[Bug gold/18695] [x86-64] Missing relocation overflow check

[ccoutant at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=18695

--- Comment #10 from Cary Coutant <ccoutant at gmail dot com> ---
Created attachment 8963
  --> https://sourceware.org/bugzilla/attachment.cgi?id=8963&action=edit
Patch to fix broken x32 overflow checks

Fix incorrect x32 overflow checking for refs to weak undef symbols.

On x32, a pc-relative reference to an undef weak symbol (value 0)
with a negative addend (typically -4) generates a spurious overflow
error because Symbol_value::value() returns a 32-bit negative number
as an unsigned number, which gets zero-extended before subtracting
the PC value. This patch fixes the problem by special-casing the
negative addend, and adding it to the value after widening it to
64 bits. Symbol_value::value() does not need the addend if it's
negative, since it is only important when processing section
symbols for merge sections, where a positive addend provides the
input section offset of the merged constant.

With this patch, I can build basic_static_pic_test in x32 mode.
HJ, I'd appreciate it if you could give it more testing before I
commit it.

2016-02-06  Cary Coutant  <address@hidden>

gold/
        * x86_64.cc (X86_64_relocate_functions::pcrela32_check): Fix x32
        overflow checking when symbol value + addend < 0.

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