From: Mark Wielaard <mark@klomp.org>
Date: Sat, 18 Sep 2021 20:16:33 +0000 (+0200)
Subject: readdwarf3: Reuse abbrev if possible between units
X-Git-Tag: VALGRIND_3_18_0~72
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ab6795f5c23ff155d62e6f77ec6c28817a52cd15;p=thirdparty%2Fvalgrind.git

readdwarf3: Reuse abbrev if possible between units

Instead of destroying the ht_abbrvs after processing a CU save it
and the offset so it can be reused for the next CU if that happens
to have the same abbrev offset. dwz compressed DWARF often reuse
the same abbrev for multiple CUs.
---

diff --git a/coregrind/m_debuginfo/readdwarf3.c b/coregrind/m_debuginfo/readdwarf3.c
index b02e239900..0c86b712ef 100644
--- a/coregrind/m_debuginfo/readdwarf3.c
+++ b/coregrind/m_debuginfo/readdwarf3.c
@@ -470,6 +470,7 @@ typedef
       struct _DebugInfo* di;
       /* --- a hash table of g_abbv (i.e. parsed abbreviations) --- */
       VgHashTable *ht_abbvs;
+      ULong debug_abbrev_offset;
 
       /* True if this came from .debug_types; otherwise it came from
          .debug_info.  */
@@ -1101,13 +1102,6 @@ static g_abbv* get_abbv (const CUConst* cc, ULong abbv_code)
    return abbv;
 }
 
-/* Free the memory allocated in CUConst. */
-static void clear_CUConst (CUConst* cc)
-{
-   VG_(HT_destruct) ( cc->ht_abbvs, ML_(dinfo_free));
-   cc->ht_abbvs = NULL;
-}
-
 /* Parse the Compilation Unit header indicated at 'c' and 
    initialise 'cc' accordingly. */
 static __attribute__((noinline))
@@ -1115,6 +1109,8 @@ void parse_CU_Header ( /*OUT*/CUConst* cc,
                        Bool td3,
                        Cursor* c, 
                        DiSlice escn_debug_abbv,
+                       ULong last_debug_abbrev_offset,
+                       VgHashTable *last_ht_abbvs,
 		       Bool type_unit,
                        Bool alt_info )
 {
@@ -1190,7 +1186,15 @@ void parse_CU_Header ( /*OUT*/CUConst* cc,
    cc->debug_abbv.ioff += debug_abbrev_offset;
    cc->debug_abbv.szB  -= debug_abbrev_offset;
 
-   init_ht_abbvs(cc, td3);
+   cc->debug_abbrev_offset = debug_abbrev_offset;
+   if (last_ht_abbvs != NULL
+       && debug_abbrev_offset == last_debug_abbrev_offset) {
+      cc->ht_abbvs = last_ht_abbvs;
+   } else {
+      if (last_ht_abbvs != NULL)
+         VG_(HT_destruct) (last_ht_abbvs, ML_(dinfo_free));
+      init_ht_abbvs(cc, td3);
+   }
 }
 
 /* This represents a single signatured type.  It maps a type signature
@@ -5141,6 +5145,8 @@ void new_dwarf3_reader_wrk (
       TRACE_D3("\n------ Collecting signatures from "
                ".debug_types section ------\n");
 
+      ULong last_debug_abbrev_offset = (ULong) -1;
+      VgHashTable *last_ht_abbvs = NULL;
       while (True) {
          UWord   cu_start_offset, cu_offset_now;
          CUConst cc;
@@ -5149,7 +5155,9 @@ void new_dwarf3_reader_wrk (
          TRACE_D3("\n");
          TRACE_D3("  Compilation Unit @ offset 0x%lx:\n", cu_start_offset);
          /* parse_CU_header initialises the CU's abbv hash table.  */
-         parse_CU_Header( &cc, td3, &info, escn_debug_abbv, True, False );
+         parse_CU_Header( &cc, td3, &info, escn_debug_abbv,
+                          last_debug_abbrev_offset, last_ht_abbvs,
+                          True, False );
 
          /* Needed by cook_die.  */
          cc.types_cuOff_bias = escn_debug_info.szB;
@@ -5163,7 +5171,8 @@ void new_dwarf3_reader_wrk (
          cu_offset_now = (cu_start_offset + cc.unit_length
                           + (cc.is_dw64 ? 12 : 4));
 
-         clear_CUConst ( &cc);
+         last_debug_abbrev_offset = cc.debug_abbrev_offset;
+         last_ht_abbvs = cc.ht_abbvs;
 
          if (cu_offset_now >= escn_debug_types.szB) {
             break;
@@ -5171,6 +5180,8 @@ void new_dwarf3_reader_wrk (
 
          set_position_of_Cursor ( &info, cu_offset_now );
       }
+      if (last_ht_abbvs != NULL)
+         VG_(HT_destruct) (last_ht_abbvs, ML_(dinfo_free));
    }
 
    /* Perform three DIE-reading passes.  The first pass reads DIEs from
@@ -5229,6 +5240,8 @@ void new_dwarf3_reader_wrk (
          TRACE_D3("\n------ Parsing .debug_types section ------\n");
       }
 
+      ULong last_debug_abbrev_offset = (ULong) -1;
+      VgHashTable *last_ht_abbvs = NULL;
       while (True) {
          ULong   cu_start_offset, cu_offset_now;
          CUConst cc;
@@ -5277,9 +5290,11 @@ void new_dwarf3_reader_wrk (
          /* parse_CU_header initialises the CU's hashtable of abbvs ht_abbvs */
          if (pass == 0) {
             parse_CU_Header( &cc, td3, &info, escn_debug_abbv_alt,
+                             last_debug_abbrev_offset, last_ht_abbvs,
                              False, True );
          } else {
             parse_CU_Header( &cc, td3, &info, escn_debug_abbv,
+                             last_debug_abbrev_offset, last_ht_abbvs,
                              pass == 2, False );
          }
          cc.escn_debug_str      = pass == 0 ? escn_debug_str_alt
@@ -5370,12 +5385,15 @@ void new_dwarf3_reader_wrk (
             typestack_preen( &typarser, td3, -2 );
          }
 
-         clear_CUConst(&cc);
+         last_debug_abbrev_offset = cc.debug_abbrev_offset;
+         last_ht_abbvs = cc.ht_abbvs;
 
          if (cu_offset_now == section_size)
             break;
          /* else keep going */
       }
+      if (last_ht_abbvs != NULL)
+         VG_(HT_destruct) (last_ht_abbvs, ML_(dinfo_free));
    }
 
    if (fndn_ix_Table != NULL)