[U-Boot] SPL size issues on OMAP4

[Michael Trimarchi]

Hi

cc: Mailing List

On 07/11/2013 07:33 PM, Michael Trimarchi wrote:
> Hi Michael
> 
> On 07/11/2013 07:01 PM, Michael Cashwell wrote:
>> Greetings,
>>
>> I've been absent for a while and couldn't find a way to search the list archives so I apologize if this has already been discussed…
>>
>> I've been fighting the SPL binary growing too large on OMAP4 (using custom configs and features). It's annoying that too large just fails to run with no build or runtime notice. But that's a different issue.
>>
>> My main issue is that in looking through the map for SPL I've repeatedly found code that I don't need and have a pretty good handle on that. My issue is that code that is compiled but eliminated because it's not called leaves behind all of its anonymous strings ("like this"). In my latest build I have the following sections that are all anonymous strings:
>>
>> 0x4030b638      0x232 arch/arm/cpu/armv7/omap-common/libomap-common.o
>> 0x4030b8b5       0x19 arch/arm/cpu/armv7/omap4/libomap4.o
>> 0x4030b9ad       0xbe common/spl/libspl.o
>> 0x4030ba6b       0x57 drivers/gpio/libgpio.o
>> 0x4030bac2      0x44c drivers/i2c/libi2c.o
>> 0x4030bf0e      0x302 drivers/mmc/libmmc.o
>> 0x4030c27e       0x15 drivers/serial/libserial.o
>> 0x4030c293      0x145 drivers/spi/libspi.o
>> 0x4030c4d8       0x53 lib/libgeneric.o
>>
>> with more than half being unreferenced. This is a big deal when you only have about 25K of SRAM for code and data.
>>
> 
> I don't give an answer but some suggestions:
> 
> - using a raw partition to boot and remove the vfat support in first stage boot
> - safety you can add 2Kb more to CONFIG_SPL_MAX_SIZE (tested on serial boot too)
> - do some tests on different toolchains
> 
> Try to move all in the second stage when it's possible
> 
> Michael
> 

Michael

>> In searching the web it seems that dead code and data are removed using --gc-sections, -ffunction-sections and -fdata-sections which u-boot is using correctly.
>>
>> But it seems that gcc puts all anonymous strings into the same section (.rodata or .rodata.str1.1 if string merging is on) which prevents them from participating in the stripping process.
>>
>> Interestingly, it puts its own __func__ strings into separate sections and they are eliminated if the function go away. It just doesn't do this for plain "" strings.  Grrr.
>>
>> I was shocked to find gcc posts asking about this more than 13 years ago with barely any traction at all. Given that embarrassing history I'm not hopefully that the gcc folks will ever address this.
>>
>> Is there a work around I haven't thought of? I'm thinking along the lines of disabling all printfs in SPL in the hope that will take the strings away (since many are some sort of debug / progress message).
>>
>> Any thoughts or guidance would be appreciated.
>>
>> -Mike
>>
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>