Adjust byte order variable display/change if DW_AT_endianity is present.

  - Rationale:
It is possible for compilers to indicate the desired byte order
interpretation of scalar variables using the DWARF attribute:
   DW_AT_endianity

A type flagged with this variable would typically use one of:
   DW_END_big
   DW_END_little
which instructs the debugger what the desired byte order interpretation
of the variable should be.

The GCC compiler (as of V6) has a mechanism for setting the desired byte
ordering of the fields within a structure or union.  For, example, on a
little endian target, a structure declared as:
   struct big {
       int v;
       short a[4];
   } __attribute__( ( scalar_storage_order( "big-endian" ) ) );
could be used to ensure all the structure members have a big-endian
interpretation (the compiler would automatically insert byte swap
instructions before and after respective store and load instructions).

- To reproduce
GCC V8+ is required to correctly emit DW_AT_endianity DWARF attributes
in all situations when the scalar_storage_order attribute is used.

A fix for (dwarf endianity instrumentation) for GCC V6-V7 can be found
in the URL field of the following PR:
   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82509

- Test-case:
A new test case (testsuite/gdb.base/endianity.*) is included with this
patch.

Manual testing for mixed endianity code has also been done with GCC V8.
See:
   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82509#c4

- Observed vs. expected:

Without this change, using scalar_storage_order that doesn't match the
target, such as

struct otherendian
{
  int v;
} __attribute__( ( scalar_storage_order( "big-endian" ) ) );

would behave like the following on a little endian target:

   Breakpoint 1 at 0x401135: file endianity.c, line 41.
   (gdb) run
   Starting program: /home/pjoot/freeware/t/a.out
   Missing separate debuginfos, use: debuginfo-install glibc-2.17-292.el7.x86_64

   Breakpoint 1, main () at endianity.c:41
   41        struct otherendian o = {3};
   (gdb) n
   43        do_nothing (&o); /* START */
   (gdb) p o
   $1 = {v = 50331648}
   (gdb) p /x
   $2 = {v = 0x3000000}

whereas with this gdb enhancement we can access the variable with the user
specified endianity:

   Breakpoint 1, main () at endianity.c:41
   41        struct otherendian o = {3};
   (gdb) p o
   $1 = {v = 0}
   (gdb) n
   43        do_nothing (&o); /* START */
   (gdb) p o
   $2 = {v = 3}
   (gdb) p o.v = 4
   $3 = 4
   (gdb) p o.v
   $4 = 4
   (gdb) x/4xb &o.v
   0x7fffffffd90c: 0x00    0x00    0x00    0x04

(observe that the 4 byte int variable has a big endian representation in the
 hex dump.)

- FSF copyright Assignment

I am contributing on behalf of my employer, LzLabs GbmH.  The FSF attribution documentation for binutils and gdb are both complete and signed back.

- Changelogs:

gdb/ChangeLog:

