[U-Boot] [RFC PATCH] arm: lds: Remove libgcc eabi exception handling tables

[Michal Simek]

Hi Albert,

On 05/14/2013 05:44 PM, Albert ARIBAUD wrote:
> Hi Michal,
> 
> On Mon, 13 May 2013 09:45:12 +0200, Michal Simek <monstr at monstr.eu>
> wrote:
> 
>> On 05/10/2013 09:07 PM, Albert ARIBAUD wrote:
>>> Hi Michal,
>>>
>>> On Thu,  9 May 2013 11:35:33 +0200, Michal Simek
>>> <michal.simek at xilinx.com> wrote:
>>>
>>>> Remove ARM eabi exception handling tables (for frame unwinding).
>>>> AFAICT, u-boot stubs away the frame unwiding routines, so the tables will
>>>> more or less just consume space. It should be OK to remove them.
>>>>
>>>> Signed-off-by: Edgar E. Iglesias <edgar.iglesias at xilinx.com>
>>>> Signed-off-by: Michal Simek <michal.simek at xilinx.com>
>>>> ---
>>>> Other options could be to complete u-boot/arch/arm/lib/* so that
>>>> libgcc routines with exception handling dont get pulled in. Or
>>>> to avoid user code (like the mentioned patch) which causes external
>>>> libgcc functions to get pulled in...
>>>
>>> Er... which mentioned patch?
>>
>> Ah yeah. Let me give you background.
>> After adding:
>> "arm: zynq: U-Boot udelay < 1000 FIX"
>> (sha1: d54cc007878697a92e7f696b71a3eb203c0386e2)
>>
>> we have found that new program header is added to u-boot for zynq.
>>
>> Program Header:
>> 0x70000001 off    0x000405fc vaddr 0x040385fc paddr 0x040385fc align 2**2
>>          filesz 0x00000020 memsz 0x00000020 flags r--
>>     LOAD off    0x00008000 vaddr 0x04000000 paddr 0x04000000 align 2**15
>>          filesz 0x00041240 memsz 0x00041240 flags rwx
>>    STACK off    0x00000000 vaddr 0x00000000 paddr 0x00000000 align 2**2
>>          filesz 0x00000000 memsz 0x00000000 flags rwx
>>
>> Tracing down this we found that uldivmod is used
>>     27: 00000000     0 NOTYPE  GLOBAL DEFAULT  UND __aeabi_uldivmod
>>
>> Based on that Edgar proposed this patch.
> 
> Ok, so Michal and I just did some fiddling with zynq builds and
> *exidx* sections.
> 
> By default the *exidx* sections are between rodata and data, so
> removing them causes many apparent changes at the binary level.
> However, builds of zynq based on ARM master with the patch above vs
> master with a patch mapping *exidx* sections after BSS gives identical
> binaries. Thus the RFC has no functional effect. 
> 
> Also, ARM EHABI states that [exception] Tables are not required for ABI
> compliance at the C/Assembler level but are required for C++.
> 
> http://infocenter.arm.com/help/topic/com.arm.doc.ihi0038a/IHI0038A_ehabi.pdf
> 
> So as long as we don't put any C++ code in U-Boot (a prospect that I
> don't see happening any time soon), this RFC is safe and either is a
> no-op or removes useless bytes from the binary.

Any update on this?
Have you decided to add or not to add to this release?
If you I need to fix zynq timer code do not use exception handling table.

Thanks,
Michal

-- 
Michal Simek, Ing. (M.Eng), OpenPGP -> KeyID: FE3D1F91
w: www.monstr.eu p: +42-0-721842854
Maintainer of Linux kernel - Microblaze cpu - http://www.monstr.eu/fdt/
Maintainer of Linux kernel - Xilinx Zynq ARM architecture
Microblaze U-BOOT custodian and responsible for u-boot arm zynq platform


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