Re: [PATCH 1/4] gdb.base/nodebug.exp: Add long double testing

[Andrew Burgess <aburgess@redhat.com>]

Pedro Alves <pedro@palves.net> writes:

> On 2026-07-16 22:14, Andrew Burgess wrote:
>> Pedro Alves <pedro@palves.net> writes:
> ...
>
>> Not that it really matters, but the ordering seems a bit weird, the
>> existing functions are all:
>> 
>> X
>> X_noproto
>> Y
>> Y_noproto
>> etc...
>> 
>> but you broke this pattern.  
>
> Whoops, that was not intentional.  I think I misread the pattern earlier.  I reordered it now:
>
>  $ grep "^mult" testsuite/gdb.base/nodebug.c
>  multf (float v1, float v2)
>  multf_noproto (v1, v2)
>  mult (double v1, double v2)
>  mult_noproto (v1, v2)
>  mult_long_double (long double v1, long double v2)
>  mult_long_double_noproto (v1, v2)
>
> Thanks for spotting this.
>
>> I only mention it because I have some
>> actual worthwhile points to raise below...
>> 
>>> +
>>>  uint8_t
>>>  add8 (uint8_t v1, uint8_t v2)
>>>  {
>>> diff --git a/gdb/testsuite/gdb.base/nodebug.exp b/gdb/testsuite/gdb.base/nodebug.exp
>>> index e4138a801da..1a16e86ed2c 100644
>>> --- a/gdb/testsuite/gdb.base/nodebug.exp
>>> +++ b/gdb/testsuite/gdb.base/nodebug.exp
>>> @@ -78,6 +78,12 @@ proc test_call_promotion {} {
>>>      gdb_test "p ((double (*) ()) mult_noproto)(2.0f, 3.0f)" " = 6"
>>>      gdb_test "p ((double (*) ()) mult_noproto)(2.0, 3.0)" " = 6"
>>>  
>>> +    # Same, but for long double.
>>> +    gdb_test "p (long double) mult_long_double(2.0L, 3.0L)" " = 6"
>>> +    gdb_test "p ((long double (*) (long double, long double)) mult_long_double)(2.0L, 3.0L)" " = 6"
>>> +    gdb_test "p ((long double (*) (long double, long double)) mult_long_double)(2, 3)" " = 6"
>>> +    gdb_test "p ((long double (*) ()) mult_long_double_noproto)(2.0L, 3.0L)" " = 6"
>> 
>> I noticed that the double test also includes a case which tests float to
>> double promotion, but that case is skipped here.  Wouldn't it be a good
>> idea to include both float to long double and double to long double
>> tests here too?
>
> That's because the double test is exercising the standard C default argument
> promotion rules, for floating point, which says that for non-prototyped functions,
> float is promoted to double.
>
> So for this float function:
>
>   float
>   multf_noproto (v1, v2)
>     float v1, v2;
>   {
>     return v1 * v2;
>   }
>
> called like so:
>
>   multif_noproto (1.0f, 2.0f);
>
> this happens:
>
>  1. Caller promotes 1.0f/2.0f to double, passes the double values.
>  2. Callee receives doubles.
>  3. Callee's prologue converts to float, because the declared param type is float.
>  4. Body uses v1/v2 as float.
>
> ================================
>
> And for the double case:
>
>   double
>   mult_noproto (v1, v2)
>     double v1, v2;
>   {
>     return v1 * v2;
>   }
>
> called like so:
>
>   multi_noproto (1.0f, 2.0f);
>
> this happens:
>
>  1. Caller promotes 1.0f/2.0f to double, passes the double values.
>  2. Callee receives a double.
>  3. Body uses v1/v2 as double.
>
> ================================
>
> The long double case is different.  The C default promotion is float->double, NOT float->long double. 
>
>   long double
>   mult_long_double_noproto (v1, v2)
>     long double v1, v2;
>   {
>     return v1 * v2;
>   }
>
>   mult_long_double_noproto (1.0f, 2.0f);
>
> so this happens:
>
>  1. Caller promotes 1.0f/2.0f to double, passes the double values.
>  2. Callee receives doubles.
>  3. Body uses v1/v2 as long double. (with no conversion!  undefined behavior.)
>
> On ABIs where double and long double are distinct types/sizes, the body sees bogus/corrupt values.
>
> ===============================
>
> For the prototyped case, the calls where we pass int, like:
>
>   p ((float (*) (float, float)) multf)(2, 3)
>
> cover coercion from int to declared type, which is basically testing that gdb does a cast there.
> testing float -> double, etc. for the prototyped cases would not add extra coverage, as it'd just
> be testing that gdb knows how to cast from float -> double.
>
>
>
> I've added some comments to the test to try to make it a little clearer.  I also corrected a couple
> references to "coercion" to "promotion" to be more accurate.  The existing comments are using the terms
> interchangeably, but that's not 100% correct.
>
> Let me know what you think.

Sorry, missed this.  Thanks for the explanation above.  LGTM.

