[Bug ld/20828] GC-ed DSO symbols make corresponding symbols defined by a linker script local

[Maciej W. Rozycki]

On Thu, 19 Jan 2017, Nick Clifton wrote:

> Checking Binutils in: bfin-elf ... LD REGRESSION: PR ld/20828 dynamic symbols with 

 As noted before, `_edata' is removed with `--gc-sections' and 
`--version-script' combined, where it is supposed to be exported.  This is 
regardless of the presence of `libpr20828.so' in the link, so it does not 
seem related to PR ld/20828 (same with `bfin-uclinux', so this is a 
genuine backend bug).

> Checking Binutils in: riscv32-elf ... LD REGRESSION: PR ld/20828 dynamic symbols with 

 LD segfaults with the initial `libpr20828.so' link (same with 
`riscv32-linux' BTW), so this is not related to PR ld/20828.  
Consequently all the subsequent dependent tests fail.

 It may be something missing from the linker script used, which is 
required by this port, but then LD should complain rather than crash (ISTR 
`aarch64' and `arm' ports segfaulting too if `.got' and/or `.got.plt' 
sections were discarded from output; this may be something worth looking 
into and handling gracefully as well).

> Checking Binutils in: metag-elf ... LD REGRESSION: PR ld/20828 dynamic symbols with

 Same as with `bfin-elf' (and likewise `metag-linux').

> Checking Binutils in: riscv64-elf ... LD REGRESSION: PR ld/20828 dynamic symbols with

 Same as with `riscv32-elf' (and likewise `riscv64-linux').

> Checking Binutils in: x86_64-solaris2 ... LD REGRESSION: PR ld/20828 dynamic symbols with

 There are two issues here -- one is trivial with `libpr20828.so' having 
extra symbols between `_fdata' and `_edata':

Symbol table '.dynsym' contains 6 entries:
   Num:    Value          Size Type    Bind   Vis      Ndx Name
     0: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT  UND
     1: 0000000000000000     0 NOTYPE  GLOBAL DEFAULT    1 _fdata
     2: 0000000000000000     0 OBJECT  GLOBAL DEFAULT    1 _DYNAMIC
     3: 0000000000000000     0 OBJECT  GLOBAL DEFAULT  ABS _PROCEDURE_LINKAGE_TABLE_
     4: 0000000000000000     0 NOTYPE  GLOBAL DEFAULT    1 _edata
     5: 00000000000001b8     0 OBJECT  GLOBAL DEFAULT    4 _GLOBAL_OFFSET_TABLE_

so this will be a straightforward dump pattern fix.

 The other is tricky -- the sole version script used is as follows:

{ global: _edata; local: *; };

and yet LD complains:

ld: anonymous version tag cannot be combined with other version tags

(so where's the non-anonymous version tag?).  I'll look into it.

> Checking Binutils in: mn10300-elf ... LD REGRESSION: PR ld/20828 dynamic symbols with

 Same as with `bfin-elf'.  I have checked `mn10300-linux' too, but all 
tests fail with:

Assembler messages:
Fatal error: selected target format 'elf32-am33lin' unknown

> Checking Binutils in: score-elf ... LD REGRESSION: PR ld/20828 dynamic symbols with

 As noted before, `_fdata' is exported with `--gc-sections' and 
`--version-script' combined, where it is supposed to be removed.  This 
only happens in the presence of `libpr20828.so' in the link, so it may be 
related to PR ld/20828.  I'll have a look into it.
 
> Checking Binutils in: sh-elf ... LD REGRESSION: PR ld/20828 dynamic symbols with

 Same as with `bfin-elf' (`sh-linux' is fine).

 I'll see if I can figure out easily what is going on with `bfin-elf' 
etc., but I am not going to dive into generic port breakage and I do 
encourage port maintainers to verify their port instead.

  Maciej