binutils-gdb/gdb/ui-file.c
Simon Marchi 7c4e78cf63 Implement write_async_safe for mi_console_file (PR 22299)
Enabling "set debug lin-lwp 1" with the MI interpreter doesn't work.
When the sigchld_handler function wants to print a debug output
("sigchld\n"), it uses ui_file_write_async_safe.  This ends up in the
default implementation of ui_file::write_async_safe, which aborts GDB.

This patch implements the write_async_safe method for mi_console_file.
The "normal" MI output is line buffered, which means the output
accumulates in m_buffer until a \n is written, at which point it's
flushed in m_raw.  The implementation of write_async_safe provided by
this patch bypasses this buffer and writes directly to m_raw.  There are
two reasons for this:

(1) Appending to m_buffer (therefore to an std::string) is probably not
    async-safe, as it may allocate memory.
(2) We may have a partial output already in m_buffer, so that would lead
    to some nested MI output, not so great.

There is probably still a chance to have bad MI output, if
sigchld_handler is invoked in the middle of mi_console_file's flush, and
the line being flushed is only partially sent to m_raw.  The solution
would probably be to block signals during flushing.  Since this is only
used for debug output, I don't know if it's worth the effort to do that.

To implement write_async_safe, I needed to use the fputstrn_unfiltered,
which does the necessary escaping (e.g. replace \n with \\n).  I started
by adding printchar's callback parameters to fputstrn_unfiltered, to be
able to pass async-safe versions of them.  It's not easy to provide an
async-safe version of do_fprintf, but it turns out that we can easily
replace printchar's callbacks with a single do_fputc quite easily.  The
async-safe version of do_fputc simply calls the underlying ui_file's
write_async_safe method.

gdb/ChangeLog:

	PR mi/22299
	* mi/mi-console.c (do_fputc_async_safe): New.
	(mi_console_file::write_async_safe): New.
	(mi_console_file::flush): Adjust calls to fputstrn_unfiltered.
	* mi/mi-console.h (class mi_console_file) <write_async_safe>:
	New.
	* ui-file.c (ui_file::putstrn): Adjust call to
	fputstrn_unfiltered.
	* utils.c (printchar): Replace do_fputs and do_fprintf
	parameters by do_fputc.
	(fputstr_filtered): Adjust call to printchar.
	(fputstr_unfiltered): Likewise.
	(fputstrn_filtered): Likewise.
	(fputstrn_unfiltered): Add do_fputc parameter, pass to
	printchar.
	* utils.h (do_fputc_ftype): New typedef.
	(fputstrn_unfiltered): Add do_fputc parameter.
2018-04-07 13:48:06 -04:00

