gdb/disasm: mark functions passed to the disassembler noexcept

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.

1 files changed, 13 insertions, 12 deletions

diff --git a/gdb/disasm.c b/gdb/disasm.c
index 60f95c3..e64cf69 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;
 }