llvm dev - Sep 2013 - [LLVMdev] LLVM ERROR: expected relocatable expression

On 09/20/2013 06:00 PM, Eli Friedman wrote:
> On Fri, Sep 20, 2013 at 2:50 PM, Sid Manning <sidneym at codeaurora.org
> <mailto:sidneym at codeaurora.org>> wrote:
>
>
>     This example generates the following error:
>     .Ltmp3:
>     .Ltmp5:
>     .Ltmp13:
>              .word   (.Ltmp5-.Ltmp3)-.Ltmp13
>
>     ./llvm-mc ex.s -filetype=obj
>     LLVM ERROR: expected relocatable expression when using:
>
>
> Umm, isn't this equivalent to the following?  What do you expect LLVM
to
> do with it?
>
> .Ltmp13:
>      .word -.Ltmp13
I removed the target specific assembly to produce a simple generic 
example.  It was derived from eh_frame code the compiler was emitting.

(.Ltmp5-.Ltmp3)+.Ltmp13 does not generate the error.
>
> -Eli

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On Sun, Sep 22, 2013 at 12:23 PM, Sid Manning <sidneym at
codeaurora.org>wrote:
> On 09/20/2013 06:00 PM, Eli Friedman wrote:
>
>> On Fri, Sep 20, 2013 at 2:50 PM, Sid Manning <sidneym at
codeaurora.org
>> <mailto:sidneym at codeaurora.org**>> wrote:
>>
>>
>>     This example generates the following error:
>>     .Ltmp3:
>>     .Ltmp5:
>>     .Ltmp13:
>>              .word   (.Ltmp5-.Ltmp3)-.Ltmp13
>>
>>     ./llvm-mc ex.s -filetype=obj
>>     LLVM ERROR: expected relocatable expression when using:
>>
>>
>> Umm, isn't this equivalent to the following?  What do you expect
LLVM to
>> do with it?
>>
>> .Ltmp13:
>>      .word -.Ltmp13
>>
>
> I removed the target specific assembly to produce a simple generic example.

Then you must have reduced it too much; your example is simply invalid
(although the compiler's error message isn't great).

-Eli
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Hi Eli,

Slightly changed the example :-

.section somedata
.Ltmpa:
.word 100
.Ltmpb:
.word 60
.Ltmpc:
.word 40
.Ltmpd:
.word   (.Ltmpa-.Ltmpb)-.Ltmpc

The GNU assembler properly handles the above.

$as -c x.s -o x.o
$readelf -x 4 x.o

Hex dump of section 'somedata':
  NOTE: This section has relocations against it, but these have NOT been 
applied to this dump.
   0x00000000 64003c00 28000000                   d.<.(...
^^^^ (Calculated properly too!)
With clang/llvm-mc

$ llvm-mc -filetype=obj x.s -o x.o
LLVM ERROR: expected relocatable expression

Looks like llvm-mc is more restrictive ?

Thanks

Shankar Easwaran

-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by the
Linux Foundation

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