From: Simon Marchi <simon.marchi@efficios.com>
To: Andrew Burgess <aburgess@redhat.com>,
Simon Marchi <simon.marchi@polymtl.ca>,
gdb-patches@sourceware.org
Subject: Re: [PATCH 06/24] gdb: fix bugs in {get,put}_frame_register_bytes
Date: Mon, 13 Nov 2023 14:51:28 -0500 [thread overview]
Message-ID: <0c13a505-b04a-4d48-afa0-91517a87de70@efficios.com> (raw)
In-Reply-To: <8734x9snoj.fsf@redhat.com>
On 11/13/23 10:00, Andrew Burgess wrote:
> Simon Marchi <simon.marchi@polymtl.ca> writes:
>
>> From: Simon Marchi <simon.marchi@efficios.com>
>>
>> I found this only by inspection: the myaddr pointer in
>> {get,put}_frame_register_bytes is reset to `buffer.data ()` at each
>> iteration. This means that we will always use the bytes at the
>> beginning of `buffer` to read or write to the registers, instead of
>> progressing in `buffer`.
>>
>> Fix this by re-writing the functions to chip away the beginning of the
>> buffer array_view as we progress in reading or writing the data.
>>
>> These bugs was introduced almost 3 years ago [1], and yet nobody
>> complained. I'm wondering which architecture relies on that register
>> "overflow" behavior (reading or writing multiple consecutive registers
>> with one {get,put}_frame_register_bytes calls), and in which situation.
>> I find these functions a bit dangerous, if a caller mis-calculates
>> things, it could end up silently reading or writing to the next
>> register, even if it's not the intent.
>>
>> If I could change it, I would prefer to have functions specifically made
>> for that ({get,put}_frame_register_bytes_consecutive or something like
>> that) and make {get,put}_frame_register_bytes only able to write within
>> a single register (which I presume represents most of the use cases of
>> the current {get,put}_frame_register_bytes). If a caller mis-calculates
>> things and an overflow occurs while calling
>> {get,put}_frame_register_bytes, it would hit an assert. The problem is
>> knowing which callers rely on the overflow behavior and which don't.
>
> I agree that this overflow behaviour sucks.
>
> I have a memory of being told (years ago now) that this was a result of
> some older compilers not emitting correct DWARF for compound value
> locations, instead the compiler would just emit a single register
> location, and assume that the debugger would read from consecutive DWARF
> registers. Note, this code assumes that the DWARF register numbering is
> the same as GDB's register numbering, which is not always the case.
>
> Personally, I'd love for GDB to be more aggressive about removing some
> of this legacy behaviour. What I'd like to do is move things like this
> behind a switch, say 'set maintenance deprecated-features on|off', which
> would be off by default, but when it is turned on we'd print a message
> saying:
>
> The feature you turned this on for is deprecated, and will be removed
> from future versions of GDB. To avoid this feature removed, please
> file a bug report here <url> describing the deprecated feature that
> you are using.
>
> Then if nobody complains after a couple of years, we can start deleting
> things.
>
> Anyway... just putting my thoughts down. I think this patch is fine.
Agreed, it would be nice.
