[Bug target/66912] New: Copy relocation against protected symbol doesn't work

[Bug target/66912] New: Copy relocation against protected symbol doesn't work

[nsz at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66912

            Bug ID: 66912
           Summary: Copy relocation against protected symbol doesn't work
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: nsz at gcc dot gnu.org
  Target Milestone: ---

same as bug 65248 but for arm and aarch64.

On aarch64, gcc -S -O -fpic compiles

__attribute__((visibility("protected"))) int n;
int f () { return n; }

into

f:
        adrp    x0, n
        ldr     w0, [x0, #:lo12:n]
        ret
        .size   f, .-f
        .protected      n
        .comm   n,4,4

so the address of n is not loaded from GOT,
which means copy reloc against it in the main
executable won't work.

The expected code is

f:
        adrp    x0, :got:n
        ldr     x0, [x0, #:got_lo12:n]
        ldr     w0, [x0]
        ret

[Bug target/66912] Copy relocation against protected symbol doesn't work

[rearnsha at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66912

--- Comment #1 from Richard Earnshaw <rearnsha at gcc dot gnu.org> ---
Erm, isn't that the whole point of marking the symbol 'protected'?

>From the ELF spec:

<quote>
STV_PROTECTED
    A symbol defined in the current component is protected if it is visible in
other components but not preemptable, meaning that any reference to such a
symbol from within the defining component must be resolved to the definition in
that component, even if there is a definition in another component that would
preempt by the default rules. A symbol with STB_LOCAL binding may not have
STV_PROTECTED visibility. If a symbol definition with STV_PROTECTED visibility
from a shared object is taken as resolving a reference from an executable or
another shared object, the SHN_UNDEF symbol table entry created has STV_DEFAULT
visibility.
</quote>

If we know it will resolve to the definition inside this DSO, then we don't
need to indirect via the GOT to address it.

[Bug target/66912] Copy relocation against protected symbol doesn't work

[nsz at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66912

--- Comment #2 from nsz at gcc dot gnu.org ---
protected only means it cannot be overridden.

so we know the symbol will be resolved to the local one,
however it may be visible externally and then the address
must be the same in the other modules which is a problem
if the main executable has a copy reloc against this symbol.

[Bug target/66912] Copy relocation against protected symbol doesn't work

[nsz at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66912

--- Comment #3 from nsz at gcc dot gnu.org ---
Author: nsz
Date: Tue Oct 20 09:37:27 2015
New Revision: 229024

URL: https://gcc.gnu.org/viewcvs?rev=229024&root=gcc&view=rev
Log:
Fix default_binds_local_p_2 for extern protected data

gcc:

        PR target/66912
        * varasm.c (default_binds_local_p_2): Turn on extern_protected_data.

gcc/testsuite:

        PR target/66912
        * gcc.target/aarch64/pr66912.c: New.
        * gcc.target/arm/pr66912.c: New.


Added:
    trunk/gcc/testsuite/gcc.target/aarch64/pr66912.c
    trunk/gcc/testsuite/gcc.target/arm/pr66912.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/varasm.c

[Bug target/66912] Copy relocation against protected symbol doesn't work

[nsz at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66912

--- Comment #4 from nsz at gcc dot gnu.org ---
Author: nsz
Date: Tue Oct 20 09:50:58 2015
New Revision: 229030

URL: https://gcc.gnu.org/viewcvs?rev=229030&root=gcc&view=rev
Log:
Fix default_binds_local_p_2 for extern protected data

        Backport from mainline r229024
        2015-10-20  Szabolcs Nagy  <szabolcs.nagy@arm.com>

gcc:
        PR target/66912
        * varasm.c (default_binds_local_p_2): Turn on extern_protected_data.

gcc/testsuite:

        PR target/66912
        * gcc.target/aarch64/pr66912.c: New.
        * gcc.target/arm/pr66912.c: New.


Added:
    branches/gcc-5-branch/gcc/testsuite/gcc.target/aarch64/pr66912.c
    branches/gcc-5-branch/gcc/testsuite/gcc.target/arm/pr66912.c
Modified:
    branches/gcc-5-branch/gcc/ChangeLog
    branches/gcc-5-branch/gcc/testsuite/ChangeLog
    branches/gcc-5-branch/gcc/varasm.c

[Bug target/66912] Copy relocation against protected symbol doesn't work

[nsz at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66912

nsz at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |FIXED
   Target Milestone|---                         |5.3

--- Comment #5 from nsz at gcc dot gnu.org ---
fixed in r229030.