Re: [PATCH 08/10] Handle "show remote memory-write-packet-size" when not connected

Sergio Durigan Junior
2018-05-22T21:43:35Z

On Monday, May 21 2018, Pedro Alves wrote:

> On 05/18/2018 10:26 PM, Simon Marchi wrote:
>> On 2018-05-16 10:18 AM, Pedro Alves wrote:
>>> Currently "show remote memory-write-packet-size" says that the packet
>>> size is limited to whatever is stored in the remote_state global, even
>>> if not connected to a target.
>>>
>>> When we get to support multiple instances of remote targets, there
>>> won't be a remote_state global anymore, so that must be replaced by
>>> something else.
>>>
>>> Since it doesn't make sense to print the limit of the packet size of a
>>> non-existing connection, this patch makes us say that the limit will
>>> be further reduced when we connect.
>>>
>>> The text is taken from the command's online help, which says:
>>>
>>> "The actual limit is further reduced dependent on the target."
>>
>> The result sounds a bit weird:
>>
>> (gdb) show remote memory-read-packet-size
>> The memory-read-packet-size is 0. The actual limit will be further reduced dependent on the target.
>> (gdb) show remote memory-write-packet-size
>> The memory-write-packet-size is 0. The actual limit will be further reduced dependent on the target.
>>
>> How can the limit be reduced if it is zero? I don't really know about
>> this code, is zero a special value that means no limit? Perhaps it should be
>> handled differently to make the message clearer.
>
> Yeah, I think the command itself it pretty obscure/weird.
>
> "0" means "default packet size". I.e., whatever packet size
> the remote can handle. And if you do
> "set remote memory-write-packet fixed", then GDB picks
> an arbitrary default...
> I've spent a few hours today staring at this, trying to
> come up with something reasonable-ish, and this is what
> I came up with. I even caught a bug. I don't think it's worth
> it to polish this much more, as this is a pretty obscure
> command that most probably nobody uses nowadays.
>
> WDYT?

I'm seeing a few failures on Debian-s390x-native-extended-gdbserver-m64:

PASS -> FAIL: gdb.base/remote.exp: write-packet default
PASS -> FAIL: gdb.base/remote.exp: set write-packet - small
PASS -> FAIL: gdb.base/remote.exp: set write-packet - very-small
new FAIL: gdb.base/remote.exp: write-packet default again
new FAIL: gdb.base/remote.exp: write-packet default limit again
PASS -> FAIL: gdb.reverse/s390-mvcle.exp: check MVCLE record 2
PASS -> FAIL: gdb.reverse/s390-mvcle.exp: check MVCLE record 3
PASS -> KFAIL: gdb.threads/process-dies-while-handling-bp.exp: non_stop=off: cond_bp_target=0: inferior 1 exited

gdb.log shows:

...
show remote memory-write-packet-size
The memory-write-packet-size is 0 (default). Packets are limited to 16383 bytes.
(gdb) FAIL: gdb.base/remote.exp: write-packet default
set remote memory-write-packet-size
Argument required (integer, `fixed' or `limited').
(gdb) PASS: gdb.base/remote.exp: set write-packet - NULL
set remote memory-write-packet-size 20
(gdb) PASS: gdb.base/remote.exp: set remote memory-write-packet-size 20
show remote memory-write-packet-size
The memory-write-packet-size is 20. Packets are limited to 20 bytes.
(gdb) FAIL: gdb.base/remote.exp: set write-packet - small
set remote memory-write-packet-size 1
(gdb) PASS: gdb.base/remote.exp: set remote memory-write-packet-size 1
show remote memory-write-packet-size
The memory-write-packet-size is 1. Packets are limited to 20 bytes.
(gdb) FAIL: gdb.base/remote.exp: set write-packet - very-small
set remote memory-write-packet-size 0
(gdb) PASS: gdb.base/remote.exp: set remote memory-write-packet-size 0
show remote memory-write-packet-size
The memory-write-packet-size is 0 (default). Packets are limited to 16383 bytes.
(gdb) FAIL: gdb.base/remote.exp: write-packet default again
set remote memory-write-packet-size fixed
The target may not be able to correctly handle a memory-write-packet-size
of 16384 bytes. Change the packet size? (y or n) y
(gdb) PASS: gdb.base/remote.exp: set remote memory-write-packet-size fixed
show remote memory-write-packet-size
The memory-write-packet-size is 0 (default). Packets are fixed at 16384 bytes.
(gdb) PASS: gdb.base/remote.exp: write-packet default fixed
set remote memory-write-packet-size limit
(gdb) PASS: gdb.base/remote.exp: set remote memory-write-packet-size limit
show remote memory-write-packet-size
The memory-write-packet-size is 0 (default). Packets are limited to 16383 bytes.
(gdb) FAIL: gdb.base/remote.exp: write-packet default limit again
set remote memory-write-packet-size 398
(gdb) PASS: gdb.base/remote.exp: timed download `remote' - limit, 398 - set packet size
set remote memory-write-packet-size limit
...

