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Re: [PATCH] Added information about inline assembler in stack calculations (.su files)


On 12/1/18 1:15 AM, Jeff Law wrote:
> On 11/26/18 7:02 AM, Torbjorn SVENSSON wrote:
>> Hi,
>>
>> Attached is a small patch that, in case of inline assembler code,
>> indicates that the function stack usage is uncertain due to inline
>> assembler.
>>
>> The test suite are using "nop" as an assembler instruction on all
>> targets, is this acceptable or is there a better way to test this?
>>
>> Patch has been tested on gcc-arm-none-eabi-7-2018-q2-update for both
>> arm-none-eabi and x86_64-linux-gnu and SVN head (r266454) for
>> x86_64-linux-gnu.
> One could argue that allocating stack space inside an ASM is a really
> bad idea.  Consider things like dwarf debugging and unwind tables.  If
> you're allocating stack inside an ASM that stuff is going to be totally
> wrong.
>
> So I think my question before moving forward with something like this is
> whether or not it makes sense at all to bother dumping data for a
> scenario that we'd probably suggest developers avoid to begin with.
>
> jeff
Hi,

The purpose of the patch is to notify when the reported stack usage might be
incorrect. Even if it's bad practice to alter stack in asm, there are 
use cases
in the embedded world that makes sense. A notable common use case is 
FreeRTOS
task switch using ARM "naked" attribute and inline asm, which reports "0 
static",
which gives a faulty stack usage. We have considered the other option to
report a warning for these cases, but that alternative hasn't appealed 
to us.

Niklas

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