2019-11-14  Peeter Joot  <peeter.joot@lzlabs.com>

Byte reverse display of variables with DW_END_big, DW_END_little
(DW_AT_endianity) dwarf attributes if different than the native
byte order.
* ada-lang.c (ada_value_binop):
Use type_byte_order instead of gdbarch_byte_order.
* ada-valprint.c (printstr):
(ada_val_print_string):
Use type_byte_order instead of gdbarch_byte_order.
* c-lang.c (c_get_string):
Use type_byte_order instead of gdbarch_byte_order.
* c-valprint.c (c_val_print_array):
Use type_byte_order instead of gdbarch_byte_order.
* cp-valprint.c (cp_print_class_member):
Use type_byte_order instead of gdbarch_byte_order.
* dwarf2loc.c (rw_pieced_value):
Use type_byte_order instead of gdbarch_byte_order.
* dwarf2read.c (read_base_type): Handle DW_END_big,
DW_END_little
* f-lang.c (f_get_encoding):
Use type_byte_order instead of gdbarch_byte_order.
* findvar.c (default_read_var_value):
Use type_byte_order instead of gdbarch_byte_order.
* gdbtypes.c (check_types_equal):
Require matching TYPE_ENDIANITY_BIG, and
TYPE_ENDIANITY_LITTLE if set.
(recursive_dump_type): Print TYPE_ENDIANITY_BIG,
and TYPE_ENDIANITY_LITTLE if set.
(type_byte_order): new function.
* gdbtypes.h (TYPE_ENDIANITY_BIG, TYPE_ENDIANITY_LITTLE): New macro.
(struct main_type) <flag_endianity_big, flag_endianity_little>:
New field.
(type_byte_order): New function.
* infcmd.c (default_print_one_register_info):
Use type_byte_order instead of gdbarch_byte_order.
* p-lang.c (pascal_printstr):
Use type_byte_order instead of gdbarch_byte_order.
* p-valprint.c (pascal_val_print):
Use type_byte_order instead of gdbarch_byte_order.
* printcmd.c (print_scalar_formatted):
Use type_byte_order instead of gdbarch_byte_order.
* solib-darwin.c (darwin_current_sos):
Use type_byte_order instead of gdbarch_byte_order.
* solib-svr4.c (solib_svr4_r_ldsomap):
Use type_byte_order instead of gdbarch_byte_order.
* stap-probe.c (stap_modify_semaphore):
Use type_byte_order instead of gdbarch_byte_order.
* target-float.c (target_float_same_format_p):
Use type_byte_order instead of gdbarch_byte_order.
* valarith.c (scalar_binop):
Use type_byte_order instead of gdbarch_byte_order.
* valops.c (value_cast):
Use type_byte_order instead of gdbarch_byte_order.
* valprint.c (generic_emit_char):
(generic_printstr):
(val_print_string):
Use type_byte_order instead of gdbarch_byte_order.
* value.c (unpack_long):
(unpack_bits_as_long):
(unpack_value_bitfield):
(modify_field):
(pack_long):
(pack_unsigned_long):
Use type_byte_order instead of gdbarch_byte_order.

gdb/testsuite/ChangeLog:

2019-11-14  Peeter Joot  <peeter.joot@lzlabs.com>

* gdb.base/endianity.c: New test.
* gdb.base/endianity.exp: New file.
---
 gdb/ada-lang.c                       |  2 +-
 gdb/ada-valprint.c                   |  4 ++--
 gdb/c-lang.c                         |  2 +-
 gdb/c-valprint.c                     |  3 +--
 gdb/cp-valprint.c                    |  2 +-
 gdb/dwarf2loc.c                      |  2 +-
 gdb/dwarf2read.c                     | 18 +++++++++++----
 gdb/f-lang.c                         |  2 +-
 gdb/findvar.c                        |  2 +-
 gdb/gdbtypes.c                       | 21 +++++++++++++++++
 gdb/gdbtypes.h                       | 20 ++++++++++++++++
 gdb/infcmd.c                         |  2 +-
 gdb/p-lang.c                         |  2 +-
 gdb/p-valprint.c                     |  2 +-
 gdb/printcmd.c                       |  2 +-
 gdb/solib-darwin.c                   |  2 +-
 gdb/solib-svr4.c                     |  2 +-
 gdb/stap-probe.c                     |  7 +++---
 gdb/target-float.c                   |  6 ++---
 gdb/testsuite/gdb.base/endianity.c   | 44 ++++++++++++++++++++++++++++++++++++
 gdb/testsuite/gdb.base/endianity.exp | 38 +++++++++++++++++++++++++++++++
 gdb/valarith.c                       |  8 +++----
 gdb/valops.c                         |  2 +-
 gdb/valprint.c                       |  6 ++---
 gdb/value.c                          | 12 +++++-----
 25 files changed, 171 insertions(+), 42 deletions(-)
 create mode 100644 gdb/testsuite/gdb.base/endianity.c
 create mode 100644 gdb/testsuite/gdb.base/endianity.exp

--
2.9.1.200.gb1ec08f

Adjust byte order variable display/change if DW_AT_endianity is present.

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