[binutils-gdb] Introduce gdb_exception_forced_quit

[binutils-gdb] Introduce gdb_exception_forced_quit

[Kevin Buettner]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=522044dc5fa76f9fef70fe746274daf09bbf64fe

commit 522044dc5fa76f9fef70fe746274daf09bbf64fe
Author: Kevin Buettner <kevinb@redhat.com>
Date:   Mon Feb 27 16:11:37 2023 -0700

    Introduce gdb_exception_forced_quit
    
    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.
    
    Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=26761
    Tested-by: Tom de Vries <tdevries@suse.de>
    Approved-by: Pedro Alves <pedro@palves.net>

Diff:
---
 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 */