[gdb] Handle ^C during disassembly

In PR gdb/32025, a fatal error was reported when sending a SIGINT to gdb while
disassembling.

I managed to reproduce this on aarch64-linux in a Leap 15.5 container using
this trigger patch:
...
 gdb_disassembler_memory_reader::dis_asm_read_memory
   (bfd_vma memaddr, gdb_byte *myaddr, unsigned int len,
    struct disassemble_info *info) noexcept
 {
+  set_quit_flag ();
   return target_read_code (memaddr, myaddr, len);
 }
...
and a simple gdb command line calling the disassemble command:
...
$ gdb -q -batch a.out -ex "disassemble main"
...

The following scenario leads to the fatal error:
- the disassemble command is executed,
- set_quit_flag is called in
  gdb_disassembler_memory_reader::dis_asm_read_memory, pretending that a
  user pressed ^C,
- target_read_code calls QUIT, which throws a
  gdb_exception_quit,
- the exception propagation mechanism reaches c code in libopcodes and a fatal
  error triggers because the c code is not compiled with -fexception.

Fix this by:
- wrapping the body of gdb_disassembler_memory_reader::dis_asm_read_memory in
  catch_exceptions (which consequently needs moving to a header file), and
- reraising the caught exception in default_print_insn using QUIT.

Tested on aarch64-linux.

Approved-By: Andrew Burgess <aburgess@redhat.com>

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=32025

1 files changed, 6 insertions, 1 deletions

diff --git a/gdb/arch-utils.c b/gdb/arch-utils.c
index 13984eb..3247c36 100644
--- a/gdb/arch-utils.c
+++ b/gdb/arch-utils.c
@@ -37,6 +37,7 @@
 #include "auxv.h"
 #include "observable.h"
 #include "solib-target.h"
+#include "event-top.h"
 
 #include "gdbsupport/version.h"
 
@@ -1040,7 +1041,11 @@ default_print_insn (bfd_vma memaddr, disassemble_info *info)
 				 info->mach, current_program_space->exec_bfd ());
 
   gdb_assert (disassemble_fn != NULL);
-  return (*disassemble_fn) (memaddr, info);
+  int res = (*disassemble_fn) (memaddr, info);
+
+  QUIT;
+
+  return res;
 }
 
 /* See arch-utils.h.  */