[Bug ld/22269] Undefined weak symbols isn't resolved to 0 in static PIE

[hjl.tools at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=22269

--- Comment #5 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to Alan Modra from comment #4)
> I agree that undefined weak symbols probably ought to resolve to 0 in a
> static PIE.  To do that on ppc it would be reasonable to add the following
> to elf32.em after_parse
> 
>   if (link_info.dynamic_undefined_weak == -1
>       && link_info.nointerp)
>     link_info.dynamic_undefined_weak = FALSE;

For powerpc, I got

address@hidden pr22263]$ cat x.c
__thread int * foo;

void
bar (void)
{
  *foo = 1;
}
address@hidden pr22263]$ cat y.c
extern __thread int *foo;

static int x;

extern void bar (void);

int
_start ()
{
  foo = &x;
  return 0;
}
address@hidden pr22263]$ make
/export/gnu/import/git/toolchain/install/compilers/powerpc-linux-gnu/bin/powerpc-glibc-linux-gnu-gcc
-fPIE -O2   -c -o x.o x.c
/export/gnu/import/git/toolchain/install/compilers/powerpc-linux-gnu/bin/powerpc-glibc-linux-gnu-gcc
-fPIE -O2   -c -o y.o y.c
./ld -pie -o x x.o y.o
readelf -rW x

Relocation section '.rela.dyn' at offset 0x1ac contains 1 entries:
 Offset     Info    Type                Sym. Value  Symbol's Name + Addend
0001ff68  00000016 R_PPC_RELATIVE                    20000
address@hidden pr22263]$ 

There should be no dynamic relocations.

> or perhaps something a little more specific to static PIE..
> 
> However, that results in
> FAIL: ld-i386/pr19636-1d
> FAIL: ld-i386/pr19636-1e
> FAIL: ld-i386/pr19636-1f
> FAIL: ld-x86-64/pr19636-2d
> FAIL: ld-x86-64/pr19636-2e
> FAIL: ld-x86-64/pr19636-2f
> 
> So, why does x86 make undefined weak symbols dynamic in the -d tests (which
> are -pie --no-dynamic-linker)?

With your patch, I got

address@hidden ld]$ cat
/export/gnu/import/git/sources/binutils-gdb/ld/testsuite/ld-x86-64/pr19636-2.s
        .text
        .weak func1
        .weak func2
        .weak func3
        .globl _start
_start:
        cmp address@hidden(%rip),%rax
        jmp address@hidden(%rip)
        call address@hidden
address@hidden ld]$ cat 1
/export/build/gnu/binutils/build-x86_64-linux/ld/../gas/as-new  --64
-mrelax-relocations=no  -o tmpdir/pr19636-2.o
/export/gnu/import/git/sources/binutils-gdb/ld/testsuite/ld-x86-64/pr19636-2.s
./ld-new -z norelro 
-L/export/gnu/import/git/sources/binutils-gdb/ld/testsuite/ld-x86-64  -pie -m
elf_x86_64 --no-dynamic-linker --hash-style=sysv -o tmpdir/dump
tmpdir/pr19636-2.o 
/export/build/gnu/binutils/build-x86_64-linux/ld/../binutils/objdump  -dw
tmpdir/dump
address@hidden ld]$ sh 1

tmpdir/dump:     file format elf64-x86-64


Disassembly of section .text:

0000000000000111 <_start>:
 111:   48 3b 05 e0 00 20 00    cmp    0x2000e0(%rip),%rax        # 2001f8
<.got>
 118:   ff 25 e2 00 20 00       jmpq   *0x2000e2(%rip)        # 200200
<.got+0x8>
 11e:   e8 dd fe ff ff          callq  0 <_start-0x111>
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Since call is PC relative, this doesn't branch to address 0.

address@hidden ld]$ ld -z norelro 
-L/export/gnu/import/git/sources/binutils-gdb/ld/testsuite/ld-x86-64  -pie -m
elf_x86_64 --no-dynamic-linker --hash-style=sysv -o tmpdir/dump
tmpdir/pr19636-2.o 
address@hidden ld]$ objdump  -dw tmpdir/dump

tmpdir/dump:     file format elf64-x86-64


Disassembly of section .plt:

0000000000000120 <.plt>:
 120:   ff 35 2a 01 20 00       pushq  0x20012a(%rip)        # 200250
<_GLOBAL_OFFSET_TABLE_+0x8>
 126:   ff 25 2c 01 20 00       jmpq   *0x20012c(%rip)        # 200258
<_GLOBAL_OFFSET_TABLE_+0x10>
 12c:   0f 1f 40 00             nopl   0x0(%rax)
 130:   ff 25 2a 01 20 00       jmpq   *0x20012a(%rip)        # 200260
<_GLOBAL_OFFSET_TABLE_+0x18>
 136:   68 00 00 00 00          pushq  $0x0
 13b:   e9 00 00 00 00          jmpq   140 <_start>

Disassembly of section .text:

0000000000000140 <_start>:
 140:   48 3b 05 f1 00 20 00    cmp    0x2000f1(%rip),%rax        # 200238
<.got>
 147:   ff 25 f3 00 20 00       jmpq   *0x2000f3(%rip)        # 200240
<.got+0x8>
 14d:   e8 de ff ff ff          callq  130 <.plt+0x10>
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

This branches to the PLT entry which branches to address 0 via indirect
GOT branch.

address@hidden ld]$

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