How can I make gdb print unprintable characters of a string in hex instead of octal while preserving the ascii characters in ascii form?

Suppose I have a buffer buf whose c string representation is

 char* buf = "Hello World \x1c"

When I print this buf in gdb using the command p buf, I get the following

 $1 = "Hello World \034"

Is there a print command or a gdb setting that will print the following instead?

$1 = "Hello World \x1c"

I have tried various format parameters such as /c and /x, but none of them get the effect that I am looking for. I have also played with printf but was unable to achieve the desired effect.

Update: I am using "GNU gdb (GDB) 7.0.1-debian".

Update: I have played with x as well.

If I do x/c it prints octal and decimal for nonprintable characters, and then prints printable characters with the ascii and decimal.

If I do x/s it outputs exactly the same as the p command.

If I do x/x it just outputs hex but then we lose the ascii characters for the printable part.

Update: This reference, unless incomplete, suggests that what I desire is not available, but can anyone confirm?

Solution

In the absence of an existing solution, I created this gdb command which prints ascii and hex for strings that have mixed printable ascii and non-printable characters. The source is reproduced below.

    from __future__ import print_function
    
    import gdb
    import string
    class PrettyPrintString (gdb.Command):
        "Command to print strings with a mix of ascii and hex."
    
        def __init__(self):
            super (PrettyPrintString, self).__init__("ascii-print",
                    gdb.COMMAND_DATA,
                    gdb.COMPLETE_EXPRESSION, True)
            gdb.execute("alias -a pp = ascii-print", True)
    
        def invoke(self, arg, from_tty):
            arg = arg.strip()
            if arg == "":
                print("Argument required (starting display address).")
                return
            startingAddress = gdb.parse_and_eval(arg)
            p = 0
            print('"', end='')
            while startingAddress[p] != ord("\0"):
                charCode = int(startingAddress[p].cast(gdb.lookup_type("char")))
                if chr(charCode) in string.printable:
                    print("%c" % chr(charCode), end='')
                else:
                    print("\\x%x" % charCode, end='')
                p += 1
            print('"')
    
    PrettyPrintString()

To use this, one can simply put the source AsciiPrintCommand.py and then run the following in gdb. For convenience, one can put put the above source command into their $HOME/.gdbinit.

ascii-print buf
"Hello World \x1c"

Here are step-by-step instructions for gdb v12.1 on Ubuntu x64 22.04 LTS:

1 - Create a folder called ~/.config/gdb" 2 - In that folder create a text file called "AsciiPrintCommand.py".
3 - Copy this solutions source code into that file - Important remove all excess indentation from all lines (e.g. 1st line should read "from" and not " from"
4 - In that same folder create another file "gdbinit" containing... set output-radix 16
source ~/.config/gdb/AsciiPrintCommand.py
5 - run up gdb
6 - to test it worked type ---> ascii-print "hello"
This method works for starting gdb from any dir, and also from inside a 32bit schroot. Putting these files into ~/.config avoids the gdb "file or directory doesn't exist" bug when trying to gdbinit from mounted paths.