Re: [PATCH v3] gdb: call check_typedef at beginning of dwarf_expr_context::fetch_result

[Luis Machado <luis.machado@arm.com>]

On 8/18/22 17:16, Simon Marchi via Gdb-patches wrote:
> On 7/28/22 11:33, Simon Marchi wrote:
>> From: Simon Marchi <simon.marchi@polymtl.ca>
>>
>> New in this version:
>>
>>   - add architecture check in test
>>   - add aarch64 version of the .S
>>
>> Bug 29374 shows this crash:
>>
>>      $ ./gdb -nx --data-directory=data-directory -q -batch -ex "catch throw" -ex r -ex bt a.out
>>      ...
>>      /home/simark/src/binutils-gdb/gdb/../gdbsupport/array-view.h:217: internal-error: copy: Assertion `dest.size () == src.size ()' failed.
>>
>> The backtrace is:
>>
>>      #0  internal_error (file=0x5555606504c0 "/home/simark/src/binutils-gdb/gdb/../gdbsupport/array-view.h", line=217, fmt=0x55556064b700 "%s: Assertion `%s' failed.") at /home/simark/src/binutils-gdb/gdbsupport/errors.cc:51
>>      #1  0x000055555d41c0bb in gdb::copy<unsigned char const, unsigned char> (src=..., dest=...) at /home/simark/src/binutils-gdb/gdb/../gdbsupport/array-view.h:217
>>      #2  0x000055555deef28c in dwarf_expr_context::fetch_result (this=0x7fffffffb830, type=0x621007a86830, subobj_type=0x621007a86830, subobj_offset=0, as_lval=false) at /home/simark/src/binutils-gdb/gdb/dwarf2/expr.c:1040
>>      #3  0x000055555def0015 in dwarf_expr_context::evaluate (this=0x7fffffffb830, addr=0x62f00004313e "0", len=1, as_lval=false, per_cu=0x60b000069550, frame=0x621007c9e910, addr_info=0x0, type=0x621007a86830, subobj_type=0x621007a86830, subobj_offset=0) at /home/simark/src/binutils-gdb/gdb/dwarf2/expr.c:1091
>>      #4  0x000055555e084327 in dwarf2_evaluate_loc_desc_full (type=0x621007a86830, frame=0x621007c9e910, data=0x62f00004313e "0", size=1, per_cu=0x60b000069550, per_objfile=0x613000006080, subobj_type=0x621007a86830, subobj_byte_offset=0, as_lval=false) at /home/simark/src/binutils-gdb/gdb/dwarf2/loc.c:1485
>>      #5  0x000055555e0849e2 in dwarf2_evaluate_loc_desc (type=0x621007a86830, frame=0x621007c9e910, data=0x62f00004313e "0", size=1, per_cu=0x60b000069550, per_objfile=0x613000006080, as_lval=false) at /home/simark/src/binutils-gdb/gdb/dwarf2/loc.c:1529
>>      #6  0x000055555e0828c6 in dwarf_entry_parameter_to_value (parameter=0x621007a96e58, deref_size=0x0, type=0x621007a86830, caller_frame=0x621007c9e910, per_cu=0x60b000069550, per_objfile=0x613000006080) at /home/simark/src/binutils-gdb/gdb/dwarf2/loc.c:1235
>>      #7  0x000055555e082f55 in value_of_dwarf_reg_entry (type=0x621007a86890, frame=0x621007acc510, kind=CALL_SITE_PARAMETER_DWARF_REG, kind_u=...) at /home/simark/src/binutils-gdb/gdb/dwarf2/loc.c:1332
>>      #8  0x000055555e083449 in value_of_dwarf_block_entry (type=0x621007a86890, frame=0x621007acc510, block=0x61e000033568 "T\004\205\001\240\004\004\243\001T\237\004\240\004\261\004\001T\004\261\004\304\005\004\243\001T\237\004\304\005\310\005\001T\004\310\005\311\005\004\243\001T\237", block_len=1) at /home/simark/src/binutils-gdb/gdb/dwarf2/loc.c:1365
>>      #9  0x000055555e094d40 in loclist_read_variable_at_entry (symbol=0x621007a99bd0, frame=0x621007acc510) at /home/simark/src/binutils-gdb/gdb/dwarf2/loc.c:3889
>>      #10 0x000055555f5192e0 in read_frame_arg (fp_opts=..., sym=0x621007a99bd0, frame=0x621007acc510, argp=0x7fffffffbf20, entryargp=0x7fffffffbf60) at /home/simark/src/binutils-gdb/gdb/stack.c:559
>>      #11 0x000055555f51c352 in print_frame_args (fp_opts=..., func=0x621007a99ad0, frame=0x621007acc510, num=-1, stream=0x6030000bad90) at /home/simark/src/binutils-gdb/gdb/stack.c:887
>>      #12 0x000055555f521919 in print_frame (fp_opts=..., frame=0x621007acc510, print_level=1, print_what=LOCATION, print_args=1, sal=...) at /home/simark/src/binutils-gdb/gdb/stack.c:1390
