gdb: error if /r and /b are used with disassemble command

The disassembler gained a new /b flag in this commit:

  commit d4ce49b7ac077a9882d6a5e689e260300045ca88
  Date:   Tue Jun 21 20:23:35 2022 +0100

      gdb: disassembler opcode display formatting

The /b and /r flags result in the instruction opcodes displayed in
different formats, so it's not possible to have both at the same
time.  Currently the /b flag overrides the /r flag.

We have a similar situation with the /m and /s flags, but here, if the
user tries to use both flags then they will get an error.

I think the error is clearer, so in this commit I propose that we add
an error if /r and /b are both used.

Obviously this change breaks backwards compatibility.  I don't have a
compelling argument for why we should make the change beyond my
feeling that it was a mistake not to add this error from the start,
and that the new behaviour is better.

Reviewed-By: Eli Zaretskii <eliz@gnu.org>

1 files changed, 14 insertions, 6 deletions

diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index db1a82e..2cd565e 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -10060,12 +10060,20 @@ This specialized command dumps a range of memory as machine
 instructions.  It can also print mixed source+disassembly by specifying
 the @code{/m} or @code{/s} modifier and print the raw instructions in
 hex as well as in symbolic form by specifying the @code{/r} or @code{/b}
-modifier.  The default memory range is the function surrounding the
-program counter of the selected frame.  A single argument to this
-command is a program counter value; @value{GDBN} dumps the function
-surrounding this value.  When two arguments are given, they should be
-separated by a comma, possibly surrounded by whitespace.  The arguments
-specify a range of addresses to dump, in one of two forms:
+modifier.
+
+Only one of @code{/m} and @code{/s} can be used, attempting to use
+both flag will give an error.
+
+Only one of @code{/r} and @code{/b} can be used, attempting to use
+both flag will give an error.
+
+The default memory range is the function surrounding the program
+counter of the selected frame.  A single argument to this command is a
+program counter value; @value{GDBN} dumps the function surrounding
+this value.  When two arguments are given, they should be separated by
+a comma, possibly surrounded by whitespace.  The arguments specify a
+range of addresses to dump, in one of two forms:
 
 @table @code
 @item @var{start},@var{end}