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stack overflow docs (#13399)

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* stack overflow docs

* whitespace
This commit is contained in:
Jack May
2020-11-04 13:35:59 -08:00
committed by GitHub
parent cb2e8f9084
commit 8aa00381ef
1 changed files with 26 additions and 6 deletions
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docs/src/developing/deployed-programs/overview.md
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@ -43,12 +43,32 @@ the attempted violation.
## Stack ## Stack
BPF uses stack frames instead of a variable stack pointer. Each stack frame is BPF uses stack frames instead of a variable stack pointer. Each stack frame is
4KB in size. If a program violates that stack frame size, the compiler will 4KB in size.
report the overrun as a warning. The reason a warning is reported rather than an
error is because some dependent crates may include functionality that violates If a program violates that stack frame size, the compiler will report the
the stack frame restrictions even if the program doesn't use that functionality. overrun as a warning.
If the program violates the stack size at runtime, an `AccessViolation` error
will be reported. For example: `Error: Function
_ZN16curve25519_dalek7edwards21EdwardsBasepointTable6create17h178b3d2411f7f082E
Stack offset of -30728 exceeded max offset of -4096 by 26632 bytes, please
minimize large stack variables`
The message identifies which symbol is exceeding its stack frame but the name
might be mangled if it is a Rust or C++ symbol. To demangle a Rust symbol use
[rustfilt](https://github.com/luser/rustfilt). The above warning came from a
Rust program, so the demangled symbol name is:
```bash
$ rustfilt _ZN16curve25519_dalek7edwards21EdwardsBasepointTable6create17h178b3d2411f7f082E
curve25519_dalek::edwards::EdwardsBasepointTable::create
```
To demangle a C++ symbol use `c++filt` from binutils.
The reason a warning is reported rather than an error is because some dependent
crates may include functionality that violates the stack frame restrictions even
if the program doesn't use that functionality. If the program violates the stack
size at runtime, an `AccessViolation` error will be reported.
BPF stack frames occupy a virtual address range starting at 0x200000000. BPF stack frames occupy a virtual address range starting at 0x200000000.