[PATCH] Implement write_async_safe for mi_console_file (PR 22299)
Simon Marchi
simon.marchi@polymtl.ca
Sat Mar 24 19:10:00 GMT 2018
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.
---
gdb/mi/mi-console.c | 33 +++++++++++++++++++++++++++++++--
gdb/mi/mi-console.h | 2 ++
gdb/ui-file.c | 2 +-
gdb/utils.c | 50 +++++++++++++++++++++++++-------------------------
gdb/utils.h | 3 +++
5 files changed, 62 insertions(+), 28 deletions(-)
diff --git a/gdb/mi/mi-console.c b/gdb/mi/mi-console.c
index 43d5388cd07c..248d070f1831 100644
--- a/gdb/mi/mi-console.c
+++ b/gdb/mi/mi-console.c
@@ -48,6 +48,34 @@ mi_console_file::write (const char *buf, long length_buf)
this->flush ();
}
+/* Write C to STREAM's in an async-safe way. */
+
+static int
+do_fputc_async_safe (int c, ui_file *stream)
+{
+ char ch = c;
+ stream->write_async_safe (&ch, 1);
+ return c;
+}
+
+void
+mi_console_file::write_async_safe (const char *buf, long length_buf)
+{
+ m_raw->write_async_safe (m_prefix, strlen (m_prefix));
+ if (m_quote)
+ {
+ m_raw->write_async_safe (&m_quote, 1);
+ fputstrn_unfiltered (buf, length_buf, m_quote, do_fputc_async_safe,
+ m_raw);
+ m_raw->write_async_safe (&m_quote, 1);
+ }
+ else
+ fputstrn_unfiltered (buf, length_buf, 0, do_fputc_async_safe, m_raw);
+
+ char nl = '\n';
+ m_raw->write_async_safe (&nl, 1);
+}
+
void
mi_console_file::flush ()
{
@@ -63,13 +91,14 @@ mi_console_file::flush ()
if (m_quote)
{
fputc_unfiltered (m_quote, m_raw);
- fputstrn_unfiltered (buf, length_buf, m_quote, m_raw);
+ fputstrn_unfiltered (buf, length_buf, m_quote, fputc_unfiltered,
+ m_raw);
fputc_unfiltered (m_quote, m_raw);
fputc_unfiltered ('\n', m_raw);
}
else
{
- fputstrn_unfiltered (buf, length_buf, 0, m_raw);
+ fputstrn_unfiltered (buf, length_buf, 0, fputc_unfiltered, m_raw);
fputc_unfiltered ('\n', m_raw);
}
gdb_flush (m_raw);
diff --git a/gdb/mi/mi-console.h b/gdb/mi/mi-console.h
index fbfa03b8e1ed..d98a0c80f265 100644
--- a/gdb/mi/mi-console.h
+++ b/gdb/mi/mi-console.h
@@ -39,6 +39,8 @@ public:
void write (const char *buf, long length_buf) override;
+ void write_async_safe (const char *buf, long length_buf) override;
+
private:
/* The wrapped raw output stream. */
ui_file *m_raw;
diff --git a/gdb/ui-file.c b/gdb/ui-file.c
index 84ad6031a484..17515097563e 100644
--- a/gdb/ui-file.c
+++ b/gdb/ui-file.c
@@ -52,7 +52,7 @@ ui_file::putstr (const char *str, int quoter)
void
ui_file::putstrn (const char *str, int n, int quoter)
{
- fputstrn_unfiltered (str, n, quoter, this);
+ fputstrn_unfiltered (str, n, quoter, fputc_unfiltered, this);
}
int
diff --git a/gdb/utils.c b/gdb/utils.c
index 3886efd840f3..0379e0532b90 100644
--- a/gdb/utils.c
+++ b/gdb/utils.c
@@ -1188,9 +1188,7 @@ parse_escape (struct gdbarch *gdbarch, const char **string_ptr)
character. */
static void
-printchar (int c, void (*do_fputs) (const char *, struct ui_file *),
- void (*do_fprintf) (struct ui_file *, const char *, ...)
