Ah, I see. It looks like you have to set this before you create the process.
If I put this setting in my .lldbinit, or on the command line before I do "run"
it does limit the read size. But apparently once we've created the memory
cache we don't replace it when this value changes.
That's still worth a bug either to fix it or to make the help string for this
setting tell you how to use it.
Jim
> On Jun 21, 2018, at 1:47 PM, Jim Ingham <jing...@apple.com> wrote:
>
> A quick scan of the code looks like this should be hooked up, but you are
> right, it doesn't seem to actually limit the cache page size. There's only
> one test for this and that one just checks that the setting has some
> particular value for android. Can you file a bug for this with bugs.llvm.org?
>
> Jim
>
>
>> On Jun 21, 2018, at 11:51 AM, Andrew Baumann <andrew.baum...@microsoft.com>
>> wrote:
>>
>> Thanks! Disabling the cache worked.
>>
>> Curiously, setting the line size seems to have no effect – it defaults to
>> 512 (words, bytes, ...?), and still tries to read a page of guest memory
>> regardless of how small I set it.
>>
>> Andrew
>>
>> From: jing...@apple.com <jing...@apple.com> on behalf of Jim Ingham
>> <jing...@apple.com>
>> Sent: Thursday, June 21, 2018 11:32:03 AM
>> To: Andrew Baumann
>> Cc: lldb-dev@lists.llvm.org
>> Subject: Re: [lldb-dev] Accessing only specific words in guest memory
>>
>> By default, lldb uses a memory cache to avoid making lots of tiny memory
>> requests, which tends to be inefficient especially when talking to a remote
>> device. You can turn this off with the
>> "target.process.disable-memory-cache" setting.
>>
>> You can also adjust the cache page size with
>> "target.process.memory-cache-line-size".
>>
>> We don't yet have a memory map command to tell us what regions to read and
>> not to read. So if you try to actually print the structure (with "frame
>> var" or "expr") we will grab the whole thing. But turning off the cache
>> should allow you to avoid the disallowed regions manually.
>>
>> Jim
>>
>>> On Jun 21, 2018, at 11:20 AM, Andrew Baumann via lldb-dev
>>> <lldb-dev@lists.llvm.org> wrote:
>>>
>>> Hi,
>>>
>>> I’m trying to use lldb 6.0 on Linux to debug a process that has an SGX
>>> enclave inside it. One of the data structures there (the “TCS”) only
>>> permits access to certain fields. The problem is that when I try to access
>>> those fields in LLDB, it tries to read an entire page of memory from the
>>> guest, even if I only wanted to read one word. It then fails the operation
>>> when access to later parts of the page fails.
>>>
>>> e.g., this LLDB command:
>>>
>>> (lldb) x/1g 0x200005000
>>> error: memory read failed for 0x200005000
>>>
>>> Triggered this series of failures in the lldb-server process:
>>>
>>> read(7, "$x200005000,200#ed", 8192) = 18
>>> gettid() = 18169
>>> process_vm_readv(18174, [{iov_base=0x556a00151cf0, iov_len=512}], 1,
>>> [{iov_base=0x200005000, iov_len=512}], 1, 0) = -1 EFAULT (Bad address)
>>> ptrace(PTRACE_PEEKDATA, 18174, 0x200005000, [NULL]) = 0
>>> ptrace(PTRACE_PEEKDATA, 18174, 0x200005008, [NULL]) = 0
>>> ptrace(PTRACE_PEEKDATA, 18174, 0x200005010, [0xd000]) = 0
>>> ptrace(PTRACE_PEEKDATA, 18174, 0x200005018, [0x300000001]) = 0
>>> ptrace(PTRACE_PEEKDATA, 18174, 0x200005020, [0x1d950]) = 0
>>> ptrace(PTRACE_PEEKDATA, 18174, 0x200005028, [0x3fffc00be750]) = 0
>>> ptrace(PTRACE_PEEKDATA, 18174, 0x200005030, [0xa000]) = 0
>>> ptrace(PTRACE_PEEKDATA, 18174, 0x200005038, [0xb000]) = 0
>>> ptrace(PTRACE_PEEKDATA, 18174, 0x200005040, [0xffffffffffffffff]) = 0
>>> ptrace(PTRACE_PEEKDATA, 18174, 0x200005048, 0x7ffc96125858) = -1 EIO
>>> (Input/output error)
>>> write(7, "$E08#ad", 7) = 7
>>>
>>> How can I convince lldb to access just the words I asked it for?
>>>
>>> Thanks,
>>> Andrew
>>> _______________________________________________
>>> lldb-dev mailing list
>>> lldb-dev@lists.llvm.org
>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev
>
_______________________________________________
lldb-dev mailing list
lldb-dev@lists.llvm.org
http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev
