[binutils-gdb] gdb: use gdb:hash_enum as hash function in offset_map_type

[binutils-gdb] gdb: use gdb:hash_enum as hash function in offset_map_type

[Simon Marchi]

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https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=1b95cdb76caca1b7a9ecf9324acf23139f11f7d1

commit 1b95cdb76caca1b7a9ecf9324acf23139f11f7d1
Author: Simon Marchi <simon.marchi@efficios.com>
Date:   Tue Apr 28 09:49:58 2020 -0400

    gdb: use gdb:hash_enum as hash function in offset_map_type
    
    When building with g++ 4.8, we get this error (just an excerpt, because
    g++ outputs a very long error message):
    
          CXX    dwarf2/read.o
        ...
        /home/smarchi/src/binutils-gdb/gdb/dwarf2/read.c:14616:31:   required from here
        /usr/include/c++/4.8/bits/hashtable_policy.h:1070:12: error: invalid use of incomplete type ‘struct std::hash<sect_offset>’
             struct _Hash_code_base<_Key, _Value, _ExtractKey, _H1, _H2,
    
    This is the same problem and fix as in commit f23f598e28ad ("[gdb] Fix
    build breaker with gcc 4.8").  Pass an explicit hash function rather
    than relying on the default std::hash<sect_offset>.
    
    gdb/ChangeLog:
    
            PR gdb/25881
            * dwarf2/read.c (offset_map_type): Use
            gdb:hash_enum<sect_offset> as hash function.

Diff:
---
 gdb/ChangeLog     | 6 ++++++
 gdb/dwarf2/read.c | 3 ++-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 76f6cf78961..f7931c23c60 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,9 @@
+2020-04-28  Simon Marchi  <simon.marchi@efficios.com>
+
+	PR gdb/25881
+	* dwarf2/read.c (offset_map_type): Use
+	gdb:hash_enum<sect_offset> as hash function.
+
 2020-04-28  Tom de Vries  <tdevries@suse.de>
 
 	* dwarf2/read.c (process_structure_scope): Add symbol for struct decl
diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index 82564edd7b2..c5528887faf 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -14513,7 +14513,8 @@ dwarf2_add_type_defn (struct field_info *fip, struct die_info *die,
 
 /* A convenience typedef that's used when finding the discriminant
    field for a variant part.  */
-typedef std::unordered_map<sect_offset, int> offset_map_type;
+typedef std::unordered_map<sect_offset, int, gdb::hash_enum<sect_offset>>
+  offset_map_type;
 
 /* Compute the discriminant range for a given variant.  OBSTACK is
    where the results will be stored.  VARIANT is the variant to