[gold] 2.27 generates GOT where 2.26 did not

[gold] 2.27 generates GOT where 2.26 did not

[Jethro Beekman]

I have these two files:

// asm_var.S
.section .rodata
.global asm_var
.protected asm_var
.size asm_var, 8
asm_var:
	.org .+8

// get_addr.c
extern unsigned long asm_var;

void* get_addr() {
	return &asm_var;
}

That I compile with:
gcc -O3 -fuse-ld=gold -fPIC -shared -nostdlib -Wl,-Bsymbolic asm_var.S get_addr.c

With gold 2.26.1 (and most likely older versions as well), this results in:

00000000000002f0 <get_addr>:
 2f0:	48 8d 05 01 00 00 00 	lea    0x1(%rip),%rax    # 2f8 <asm_var>
 2f7:	c3                   	retq

Yet with 2.27 this results in:

0000000000000340 <get_addr>:
 340:	48 8b 05 99 1c 00 00 	mov    0x1c99(%rip),%rax # 1fe0 <_DYNAMIC+0x110>
 347:	c3                   	retq

What's at 1fe0?

000000001fe0  000500000006 R_X86_64_GLOB_DAT 0000000000000348 asm_var + 0

Is this a regression in 2.27? I really don't want to use the GOT. Is there a
flag I can pass to get the old behavior?

Jethro Beekman

Re: [gold] 2.27 generates GOT where 2.26 did not

[Andrew Pinski]

On Thu, Aug 11, 2016 at 5:31 PM, Jethro Beekman <binutils@jbeekman.nl> wrote:
> I have these two files:
>
> // asm_var.S
> .section .rodata
> .global asm_var
> .protected asm_var
> .size asm_var, 8
> asm_var:
>         .org .+8
>
> // get_addr.c
> extern unsigned long asm_var;
>
> void* get_addr() {
>         return &asm_var;
> }
>
> That I compile with:
> gcc -O3 -fuse-ld=gold -fPIC -shared -nostdlib -Wl,-Bsymbolic asm_var.S get_addr.c
>
> With gold 2.26.1 (and most likely older versions as well), this results in:
>
> 00000000000002f0 <get_addr>:
>  2f0:   48 8d 05 01 00 00 00    lea    0x1(%rip),%rax    # 2f8 <asm_var>
>  2f7:   c3                      retq
>
> Yet with 2.27 this results in:
>
> 0000000000000340 <get_addr>:
>  340:   48 8b 05 99 1c 00 00    mov    0x1c99(%rip),%rax # 1fe0 <_DYNAMIC+0x110>
>  347:   c3                      retq
>
> What's at 1fe0?
>
> 000000001fe0  000500000006 R_X86_64_GLOB_DAT 0000000000000348 asm_var + 0
>
> Is this a regression in 2.27? I really don't want to use the GOT. Is there a
> flag I can pass to get the old behavior?

IIRC this is correct behavior for x86_64 due to copy relocs.

Thanks,
Andrew

>
> Jethro Beekman

Re: [gold] 2.27 generates GOT where 2.26 did not

[Jethro Beekman]

On 11-08-16 20:10, Andrew Pinski wrote:
> On Thu, Aug 11, 2016 at 5:31 PM, Jethro Beekman <binutils@jbeekman.nl> wrote:
>> Is this a regression in 2.27? I really don't want to use the GOT. Is there a
>> flag I can pass to get the old behavior?
> 
> IIRC this is correct behavior for x86_64 due to copy relocs.

I get the same thing if I pass -Wl,-z,nocopyreloc

Jethro

Re: [gold] 2.27 generates GOT where 2.26 did not

[Jethro Beekman]

On 11-08-16 17:31, Jethro Beekman wrote:
> I have these two files:
> 
> // asm_var.S
> .section .rodata
> .global asm_var
> .protected asm_var
> .size asm_var, 8
> asm_var:
> 	.org .+8
> 
> // get_addr.c
> extern unsigned long asm_var;
> 
> void* get_addr() {
> 	return &asm_var;
> }
> 
> That I compile with:
> gcc -O3 -fuse-ld=gold -fPIC -shared -nostdlib -Wl,-Bsymbolic asm_var.S get_addr.c
> 
> With gold 2.26.1 (and most likely older versions as well), this results in:
> 
> 00000000000002f0 <get_addr>:
>  2f0:	48 8d 05 01 00 00 00 	lea    0x1(%rip),%rax    # 2f8 <asm_var>
>  2f7:	c3                   	retq
> 
> Yet with 2.27 this results in:
> 
> 0000000000000340 <get_addr>:
>  340:	48 8b 05 99 1c 00 00 	mov    0x1c99(%rip),%rax # 1fe0 <_DYNAMIC+0x110>
>  347:	c3                   	retq
> 
> What's at 1fe0?
> 
> 000000001fe0  000500000006 R_X86_64_GLOB_DAT 0000000000000348 asm_var + 0
> 
> Is this a regression in 2.27? I really don't want to use the GOT. Is there a
> flag I can pass to get the old behavior?

I think I found another, possibly related, regression. If I add another file "map":

{
local:
	*;
};

And compile with -Wl,--version-script,map on 2.26 I get:

DYNAMIC SYMBOL TABLE:
no symbols

But on 2.27 I get:

DYNAMIC SYMBOL TABLE:
00000000000002a8 l    D  .rodata	0000000000000008 .protected asm_var

Jethro Beekman