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Avoid redundant instructions in x86 inline asm #233

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Feb 22, 2022
Merged

Avoid redundant instructions in x86 inline asm #233

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95b301b
Minor code simplification using `cfg_attr`.
sunfishcode Feb 15, 2022
b233ea8
Avoid an unnecessary push/pop in the x86 indirect_syscall5 path.
sunfishcode Feb 15, 2022
e3618be
Tidy up comments in the x86 syscall code.
sunfishcode Feb 15, 2022
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42 changes: 10 additions & 32 deletions src/imp/linux_raw/arch/inline/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2,36 +2,14 @@
//! much like regular calls, with custom calling conventions, and calling
//! conventions are otherwise the compiler's job. But for now, use inline asm.

#[cfg(target_arch = "aarch64")]
mod aarch64;
#[cfg(target_arch = "arm")]
mod arm;
#[cfg(target_arch = "mips")]
mod mips;
#[cfg(target_arch = "mips64")]
mod mips64;
#[cfg(target_arch = "powerpc64")]
mod powerpc64;
#[cfg(target_arch = "riscv64")]
mod riscv64;
#[cfg(target_arch = "x86")]
mod x86;
#[cfg(target_arch = "x86_64")]
mod x86_64;
#[cfg_attr(target_arch = "aarch64", path = "aarch64.rs")]
#[cfg_attr(target_arch = "arm", path = "arm.rs")]
#[cfg_attr(target_arch = "mips", path = "mips.rs")]
#[cfg_attr(target_arch = "mips64", path = "mips64.rs")]
#[cfg_attr(target_arch = "powerpc64", path = "powerpc64.rs")]
#[cfg_attr(target_arch = "riscv64", path = "riscv64.rs")]
#[cfg_attr(target_arch = "x86", path = "x86.rs")]
#[cfg_attr(target_arch = "x86_64", path = "x86_64.rs")]
mod target_arch;

#[cfg(target_arch = "aarch64")]
pub(in crate::imp) use self::aarch64::*;
#[cfg(target_arch = "arm")]
pub(in crate::imp) use self::arm::*;
#[cfg(target_arch = "mips")]
pub(in crate::imp) use self::mips::*;
#[cfg(target_arch = "mips64")]
pub(in crate::imp) use self::mips64::*;
#[cfg(target_arch = "powerpc64")]
pub(in crate::imp) use self::powerpc64::*;
#[cfg(target_arch = "riscv64")]
pub(in crate::imp) use self::riscv64::*;
#[cfg(target_arch = "x86")]
pub(in crate::imp) use self::x86::*;
#[cfg(target_arch = "x86_64")]
pub(in crate::imp) use self::x86_64::*;
pub(in crate::imp) use self::target_arch::*;
19 changes: 7 additions & 12 deletions src/imp/linux_raw/arch/inline/x86.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -153,15 +153,13 @@ pub(in crate::imp) unsafe fn indirect_syscall5(
// registers free. Use eax as a temporary pointer to a slice, since it
// gets clobbered as the return value anyway.
asm!(
"push ebp",
"push esi",
"push DWORD PTR [eax + 0]",
"mov esi, DWORD PTR [eax + 4]",
"mov eax, DWORD PTR [eax + 8]",
"call DWORD PTR [esp]",
"pop esi",
"pop esi",
"pop ebp",
inout("eax") &[callee as usize, a3.to_asm(), nr.to_asm()] => r0,
in("ebx") a0.to_asm(),
in("ecx") a1.to_asm(),
Expand Down Expand Up @@ -402,8 +400,10 @@ pub(in crate::imp) unsafe fn syscall5(
a4: ArgReg<'_, A4>,
) -> RetReg<R0> {
let r0;
// As in syscall 4, use xchg to handle a3. a4 should go in edi, and
// we can use that register as an operand.
// As in `syscall4`, use xchg to handle a3. a4 should go in edi, and we can
// use that register as an operand. Unlike in `indirect_syscall5`, we don't
// have a `callee` operand taking up a register, so we have enough
// registers and don't need to use a slice.
asm!(
"xchg esi, {a3}",
"int $$0x80",
Expand All @@ -430,6 +430,7 @@ pub(in crate::imp) unsafe fn syscall5_readonly(
a4: ArgReg<'_, A4>,
) -> RetReg<R0> {
let r0;
// See the comments in `syscall5`.
asm!(
"xchg esi, {a3}",
"int $$0x80",
Expand Down Expand Up @@ -457,14 +458,7 @@ pub(in crate::imp) unsafe fn syscall6(
a5: ArgReg<'_, A5>,
) -> RetReg<R0> {
let r0;
// Oof. a3 should go in esi, and a5 should go in ebp, and `asm!` won't
// let us use either of those registers as operands. And we can't request
// stack slots. And there are no other registers free. Use eax as a
// temporary pointer to a slice, since it gets clobbered as the return
// value anyway.
//
// This is another reason that syscalls should be compiler intrinsics
// rather than inline asm.
// See the comments in `indirect_syscall6`.
asm!(
"push ebp",
"push esi",
Expand Down Expand Up @@ -496,6 +490,7 @@ pub(in crate::imp) unsafe fn syscall6_readonly(
a5: ArgReg<'_, A5>,
) -> RetReg<R0> {
let r0;
// See the comments in `indirect_syscall6`.
asm!(
"push ebp",
"push esi",
Expand Down