[PATCHv3,2/3] gdb/disasm: mark functions passed to the disassembler noexcept

Message ID 2513c776a59b7d7e1446a81c10157bc40e3e8ba3.1668790576.git.aburgess@redhat.com
State New
Headers
Series gdb/python: avoid throwing an exception over libopcodes code |

Commit Message

Andrew Burgess Nov. 18, 2022, 4:57 p.m. UTC
  While working on another patch, Simon pointed out that GDB could be
improved by marking the functions passed to the disassembler as
noexcept.

  https://sourceware.org/pipermail/gdb-patches/2022-October/193084.html

The reason this is important is the on some hosts, libopcodes, being C
code, will not be compiled with support for handling exceptions.  As
such, an attempt to throw an exception over libopcodes code will cause
GDB to terminate.

See bug gdb/29712 for an example of when this happened.

In this commit all the functions that are passed to the disassembler,
and which might be used as callbacks by libopcodes are marked
noexcept.

Ideally, I would have liked to change these typedefs:

  using read_memory_ftype = decltype (disassemble_info::read_memory_func);
  using memory_error_ftype = decltype (disassemble_info::memory_error_func);
  using print_address_ftype = decltype (disassemble_info::print_address_func);
  using fprintf_ftype = decltype (disassemble_info::fprintf_func);
  using fprintf_styled_ftype = decltype (disassemble_info::fprintf_styled_func);

which are declared in disasm.h, as including the noexcept keyword.
However, when I tried this, I ran into this warning/error:

  In file included from ../../src/gdb/disasm.c:25:
  ../../src/gdb/disasm.h: In constructor ‘gdb_printing_disassembler::gdb_printing_disassembler(gdbarch*, ui_file*, gdb_disassemble_info::read_memory_ftype, gdb_disassemble_info::memory_error_ftype, gdb_disassemble_info::print_address_ftype)’:
  ../../src/gdb/disasm.h:116:3: error: mangled name for ‘gdb_printing_disassembler::gdb_printing_disassembler(gdbarch*, ui_file*, gdb_disassemble_info::read_memory_ftype, gdb_disassemble_info::memory_error_ftype, gdb_disassemble_info::print_address_ftype)’ will change in C++17 because the exception specification is part of a function type [-Werror=noexcept-type]
    116 |   gdb_printing_disassembler (struct gdbarch *gdbarch,
        |   ^~~~~~~~~~~~~~~~~~~~~~~~~

So I've left that change out.  This does mean that if somebody adds a
new use of the disassembler classes in the future, and forgets to mark
the callbacks as noexcept, this will compile fine.  We'll just have to
manually check for that during review.
---
 gdb/disasm-selftests.c |  5 +++--
 gdb/disasm.c           | 25 +++++++++++++------------
 gdb/disasm.h           | 22 ++++++++++++++--------
 gdb/guile/scm-disasm.c |  2 +-
 gdb/python/py-disasm.c | 12 ++++++------
 5 files changed, 37 insertions(+), 29 deletions(-)
  

Patch

diff --git a/gdb/disasm-selftests.c b/gdb/disasm-selftests.c
index db2d1e0ac59..10df1a1980d 100644
--- a/gdb/disasm-selftests.c
+++ b/gdb/disasm-selftests.c
@@ -234,7 +234,8 @@  print_one_insn_test (struct gdbarch *gdbarch)
     size_t m_len;
 
     static int read_memory (bfd_vma memaddr, gdb_byte *myaddr,
-			    unsigned int len, struct disassemble_info *info)
+			    unsigned int len,
+			    struct disassemble_info *info) noexcept
     {
       gdb_disassembler_test *self
 	= static_cast<gdb_disassembler_test *>(info->application_data);
@@ -296,7 +297,7 @@  memory_error_test (struct gdbarch *gdbarch)
 
     static int read_memory (bfd_vma memaddr, gdb_byte *myaddr,
 			    unsigned int len,
-			    struct disassemble_info *info)
+			    struct disassemble_info *info) noexcept
     {
       /* Always return an error.  */
       return -1;
diff --git a/gdb/disasm.c b/gdb/disasm.c
index 60f95c398a9..e64cf69b250 100644
--- a/gdb/disasm.c
+++ b/gdb/disasm.c
@@ -191,7 +191,7 @@  line_has_code_p (htab_t table, struct symtab *symtab, int line)
 int
 gdb_disassembler_memory_reader::dis_asm_read_memory
   (bfd_vma memaddr, gdb_byte *myaddr, unsigned int len,
-   struct disassemble_info *info)
+   struct disassemble_info *info) noexcept
 {
   return target_read_code (memaddr, myaddr, len);
 }
@@ -199,8 +199,8 @@  gdb_disassembler_memory_reader::dis_asm_read_memory
 /* Wrapper of memory_error.  */
 
