[U-Boot] [PATCH v2 4/9] arm: add _thumb1_case_uqi to libgcc

[V, Aneesh]

On Mon, Aug 13, 2012 at 5:36 PM, Allen Martin <amartin at nvidia.com> wrote:
> On Mon, Aug 13, 2012 at 04:44:05PM -0700, Stephen Warren wrote:
>> On 08/01/2012 02:32 PM, Allen Martin wrote:
>> > Add function required by some thumb switch statements
>>
>> > diff --git a/arch/arm/lib/_thumb1_case_uqi.S b/arch/arm/lib/_thumb1_case_uqi.S
>>
>> > +   .force_thumb
>>
>> I believe that line should be removed.
>>
>> The issue here is that when gcc emits Thumb code to call this function,
>> it actually emits:
>>
>> >   108af8:       f000 f94a       bl      108d90 <____gnu_thumb1_case_uqi_from_thumb>
>>
>> which is implemented as:
>>
>> > 00108d90 <____gnu_thumb1_case_uqi_from_thumb>:
>> >   108d90:       4778            bx      pc
>> >   108d92:       46c0            nop                     ; (mov r8, r8)
>> >   108d94:       eafffde1        b       108520 <__gnu_thumb1_case_uqi>
>>
>> i.e. it switches to ARM mode then jumps to that function. Hence,
>> __gnu_thumb1_case_uqi must be compiled as ARM, not as Thumb.
>
> The function is supposed to be thumb code, it's basically a thumb
> optimization of a switch statement, and in the ARM case the compiler
> just emits the code directly instead of calling into libgcc.  So it
> doesn't really make sense for the function to be anything but thumb.
>
> I think the real problem is the linker incorrectly thought the code
> was ARM so it generated a thumb to ARM interworking veneer.
>
> Can you try adding a ".type __gnu_thumb1_case_uqi STT_FUNC" instead?
> I've seen cases where the assembler generates the wrong type of symbol
> without some explicit guidance which messes up the linker's
> interworking generator.  This might be one of those.

Yes, not having STT_FUNC or %function is troublesome. I have faced this
before.

Maybe you should wrap the assembly functions with standard ENTRY,
END_PROC macros from linkage.h. This will take care of STT_FUNC

best regards,
Aneesh