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* [binutils-gdb] gdb: move setbuf calls out of gdb_readline_no_editing_callback
@ 2022-04-24 15:43 Joel Brobecker
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From: Joel Brobecker @ 2022-04-24 15:43 UTC (permalink / raw)
To: gdb-cvs
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=ac16b09d7e5fd0013ffa27e4d0531c0af12a529a
commit ac16b09d7e5fd0013ffa27e4d0531c0af12a529a
Author: Andrew Burgess <aburgess@redhat.com>
Date: Sun Apr 24 08:39:19 2022 -0700
gdb: move setbuf calls out of gdb_readline_no_editing_callback
After this commit:
commit d08cbc5d3203118da5583296e49273cf82378042
Date: Wed Dec 22 12:57:44 2021 +0000
gdb: unbuffer all input streams when not using readline
Issues were reported with some MS-Windows hosts, see the thread
starting here:
https://sourceware.org/pipermail/gdb-patches/2022-March/187004.html
Filed in bugzilla as: PR mi/29002
The problem seems to be that calling setbuf on terminal file handles
is not always acceptable, see this mail for more details:
https://sourceware.org/pipermail/gdb-patches/2022-April/187310.html
This commit does two things, first moving the setbuf calls out of
gdb_readline_no_editing_callback so that we don't end up calling
setbuf so often.
Then, for MS-Windows hosts, we don't call setbuf for terminals, this
appears to resolve the issues that have been reported.
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29002
Diff:
---
gdb/event-top.c | 13 -------------
gdb/top.c | 39 +++++++++++++++++++++++++++++++++++++++
2 files changed, 39 insertions(+), 13 deletions(-)
diff --git a/gdb/event-top.c b/gdb/event-top.c
index 35664312f42..74960c8ed3c 100644
--- a/gdb/event-top.c
+++ b/gdb/event-top.c
@@ -863,19 +863,6 @@ gdb_readline_no_editing_callback (gdb_client_data client_data)
FILE *stream = ui->instream != nullptr ? ui->instream : ui->stdin_stream;
gdb_assert (stream != nullptr);
- /* Unbuffer the input stream, so that, later on, the calls to fgetc
- fetch only one char at the time from the stream. The fgetc's will
- get up to the first newline, but there may be more chars in the
- stream after '\n'. If we buffer the input and fgetc drains the
- stream, getting stuff beyond the newline as well, a select, done
- afterwards will not trigger.
-
- This unbuffering was, at one point, not applied if the input stream
- was a tty, however, the buffering can cause problems, even for a tty,
- in some cases. Please ensure that any changes in this area run the MI
- tests with the FORCE_SEPARATE_MI_TTY=1 flag being passed. */
- setbuf (stream, NULL);
-
/* We still need the while loop here, even though it would seem
obvious to invoke gdb_readline_no_editing_callback at every
character entered. If not using the readline library, the
diff --git a/gdb/top.c b/gdb/top.c
index 73cb389a141..86c9971fa6d 100644
--- a/gdb/top.c
+++ b/gdb/top.c
@@ -257,6 +257,41 @@ void (*deprecated_context_hook) (int id);
/* The highest UI number ever assigned. */
static int highest_ui_num;
+/* Unbuffer STREAM. This is a wrapper around setbuf(STREAM, nullptr)
+ which applies some special rules for MS-Windows hosts. */
+
+static void
+unbuffer_stream (FILE *stream)
+{
+ /* Unbuffer the input stream so that in gdb_readline_no_editing_callback,
+ the calls to fgetc fetch only one char at the time from STREAM.
+
+ This is important because gdb_readline_no_editing_callback will read
+ from STREAM up to the first '\n' character, after this GDB returns to
+ the event loop and relies on a select on STREAM indicating that more
+ input is pending.
+
+ If STREAM is buffered then the fgetc calls may have moved all the
+ pending input from the kernel into a local buffer, after which the
+ select will not indicate that more input is pending, and input after
+ the first '\n' will not be processed immediately.
+
+ Please ensure that any changes in this area run the MI tests with the
+ FORCE_SEPARATE_MI_TTY=1 flag being passed. */
+
+#ifdef __MINGW32__
+ /* With MS-Windows runtime, making stdin unbuffered when it's
+ connected to the terminal causes it to misbehave. */
+ if (!ISATTY (stream))
+ setbuf (stream, nullptr);
+#else
+ /* On GNU/Linux the issues described above can impact GDB even when
+ dealing with input from a terminal. For now we unbuffer the input
+ stream for everyone except MS-Windows. */
+ setbuf (stream, nullptr);
+#endif
+}
+
/* See top.h. */
ui::ui (FILE *instream_, FILE *outstream_, FILE *errstream_)
@@ -283,6 +318,8 @@ ui::ui (FILE *instream_, FILE *outstream_, FILE *errstream_)
{
buffer_init (&line_buffer);
+ unbuffer_stream (instream_);
+
if (ui_list == NULL)
ui_list = this;
else
@@ -412,6 +449,8 @@ read_command_file (FILE *stream)
{
struct ui *ui = current_ui;
+ unbuffer_stream (stream);
+
scoped_restore save_instream
= make_scoped_restore (&ui->instream, stream);
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