RE: AIX support - Mailing list pgsql-hackers

    > Do you still need mkldexport.sh? Surely there's a better way to do that

    > in year 2024. Some quick googling says there's a '-bexpall' option to

    > 'ld', which kind of sounds like what we want. Will that work? How do

    > other programs do this?

We have noticed couple of caveats with these flags -bexpall/-bexpfull in other

opensource tools on AIX.  This option would export too many symbols causing

problems because a shared library may re-export symbols from another library

causing confused dependencies, duplicate symbols.

We have similar discussion wrt to these flag in Cmake

    https://gitlab.kitware.com/cmake/cmake/-/issues/19163

Also, I tried some sample program to verify the same as below

    >> cat foo.c

        #include <stdio.h>

        #include <string.h>

        int func1()

        {

            char str1[] = "Hello ", str2[] = "world! ";

            strcat(str1,str2);

            puts(str1);

            return 0;

        }

    >> gcc -c foo.c -o foo.o

    >> gcc -shared -Wl,-bexpall -o foo.so foo.o

    >> dump -Tov foo.so

    foo.so:

                            ***Object Module Header***

    # Sections      Symbol Ptr      # Symbols       Opt Hdr Len     Flags

             4      0x00000d88            120                72     0x3002

    Flags=( EXEC DYNLOAD SHROBJ DEP_SYSTEM )

    Timestamp = "Sep 17 10:17:35 2024"

    Magic = 0x1df  (32-bit XCOFF)

                            ***Optional Header***

    Tsize       Dsize       Bsize       Tstart      Dstart

    0x00000548  0x0000010c  0x00000004  0x10000128  0x20000670

    SNloader    SNentry     SNtext      SNtoc       SNdata

    0x0004      0x0000      0x0001      0x0002      0x0002

    TXTalign    DATAalign   TOC         vstamp      entry

    0x0005      0x0004      0x20000750  0x0001      0xffffffff

    maxSTACK    maxDATA     SNbss       magic       modtype

    0x00000000  0x00000000  0x0003      0x010b        RE

                            ***Loader Section***

                            ***Loader Symbol Table Information***

    [Index]      Value      Scn     IMEX Sclass   Type           IMPid Name

    [0]     0x2000068c    .data              RW SECdef        [noIMid] __rtinit

    [1]     0x00000000    undef      IMP     DS EXTref libgcc_s.a(shr.o) __cxa_finalize

    [2]     0x00000000    undef      IMP     DS EXTref libgcc_s.a(shr.o) _GLOBAL__AIXI_shr_o

    [3]     0x00000000    undef      IMP     DS EXTref libgcc_s.a(shr.o) _GLOBAL__AIXD_shr_o

    [4]     0x00000000    undef      IMP     DS EXTref   libc.a(shr.o) __strtollmax

    [5]     0x00000000    undef      IMP     DS EXTref   libc.a(shr.o) puts

    [6]     0x200006f4    .data      EXP     DS   Ldef        [noIMid] __init_aix_libgcc_cxa_atexit

    [7]     0x20000724    .data      EXP     DS   Ldef        [noIMid] _GLOBAL__AIXI_foo_so

    [8]     0x20000730    .data      EXP     DS   Ldef        [noIMid] _GLOBAL__AIXD_foo_so

>>    [9]     0x2000073c    .data      EXP     DS SECdef        [noIMid] strcat

    [10]    0x20000744    .data      EXP     DS   Ldef        [noIMid] func1

The code makes use of strcat from libc but re-exports the symbol (because of -bexpall). 

As of now due to the limitation with these flags (-bexpall / -bexpfull ? ), the

solution here is to continue to extract the symbols from the object files and

use that export file as part of building the shared library. (Continue to use

the mkldexport.sh script to generate the export symbols).

Thanks,

Sriram.