This is on a try build; unfortunately our BuildBot has a very big queue
right now and the "official" commit hasn't been tested yet.

Please let me know if you need more info. I haven't actually tested to
see if this was the exact commit that caused the regression, but it
seems to be the one.

> ------------------
> From dcca1d189d4e3bdd21af369fa8dc5b450d3effad Mon Sep 17 00:00:00 2001
> From: Pedro Alves <palves@redhat.com>
> Date: Mon, 21 May 2018 19:46:43 +0100
> Subject: [PATCH] Handle "show remote memory-write-packet-size" when not
> connected
>
> Currently "show remote memory-write-packet-size" says that the packet
> size is limited to whatever is stored in the remote_state global, even
> if not connected to a target.
>
> When we get to support multiple instances of remote targets, there
> won't be a remote_state global anymore, so that must be replaced by
> something else.
>
> Since it doesn't make sense to print the limit of the packet size of a
> non-existing connection, this patch makes us say that the limit will
> be further reduced when we connect.
>
> The text is taken from the command's online help, which says:
>
> "The actual limit is further reduced dependent on the target."
>
> Note that a value of "0" is special, as per "help set remote
> memory-write-packet-size":
>
> ~~~
> Specify the number of bytes in a packet or 0 (zero) for the
> default packet size.
> ~~~
>
> I've tweaked "show remote memory-write-packet-size" to include
> "(default)" in the output in that case, like this:
>
> (gdb) show remote memory-write-packet-size
> The memory-write-packet-size is 0 (default). The actual limit will be further reduced dependent on the target.
>
> While working on this, I noticed that an explicit "set remote
> write-packet-size 0" does not makes GDB go back to the exact same
> state as the default state when GDB starts up:
>
> (gdb) show remote memory-write-packet-size
> The memory-write-packet-size is 0. [...]
> ^^
>
> (gdb) set remote memory-write-packet-size 0
> (gdb) show remote memory-write-packet-size
> The memory-write-packet-size is 16384. [...]
> ^^^^^
>
> The "16384" number comes from DEFAULT_MAX_MEMORY_PACKET_SIZE.
>
> I think this happens because git commit a5c0808e221c ("gdb: remove
> packet size limit") at
> <https://sourceware.org/ml/gdb-patches/2015-08/msg00743.html>, added
> this:
>
> /* So that the query shows the correct value. */
> if (size <= 0)
> size = DEFAULT_MAX_MEMORY_PACKET_SIZE;
>
> to set_memory_packet_size, but despite what the comment suggests, that
> also has the side-effect of recording DEFAULT_MAX_MEMORY_PACKET_SIZE
> in config->size.
>
> Finally, DEFAULT_MAX_MEMORY_PACKET_SIZE only makes sense for "set
> remote memory-write-packet-size fixed", so I've renamed it
> accordingly, to make it a little bit clearer.
>
> gdb/ChangeLog:
> yyyy-mm-dd Pedro Alves <palves@redhat.com>
>
> * remote.c (DEFAULT_MAX_MEMORY_PACKET_SIZE): Rename to ...
> (DEFAULT_MAX_MEMORY_PACKET_SIZE_FIXED): ... this.
> (get_fixed_memory_packet_size): New.
> (get_memory_packet_size): Use it.
> (set_memory_packet_size): Don't override the config size with
> DEFAULT_MAX_MEMORY_PACKET_SIZE.
> (show_memory_packet_size): Use get_fixed_memory_packet_size.
> Don't refer to get_memory_packet_size if not connected to a remote
