Re: [PATCH v4 1/8] Introduce gdb_exception_forced_quit

Pedro Alves
2023-01-30T18:57:14Z

On 2023-01-12 1:56 a.m., Kevin Buettner wrote:
> This commit adds a new exception 'gdb_exception_forced_quit', reason
> code 'REASON_FORCED_QUIT', return mask 'RETURN_MASK_FORCED_QUIT', and
> a wrapper for throwing the exception, throw_forced_quit().
>
> The addition of this exception plus supporting code will allow us to
> recognize that a SIGTERM has been received by GDB and then propagate
> recognition of that fact to the upper levels of GDB where it can be
> correctly handled. At the moment, when GDB receives a SIGTERM, it
> will attempt to exit via a series of calls from the QUIT checking
> code. However, before it can exit, it must do various cleanups, such
> as killing or detaching all inferiors. Should these cleanups be
> attempted while GDB is executing very low level code, such as reading
> target memory from within ps_xfer_memory(), it can happen that some of
> GDB's state is out of sync with regard to the cleanup code's
> expectations. In the case just mentioned, it's been observed that
> inferior_ptid and the current_thread_ are not in sync; this triggers
> an assert / internal error.
>
> This commit only introduces the exception plus supporting machinery;
> changes which use this new exception are in later commits in this
> series.

OK.

>
> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=26761
> ---
> gdbsupport/common-exceptions.cc | 14 ++++++++++++++
> gdbsupport/common-exceptions.h | 22 +++++++++++++++++++++-
> 2 files changed, 35 insertions(+), 1 deletion(-)
>
> diff --git a/gdbsupport/common-exceptions.cc b/gdbsupport/common-exceptions.cc
> index d0dd8081c41..edc1b56181a 100644
> --- a/gdbsupport/common-exceptions.cc
> +++ b/gdbsupport/common-exceptions.cc
> @@ -184,6 +184,8 @@ throw_exception (gdb_exception &&exception)
> {
> if (exception.reason == RETURN_QUIT)
> throw gdb_exception_quit (std::move (exception));
> + else if (exception.reason == RETURN_FORCED_QUIT)
> + throw gdb_exception_forced_quit (std::move (exception));
> else if (exception.reason == RETURN_ERROR)
> throw gdb_exception_error (std::move (exception));
> else
> @@ -196,6 +198,8 @@ throw_it (enum return_reason reason, enum errors error, const char *fmt,
> {
> if (reason == RETURN_QUIT)
> throw gdb_exception_quit (fmt, ap);
> + else if (reason == RETURN_FORCED_QUIT)
> + throw gdb_exception_forced_quit (fmt, ap);
> else if (reason == RETURN_ERROR)
> throw gdb_exception_error (error, fmt, ap);
> else
> @@ -233,3 +237,13 @@ throw_quit (const char *fmt, ...)
> throw_vquit (fmt, args);
> va_end (args);
> }
> +
> +void
> +throw_forced_quit (const char *fmt, ...)
> +{
> + va_list args;
> +
> + va_start (args, fmt);
> + throw_it (RETURN_FORCED_QUIT, GDB_NO_ERROR, fmt, args);
> + va_end (args);
> +}
> diff --git a/gdbsupport/common-exceptions.h b/gdbsupport/common-exceptions.h
> index a2a4f5a3892..f9b59ece736 100644
> --- a/gdbsupport/common-exceptions.h
> +++ b/gdbsupport/common-exceptions.h
> @@ -32,6 +32,8 @@
>
> enum return_reason
> {
> + /* SIGTERM sent to GDB. */
> + RETURN_FORCED_QUIT = -3,
> /* User interrupt. */
> RETURN_QUIT = -2,
> /* Any other error. */
> @@ -42,9 +44,10 @@ enum return_reason
>
> typedef enum
> {
> + RETURN_MASK_FORCED_QUIT = RETURN_MASK (RETURN_FORCED_QUIT),
> RETURN_MASK_QUIT = RETURN_MASK (RETURN_QUIT),
> RETURN_MASK_ERROR = RETURN_MASK (RETURN_ERROR),
> - RETURN_MASK_ALL = (RETURN_MASK_QUIT | RETURN_MASK_ERROR)
> + RETURN_MASK_ALL = (RETURN_MASK_FORCED_QUIT | RETURN_MASK_QUIT | RETURN_MASK_ERROR)
> } return_mask;
>
> /* Describe all exceptions. */
> @@ -294,6 +297,21 @@ struct gdb_exception_quit : public gdb_exception
> }
> };
>
> +struct gdb_exception_forced_quit : public gdb_exception
> +{
> + gdb_exception_forced_quit (const char *fmt, va_list ap)
> + ATTRIBUTE_PRINTF (2, 0)
> + : gdb_exception (RETURN_FORCED_QUIT, GDB_NO_ERROR, fmt, ap)
> + {
> + }
> +
> + explicit gdb_exception_forced_quit (gdb_exception &&ex) noexcept
> + : gdb_exception (std::move (ex))
> + {
> + gdb_assert (ex.reason == RETURN_FORCED_QUIT);
> + }
> +};
> +
> /* An exception type that inherits from both std::bad_alloc and a gdb
> exception. This is necessary because operator new can only throw
> std::bad_alloc, and OTOH, we want exceptions thrown due to memory
> @@ -336,5 +354,7 @@ extern void throw_error (enum errors error, const char *fmt, ...)
> ATTRIBUTE_NORETURN ATTRIBUTE_PRINTF (2, 3);
> extern void throw_quit (const char *fmt, ...)
> ATTRIBUTE_NORETURN ATTRIBUTE_PRINTF (1, 2);
> +extern void throw_forced_quit (const char *fmt, ...)
> + ATTRIBUTE_NORETURN ATTRIBUTE_PRINTF (1, 2);
>
> #endif /* COMMON_COMMON_EXCEPTIONS_H */
>