value_format)) {
+      return OTS_FAILURE_MSG("Failed to parse format 1 single adjustment table");
     }
   } else if (format == 2) {
     uint16_t value_count = 0;
     if (!subtable.ReadU16(&value_count)) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Failed to parse format 2 single adjustment table");
     }
     for (unsigned i = 0; i < value_count; ++i) {
-      if (!ParseValueRecord(&subtable, data, length, value_format)) {
-        return OTS_FAILURE();
+      if (!ParseValueRecord(file, &subtable, data, length, value_format)) {
+        return OTS_FAILURE_MSG("Failed to parse value record %d in format 2 single adjustment table", i);
       }
     }
   } else {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Bad format %d in single adjustment table", format);
   }
 
   if (offset_coverage < subtable.offset() || offset_coverage >= length) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Bad coverage offset %d in single adjustment table", offset_coverage);
   }
 
-  if (!ots::ParseCoverageTable(data + offset_coverage,
+  if (!ots::ParseCoverageTable(file, data + offset_coverage,
                                length - offset_coverage,
                                file->maxp->num_glyphs)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Failed to parse coverage table in single adjustment table");
   }
 
   return true;
 }
 
-bool ParsePairSetTable(const uint8_t *data, const size_t length,
+bool ParsePairSetTable(const ots::OpenTypeFile *file,
+                       const uint8_t *data, const size_t length,
                        const uint16_t value_format1,
                        const uint16_t value_format2,
                        const uint16_t num_glyphs) {
   ots::Buffer subtable(data, length);
 
   uint16_t value_count = 0;
   if (!subtable.ReadU16(&value_count)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Failed to read pair set table structure");
   }
   for (unsigned i = 0; i < value_count; ++i) {
     // Check pair value record.
     uint16_t glyph_id = 0;
     if (!subtable.ReadU16(&glyph_id)) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Failed to read glyph in pair value record %d", i);
     }
     if (glyph_id >= num_glyphs) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("glyph id %d too high >= %d", glyph_id, num_glyphs);
     }
-    if (!ParseValueRecord(&subtable, data, length, value_format1)) {
-      return OTS_FAILURE();
+    if (!ParseValueRecord(file, &subtable, data, length, value_format1)) {
+      return OTS_FAILURE_MSG("Failed to parse value record in format 1 pair set table");
     }
-    if (!ParseValueRecord(&subtable, data, length, value_format2)) {
-      return OTS_FAILURE();
+    if (!ParseValueRecord(file, &subtable, data, length, value_format2)) {
+      return OTS_FAILURE_MSG("Failed to parse value record in format 2 pair set table");
     }
   }
   return true;
 }
 
-bool ParsePairPosFormat1(const uint8_t *data, const size_t length,
+bool ParsePairPosFormat1(const ots::OpenTypeFile *file,
+                         const uint8_t *data, const size_t length,
                          const uint16_t value_format1,
                          const uint16_t value_format2,
                          const uint16_t num_glyphs) {
   ots::Buffer subtable(data, length);
 
   // Skip 8 bytes that are already read before.
   if (!subtable.Skip(8)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Failed to read pair pos table structure");
   }
 
   uint16_t pair_set_count = 0;
   if (!subtable.ReadU16(&pair_set_count)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Failed to read pair pos set count");
   }
 
   const unsigned pair_pos_end = 2 * static_cast<unsigned>(pair_set_count) + 10;
   if (pair_pos_end > std::numeric_limits<uint16_t>::max()) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Bad pair set length %d", pair_pos_end);
   }
   for (unsigned i = 0; i < pair_set_count; ++i) {
     uint16_t pair_set_offset = 0;
     if (!subtable.ReadU16(&pair_set_offset)) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Failed to read pair set offset for pair set %d", i);
     }
     if (pair_set_offset < pair_pos_end || pair_set_offset >= length) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Bad pair set offset %d for pair set %d", pair_set_offset, i);
     }
     // Check pair set tables
-    if (!ParsePairSetTable(data + pair_set_offset, length - pair_set_offset,
+    if (!ParsePairSetTable(file, data + pair_set_offset, length - pair_set_offset,
                            value_format1, value_format2,
                            num_glyphs)) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Failed to parse pair set table %d", i);
     }
   }
 
   return true;
 }
 
-bool ParsePairPosFormat2(const uint8_t *data, const size_t length,
+bool ParsePairPosFormat2(const ots::OpenTypeFile *file,
+                         const uint8_t *data, const size_t length,
                          const uint16_t value_format1,
                          const uint16_t value_format2,
                          const uint16_t num_glyphs) {
   ots::Buffer subtable(data, length);
 
