Re: AIX support

On 04/04/2025 22:31, Srirama Kucherlapati wrote:
 > - src/backend/port/aix/mkldexport.sh>
>    - When building shared libraries from various archives on AIX, we encounter a
>       situation where symbols are not exported. To resolve this, we require an export
>       file. For instance, the command is used to export symbols.
> 
>       gcc -shared libtest.so libtest.a -Wl,-bE:test.exp
> 
>       However, if we directly provide object files in the command line instead of an
>       archive, the symbols will be exported automatically, as demonstrated by the command
> 
>       gcc -shared libtest.so test1.o test2.o test3.o.

Oh, that's interesting. So if we do that, we don't need mkldepxort.sh 
anymore?

>     - WRT to the MEMSET_LOOP_LIMIT flag, this is set to “0”, which would 
> internally use
> 
>       The system call memset() as mentioned in the below link as well
> 
> https://www.postgresql.org/message- 
> id/20060203135315.E08B09DC816%40postgresql.org <https:// 
> www.postgresql.org/message-id/20060203135315.E08B09DC816%40postgresql.org>

Yes, I understand what it does. But why? Whatever benchmarking was done 
back in 2006 by is no longer relevant.

> With all the above changes we have built and ran the tests. As of now we see
> 
> there is only one test case that is failing, which seems to have been
> 
> introduced recently. And this might not be related to the above changes as
> 
> earlier there were no test cases failing.
> 
> 64 not ok 12    + float8                   235 ms
> 
> 297 # 1 of 226 tests failed.
> 
> 20 +ERROR:  value out of range: overflow
> 
> 21  -- test overflow/underflow handling
> 
> 22  SELECT gamma(float8 '-infinity');
> 
> 23  ERROR:  value out of range: overflow

Yeah, that function is new. I don't know if it's a pre-existing problem 
or something specific to AIX. Please check the archives for prior 
discussion on that; if you can reproduce it, maybe you can help to fix it?

>  12 files changed, 224 insertions(+), 20 deletions(-)

I'm glad to see this patch shrinking :-)

> diff --git a/src/include/port/aix.h b/src/include/port/aix.h
> new file mode 100644
> index 00000000000..7d08480c8c0
> --- /dev/null
> +++ b/src/include/port/aix.h
> @@ -0,0 +1,4 @@
> +/*
> + * src/include/port/aix.h
> + */
> +

Useless.

> diff --git a/src/include/storage/s_lock.h b/src/include/storage/s_lock.h
> index 2f73f9fcf57..5da9b3acda4 100644
> --- a/src/include/storage/s_lock.h
> +++ b/src/include/storage/s_lock.h
> @@ -421,17 +421,15 @@ tas(volatile slock_t *lock)
>  	__asm__ __volatile__(
>  "	lwarx   %0,0,%3,1	\n"
>  "	cmpwi   %0,0		\n"
> -"	bne     1f			\n"
> +"	bne     $+16		\n"		/* branch to li %1,1 */
>  "	addi    %0,%0,1		\n"
>  "	stwcx.  %0,0,%3		\n"
> -"	beq     2f			\n"
> -"1: \n"
> +"	beq     $+12		\n"		/* branch to lwsync */
>  "	li      %1,1		\n"
> -"	b       3f			\n"
> -"2: \n"
> +"	b       $+12		\n"		/* branch to end of asm sequence */
>  "	lwsync				\n"
>  "	li      %1,0		\n"
> -"3: \n"
> +
>  :	"=&b"(_t), "=r"(_res), "+m"(*lock)
>  :	"r"(lock)
>  :	"memory", "cc");

Why is this change needed?

Yes, I know we've been over this many times already. I still don't 
understand why it's needed. The onus is on you to explain it adequately, 
in comments in the patch, so that I and others understand it. Or even 
better, remove it if it's not necessary.

> diff --git a/src/makefiles/Makefile.aix b/src/makefiles/Makefile.aix
> new file mode 100644
> index 00000000000..d33918f91b9
> --- /dev/null
> +++ b/src/makefiles/Makefile.aix
> @@ -0,0 +1,39 @@
> +# MAKE_EXPORTS is required for svr4 loaders that want a file of
> +# symbol names to tell them what to export/import.
> +MAKE_EXPORTS= true

Oh this is interesting. I think MAKE_EXPORTS is actually a leftover that 
I failed to remove when I removed the AIX support; it's not used on any 
currently-supported platform.

> +# -blibpath must contain ALL directories where we should look for libraries
> +libpath := $(shell echo $(subst -L,:,$(filter -L/%,$(LDFLAGS))) | sed -e's/ //g'):/usr/lib:/lib

Is this still sensible on modern AIX systems? What happens if you leave 
it out?

> +# when building with gcc, need to make sure that libgcc can be found
> +ifeq ($(GCC), yes)
> +libpath := $(libpath):$(dir $(shell gcc -print-libgcc-file-name))
> +endif

Same here. Still relevant? What happens if you leave it out?

> +# gcc needs to know it's building a shared lib, otherwise it'll not emit
> +# correct code / link to the right support libraries
> +ifeq ($(GCC), yes)
> +LDFLAGS_SL += -shared
> +endif

On other platforms, we have this in LINK.shared, see src/Makefile.shlib. 
Should we do the same on AIX; if not, why not?

> +# env var name to use in place of LD_LIBRARY_PATH
> +ld_library_path_var = LIBPATH

Does AIX have LD_LIBRARY_PATH? This suggests that it does:

https://www.ibm.com/support/pages/aix-libpath-recommendations

What's the difference between LIBPATH and LD_LIBRARY_PATH? Why prefer 
LIBPATH?


Separately from the remaining issues with this patch, I still feel 
pretty reluctant with accepting this, because if I commit this patch, 
I'm on the hook to keep it working. I do regularly commit stuff that I'm 
not personally that interested in, but a new port is different:

If something breaks on AIX, I have no means (or interest!) in debugging 
it. That means that I need to be pretty confident that there are others 
who are interested and invested in keeping working, take ownership, will 
help to debug problems in a timely fashion, and can submit high-quality 
fixes. I am not seeing that.

I also notice that all the AIX systems we have in the buildfarm are still:

- maintained by Noah, who - correct me if I'm wrong - is not 
particularly interested in AIX or keen on maintaining them
- are on AIX 7.1.5, which I believe is already end-of-line
- running on power7 hardware which is 15 years old.

That's not very reassuring.

-- 
Heikki Linnakangas
Neon (https://neon.tech)