> target. Show "(default)" if configured size is 0.
>
> gdb/testsuite/ChangeLog:
> yyyy-mm-dd Pedro Alves <palves@redhat.com>
>
> * gdb.base/remote.exp: Adjust expected output of "show remote
> memory-write-packet-size". Add tests for "set remote
> memory-write-packet-size 0" and "set remote
> memory-write-packet-size fixed/limit".
> ---
> gdb/remote.c | 60 ++++++++++++++++++++++++++-------------
> gdb/testsuite/gdb.base/remote.exp | 30 ++++++++++++++++++--
> 2 files changed, 67 insertions(+), 23 deletions(-)
>
> diff --git a/gdb/remote.c b/gdb/remote.c
> index 59880a93a8..72254dba31 100644
> --- a/gdb/remote.c
> +++ b/gdb/remote.c
> @@ -1328,16 +1328,29 @@ struct memory_packet_config
> int fixed_p;
> };
>
> -/* The default max memory-write-packet-size. The 16k is historical.
> - (It came from older GDB's using alloca for buffers and the
> - knowledge (folklore?) that some hosts don't cope very well with
> - large alloca calls.) */
> -#define DEFAULT_MAX_MEMORY_PACKET_SIZE 16384
> +/* The default max memory-write-packet-size, when the setting is
> + "fixed". The 16k is historical. (It came from older GDB's using
> + alloca for buffers and the knowledge (folklore?) that some hosts
> + don't cope very well with large alloca calls.) */
> +#define DEFAULT_MAX_MEMORY_PACKET_SIZE_FIXED 16384
>
> /* The minimum remote packet size for memory transfers. Ensures we
> can write at least one byte. */
> #define MIN_MEMORY_PACKET_SIZE 20
>
> +/* Get the memory packet size, assuming it is fixed. */
> +
> +static long
> +get_fixed_memory_packet_size (struct memory_packet_config *config)
> +{
> + gdb_assert (config->fixed_p);
> +
> + if (config->size <= 0)
> + return DEFAULT_MAX_MEMORY_PACKET_SIZE_FIXED;
> + else
> + return config->size;
> +}
> +
> /* Compute the current size of a read/write packet. Since this makes
> use of ``actual_register_packet_size'' the computation is dynamic. */
>
> @@ -1349,12 +1362,7 @@ get_memory_packet_size (struct memory_packet_config *config)
>
> long what_they_get;
> if (config->fixed_p)
> - {
> - if (config->size <= 0)
> - what_they_get = DEFAULT_MAX_MEMORY_PACKET_SIZE;
> - else
> - what_they_get = config->size;
> - }
> + what_they_get = get_fixed_memory_packet_size (config);
> else
> {
> what_they_get = get_remote_packet_size ();
> @@ -1414,16 +1422,17 @@ set_memory_packet_size (const char *args, struct memory_packet_config *config)
> something arbitrarily large. */
> }
>
> - /* So that the query shows the correct value. */
> - if (size <= 0)
> - size = DEFAULT_MAX_MEMORY_PACKET_SIZE;
> -
> /* Extra checks? */
> if (fixed_p && !config->fixed_p)
> {
> + /* So that the query shows the correct value. */
> + long query_size = (size <= 0
> + ? DEFAULT_MAX_MEMORY_PACKET_SIZE_FIXED
> + : size);
> +
> if (! query (_("The target may not be able to correctly handle a %s\n"
> "of %ld bytes. Change the packet size? "),
> - config->name, size))
> + config->name, query_size))
> error (_("Packet size not changed."));
> }
> /* Update the config. */
> @@ -1434,13 +1443,24 @@ set_memory_packet_size (const char *args, struct memory_packet_config *config)
> static void
> show_memory_packet_size (struct memory_packet_config *config)
> {
> - printf_filtered (_("The %s is %ld. "), config->name, config->size);
