From 7c4e78cf63f6436ae43e8289badba78d81e2eb2c Mon Sep 17 00:00:00 2001 From: Simon Marchi Date: Sat, 7 Apr 2018 13:48:05 -0400 Subject: 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) : 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/utils.h | 3 +++ 1 file changed, 3 insertions(+) (limited to 'gdb/utils.h') diff --git a/gdb/utils.h b/gdb/utils.h index 9a1fb34..4dec889 100644 --- a/gdb/utils.h +++ b/gdb/utils.h @@ -418,7 +418,10 @@ 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. */ -- cgit v1.1