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/* UI_FILE - a generic STDIO like output stream.
Copyright (C) 1999-2018 Free Software Foundation, Inc.
This file is part of GDB.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
/* Implement the ``struct ui_file'' object. */
#include "defs.h"
#include "ui-file.h"
#include "gdb_obstack.h"
#include "gdb_select.h"
#include "filestuff.h"
null_file null_stream;
ui_file::ui_file ()
{}
ui_file::~ui_file ()
{}
void
ui_file::printf (const char *format, ...)
{
va_list args;
va_start (args, format);
vfprintf_unfiltered (this, format, args);
va_end (args);
}
void
ui_file::putstr (const char *str, int quoter)
{
fputstr_unfiltered (str, quoter, this);
}
void
ui_file::putstrn (const char *str, int n, int quoter)
{
fputstrn_unfiltered (str, n, quoter, fputc_unfiltered, this);
}
int
ui_file::putc (int c)
{
return fputc_unfiltered (c, this);
}
void
ui_file::vprintf (const char *format, va_list args)
{
vfprintf_unfiltered (this, format, args);
}
void
null_file::write (const char *buf, long sizeof_buf)
{
/* Discard the request. */
}
void
null_file::puts (const char *)
{
/* Discard the request. */
}
void
null_file::write_async_safe (const char *buf, long sizeof_buf)
{
/* Discard the request. */
}
void
gdb_flush (struct ui_file *file)
{
file->flush ();
}
int
ui_file_isatty (struct ui_file *file)
{
return file->isatty ();
}
void
ui_file_write (struct ui_file *file,
const char *buf,
long length_buf)
{
file->write (buf, length_buf);
}
void
ui_file_write_async_safe (struct ui_file *file,
const char *buf,
long length_buf)
{
file->write_async_safe (buf, length_buf);
}
long
ui_file_read (struct ui_file *file, char *buf, long length_buf)
{
return file->read (buf, length_buf);
}
void
fputs_unfiltered (const char *buf, struct ui_file *file)
{
file->puts (buf);
}
string_file::~string_file ()
{}
void
string_file::write (const char *buf, long length_buf)
{
m_string.append (buf, length_buf);
}
stdio_file::stdio_file (FILE *file, bool close_p)
{
set_stream (file);
m_close_p = close_p;
}
stdio_file::stdio_file ()
: m_file (NULL),
m_fd (-1),
m_close_p (false)
{}
stdio_file::~stdio_file ()
{
if (m_close_p)
fclose (m_file);
}
void
stdio_file::set_stream (FILE *file)
{
m_file = file;
m_fd = fileno (file);
}
bool
stdio_file::open (const char *name, const char *mode)
{
/* Close the previous stream, if we own it. */
if (m_close_p)
{
fclose (m_file);
m_close_p = false;
}
gdb_file_up f = gdb_fopen_cloexec (name, mode);
if (f == NULL)
return false;
set_stream (f.release ());
m_close_p = true;
return true;
}
void
stdio_file::flush ()
{
fflush (m_file);
}
long
stdio_file::read (char *buf, long length_buf)
{
/* Wait until at least one byte of data is available, or we get
interrupted with Control-C. */
{
fd_set readfds;
FD_ZERO (&readfds);
FD_SET (m_fd, &readfds);
if (interruptible_select (m_fd + 1, &readfds, NULL, NULL, NULL) == -1)
return -1;
}
return ::read (m_fd, buf, length_buf);
}
void
stdio_file::write (const char *buf, long length_buf)
{
/* Calling error crashes when we are called from the exception framework. */
if (fwrite (buf, length_buf, 1, m_file))
{
/* Nothing. */
}
}
void
stdio_file::write_async_safe (const char *buf, long length_buf)
{
/* This is written the way it is to avoid a warning from gcc about not using the
result of write (since it can be declared with attribute warn_unused_result).
Alas casting to void doesn't work for this. */
if (::write (m_fd, buf, length_buf))
{
/* Nothing. */
}
}
void
stdio_file::puts (const char *linebuffer)
{
/* Calling error crashes when we are called from the exception framework. */
if (fputs (linebuffer, m_file))
{
/* Nothing. */
}
}
bool
stdio_file::isatty ()
{
return ::isatty (m_fd);
}
/* This is the implementation of ui_file method 'write' for stderr.
gdb_stdout is flushed before writing to gdb_stderr. */
void
stderr_file::write (const char *buf, long length_buf)
{
gdb_flush (gdb_stdout);
stdio_file::write (buf, length_buf);
}
/* This is the implementation of ui_file method 'puts' for stderr.
gdb_stdout is flushed before writing to gdb_stderr. */
void
stderr_file::puts (const char *linebuffer)
{
gdb_flush (gdb_stdout);
stdio_file::puts (linebuffer);
}
stderr_file::stderr_file (FILE *stream)
: stdio_file (stream)
{}
tee_file::tee_file (ui_file *one, bool close_one,
ui_file *two, bool close_two)
: m_one (one),
m_two (two),
m_close_one (close_one),
m_close_two (close_two)
{}
tee_file::~tee_file ()
{
if (m_close_one)
delete m_one;
if (m_close_two)
delete m_two;
}
void
tee_file::flush ()
{
m_one->flush ();
m_two->flush ();
}
void
tee_file::write (const char *buf, long length_buf)
{
m_one->write (buf, length_buf);
m_two->write (buf, length_buf);
}
void
tee_file::write_async_safe (const char *buf, long length_buf)
{
m_one->write_async_safe (buf, length_buf);
m_two->write_async_safe (buf, length_buf);
}
void
tee_file::puts (const char *linebuffer)
{
m_one->puts (linebuffer);
m_two->puts (linebuffer);
}
bool
tee_file::isatty ()
{
return m_one->isatty ();
}