> + if (config->size == 0)
> + printf_filtered (_("The %s is 0 (default). "), config->name);
> + else
> + printf_filtered (_("The %s is %ld. "), config->name, config->size);
> if (config->fixed_p)
> printf_filtered (_("Packets are fixed at %ld bytes.\n"),
> - get_memory_packet_size (config));
> + get_fixed_memory_packet_size (config));
> else
> - printf_filtered (_("Packets are limited to %ld bytes.\n"),
> - get_memory_packet_size (config));
> + {
> + struct remote_state *rs = get_remote_state ();
> +
> + if (rs->remote_desc != NULL)
> + printf_filtered (_("Packets are limited to %ld bytes.\n"),
> + get_memory_packet_size (config));
> + else
> + puts_filtered ("The actual limit will be further reduced "
> + "dependent on the target.\n");
> + }
> }
>
> static struct memory_packet_config memory_write_packet_config =
> diff --git a/gdb/testsuite/gdb.base/remote.exp b/gdb/testsuite/gdb.base/remote.exp
> index 26361af9a5..ba34441af2 100644
> --- a/gdb/testsuite/gdb.base/remote.exp
> +++ b/gdb/testsuite/gdb.base/remote.exp
> @@ -35,7 +35,7 @@ if {$result != "" } then {
> #
>
> gdb_test "show remote memory-write-packet-size" \
> - "The memory-write-packet-size is 0. Packets are limited to \[0-9\]+ bytes." \
> + "The memory-write-packet-size is 0 \\(default\\). The actual limit will be further reduced dependent on the target\." \
> "write-packet default"
>
> gdb_test "set remote memory-write-packet-size" \
> @@ -44,14 +44,38 @@ gdb_test "set remote memory-write-packet-size" \
>
> gdb_test_no_output "set remote memory-write-packet-size 20"
> gdb_test "show remote memory-write-packet-size" \
> - "The memory-write-packet-size is 20. Packets are limited to 20 bytes." \
> + "The memory-write-packet-size is 20. The actual limit will be further reduced dependent on the target\." \
> "set write-packet - small"
>
> gdb_test_no_output "set remote memory-write-packet-size 1"
> gdb_test "show remote memory-write-packet-size" \
> - "The memory-write-packet-size is 1. Packets are limited to 20 bytes." \
> + "The memory-write-packet-size is 1. The actual limit will be further reduced dependent on the target\." \
> "set write-packet - very-small"
>
> +gdb_test_no_output "set remote memory-write-packet-size 0"
> +gdb_test "show remote memory-write-packet-size" \
> + "The memory-write-packet-size is 0 \\(default\\). The actual limit will be further reduced dependent on the target\." \
> + "write-packet default again"
> +
> +set test "set remote memory-write-packet-size fixed"
> +gdb_test_multiple $test $test {
> + -re "Change the packet size. .y or n. " {
> + gdb_test_multiple "y" $test {
> + -re "$gdb_prompt $" {
> + pass $test
> + }
> + }
> + }
> +}
> +gdb_test "show remote memory-write-packet-size" \
> + "The memory-write-packet-size is 0 \\(default\\). Packets are fixed at 16384 bytes\." \
> + "write-packet default fixed"
> +
> +gdb_test_no_output "set remote memory-write-packet-size limit"
> +gdb_test "show remote memory-write-packet-size" \
> + "The memory-write-packet-size is 0 \\(default\\). The actual limit will be further reduced dependent on the target\." \
> + "write-packet default limit again"
> +
> #
> # Part TWO: Check the download behavior.
> #
> --
> 2.14.3

--
Sergio
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