Approved-By: Andrew Burgess <aburgess@redhat.com>

Thanks,
Andrew

>
> From 3f7db94982bb02473e89199a93dde2d27e06014a Mon Sep 17 00:00:00 2001
> From: Pedro Alves <pedro@palves.net>
> Date: Tue, 14 Jul 2026 00:34:43 +0100
> Subject: [PATCH] gdb.base/nodebug.exp: Add long double testing
>
> gdb.base/nodebug.exp is missing testing calling long double functions.
> This commit adds such tests.
>
> With a GDB that doesn't know that "long double" is 64-bit on
> x86_64-pc-windows-msvc, we get:
>
>  FAIL: gdb.base/nodebug.exp: p (long double) mult_long_double(2.0L, 3.0L)
>  FAIL: gdb.base/nodebug.exp: p ((long double (*) (long double, long double)) mult_long_double)(2.0L, 3.0L)
>  FAIL: gdb.base/nodebug.exp: p ((long double (*) (long double, long double)) mult_long_double)(2, 3)
>  FAIL: gdb.base/nodebug.exp: p ((long double (*) ()) mult_long_double_noproto)(2.0L, 3.0L)
>
> Passes cleanly on:
>
>  - x86_64-pc-linux-gnu
>  - x86_64-w64-mingw32
>  - x86_64-pc-windows-msvc, with the "long double" fix
>
> Change-Id: If9ee749187e1d30fedcba17ae12634f3bd90de2f
> ---
>  gdb/testsuite/gdb.base/nodebug.c   | 13 +++++++++++++
>  gdb/testsuite/gdb.base/nodebug.exp | 21 ++++++++++++++++-----
>  2 files changed, 29 insertions(+), 5 deletions(-)
>
> diff --git a/gdb/testsuite/gdb.base/nodebug.c b/gdb/testsuite/gdb.base/nodebug.c
> index c7bc93991b8..00e854844bf 100644
> --- a/gdb/testsuite/gdb.base/nodebug.c
> +++ b/gdb/testsuite/gdb.base/nodebug.c
> @@ -79,6 +79,19 @@ mult_noproto (v1, v2)
>    return v1 * v2;
>  }
>  
> +long double
> +mult_long_double (long double v1, long double v2)
> +{
> +  return v1 * v2;
> +}
> +
> +long double
> +mult_long_double_noproto (v1, v2)
> +  long double v1, v2;
> +{
> +  return v1 * v2;
> +}
> +
>  uint8_t
>  add8 (uint8_t v1, uint8_t v2)
>  {
> diff --git a/gdb/testsuite/gdb.base/nodebug.exp b/gdb/testsuite/gdb.base/nodebug.exp
> index e4138a801da..7a5ab273bde 100644
> --- a/gdb/testsuite/gdb.base/nodebug.exp
> +++ b/gdb/testsuite/gdb.base/nodebug.exp
> @@ -51,8 +51,8 @@ proc nodebug_runto {func} {
>  }
>  
>  # Test calling no-debug functions involving argument types that may
> -# require coercion/promotion, both prototyped and unprototyped, both
> -# return-type-cast style, and function-pointer-cast styles.
> +# require coercion or promotion, both prototyped and unprototyped,
> +# both return-type-cast style, and function-pointer-cast styles.
>  proc test_call_promotion {} {
>      if {[target_info exists gdb,cannot_call_functions]} {
>  	return
> @@ -60,14 +60,15 @@ proc test_call_promotion {} {
>  
>      # Call prototyped function with float parameters via both
>      # return-type cast and function-pointer cast.  This checks that
> -    # GDB doesn't do float->double coercion.
> +    # GDB doesn't do float->double promotion.
>      gdb_test "p (float) multf(2.0f, 3.0f)" " = 6"
> -    gdb_test "p ((float (*) (float, float)) multf)(2, 3)" " = 6"
>      gdb_test "p ((float (*) (float, float)) multf)(2.0f, 3.0f)" " = 6"
> +    # This tests int->float coercion.
> +    gdb_test "p ((float (*) (float, float)) multf)(2, 3)" " = 6"
>  
>      # Call unprototyped function with float parameters via
>      # function-pointer cast, only.  return-type cast assumes
> -    # protototyped.  Check that GDB does float->double coercion.
> +    # prototyped.  Check that GDB does float->double promotion.
>      gdb_test "p ((float (*) ()) multf_noproto)(2.0f, 3.0f)" " = 6"
>      gdb_test "p ((float (*) ()) multf_noproto)(2.0, 3.0)" " = 6"
>  
> @@ -78,6 +79,16 @@ proc test_call_promotion {} {
>      gdb_test "p ((double (*) ()) mult_noproto)(2.0f, 3.0f)" " = 6"
>      gdb_test "p ((double (*) ()) mult_noproto)(2.0, 3.0)" " = 6"
>  
> +    # Same, but for long double.
> +    gdb_test "p (long double) mult_long_double(2.0L, 3.0L)" " = 6"
> +    gdb_test "p ((long double (*) (long double, long double)) mult_long_double)(2.0L, 3.0L)" " = 6"
> +    gdb_test "p ((long double (*) (long double, long double)) mult_long_double)(2, 3)" " = 6"
> +    # For unprototyped calls, the standard C default argument
> +    # promotion (for floating point) applies only to float and
> +    # promotes to double, so test only with the expected type, using
> +    # L-suffixed literals to pass long doubles.
> +    gdb_test "p ((long double (*) ()) mult_long_double_noproto)(2.0L, 3.0L)" " = 6"
> +
>      # Check that GDB promotes char->int correctly.
>      gdb_test "p /d (uint8) add8((uint8) 2, (uint8) 3)" " = 5"
>      gdb_test "p /d ((uint8 (*) (uint8, uint8)) add8)((uint8) 2, (uint8) 3)" " = 5"
>
> base-commit: 490469846dcef89fe53668bdbba73591c64bed61
> -- 
> 2.54.0