> Approved-By: Andrew Burgess <aburgess@redhat.com>
Thanks,
Simon
next prev parent reply other threads:[~2023-11-13 19:51 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-08 5:00 [PATCH 00/24] Fix reading and writing pseudo registers in non-current frames Simon Marchi
2023-11-08 5:00 ` [PATCH 01/24] gdb: don't handle i386 k registers as pseudo registers Simon Marchi
2023-11-11 19:29 ` John Baldwin
2023-11-08 5:00 ` [PATCH 02/24] gdb: use reg_buffer_common throughout gdbsupport/common-regcache.h Simon Marchi
2023-11-11 19:42 ` John Baldwin
2023-11-08 5:00 ` [PATCH 03/24] gdb: make store_integer take an array_view Simon Marchi
2023-11-08 5:00 ` [PATCH 04/24] gdb: simplify conditions in regcache::{read,write,raw_collect,raw_supply}_part Simon Marchi
2023-11-08 5:00 ` [PATCH 05/24] gdb: change regcache interface to use array_view Simon Marchi
2023-11-13 13:43 ` Andrew Burgess
2023-11-13 14:00 ` Andrew Burgess
2023-11-13 16:47 ` Simon Marchi
2023-11-08 5:00 ` [PATCH 06/24] gdb: fix bugs in {get,put}_frame_register_bytes Simon Marchi
2023-11-13 15:00 ` Andrew Burgess
2023-11-13 19:51 ` Simon Marchi [this message]
2023-11-08 5:00 ` [PATCH 07/24] gdb: make put_frame_register take an array_view Simon Marchi
2023-11-08 5:00 ` [PATCH 08/24] gdb: change value_of_register and value_of_register_lazy to take the next frame Simon Marchi
2023-11-08 5:00 ` [PATCH 09/24] gdb: remove frame_register Simon Marchi
2023-11-08 5:00 ` [PATCH 10/24] gdb: make put_frame_register take the next frame Simon Marchi
2023-11-08 5:00 ` [PATCH 11/24] gdb: make put_frame_register_bytes " Simon Marchi
2023-11-08 5:00 ` [PATCH 12/24] gdb: make get_frame_register_bytes " Simon Marchi
2023-11-08 5:00 ` [PATCH 13/24] gdb: add value::allocate_register Simon Marchi
2023-11-08 5:00 ` [PATCH 14/24] gdb: read pseudo register through frame Simon Marchi
2023-11-11 20:11 ` John Baldwin
2023-11-08 5:00 ` [PATCH 15/24] gdb: change parameter name in frame_unwind_register_unsigned declaration Simon Marchi
2023-11-08 5:01 ` [PATCH 16/24] gdb: rename gdbarch_pseudo_register_write to gdbarch_deprecated_pseudo_register_write Simon Marchi
2023-11-14 12:12 ` Andrew Burgess
2023-11-14 15:16 ` Simon Marchi
2023-11-08 5:01 ` [PATCH 17/24] gdb: add gdbarch_pseudo_register_write that takes a frame Simon Marchi
2023-11-14 12:20 ` Andrew Burgess
2023-11-14 15:20 ` Simon Marchi
2023-11-08 5:01 ` [PATCH 18/24] gdb: migrate i386 and amd64 to the new gdbarch_pseudo_register_write Simon Marchi
2023-11-11 20:16 ` John Baldwin
2023-11-13 2:59 ` Simon Marchi
2023-11-08 5:01 ` [PATCH 19/24] gdb: make aarch64_za_offsets_from_regnum return za_offsets Simon Marchi
2023-11-08 5:01 ` [PATCH 20/24] gdb: add missing raw register read in aarch64_sme_pseudo_register_write Simon Marchi
2023-11-08 5:01 ` [PATCH 21/24] gdb: migrate aarch64 to new gdbarch_pseudo_register_write Simon Marchi
2023-11-08 5:01 ` [PATCH 22/24] gdb: migrate arm to gdbarch_pseudo_register_read_value Simon Marchi
2023-11-08 5:01 ` [PATCH 23/24] gdb: migrate arm to new gdbarch_pseudo_register_write Simon Marchi
2023-11-08 5:01 ` [PATCH 24/24] gdb/testsuite: add tests for unwinding of pseudo registers Simon Marchi
2023-11-08 5:16 ` [PATCH 00/24] Fix reading and writing pseudo registers in non-current frames Simon Marchi
2023-11-09 3:05 ` Simon Marchi
2023-11-08 11:57 ` Luis Machado
2023-11-08 15:47 ` Simon Marchi
2023-11-08 17:08 ` Luis Machado
2023-11-08 19:34 ` Simon Marchi
2023-11-09 19:04 ` Simon Marchi
2023-11-13 13:10 ` Luis Machado
2023-11-13 15:08 ` Luis Machado
2023-11-11 20:26 ` John Baldwin
2023-11-13 3:03 ` Simon Marchi
2023-12-01 16:27 Simon Marchi
2023-12-01 16:27 ` [PATCH 06/24] gdb: fix bugs in {get,put}_frame_register_bytes Simon Marchi
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