[edk2-devel] Casting i128 into f64 in UEFI Rust pagefaults
Ayush Singh
ayushdevel1325 at gmail.com
Mon Jul 25 17:33:57 UTC 2022
Hello everyone.While running Rust tests in UEFI environment, I have come
across a numeric test that causes a pagefault. A simple reproducible
example for this is given below:
```rust
fn main() {
use std::hint::black_box as b;
let z: i128 = b(1);
assert!((-z as f64) < 0.0);
}
```
The exception output is as follows:
```
!!!! X64 Exception Type - 0E(#PF - Page-Fault) CPU Apic ID - 00000000 !!!!
ExceptionData - 0000000000000000 I:0 R:0 U:0 W:0 P:0 PK:0 SS:0 SGX:0
RIP - 000000000603DB60, CS - 0000000000000038, RFLAGS - 0000000000000246
RAX - 0000000000000000, RCX - FFFFFFFFFFFFFFFF, RDX - FFFFFFFFFFFFFFFF
RBX - 0000000000000000, RSP - 0000000007EDF1D0, RBP - 0000000007EDF4C0
RSI - 0000000007EDF360, RDI - 0000000007EDF3C0
R8 - 0000000000000000, R9 - 0000000000000038, R10 - 0000000000000000
R11 - 0000000000000000, R12 - 00000000060C6018, R13 - 0000000007EDF520
R14 - 0000000007EDF6A8, R15 - 0000000005FA9490
DS - 0000000000000030, ES - 0000000000000030, FS - 0000000000000030
GS - 0000000000000030, SS - 0000000000000030
CR0 - 0000000080010033, CR2 - FFFFFFFFFFFFFFFF, CR3 - 0000000007C01000
CR4 - 0000000000000668, CR8 - 0000000000000000
DR0 - 0000000000000000, DR1 - 0000000000000000, DR2 - 0000000000000000
DR3 - 0000000000000000, DR6 - 00000000FFFF0FF0, DR7 - 0000000000000400
GDTR - 00000000079DE000 0000000000000047, LDTR - 0000000000000000
IDTR - 0000000007418018 0000000000000FFF, TR - 0000000000000000
FXSAVE_STATE - 0000000007EDEE30
!!!! Find image based on IP(0x603DB60)
/var/home/ayush/Documents/Programming/Rust/uefi/hello_world_std/target/x86_64-unknown-uefi/debug/deps/hello_world_std-338028f9369e2d42.pdb
(ImageBase=000000000603C000, EntryPoint=000000000603D8C0) !!!!
```
From my testing, the exception only occurs when a few conditions are met.
1. The binary is compiled in Debug mode. No error in Release mode.
2. `i128` is in a black_box [1]. Does not occur if `black_box` is not
present.
3. It has to be `i128`. `i64` or something else work fine.
4. The cast has to be done on `-z`. Doing the same with `+z` is fine.
I have also been discussing this in the Rust zulipchat [2], so feel free
to chime in there.
Additionally, here are links for more information about this program:
1. Assembly:
https://rust-lang.zulipchat.com/user_uploads/4715/od51Y9Dkfjahcg9HHcOud8Fm/hello_world_std-338028f9369e2d42.s
2. EFI Binary:
https://rust-lang.zulipchat.com/user_uploads/4715/CknqtXLR8SaJZmyOnXctQkpL/hello_world_std.efi
3. PDB file:
https://rust-lang.zulipchat.com/user_uploads/4715/zV4i6DsjgQXotp_gS1naEsU0/hello_world_std-338028f9369e2d42.pdb
Yours Sincerely,
Ayush Singh
[1]: https://doc.rust-lang.org/std/hint/fn.black_box.html
[2]:
https://rust-lang.zulipchat.com/#narrow/stream/182449-t-compiler.2Fhelp/topic/Casting.20i128.20to.20f64.20in.20black_box.20causes.20exception.20in.20UEFI
-=-=-=-=-=-=-=-=-=-=-=-
Groups.io Links: You receive all messages sent to this group.
View/Reply Online (#91818): https://edk2.groups.io/g/devel/message/91818
Mute This Topic: https://groups.io/mt/92610101/1813853
Group Owner: devel+owner at edk2.groups.io
Unsubscribe: https://edk2.groups.io/g/devel/unsub [edk2-devel-archive at redhat.com]
-=-=-=-=-=-=-=-=-=-=-=-
More information about the edk2-devel-archive
mailing list