   // Skip 8 bytes that are already read before.
   if (!subtable.Skip(8)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Failed to read pair pos format 2 structure");
   }
 
   uint16_t offset_class_def1 = 0;
   uint16_t offset_class_def2 = 0;
   uint16_t class1_count = 0;
   uint16_t class2_count = 0;
   if (!subtable.ReadU16(&offset_class_def1) ||
       !subtable.ReadU16(&offset_class_def2) ||
       !subtable.ReadU16(&class1_count) ||
       !subtable.ReadU16(&class2_count)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Failed to read pair pos format 2 data");
   }
 
   // Check class 1 records.
   for (unsigned i = 0; i < class1_count; ++i) {
     // Check class 2 records.
     for (unsigned j = 0; j < class2_count; ++j) {
-      if (value_format1 && !ParseValueRecord(&subtable, data, length,
+      if (value_format1 && !ParseValueRecord(file, &subtable, data, length,
                                              value_format1)) {
-        return OTS_FAILURE();
+        return OTS_FAILURE_MSG("Failed to parse value record 1 %d and %d", j, i);
       }
-      if (value_format2 && !ParseValueRecord(&subtable, data, length,
+      if (value_format2 && !ParseValueRecord(file, &subtable, data, length,
                                              value_format2)) {
-        return OTS_FAILURE();
+        return OTS_FAILURE_MSG("Falied to parse value record 2 %d and %d", j, i);
       }
     }
   }
 
   // Check class definition tables.
   if (offset_class_def1 < subtable.offset() || offset_class_def1 >= length ||
       offset_class_def2 < subtable.offset() || offset_class_def2 >= length) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Bad class definition table offsets %d or %d", offset_class_def1, offset_class_def2);
   }
-  if (!ots::ParseClassDefTable(data + offset_class_def1,
+  if (!ots::ParseClassDefTable(file, data + offset_class_def1,
                                length - offset_class_def1,
                                num_glyphs, kMaxClassDefValue)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Failed to parse class definition table 1");
   }
-  if (!ots::ParseClassDefTable(data + offset_class_def2,
+  if (!ots::ParseClassDefTable(file, data + offset_class_def2,
                                length - offset_class_def2,
                                num_glyphs, kMaxClassDefValue)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Failed to parse class definition table 2");
   }
 
   return true;
 }
 
 // Lookup Type 2:
 // Pair Adjustment Positioning Subtable
 bool ParsePairAdjustment(const ots::OpenTypeFile *file, const uint8_t *data,
                          const size_t length) {
   ots::Buffer subtable(data, length);
 
   uint16_t format = 0;
   uint16_t offset_coverage = 0;
   uint16_t value_format1 = 0;
   uint16_t value_format2 = 0;
   if (!subtable.ReadU16(&format) ||
       !subtable.ReadU16(&offset_coverage) ||
       !subtable.ReadU16(&value_format1) ||
       !subtable.ReadU16(&value_format2)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Failed to read pair adjustment structure");
   }
 
   if (format == 1) {
-    if (!ParsePairPosFormat1(data, length, value_format1, value_format2,
+    if (!ParsePairPosFormat1(file, data, length, value_format1, value_format2,
                              file->maxp->num_glyphs)) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Failed to parse pair pos format 1");
     }
   } else if (format == 2) {
-    if (!ParsePairPosFormat2(data, length, value_format1, value_format2,
+    if (!ParsePairPosFormat2(file, data, length, value_format1, value_format2,
                              file->maxp->num_glyphs)) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Failed to parse pair format 2");
     }
   } else {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Bad pos pair format %d", format);
   }
 
   if (offset_coverage < subtable.offset() || offset_coverage >= length) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Bad pair pos offset coverage %d", offset_coverage);
   }
-  if (!ots::ParseCoverageTable(data + offset_coverage,
+  if (!ots::ParseCoverageTable(file, data + offset_coverage,
                                length - offset_coverage,
                                file->maxp->num_glyphs)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Failed to parse coverage table");
   }
 
