Re: [PATCH] Change how "print/x" displays floating-point value

[Andrew Burgess <aburgess@redhat.com>]

Andreas Schwab <schwab@linux-m68k.org> writes:

> On Feb 18 2022, Tom Tromey via Gdb-patches wrote:
>
>> diff --git a/gdb/NEWS b/gdb/NEWS
>> index 9da74e71796..544efa3fe74 100644
>> --- a/gdb/NEWS
>> +++ b/gdb/NEWS
>> @@ -97,6 +97,12 @@ show style disassembler enabled
>>  
>>  * Changed commands
>>  
>> +print
>> +  Printing of floating-point values with base-modifying formats like
>> +  /x has been changed to display the underlying bytes of the value in
>> +  the desired base.  This was GDB's documented behavior, but was never
>> +  implemented correctly.
>
> How does that handle padding?
>
>> diff --git a/gdb/testsuite/gdb.base/printcmds.exp b/gdb/testsuite/gdb.base/printcmds.exp
>> index 37632985a07..78a2147017d 100644
>> --- a/gdb/testsuite/gdb.base/printcmds.exp
>> +++ b/gdb/testsuite/gdb.base/printcmds.exp
>> @@ -158,8 +158,14 @@ proc test_float_rejected {} {
>>  # Regression test for PR gdb/21675
>>  proc test_radices {} {
>>      gdb_test "print/o 16777211" " = 077777773"
>> -    gdb_test "print/d 1.5" " = 1"
>> -    gdb_test "print/u 1.5" " = 1"
>> +
>> +    # See PR gdb/16242 for this.
>> +    gdb_test "print/d 1.5f" " = 1069547520"
>> +    gdb_test "print/u 1.5f" " = 1069547520"
>> +    gdb_test "print/x 1.5f" " = 0x3fc00000"
>> +    gdb_test "print/t 1.5f" " = 111111110000000000000000000000"
>> +    gdb_test "print/o 1.5f" " = 07760000000"
>
> That assumes a particular representation of the float type that depends
> on the target.

Maybe we can harden the tests in this case with some logic like
(psuedo-code):

  ## Assuming printcmds.c contains:
  ##  float f_var = 1.5f;

  if { sizeof(int) == sizeof(float) } {
    set expected_value [valueof "p/d *((int *) &f_var)"]
    gdb_test "print/d f_var" "$expected_value"
  }

As I think these two methods of printing are now the same, right?

Thanks,
Andrew