- ATTRIBUTE_FPTR_PRINTF_2, struct ui_file *stream, int quoter)
+printchar (int c, do_fputc_ftype do_fputc, ui_file *stream, int quoter)
{
c &= 0xFF; /* Avoid sign bit follies */
@@ -1198,39 +1196,45 @@ printchar (int c, void (*do_fputs) (const char *, struct ui_file *),
(c >= 0x7F && c < 0xA0) || /* DEL, High controls */
(sevenbit_strings && c >= 0x80))
{ /* high order bit set */
+ do_fputc ('\\', stream);
+
switch (c)
{
case '\n':
- do_fputs ("\\n", stream);
+ do_fputc ('n', stream);
break;
case '\b':
- do_fputs ("\\b", stream);
+ do_fputc ('b', stream);
break;
case '\t':
- do_fputs ("\\t", stream);
+ do_fputc ('t', stream);
break;
case '\f':
- do_fputs ("\\f", stream);
+ do_fputc ('f', stream);
break;
case '\r':
- do_fputs ("\\r", stream);
+ do_fputc ('r', stream);
break;
case '\033':
- do_fputs ("\\e", stream);
+ do_fputc ('e', stream);
break;
case '\007':
- do_fputs ("\\a", stream);
+ do_fputc ('a', stream);
break;
default:
- do_fprintf (stream, "\\%.3o", (unsigned int) c);
- break;
+ {
+ do_fputc ('0' + ((c >> 6) & 0x7), stream);
+ do_fputc ('0' + ((c >> 3) & 0x7), stream);
+ do_fputc ('0' + ((c >> 0) & 0x7), stream);
+ break;
+ }
}
}
else
{
if (quoter != 0 && (c == '\\' || c == quoter))
- do_fputs ("\\", stream);
- do_fprintf (stream, "%c", c);
+ do_fputc ('\\', stream);
+ do_fputc (c, stream);
}
}
@@ -1243,34 +1247,30 @@ void
fputstr_filtered (const char *str, int quoter, struct ui_file *stream)
{
while (*str)
- printchar (*str++, fputs_filtered, fprintf_filtered, stream, quoter);
+ printchar (*str++, fputc_filtered, stream, quoter);
}
void
fputstr_unfiltered (const char *str, int quoter, struct ui_file *stream)
{
while (*str)
- printchar (*str++, fputs_unfiltered, fprintf_unfiltered, stream, quoter);
+ printchar (*str++, fputc_unfiltered, stream, quoter);
}
void
fputstrn_filtered (const char *str, int n, int quoter,
struct ui_file *stream)
{
- int i;
-
- for (i = 0; i < n; i++)
- printchar (str[i], fputs_filtered, fprintf_filtered, stream, quoter);
+ for (int i = 0; i < n; i++)
+ printchar (str[i], fputc_filtered, stream, quoter);
}
void
fputstrn_unfiltered (const char *str, int n, int quoter,
- struct ui_file *stream)
+ do_fputc_ftype do_fputc, struct ui_file *stream)
{
- int i;
-
- for (i = 0; i < n; i++)
- printchar (str[i], fputs_unfiltered, fprintf_unfiltered, stream, quoter);
+ for (int i = 0; i < n; i++)
+ printchar (str[i], do_fputc, stream, quoter);
}
diff --git a/gdb/utils.h b/gdb/utils.h
index 6ff18568fee7..e96f40c0c64e 100644
--- a/gdb/utils.h
+++ b/gdb/utils.h
@@ -415,7 +415,10 @@ extern void fputstr_unfiltered (const char *str, int quotr,
extern void fputstrn_filtered (const char *str, int n, int quotr,
struct ui_file * stream);
+typedef int (*do_fputc_ftype) (int c, ui_file *stream);
+
extern void fputstrn_unfiltered (const char *str, int n, int quotr,
+ do_fputc_ftype do_fputc,
struct ui_file * stream);
/* Return nonzero if filtered printing is initialized. */
--
2.16.2
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