   return true;
 }
 
 // Lookup Type 3
 // Cursive Attachment Positioning Subtable
 bool ParseCursiveAttachment(const ots::OpenTypeFile *file, const uint8_t *data,
                             const size_t length) {
   ots::Buffer subtable(data, length);
 
   uint16_t format = 0;
   uint16_t offset_coverage = 0;
   uint16_t entry_exit_count = 0;
   if (!subtable.ReadU16(&format) ||
       !subtable.ReadU16(&offset_coverage) ||
       !subtable.ReadU16(&entry_exit_count)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Failed to read cursive attachment structure");
   }
 
   if (format != 1) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Bad cursive attachment format %d", format);
   }
 
   // Check entry exit records.
   const unsigned entry_exit_records_end =
       2 * static_cast<unsigned>(entry_exit_count) + 6;
   if (entry_exit_records_end > std::numeric_limits<uint16_t>::max()) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Bad entry exit record end %d", entry_exit_records_end);
   }
   for (unsigned i = 0; i < entry_exit_count; ++i) {
     uint16_t offset_entry_anchor = 0;
     uint16_t offset_exit_anchor = 0;
     if (!subtable.ReadU16(&offset_entry_anchor) ||
         !subtable.ReadU16(&offset_exit_anchor)) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Can't read entry exit record %d", i);
     }
     // These offsets could be NULL.
     if (offset_entry_anchor) {
       if (offset_entry_anchor < entry_exit_records_end ||
           offset_entry_anchor >= length) {
-        return OTS_FAILURE();
+        return OTS_FAILURE_MSG("Bad entry anchor offset %d in entry exit record %d", offset_entry_anchor, i);
       }
-      if (!ParseAnchorTable(data + offset_entry_anchor,
+      if (!ParseAnchorTable(file, data + offset_entry_anchor,
                             length - offset_entry_anchor)) {
-        return OTS_FAILURE();
+        return OTS_FAILURE_MSG("Failed to parse entry anchor table in entry exit record %d", i);
       }
     }
     if (offset_exit_anchor) {
       if (offset_exit_anchor < entry_exit_records_end ||
          offset_exit_anchor >= length) {
-        return OTS_FAILURE();
+        return OTS_FAILURE_MSG("Bad exit anchor offset %d in entry exit record %d", offset_exit_anchor, i);
       }
-      if (!ParseAnchorTable(data + offset_exit_anchor,
+      if (!ParseAnchorTable(file, data + offset_exit_anchor,
                             length - offset_exit_anchor)) {
-        return OTS_FAILURE();
+        return OTS_FAILURE_MSG("Failed to parse exit anchor table in entry exit record %d", i);
       }
     }
   }
 
   if (offset_coverage < subtable.offset() || offset_coverage >= length) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Bad coverage offset in cursive attachment %d", offset_coverage);
   }
-  if (!ots::ParseCoverageTable(data + offset_coverage,
+  if (!ots::ParseCoverageTable(file, data + offset_coverage,
                                length - offset_coverage,
                                file->maxp->num_glyphs)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Failed to parse coverage table in cursive attachment");
   }
 
   return true;
 }
 
-bool ParseAnchorArrayTable(const uint8_t *data, const size_t length,
+bool ParseAnchorArrayTable(const ots::OpenTypeFile *file,
+                           const uint8_t *data, const size_t length,
                            const uint16_t class_count) {
   ots::Buffer subtable(data, length);
 
   uint16_t record_count = 0;
   if (!subtable.ReadU16(&record_count)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Can't read anchor array length");
   }
 