>>      #13 0x000055555f51f22e in print_frame_info (fp_opts=..., frame=0x621007acc510, print_level=1, print_what=LOCATION, print_args=1, set_current_sal=0) at /home/simark/src/binutils-gdb/gdb/stack.c:1116
>>      #14 0x000055555f526c6d in backtrace_command_1 (fp_opts=..., bt_opts=..., count_exp=0x0, from_tty=0) at /home/simark/src/binutils-gdb/gdb/stack.c:2079
>>      #15 0x000055555f527ae5 in backtrace_command (arg=0x0, from_tty=0) at /home/simark/src/binutils-gdb/gdb/stack.c:2198
>>
>> The problem is that the type that gets passed down to
>> dwarf_expr_context::fetch_result (the type of a variable of which we're
>> trying to read the entry value) is a typedef whose size has never been
>> computed yet (check_typedef has never been called on it).  As we get in
>> the DWARF_VALUE_STACK case (line 1028 of dwarf2/expr.c), the `len`
>> variable is therefore set to 0, instead of the actual type length.  We
>> then call allocate_value on subobj_type, which does call check_typedef,
>> so the length of the typedef gets filled in at that point.  We end up
>> passing to the copy function a source array view of length 0 and a
>> target array view of length 4, and the assertion fails.
>>
>> Fix this by calling check_typedef on both type and subobj_type at the
>> beginning of fetch_result.
>>
>> I tried writing a test for this using the DWARF assembler, but I haven't
>> succeeded.  It's possible that we need to get into this specific code
>> path (value_of_dwarf_reg_entry and all) to manage to get to
>> dwarf_expr_context::fetch_result with a typedef type that has never been
>> resolved.  In all my attempts, the typedef would always be resolved
>> already, so the bug wouldn't show up.
>>
>> As a fallback, I made a gdb.dwarf2 test with compiler-generated .S
>> files.  I don't particularly like those, but I think it's better than no
>> test.  The .cpp source code is the smallest reproducer I am able to make
>> from the reproducer given in the bug (thanks to Pedro for suggestions on
>> how to minimize it further than I had).  Since I tested on both amd64
>> and aarch64, I added versions of the test for these two architectures.
>>
>> Change-Id: I182733ad08e34df40d8bcc47af72c482fabf4900
>> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29374
>> ---
>>   gdb/dwarf2/expr.c                             |     5 +
>>   .../gdb.dwarf2/entry-value-typedef-aarch64.S  | 12885 +++++++++++++
>>   .../gdb.dwarf2/entry-value-typedef-amd64.S    | 15545 ++++++++++++++++
>>   .../gdb.dwarf2/entry-value-typedef.cpp        |    36 +
>>   .../gdb.dwarf2/entry-value-typedef.exp        |    45 +
>>   5 files changed, 28516 insertions(+)
>>   create mode 100644 gdb/testsuite/gdb.dwarf2/entry-value-typedef-aarch64.S
>>   create mode 100644 gdb/testsuite/gdb.dwarf2/entry-value-typedef-amd64.S
>>   create mode 100644 gdb/testsuite/gdb.dwarf2/entry-value-typedef.cpp
>>   create mode 100644 gdb/testsuite/gdb.dwarf2/entry-value-typedef.exp
> 
> I pushed this patch.
> 
> Simon

It seems newer compilers on aarch64 (g++ 9.4.0 or 11.2.0) don't like this test. They complain with:

gdb compile failed, /usr/bin/ld: /tmp/cc0vjoZT.o: relocation R_AARCH64_ADR_PREL_PG_HI21 against symbol `_ZNSsD1Ev@@GLIBCXX_3.4' which may bin
d externally can not be used when making a shared object; recompile with -fPIC
/usr/bin/ld: /tmp/cc0vjoZT.o(.text+0x38): unresolvable R_AARCH64_ADR_PREL_PG_HI21 relocation against symbol `_ZNSsD1Ev@@GLIBCXX_3.4'
/usr/bin/ld: final link failed: bad value

So the test doesn't run properly.

Building it statically makes it work though, and still shows the problem:

FAIL: gdb.dwarf2/entry-value-typedef.exp: backtrace (GDB internal error)

Hopefully that will also work fine for x86_64 (haven't tried yet).