[Bug ld/19636] New: -pie changes program behavior and generate unnecessary dynamic symbols.

[hjl.tools at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=19636

            Bug ID: 19636
           Summary: -pie changes program behavior and generate unnecessary
                    dynamic symbols.
           Product: binutils
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: ld
          Assignee: unassigned at sourceware dot org
          Reporter: hjl.tools at gmail dot com
  Target Milestone: ---

address@hidden pie-1]$ cat x.s
        .text
        .globl _start
_start:
        .byte 0
        .section        .data.rel.ro.local,"aw",%progbits
        .weak func
        .dc.a func
address@hidden pie-1]$ make
as   -o x.o x.s
./ld -pie -o x x.o
./ld -o y x.o
readelf -r --dyn-syms x

Relocation section '.rela.dyn' at offset 0x248 contains 1 entries:
  Offset          Info           Type           Sym. Value    Sym. Name +
Addend
000000200268  000300000001 R_X86_64_64       0000000000000000 func + 0

Symbol table '.dynsym' contains 6 entries:
   Num:    Value          Size Type    Bind   Vis      Ndx Name
     0: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT  UND 
     1: 0000000000000260     0 SECTION LOCAL  DEFAULT    6 
     2: 0000000000200370     0 NOTYPE  GLOBAL DEFAULT    9 __bss_start
     3: 0000000000000000     0 NOTYPE  WEAK   DEFAULT  UND func
     4: 0000000000200370     0 NOTYPE  GLOBAL DEFAULT    9 _edata
     5: 0000000000200370     0 NOTYPE  GLOBAL DEFAULT    9 _end
readelf -r --dyn-syms y

There are no relocations in this file.
address@hidden pie-1]$ 

-pie generates a dynamic relocation for func, which changes program
behavior and makes weak symbol a run-time decision instead of link-time.
Also

     2: 0000000000200370     0 NOTYPE  GLOBAL DEFAULT    9 __bss_start
     4: 0000000000200370     0 NOTYPE  GLOBAL DEFAULT    9 _edata
     5: 0000000000200370     0 NOTYPE  GLOBAL DEFAULT    9 _end

are odd since there are no dynamic relocations for those symbols.

With gold, I got

address@hidden pie-1]$ make LD=ld.gold
as   -o x.o x.s
ld.gold -pie -o x x.o
ld.gold -o y x.o
readelf -r --dyn-syms x

There are no relocations in this file.

Symbol table '.dynsym' contains 1 entries:
   Num:    Value          Size Type    Bind   Vis      Ndx Name
     0: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT  UND 
readelf -r --dyn-syms y

There are no relocations in this file.
address@hidden pie-1]$

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