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Handle unaligned mapping of .gdb_index

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The .gdb_index was designed such that all data would be aligned.
Unfortunately, we neglected to require this alignment in the objcopy
instructions in the manual.  As a result, in many cases, a .gdb_index
in the wild will not be properly aligned by mmap.  This yields
undefined behavior, which is PR gdb/23743.

This patch fixes the bug by always assuming that the mapping is
unaligned, and using extract_unsigned_integer when needed.  A new
helper class is introduced to make this less painful.

gdb/ChangeLog
2021-04-17  Tom Tromey  <tom@tromey.com>

	PR gdb/23743:
	* dwarf2/read.c (class offset_view): New.
	(struct symbol_table_slot): Remove.
	(struct mapped_index) <symbol_table, constant_pool>: Change type.
	<symbol_name_index, symbol_vec_index>: New methods.
	<symbol_name_slot_invalid, symbol_name_at, symbol_name_count>:
	Rewrite.
	(read_gdb_index_from_buffer): Update.
	(struct dw2_symtab_iterator) <vec>: Change type.
	(dw2_symtab_iter_init_common, dw2_symtab_iter_init)
	(dw2_symtab_iter_next, dw2_expand_marked_cus): Update.
	* dwarf2/index-write.c (class data_buf) <append_data>: Remove.
	<append_array, append_offset>: New methods.
	(write_hash_table, add_address_entry, write_gdbindex_1)
	(write_debug_names): Update.
	* dwarf2/index-common.h (byte_swap, MAYBE_SWAP): Remove.
This commit is contained in:
Tom Tromey 2021-04-17 13:56:36 -06:00
parent da314dd397
commit 42c2c69462
4 changed files with 132 additions and 81 deletions
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21
gdb/dwarf2/index-common.h
View file

@ -29,28 +29,15 @@
architecture-independent. */
typedef uint32_t offset_type;
#if WORDS_BIGENDIAN
/* Convert VALUE between big- and little-endian. */
/* Unpack a 32-bit little-endian value. */
static inline offset_type
byte_swap (offset_type value)
gdb_index_unpack (const gdb_byte *value)
{
offset_type result;
result = (value & 0xff) << 24;
result |= (value & 0xff00) << 8;
result |= (value & 0xff0000) >> 8;
result |= (value & 0xff000000) >> 24;
return result;
return (offset_type) extract_unsigned_integer (value, sizeof (offset_type),
BFD_ENDIAN_LITTLE);
}
#define MAYBE_SWAP(V) byte_swap (V)
#else
#define MAYBE_SWAP(V) static_cast<offset_type> (V)
#endif /* WORDS_BIGENDIAN */
/* The hash function for strings in the mapped index. This is the same as
SYMBOL_HASH_NEXT, but we keep a separate copy to maintain control over the
implementation. This is necessary because the hash function is tied to the