On 10 January 2014 08:32, Giuseppe D'Angelo <giuseppe.dang...@kdab.com> wrote:
Hi Guiseppe,
> the attached program changes the output from "true" to "false" when the
> -Bsymbolic / -Bsymbolic-functions options are passed to GCC. This happens on
> ARM -- on x86-64 output is always "true".
>
> The program involves a comparison, within a shared library, of a PMF defined
> inside the shared library itself with the same PMF passed by the
> application.
>
> At this stage I still don't know if it's a GCC problem, a ld.so problem, ABI
> constraints, undefined behaviour, or whatnot; but any help is appreciated.
>
> Compile with:
>
>> g++ -fPIC -shared -Wall -o libshared.so -Wl,-Bsymbolic shared.cpp
>> g++ -fPIE -Wall -o main main.cpp -L. -lshared
>
> (The long story is that Qt 5 is taking PMFs in its public API, and the
> comparison failing inside of Qt shared libraries is breaking code on ARM, as
> -Bsymbolic is set by default there.)
Thanks for the report and testcase.
The attached patch to ld may help. I am not yet sure whether or not it
is the correct approach but if it works for you that would be
interesting.
--
Will Newton
Toolchain Working Group, Linaro
From 8f083d831cc7441d5fddcb1a883ae1f1372cd287 Mon Sep 17 00:00:00 2001
From: Will Newton <will.new...@linaro.org>
Date: Fri, 10 Jan 2014 14:38:58 +0000
Subject: [PATCH] bfd/elf32-arm.c: Set st_value to zero for undefined symbols.
Unless point_equality_needed is set then set st_value to be zero
for undefined symbols.
bfd/ChangeLog:
2014-01-10 Will Newton <will.new...@linaro.org>
* elf32-arm.c (elf32_arm_check_relocs): Set
pointer_equality_needed for absolute references within
executable links.
(elf32_arm_finish_dynamic_symbol): Set st_value to zero
unless pointer_equality_needed is set.
ld/testsuite/ChangeLog:
2014-01-10 Will Newton <will.new...@linaro.org>
* ld-arm/ifunc-14.rd: Update symbol values.
---
bfd/elf32-arm.c | 7 ++++++-
ld/testsuite/ld-arm/ifunc-14.rd | 4 ++--
2 files changed, 8 insertions(+), 3 deletions(-)
diff --git a/bfd/elf32-arm.c b/bfd/elf32-arm.c
index 6a9e60f..3451a66 100644
--- a/bfd/elf32-arm.c
+++ b/bfd/elf32-arm.c
@@ -12675,6 +12675,11 @@ elf32_arm_check_relocs (bfd *abfd, struct bfd_link_info *info,
/* Fall through. */
case R_ARM_ABS32:
case R_ARM_ABS32_NOI:
+ if (h != NULL && info->executable)
+ {
+ h->pointer_equality_needed = 1;
+ }
+ /* Fall through. */
case R_ARM_REL32:
case R_ARM_REL32_NOI:
case R_ARM_MOVW_PREL_NC:
@@ -14040,7 +14045,7 @@ elf32_arm_finish_dynamic_symbol (bfd * output_bfd,
Otherwise, the PLT entry would provide a definition for
the symbol even if the symbol wasn't defined anywhere,
and so the symbol would never be NULL. */
- if (!h->ref_regular_nonweak)
+ if (!h->ref_regular_nonweak || !h->pointer_equality_needed)
sym->st_value = 0;
}
else if (eh->is_iplt && eh->plt.noncall_refcount != 0)
diff --git a/ld/testsuite/ld-arm/ifunc-14.rd b/ld/testsuite/ld-arm/ifunc-14.rd
index 59ea29b..9c44092 100644
--- a/ld/testsuite/ld-arm/ifunc-14.rd
+++ b/ld/testsuite/ld-arm/ifunc-14.rd
@@ -8,5 +8,5 @@ Relocation section '\.rel\.dyn' at offset 0x8000 contains 4 entries:
Relocation section '\.rel\.plt' at offset 0x8020 contains 2 entries:
Offset Info Type Sym\.Value Sym\. Name
-0001100c ......16 R_ARM_JUMP_SLOT 00009014 f2t
-00011010 ......16 R_ARM_JUMP_SLOT 00009020 f2
+0001100c ......16 R_ARM_JUMP_SLOT 00000000 f2t
+00011010 ......16 R_ARM_JUMP_SLOT 00000000 f2
--
1.8.1.4
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