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[binutils-gdb] (Ada) fix GDB crash printing packed array
- From: sergiodj+buildbot at sergiodj dot net
- To: gdb-testers at sourceware dot org
- Date: Sun, 17 Feb 2019 08:48:15 -0500
- Subject: [binutils-gdb] (Ada) fix GDB crash printing packed array
*** TEST RESULTS FOR COMMIT a2cd4f14750ae27ea5c250c98965eef842ee57db ***
Author: Joel Brobecker <email@example.com>
(Ada) fix GDB crash printing packed array
Trying to print a packed array sometimes leads to a crash (see
attached testcase for an example of when this happens):
| (gdb) p bad
|  65571 segmentation fault gdb -q foo
Variable "bad" is declared in the debug information as an array where
the array's type name has an XPnnn suffix:
| .uleb128 0xc # (DIE (0x566) DW_TAG_typedef)
| .long .LASF200 # DW_AT_name: "pck__t___XP1"
| [loc info attributes snipped]
| .long 0x550 # DW_AT_type
| .byte 0x1 # DW_AT_alignment
The signals to GDB that the debugging information follows a GNAT encoding
used for packed arrays, and an in order to decode it, we need to find
the type whose name is the same minus the "___XPnnn" suffix: "pck__t".
For that, we make a call to ada-lang.c::standard_lookup, which is
a simple function which essentially does:
| /* Return the result of a standard (literal, C-like) lookup of NAME in
| given DOMAIN, visible from lexical block BLOCK. */
| sym = lookup_symbol_in_language (name, block, domain, language_c, 0);
Unfortunately for us, while the intent of this call was to perform
an exact-match lookup, in our case, it returns ... type pck__t___XP1
instead! In other words, it finds itself back. The reason why it finds
this type is a confluence of two factors:
(1) Forcing the lookup into language_c currently does not affect
how symbol matching is done anymore, because we look at the symbol's
language to determine which kind of matching should be done;
(2) The lookup searches the local context (via block) first, beforei
doing a more general lookup. And looking at the debug info for
the main subprogram, we see that type "pck__t" is not declared
there, only in the debug info for pck.ads. In other words,
there is no way that we accidently find "pck__t" by random chance.
I believe Pedro added a new function called ada_lookup_encoded_symbol
for that specific purpose, so I started by replacing the lookup
by language above by this. Unfortunately, still no joy.
This was because, even though ada_lookup_encoded_symbol puts angle-
brackets around the search name to signal that we want a verbatim
search, we end up losing that information in the function called
to compare a symbol with the search name:
| static bool
| do_full_match (const char *symbol_search_name,
| const lookup_name_info &lookup_name,
| completion_match_result *comp_match_res)
| return full_match (symbol_search_name, ada_lookup_name (lookup_name));
(no angle brackets)
The way I fixed this was by introducing a new function called
do_exact_match, and then adjust ada_get_symbol_name_matcher to
return that function when seeing that we have a verbatim non-wild-match
As it happens, this fixes an incorrect test in gdb.ada/homony.exp,
where we were inserting a breakpoint on a symbol using the angle-brackets
notation, and got 2 locations for that breakpoint...
(gdb) b <homonym__get_value>
Breakpoint 1 at 0x4029fc: <homonym__get_value>. (2 locations)
... each location being in a different function:
(gdb) info break
Num Type Disp Enb Address What
1 breakpoint keep y <MULTIPLE>
1.1 y 0x00000000004029fc in homonym.get_value
1.2 y 0x0000000000402a3a in homonym.get_value
(gdb) x /i 0x00000000004029fc
0x4029fc <homonym__get_value+8>: movl $0x1d,-0x4(%rbp)
(gdb) x /i 0x0000000000402a3a
0x402a3a <homonym__get_value__2+8>: movl $0x11,-0x4(%rbp)
Since we used angle-brackets, we shouldn't be matching the second one,
something this patch fixes.
* ada-lang.c (standard_lookup): Use ada_lookup_encoded_symbol
instead of lookup_symbol_in_language
(do_exact_match): New function.
(ada_get_symbol_name_matcher): Return do_exact_match when
doing a verbatim match.
* gdb.ada/big_packed_array: New testcase.
* gdb.ada/homonym.exp: Fix incorrect expected output for
"break <homonym__get_value>" test.
Tested on x86_64-linux.