On Fri, Aug 12, 2011 at 8:52 AM, H.J. Lu <hjl.to...@gmail.com> wrote:
> On Fri, Aug 12, 2011 at 8:17 AM, Jan Beulich <jbeul...@novell.com> wrote:
>>>>> On 12.08.11 at 16:47, "H.J. Lu" <hjl.to...@gmail.com> wrote:
>>> On Fri, Aug 12, 2011 at 7:42 AM, Jan Beulich <jbeul...@novell.com> wrote:
>>>>>>> On 12.08.11 at 16:02, "H.J. Lu" <hjl.to...@gmail.com> wrote:
>>>>> On Fri, Aug 12, 2011 at 6:59 AM, Jan Beulich <jbeul...@novell.com> wrote:
>>>>>>>>> On 12.08.11 at 15:22, "H.J. Lu" <hjl.to...@gmail.com> wrote:
>>>>>>> On Fri, Aug 12, 2011 at 6:17 AM, Jan Beulich <jbeul...@novell.com>
>>>>>>> wrote:
>>>>>>>>>>> On 12.08.11 at 14:09, "H.J. Lu" <hjl.to...@gmail.com> wrote:
>>>>>>>>> On Fri, Aug 12, 2011 at 12:30 AM, Jan Beulich <jbeul...@novell.com>
>>>>>>>>> wrote:
>>>>>>>>>>>>> On 12.08.11 at 06:37, "H.J. Lu" <hjl.to...@gmail.com> wrote:
>>>>>>>>>>> On Mon, Aug 1, 2011 at 3:15 PM, H.J. Lu <hjl.to...@gmail.com> wrote:
>>>>>>>>>>>> Hi,
>>>>>>>>>>>>
>>>>>>>>>>>> It turns out that x32 needs R_X86_64_64. One major reason is
>>>>>>>>>>>> the displacement range of x32 is -2G to +2G. It isn't a problem
>>>>>>>>>>>> for compiler since only small model is required for x32.
>>>>>>>>>>>>
>>>>>>>>>>>> However, to address 0 to 4G directly in assembly code, we have
>>>>>>>>>>>> to use R_X86_64_64 with movabs. I am checking the follow patch
>>>>>>>>>>>> into x32 psABI to allow R_X86_64_64.
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> X32 Linker should treats R_X86_64_64 as R_X86_64_32
>>>>>>>>>>> zero-extended to 64bit for output. I will update x32 psABI with
>>>>>>>>>>
>>>>>>>>>> I'm sorry to say that, but the situation about x32 seems to be
>>>>>>>>>> getting worse with each change you do, every time again
>>>>>>>>>> revolving around mixing up ABI specification and a particular
>>>>>>>>>> implementation thereof.
>>>>>>>>>>
>>>>>>>>>> Here, if you need something zero-extended (though I can't see
>>>>>>>>>> why you would), then you should use a new relocation type. As
>>>>>>>>>> pointed out before, there are valid possible uses of R_X86_64_64
>>>>>>>>>> that would require the semantics of x86-64.
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> When does x32 need the semantics of x86-64 for R_X86_64_64?
>>>>>>>>
>>>>>>>> When referencing an assembler or linker defined constant that
>>>>>>>> exceeds 32-bit in width. Given that this is a 64-bit architecture
>>>>>>>> with 32-bit addresses, at least I would expect such to work.
>>>>>>>>
>>>>>>>
>>>>>>> Yes, it should work just fine for x32 by zero-extending 32bit
>>>>>>> address to 64bit.
>>>>>>
>>>>>> For a constant that has more than 32 significant bits???
>>>>>>
>>>>>
>>>>> Can you give me an example in assembly code?
>>>>
>>>> Something like
>>>>
>>>> .equ sym, 0x1234567890
>>>> .global sym
>>>>
>>>
>>> "sym" is truncated to 32bit:
>>
>> Yes, because of your tying of the ABI to ELF32.
>
> X32 uses ELF32 and won't change.
>
>>> Symbol table '.symtab' contains 5 entries:
>>> Num: Value Size Type Bind Vis Ndx Name
>>> 0: 00000000 0 NOTYPE LOCAL DEFAULT UND
>>> 1: 00000000 0 SECTION LOCAL DEFAULT 1
>>> 2: 00000000 0 SECTION LOCAL DEFAULT 2
>>> 3: 00000000 0 SECTION LOCAL DEFAULT 3
>>> 4: 34567890 0 NOTYPE GLOBAL DEFAULT ABS sym
>>>
>>> However, one can write
>>>
>>> .quad main + 0x8000000
>>
>> And I suppose that wouldn't work either with your R_X86_64_64
>> implied zero-extension...
>>
>
I will add R_X86_64_64 support to x32 dynamic linker. I will
also add R_X86_64_RELATIVE64 to x32 dynamic linker.
For R_X86_64_64 relocation, if addend is 0, linker will
turn it to R_X86_64_32 and zero-extends it to 64bit. Otherwise,
linker will generate R_X86_64_RELATIVE64 if it is a relocation
against a local symbol or keep R_X86_64_64 for relocations
against external symbols. We need R_X86_64_RELATIVE64
since R_X86_64_RELATIVE only updates 32bit destination.
--
H.J.
---
diff --git a/object-files.tex b/object-files.tex
index 7f0fd14..d2be264 100644
--- a/object-files.tex
+++ b/object-files.tex
@@ -483,10 +483,13 @@ or \texttt{Elf32_Rel} relocation.
\texttt{R_X86_64_TLSDESC_CALL} & 35 & none & \\
\texttt{R_X86_64_TLSDESC} & 36 & \textit{word64}$\times 2$ & \\
\texttt{R_X86_64_IRELATIVE} & 37 & \textit{wordclass} &
\texttt{indirect (B + A)}\\
+ \texttt{R_X86_64_RELATIVE64} $^{\dagger\dagger}$ & 38 &
\textit{word64} & \texttt{B + A} \\
% \texttt{R_X86_64_GOT64} & 16 & \textit{word64} & \texttt{G + A} \\
% \texttt{R_X86_64_PLT64} & 17 & \textit{word64} & \texttt{L + A - P} \\
\cline{1-4}
\multicolumn{3}{l}{\small $^\dagger$ This relocation is used only
for LP64.}\\
+ \multicolumn{3}{l}{\small $^{\dagger\dagger}$ This relocation only
+ appears in X32 executable files or shared objects.}\\
\end{tabular}
\end{center}
\Hrule