   const unsigned anchor_array_end = 2 * static_cast<unsigned>(record_count) *
       static_cast<unsigned>(class_count) + 2;
   if (anchor_array_end > std::numeric_limits<uint16_t>::max()) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Bad end of anchor array %d", anchor_array_end);
   }
   for (unsigned i = 0; i < record_count; ++i) {
     for (unsigned j = 0; j < class_count; ++j) {
       uint16_t offset_record = 0;
       if (!subtable.ReadU16(&offset_record)) {
-        return OTS_FAILURE();
+        return OTS_FAILURE_MSG("Can't read anchor array record offset for class %d and record %d", j, i);
       }
       // |offset_record| could be NULL.
       if (offset_record) {
         if (offset_record < anchor_array_end || offset_record >= length) {
-          return OTS_FAILURE();
+          return OTS_FAILURE_MSG("Bad record offset %d in class %d, record %d", offset_record, j, i);
         }
-        if (!ParseAnchorTable(data + offset_record,
+        if (!ParseAnchorTable(file, data + offset_record,
                               length - offset_record)) {
-          return OTS_FAILURE();
+          return OTS_FAILURE_MSG("Failed to parse anchor table for class %d, record %d", j, i);
         }
       }
     }
   }
   return true;
 }
 
-bool ParseLigatureArrayTable(const uint8_t *data, const size_t length,
+bool ParseLigatureArrayTable(const ots::OpenTypeFile *file,
+                             const uint8_t *data, const size_t length,
                              const uint16_t class_count) {
   ots::Buffer subtable(data, length);
 
   uint16_t ligature_count = 0;
   if (!subtable.ReadU16(&ligature_count)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Failed to read ligature count");
   }
   for (unsigned i = 0; i < ligature_count; ++i) {
     uint16_t offset_ligature_attach = 0;
     if (!subtable.ReadU16(&offset_ligature_attach)) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Can't read ligature offset %d", i);
     }
     if (offset_ligature_attach < 2 || offset_ligature_attach >= length) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Bad ligature attachment offset %d in ligature %d", offset_ligature_attach, i);
     }
-    if (!ParseAnchorArrayTable(data + offset_ligature_attach,
+    if (!ParseAnchorArrayTable(file, data + offset_ligature_attach,
                                length - offset_ligature_attach, class_count)) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Failed to parse anchor table for ligature %d", i);
     }
   }
   return true;
 }
 
 // Common parser for Lookup Type 4, 5 and 6.
 bool ParseMarkToAttachmentSubtables(const ots::OpenTypeFile *file,
                                     const uint8_t *data, const size_t length,
                                     const GPOS_TYPE type) {
   ots::Buffer subtable(data, length);
 
   uint16_t format = 0;
   uint16_t offset_coverage1 = 0;
   uint16_t offset_coverage2 = 0;
   uint16_t class_count = 0;
   uint16_t offset_mark_array = 0;
   uint16_t offset_type_specific_array = 0;
   if (!subtable.ReadU16(&format) ||
       !subtable.ReadU16(&offset_coverage1) ||
       !subtable.ReadU16(&offset_coverage2) ||
       !subtable.ReadU16(&class_count) ||
       !subtable.ReadU16(&offset_mark_array) ||
       !subtable.ReadU16(&offset_type_specific_array)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Failed to read mark attachment subtable header");
   }
 
   if (format != 1) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("bad mark attachment subtable format %d", format);
   }
 
   const unsigned header_end = static_cast<unsigned>(subtable.offset());
   if (header_end > std::numeric_limits<uint16_t>::max()) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Bad mark attachment subtable size ending at %d", header_end);
   }
   if (offset_coverage1 < header_end || offset_coverage1 >= length) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Bad coverage 1 offset %d", offset_coverage1);
   }
-  if (!ots::ParseCoverageTable(data + offset_coverage1,
+  if (!ots::ParseCoverageTable(file, data + offset_coverage1,
                                length - offset_coverage1,
                                file->maxp->num_glyphs)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Failed to parse converge 1 table");
   }
   if (offset_coverage2 < header_end || offset_coverage2 >= length) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Bad coverage 2 offset %d", offset_coverage2);
   }
-  if (!ots::ParseCoverageTable(data + offset_coverage2,
+  if (!ots::ParseCoverageTable(file, data + offset_coverage2,
                                length - offset_coverage2,
                                file->maxp->num_glyphs)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Failed to parse coverage table 2");
   }
 
   if (offset_mark_array < header_end || offset_mark_array >= length) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Bad mark array offset %d", offset_mark_array);
   }
-  if (!ParseMarkArrayTable(data + offset_mark_array,
+  if (!ParseMarkArrayTable(file, data + offset_mark_array,
                            length - offset_mark_array, class_count)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Failed to parse mark array");
   }
 
