Re: Bug#1121240: libhdf4: FTBFS on armhf (-Wincompatible-pointer-types)

Hi Emanuelle,

Thanks for helping fix this FTBFS on armhf.

On 3/4/26 9:49 AM, Emanuele Rocca wrote:
> On 2025-11-23 04:33, Sebastiaan Couwenberg wrote:
>> Making this a warning with following does not resolve the FTBFS:
>>
>>   ifneq (,$(filter $(DEB_BUILD_ARCH),armhf))
>>   export DEB_CFLAGS_MAINT_APPEND = -Wno-error=incompatible-pointer-types
>>   endif
>>
>> It then fails due to:
>>
>>   array.c:399:21: error: too many arguments to function 'xlen_funct'; expected 0, have 1
>>     399 |             len += (*xlen_funct)(vp);
>>         |                    ~^~~~~~~~~~~~ ~~
>>
> 
> The prototype of xlen_funct has no arguments defined. In C23 declaring a
> function as int foo() is equivalent as declaring that it takes no
> argument, hence calling it with arguments becomes an error. See:
> https://en.wikipedia.org/wiki/C23_(C_standard_revision)#Syntax

Upstream likely does that because the functions xlen_funct can be set to have different arguments:

  mfhdf/libsrc/nc_priv.h:HDFLIBAPI int NC_xlen_attr(NC_attr **app);
  mfhdf/libsrc/nc_priv.h:HDFLIBAPI int NC_xlen_dim(NC_dim **dpp);
  mfhdf/libsrc/nc_priv.h:HDFLIBAPI int NC_xlen_string(NC_string *cdfstr);
  mfhdf/libsrc/nc_priv.h:HDFLIBAPI int NC_xlen_var(NC_var **vpp);
  mfhdf/libsrc/array.c:                xlen_funct = NC_xlen_string;
  mfhdf/libsrc/array.c:                xlen_funct = NC_xlen_dim;
  mfhdf/libsrc/array.c:                xlen_funct = NC_xlen_var;
  mfhdf/libsrc/array.c:                xlen_funct = NC_xlen_attr;

> You can either fix the code or tell the compiler to stick to older
> versions of the standard, something like:
> 
>    export DEB_CFLAGS_MAINT_APPEND += -std=c17

This is confirmed to fix the FTBFS with GCC 15 on the armhf porterbox.

Kind Regards,

Bas