[lldb-dev] Loading object file to target flash memory using vFlashWrite

[Greg Clayton via lldb-dev]

> On Jan 9, 2018, at 3:53 PM, Owen Shaw via lldb-dev <lldb-dev at lists.llvm.org> wrote:
> 
> Looks like there was an addition about a year ago to load an object
> file to bare metal target memory via "target modules load --load".
> https://reviews.llvm.org/D28804
> 
> However, this isn't working in my case with openocd and a target that
> uses flash memory.  By comparison, gdb loads the object just fine, but
> instead of using the M memory write command, it uses vFlashErase,
> vFlashWrite, and vFlashDone.
> 
> These flash commands don't seem to be supported in lldb.  Any reason
> not to add them?
> 
> I've got a basic working implementation, which is probably easier to
> break into two reviews:
> 
> 1. Add support for qXfer:memory-map and parse the resulting xml to
> determine which memory regions are flash and what their blocksizes are
> (required for vFlashErase)
> 2. Update ProcessGDBRemote::DoWriteMemory to use the flash commands
> when writing to a flash region, while continuing to use M when writing
> to non-flash regions.
> 
> If this sounds like the right track, I'll open a Phabricator review
> for #1 to start.

Those two things sound about right. Though we typically don't like to add support for something if it isn't used. #1 would add support for "qXfer:memory-map", but nothing would use it. So it might be ok to submit #1 and #2 as one patch. I am open to suggestions from others if they believe differently. A patch should have tests for this and I am not sure how to test it, but just know that we will want some sort of tests.

> 
> One question I have relates to the load address for object sections.
> The current ObjectFile::LoadInMemory implementation will incorrectly
> place my .data section at its virtual address in RAM when it really
> should be placed at its physical address in flash memory.  I have code
> that can place it at the physical address, but it's unclear if that
> change is correct for every case.  Does anyone have insight/opinions?

Right now we just load things at the virtual address found in the ELF file. Not sure if the physical address should be used for everyone as I am not sure of exactly who is using this right now. Most of the time when I see ELF files the virtual address is equal to the physical address, so it might just be ok. Feel free to let us know what you think should happen and submit a patch. If no one has any tests that break in response to this, then we can try it and see how things go.

Greg

> 
> Thanks,
> Owen
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