   if (offset_type_specific_array < header_end ||
       offset_type_specific_array >= length) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Bad type specific array offset %d", offset_type_specific_array);
   }
   if (type == GPOS_TYPE_MARK_TO_BASE_ATTACHMENT ||
       type == GPOS_TYPE_MARK_TO_MARK_ATTACHMENT) {
-    if (!ParseAnchorArrayTable(data + offset_type_specific_array,
+    if (!ParseAnchorArrayTable(file, data + offset_type_specific_array,
                                length - offset_type_specific_array,
                                class_count)) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Failed to parse anchor array");
     }
   } else if (type == GPOS_TYPE_MARK_TO_LIGATURE_ATTACHMENT) {
-    if (!ParseLigatureArrayTable(data + offset_type_specific_array,
+    if (!ParseLigatureArrayTable(file, data + offset_type_specific_array,
                                  length - offset_type_specific_array,
                                  class_count)) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Failed to parse ligature array");
     }
   } else {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Bad attachment type %d", type);
   }
 
   return true;
 }
 
 // Lookup Type 4:
 // MarkToBase Attachment Positioning Subtable
 bool ParseMarkToBaseAttachment(const ots::OpenTypeFile *file,
                                const uint8_t *data, const size_t length) {
   return ParseMarkToAttachmentSubtables(file, data, length,
@@ skipping 13 matching lines @@
 bool ParseMarkToMarkAttachment(const ots::OpenTypeFile *file,
                                const uint8_t *data, const size_t length) {
   return ParseMarkToAttachmentSubtables(file, data, length,
                                         GPOS_TYPE_MARK_TO_MARK_ATTACHMENT);
 }
 
 // Lookup Type 7:
 // Contextual Positioning Subtables
 bool ParseContextPositioning(const ots::OpenTypeFile *file,
                              const uint8_t *data, const size_t length) {
-  return ots::ParseContextSubtable(data, length, file->maxp->num_glyphs,
+  return ots::ParseContextSubtable(file, data, length, file->maxp->num_glyphs,
                                    file->gpos->num_lookups);
 }
 
 // Lookup Type 8:
 // Chaining Contexual Positioning Subtable
 bool ParseChainedContextPositioning(const ots::OpenTypeFile *file,
                                     const uint8_t *data, const size_t length) {
-  return ots::ParseChainingContextSubtable(data, length,
+  return ots::ParseChainingContextSubtable(file, data, length,
                                            file->maxp->num_glyphs,
                                            file->gpos->num_lookups);
 }
 
 // Lookup Type 9:
 // Extension Positioning
 bool ParseExtensionPositioning(const ots::OpenTypeFile *file,
                                const uint8_t *data, const size_t length) {
   return ots::ParseExtensionSubtable(file, data, length,
                                      &kGposLookupSubtableParser);
 }
 
 }  // namespace
 
-#define DROP_THIS_TABLE \
-  do { file->gpos->data = 0; file->gpos->length = 0; } while (0)
+#define DROP_THIS_TABLE(msg_) \
+  do { \
+    file->gpos->data = 0; \
+    file->gpos->length = 0; \
+    OTS_FAILURE_MSG(msg_ ", table discarded"); \
+  } while (0)
 
 namespace ots {
 
 // As far as I checked, following fonts contain invalid GPOS table and
 // OTS will drop their GPOS table.
 //
 // # invalid delta format in device table
 // samanata.ttf
 //
 // # bad size range in device table
@@ skipping 32 matching lines @@
 // GenBkBasR.ttf
 // Padauk-Bold.ttf
 // Padauk.ttf
 //
 // # Contour point indexes aren't sorted
 // Arial Unicode.ttf
 
 bool ots_gpos_parse(OpenTypeFile *file, const uint8_t *data, size_t length) {
   // Parsing GPOS table requires num_glyphs which is contained in maxp table.
   if (!file->maxp) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("missing maxp table needed in GPOS");
   }
 
   Buffer table(data, length);
 
