.hidden overrides .symver?

[Florian Weimer <fweimer at redhat dot com>]

This question arose during glibc ABI testing on powerpc (32-bit), but I 
can reproduce it on ppc64 as well (which is how I got this example, it 
is not visible with the glibc sources because the powerpc issue is in 
architecture-specific code not shared between 32-bit and 64-bit).

There are three fils: def.s, ref.s, ver.map:

# def.s
        .section        ".text"
        .align 2
        .p2align 4,,15
        .globl symint
        .symver symint,versym@@PUBVER
        .section        ".opd","aw"
        .align 3
symint:
        .quad   .L.symint,.TOC.@tocbase
        .previous
        .type   symint, @function
.L.symint:
        li 3,0
        blr
        .long 0
        .byte 0,0,0,0,0,0,0,0
        .size   symint,.-.L.symint


# ref.s
        .section        ".text"
        .align 2
        .p2align 4,,15
        .globl pubsym
        .section        ".opd","aw"
        .align 3
pubsym:
        .quad   .L.pubsym,.TOC.@tocbase
        .previous
        .type   pubsym, @function
.L.pubsym:
        b versym
        .long 0
        .byte 0,0,0,1,128,0,0,0
        .size   pubsym,.-.L.pubsym
        .hidden versym


# ver.map
BASE {
  local:
    *;
};

PUBVER {
} BASE;

PUBVER2 {
  global:
    pubsym;
} PUBVER;


Once you have these files, run:

as -o def.o def.s
as -o ref.o ref.s
ld -s -shared -o lib-without-ref.so --version-script=ver.map def.o
ld -s -shared -o lib-with-ref.so --version-script=ver.map def.o ref.o

The surprise is that lib-without-ref.so contains a definition of versym:

Symbol table '.dynsym' contains 7 entries:
   Num:    Value          Size Type    Bind   Vis      Ndx Name
     0: 00000000000000     0 NOTYPE  LOCAL  DEFAULT  UND
     1: 000000000002f0     0 SECTION LOCAL  DEFAULT    7
     2: 00000000020000     0 SECTION LOCAL  DEFAULT   10
     3: 00000000000000     0 OBJECT  GLOBAL DEFAULT  ABS BASE
     4: 00000000000000     0 OBJECT  GLOBAL DEFAULT  ABS PUBVER2
     5: 00000000000000     0 OBJECT  GLOBAL DEFAULT  ABS PUBVER
     6: 00000000020000    20 FUNC    GLOBAL DEFAULT   10 versym@@PUBVER

But lib-with-ref.so does not:

Symbol table '.dynsym' contains 7 entries:
   Num:    Value          Size Type    Bind   Vis      Ndx Name
     0: 00000000000000     0 NOTYPE  LOCAL  DEFAULT  UND
     1: 00000000000320     0 SECTION LOCAL  DEFAULT    7
     2: 00000000020000     0 SECTION LOCAL  DEFAULT   10
     3: 00000000020010    16 FUNC    GLOBAL DEFAULT   10 pubsym@@PUBVER2
     4: 00000000000000     0 OBJECT  GLOBAL DEFAULT  ABS BASE
     5: 00000000000000     0 OBJECT  GLOBAL DEFAULT  ABS PUBVER2
     6: 00000000000000     0 OBJECT  GLOBAL DEFAULT  ABS PUBVER

Is this the intended behavior?

In our case, pubsym is defined in a C source file, and versym is 
referenced with a *declaration* with __attribute ((visibility 
("hidden"))).  This means that a mere declaration overrides aspects of 
the definition of the symbol in another translation unit, which is 
extremely surprising.

The ld version is: GNU ld version 2.25.1-22.base.el7

Thanks,
Florian