 void
-gdb_disassembler::dis_asm_memory_error (int err, bfd_vma memaddr,
-					struct disassemble_info *info)
+gdb_disassembler::dis_asm_memory_error
+  (int err, bfd_vma memaddr, struct disassemble_info *info) noexcept
 {
   gdb_disassembler *self
     = static_cast<gdb_disassembler *>(info->application_data);
@@ -211,8 +211,8 @@  gdb_disassembler::dis_asm_memory_error (int err, bfd_vma memaddr,
 /* Wrapper of print_address.  */
 
 void
-gdb_disassembler::dis_asm_print_address (bfd_vma addr,
-					 struct disassemble_info *info)
+gdb_disassembler::dis_asm_print_address
+  (bfd_vma addr, struct disassemble_info *info) noexcept
 {
   gdb_disassembler *self
     = static_cast<gdb_disassembler *>(info->application_data);
@@ -256,7 +256,7 @@  gdb_printing_disassembler::stream_from_gdb_disassemble_info (void *dis_info)
 
 int
 gdb_printing_disassembler::fprintf_func (void *dis_info,
-					 const char *format, ...)
+					 const char *format, ...) noexcept
 {
   ui_file *stream = stream_from_gdb_disassemble_info (dis_info);
 
@@ -272,9 +272,9 @@  gdb_printing_disassembler::fprintf_func (void *dis_info,
 /* See disasm.h.  */
 
 int
-gdb_printing_disassembler::fprintf_styled_func (void *dis_info,
-						enum disassembler_style style,
-						const char *format, ...)
+gdb_printing_disassembler::fprintf_styled_func
+  (void *dis_info, enum disassembler_style style,
+   const char *format, ...) noexcept
 {
   ui_file *stream = stream_from_gdb_disassemble_info (dis_info);
   gdb_printing_disassembler *dis = (gdb_printing_disassembler *) dis_info;
@@ -1220,8 +1220,8 @@  gdb_insn_length (struct gdbarch *gdbarch, CORE_ADDR addr)
 /* See disasm.h.  */
 
 int
-gdb_non_printing_disassembler::null_fprintf_func (void *stream,
-						  const char *format, ...)
+gdb_non_printing_disassembler::null_fprintf_func
+  (void *stream, const char *format, ...) noexcept
 {
   return 0;
 }
@@ -1230,7 +1230,8 @@  gdb_non_printing_disassembler::null_fprintf_func (void *stream,
 
 int
 gdb_non_printing_disassembler::null_fprintf_styled_func
-  (void *stream, enum disassembler_style style, const char *format, ...)
+  (void *stream, enum disassembler_style style,
+   const char *format, ...) noexcept
 {
   return 0;
 }
diff --git a/gdb/disasm.h b/gdb/disasm.h
index b7d16744c20..58c6c623098 100644
--- a/gdb/disasm.h
+++ b/gdb/disasm.h
@@ -51,7 +51,13 @@  struct gdb_disassemble_info
 
 protected:
 
-  /* Types for the function callbacks within m_di.  */
+  /* Types for the function callbacks within m_di.  It would be nice if
+     these function types were all defined to include the noexcept
+     keyword, as every implementation of these must be noexcept.  However,
+     using noexcept within a function typedef like this is a C++17
+     feature, trying to do this for earlier C++ versions results in a
+     warning from GCC/Clang, and the noexcept isn't checked.  After we
+     move to C++17 these should be updated to add noexcept.  */
   using read_memory_ftype = decltype (disassemble_info::read_memory_func);
   using memory_error_ftype = decltype (disassemble_info::memory_error_func);
   using print_address_ftype = decltype (disassemble_info::print_address_func);
@@ -127,7 +133,7 @@  struct gdb_printing_disassembler : public gdb_disassemble_info
   /* Callback used as the disassemble_info's fprintf_func callback.  The
      DIS_INFO pointer is a pointer to a gdb_printing_disassembler object.
      Content is written to the m_stream extracted from DIS_INFO.  */
-  static int fprintf_func (void *dis_info, const char *format, ...)
+  static int fprintf_func (void *dis_info, const char *format, ...) noexcept
     ATTRIBUTE_PRINTF(2,3);
 
   /* Callback used as the disassemble_info's fprintf_styled_func callback.
@@ -135,7 +141,7 @@  struct gdb_printing_disassembler : public gdb_disassemble_info
      object.  Content is written to the m_stream extracted from DIS_INFO.  */
   static int fprintf_styled_func (void *dis_info,
 				  enum disassembler_style style,
-				  const char *format, ...)
+				  const char *format, ...) noexcept
     ATTRIBUTE_PRINTF(3,4);
 