   OpenTypeGPOS *gpos = new OpenTypeGPOS;
   file->gpos = gpos;
 
   uint32_t version = 0;
   uint16_t offset_script_list = 0;
   uint16_t offset_feature_list = 0;
   uint16_t offset_lookup_list = 0;
   if (!table.ReadU32(&version) ||
       !table.ReadU16(&offset_script_list) ||
       !table.ReadU16(&offset_feature_list) ||
       !table.ReadU16(&offset_lookup_list)) {
-    return OTS_FAILURE();
+    DROP_THIS_TABLE("Incomplete table");
+    return true;
   }
 
   if (version != 0x00010000) {
-    OTS_WARNING("bad GPOS version");
-    DROP_THIS_TABLE;
-    return true;
-  }
-  if ((offset_script_list < kGposHeaderSize ||
-       offset_script_list >= length) ||
-      (offset_feature_list < kGposHeaderSize ||
-       offset_feature_list >= length) ||
-      (offset_lookup_list < kGposHeaderSize ||
-       offset_lookup_list >= length)) {
-    OTS_WARNING("bad offset in GPOS header");
-    DROP_THIS_TABLE;
+    DROP_THIS_TABLE("Bad version");
     return true;
   }
 
-  if (!ParseLookupListTable(file, data + offset_lookup_list,
-                            length - offset_lookup_list,
-                            &kGposLookupSubtableParser,
-                            &gpos->num_lookups)) {
-    OTS_WARNING("faild to parse lookup list table");
-    DROP_THIS_TABLE;
-    return true;
+  if (offset_lookup_list) {
+    if (offset_lookup_list < kGposHeaderSize || offset_lookup_list >= length) {
+      DROP_THIS_TABLE("Bad lookup list offset in table header");
+      return true;
+    }
+
+    if (!ParseLookupListTable(file, data + offset_lookup_list,
+                              length - offset_lookup_list,
+                              &kGposLookupSubtableParser,
+                              &gpos->num_lookups)) {
+      DROP_THIS_TABLE("Failed to parse lookup list table");
+      return true;
+    }
   }
 
   uint16_t num_features = 0;
-  if (!ParseFeatureListTable(data + offset_feature_list,
-                             length - offset_feature_list, gpos->num_lookups,
-                             &num_features)) {
-    OTS_WARNING("faild to parse feature list table");
-    DROP_THIS_TABLE;
-    return true;
+  if (offset_feature_list) {
+    if (offset_feature_list < kGposHeaderSize || offset_feature_list >= length) {
+      DROP_THIS_TABLE("Bad feature list offset in table header");
+      return true;
+    }
+
+    if (!ParseFeatureListTable(file, data + offset_feature_list,
+                               length - offset_feature_list, gpos->num_lookups,
+                               &num_features)) {
+      DROP_THIS_TABLE("Failed to parse feature list table");
+      return true;
+    }
   }
 
-  if (!ParseScriptListTable(data + offset_script_list,
-                            length - offset_script_list, num_features)) {
-    OTS_WARNING("faild to parse script list table");
-    DROP_THIS_TABLE;
-    return true;
+  if (offset_script_list) {
+    if (offset_script_list < kGposHeaderSize || offset_script_list >= length) {
+      DROP_THIS_TABLE("Bad script list offset in table header");
+      return true;
+    }
+
+    if (!ParseScriptListTable(file, data + offset_script_list,
+                              length - offset_script_list, num_features)) {
+      DROP_THIS_TABLE("Failed to parse script list table");
+      return true;
+    }
   }
 
   gpos->data = data;
   gpos->length = length;
   return true;
 }
 
 bool ots_gpos_should_serialise(OpenTypeFile *file) {
-  const bool needed_tables_dropped =
-      (file->gdef && file->gdef->data == NULL) ||
-      (file->gsub && file->gsub->data == NULL);
-  return file->gpos != NULL && file->gpos->data != NULL &&
-      !needed_tables_dropped;
+  return file->gpos != NULL && file->gpos->data != NULL;
 }
 
 bool ots_gpos_serialise(OTSStream *out, OpenTypeFile *file) {
   if (!out->Write(file->gpos->data, file->gpos->length)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Failed to write GPOS table");
   }
 
   return true;
 }
 
 void ots_gpos_free(OpenTypeFile *file) {
   delete file->gpos;
 }
 
 }  // namespace ots
 
+#undef TABLE_NAME
+#undef DROP_THIS_TABLE