[llvm-dev] Allocating shadow tables at the bottom of memory on Linux.

[Carter Cheng via llvm-dev]

Is there documentation for the hooks used by compiler-rt somewhere?

On Fri, Jul 5, 2019 at 7:30 PM Carter Cheng <cartercheng at gmail.com> wrote:

> Great, thanks for the info!
>
> On Fri, Jul 5, 2019 at 4:25 PM Tim Northover <t.p.northover at gmail.com>
> wrote:
>
>> Hi Carter,
>>
>> On Fri, 5 Jul 2019 at 09:05, Carter Cheng via llvm-dev
>> <llvm-dev at lists.llvm.org> wrote:
>> > I have been working on a llvm instrumentation pass as an exercise to
>> get up to speed on how llvm operates. I am curious about what the best way
>> would be to create a shadow table at a fixed address in low memory starting
>> at 0x10000 and extending upwards.
>>
>> Normally you'd put your data into a custom named section and then tell
>> the linker to put that section at a specific address through either
>> command-line options or a linker script.
>>
>> > I am uncertain how the code ensures that the runtime metadata doesnt
>> get overwritten by alloca calls for the stack.
>>
>> If the value is a global it'll pretty much automatically be handled by
>> the linker and OS. The stack is usually pretty small and can be placed
>> out of the way of any allocation the OS knows about (and it knows
>> about all of them because it has to actually do the allocation at the
>> end of the day).
>>
>> I think some sanitizers have a runtime that takes over the stack and
>> heap though and allocate both the "real" memory and its shadow
>> together. See compiler-rt/lib/asan for example.
>>
>> Cheers.
>>
>> Tim.
>> >
>> > Thanks in advance,
>> >
>> > Carter.
>> > _______________________________________________
>> > LLVM Developers mailing list
>> > llvm-dev at lists.llvm.org
>> > https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>
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