   /* Return true if the disassembler is considered inside a comment, false
@@ -187,14 +193,14 @@  struct gdb_non_printing_disassembler : public gdb_disassemble_info
 
   /* Callback used as the disassemble_info's fprintf_func callback, this
      doesn't write anything to STREAM, but just returns 0.  */
-  static int null_fprintf_func (void *stream, const char *format, ...)
+  static int null_fprintf_func (void *stream, const char *format, ...) noexcept
     ATTRIBUTE_PRINTF(2,3);
 
   /* Callback used as the disassemble_info's fprintf_styled_func callback,
      , this doesn't write anything to STREAM, but just returns 0.  */
   static int null_fprintf_styled_func (void *stream,
 				       enum disassembler_style style,
-				       const char *format, ...)
+				       const char *format, ...) noexcept
     ATTRIBUTE_PRINTF(3,4);
 };
 
@@ -208,7 +214,7 @@  struct gdb_disassembler_memory_reader
   /* Implements the read_memory_func disassemble_info callback.  */
   static int dis_asm_read_memory (bfd_vma memaddr, gdb_byte *myaddr,
 				  unsigned int len,
-				  struct disassemble_info *info);
+				  struct disassemble_info *info) noexcept;
 };
 
 /* A non-printing disassemble_info management class.  The disassemble_info
@@ -281,9 +287,9 @@  struct gdb_disassembler : public gdb_printing_disassembler,
   static bool use_ext_lang_colorization_p;
 
   static void dis_asm_memory_error (int err, bfd_vma memaddr,
-				    struct disassemble_info *info);
+				    struct disassemble_info *info) noexcept;
   static void dis_asm_print_address (bfd_vma addr,
-				     struct disassemble_info *info);
+				     struct disassemble_info *info) noexcept;
 
   /* Return true if we should use the extension language to apply
      disassembler styling.  This requires disassembler styling to be on
diff --git a/gdb/guile/scm-disasm.c b/gdb/guile/scm-disasm.c
index 992a64b9331..c0957559136 100644
--- a/gdb/guile/scm-disasm.c
+++ b/gdb/guile/scm-disasm.c
@@ -106,7 +106,7 @@  gdbscm_disasm_read_memory_worker (void *datap)
 static int
 gdbscm_disasm_read_memory (bfd_vma memaddr, bfd_byte *myaddr,
 			   unsigned int length,
-			   struct disassemble_info *dinfo)
+			   struct disassemble_info *dinfo) noexcept
 {
   gdbscm_disassembler *self
     = static_cast<gdbscm_disassembler *> (dinfo->application_data);
diff --git a/gdb/python/py-disasm.c b/gdb/python/py-disasm.c
index 1d460997831..a25252b4306 100644
--- a/gdb/python/py-disasm.c
+++ b/gdb/python/py-disasm.c
@@ -101,12 +101,12 @@  struct gdbpy_disassembler : public gdb_printing_disassembler
 
   /* Callbacks used by disassemble_info.  */
   static void memory_error_func (int status, bfd_vma memaddr,
-				 struct disassemble_info *info);
+				 struct disassemble_info *info) noexcept;
   static void print_address_func (bfd_vma addr,
-				  struct disassemble_info *info);
+				  struct disassemble_info *info) noexcept;
   static int read_memory_func (bfd_vma memaddr, gdb_byte *buff,
 			       unsigned int len,
-			       struct disassemble_info *info);
+			       struct disassemble_info *info) noexcept;
 
   /* Return a reference to an optional that contains the address at which a
      memory error occurred.  The optional will only have a value if a
@@ -513,7 +513,7 @@  disasmpy_info_progspace (PyObject *self, void *closure)
 int
 gdbpy_disassembler::read_memory_func (bfd_vma memaddr, gdb_byte *buff,
 				      unsigned int len,
-				      struct disassemble_info *info)
+				      struct disassemble_info *info) noexcept
 {
   gdbpy_disassembler *dis
     = static_cast<gdbpy_disassembler *> (info->application_data);
@@ -658,7 +658,7 @@  disasmpy_result_init (PyObject *self, PyObject *args, PyObject *kwargs)
 
 void
 gdbpy_disassembler::memory_error_func (int status, bfd_vma memaddr,
-				       struct disassemble_info *info)
+				       struct disassemble_info *info) noexcept
 {
   gdbpy_disassembler *dis
     = static_cast<gdbpy_disassembler *> (info->application_data);
@@ -669,7 +669,7 @@  gdbpy_disassembler::memory_error_func (int status, bfd_vma memaddr,
 
 void
 gdbpy_disassembler::print_address_func (bfd_vma addr,
-					struct disassemble_info *info)
+					struct disassemble_info *info) noexcept
 {
   gdbpy_disassembler *dis
     = static_cast<gdbpy_disassembler *> (info->application_data);