Re: m4 porting to z/OS - gnulib fix - obstack.h

[Bruno Haible]

Hello Harithamma,

Harithamma D wrote:
> I am porting m4 to z/OS and came across following compilation error related 
> to gnulib:
> 
> In file included from ./builtin.c:25:
> In file included from ./m4.h:50:
> ../lib/obstack.h:229:8: error: unknown attribute '_Noreturn' ignored 
> [-Werror,-Wunknown-attributes]
> extern __attribute_noreturn__ void (*obstack_alloc_failed_handler) (void);
>        ^
> ../lib/obstack.h:156:50: note: expanded from macro '__attribute_noreturn__'
> #  define __attribute_noreturn__ __attribute__ ((__noreturn__))
>                                                  ^
> /usr/include/le/features.h:791:26: note: expanded from macro '__noreturn__'
>     #define __noreturn__ _Noreturn
> 
> 
> The compile command used is:
> 
> source='builtin.c' object='builtin.o' libtool=no \
> DEPDIR=.deps depmode=hp2 /bin/sh ../build-aux/depcomp \
> xlclang    -I../lib -I../lib -DNSIG=42 -D_XOPEN_SOURCE=600 -D_ALL_SOURCE 
> -D_OPEN_SYS_FILE_EXT=1 -D_AE_BIMODAL=1 -D_ENHANCED_ASCII_EXT=0xFFFFFFFF  
> -fanalyzer -fno-common -Wall -Wbad-function-cast -Wdate-time 
> -Wdisabled-optimization -Wdouble-promotion -Wextra -Winit-self -Winline 
> -Winvalid-pch -Wmissing-declarations -Wmissing-include-dirs 
> -Wmissing-prototypes -Wnested-externs -Wnull-dereference 
> -Wold-style-definition -Woverlength-strings -Wpacked -Wpointer-arith -Wshadow 
> -Wstack-protector -Wstrict-overflow -Wstrict-prototypes -Wuninitialized 
> -Wunknown-pragmas -Wvariadic-macros -Wwrite-strings -Wformat=2 
> -Wno-missing-field-initializers -Werror -qascii -std=gnu11 -qnocsect 
> -qenum=int -qgonumber -O3 -std=c11 -fgnu89-inline 
> -I/home/haritha/code/m4port/m4/lib 
> -I/home/haritha/code/m4port/patches/PR1/include -c -o builtin.o builtin.c
> 
> The above error got fixed when I added the ! defined (__MVS__) condition as 
> shown in diff file attached.
> I would like to upstream these changes. Please let me know if you have any 
> concerns or questions.

Before doing that:

Since xlclang is, AFAIU, a copy of clang modified by IBM, and clang supports
__attribute__((__noreturn__)),
see https://clang.llvm.org/docs/AttributeReference.html#id20 , 
it would be more future-oriented if xlclang would support this attribute.
Can you please check with the relevant people in your company whether this
is a possible course of action?

I would prefer to deal with this in Gnulib only if the answer is "no".

Bruno