mikros/rust
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Auto merge of #87124 - Andy-Python-Programmer:code_model_uefi_patch, r=petrochenkov

Browse Source 
Use small code model for UEFI targets

* Since the code model only applies to the code and not the data and the code model
only applies to functions you call through using `call`, `jmp` and data with `lea`, etc…

  If you are calling functions using the function pointers from the UEFI structures the code
  model does not apply in that case. It’s just related to the address space size of your own binary.
  Since UEFI (uefi is all relocatable) uses relocatable PEs (relocatable code does not care about the
  code model) so, we use the small code model here.

* Since applications don't usually take gigabytes of memory, setting the
target to use the small code model should result in better codegen (comparable
with majority of other targets).

  Large code models are also known for generating horrible code, for
  example 16 bytes of code to load a single 8-byte value.

Signed-off-by: Andy-Python-Programmer <andypythonappdeveloper@gmail.com>
This commit is contained in:
bors 2021-07-17 10:15:33 +00:00
commit 64d171b8a4
1 changed files with 2 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
compiler/rustc_target/src/spec/x86_64_unknown_uefi.rs
View File

@ -5,7 +5,7 @@
// The win64 ABI is used. It differs from the sysv64 ABI, so we must use a windows target with
// LLVM. "x86_64-unknown-windows" is used to get the minimal subset of windows-specific features.
use crate::spec::{CodeModel, Target};
use crate::spec::Target;
pub fn target() -> Target {
let mut base = super::uefi_msvc_base::opts();
@ -19,15 +19,11 @@ pub fn target() -> Target {
// to leave these uninitialized, thus triggering exceptions if we make use of them. Which is
// why we avoid them and instead use soft-floats. This is also what GRUB and friends did so
// far.
//
// If you initialize FP units yourself, you can override these flags with custom linker
// arguments, thus giving you access to full MMX/SSE acceleration.
base.features = "-mmx,-sse,+soft-float".to_string();
// UEFI systems run without a host OS, hence we cannot assume any code locality. We must tell
// LLVM to expect code to reference any address in the address-space. The "large" code-model
// places no locality-restrictions, so it fits well here.
base.code_model = Some(CodeModel::Large);
Target {
llvm_target: "x86_64-unknown-windows".to_string(),
pointer_width: 64,