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Add control flow information to __rust_probestack #328

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Dec 6, 2019
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Add control flow information to __rust_probestack #328

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1 change: 1 addition & 0 deletions src/lib.rs
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
#![cfg_attr(feature = "compiler-builtins", compiler_builtins)]
#![feature(abi_unadjusted)]
#![feature(asm)]
#![feature(global_asm)]
#![feature(cfg_target_has_atomic)]
#![feature(compiler_builtins)]
#![feature(core_intrinsics)]
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232 changes: 143 additions & 89 deletions src/probestack.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -41,95 +41,149 @@
//! probes on any other architecture like ARM or PowerPC64. LLVM I'm sure would
//! be more than welcome to accept such a change!

#![cfg(not(windows))] // Windows already has builtins to do this

#[naked]
#[no_mangle]
#[cfg(all(target_arch = "x86_64", not(feature = "mangled-names")))]
pub unsafe extern "C" fn __rust_probestack() {
// Our goal here is to touch each page between %rsp+8 and %rsp+8-%rax,
// ensuring that if any pages are unmapped we'll make a page fault.
//
// The ABI here is that the stack frame size is located in `%eax`. Upon
// return we're not supposed to modify `%esp` or `%eax`.
asm!("
pushq %rbp
movq %rsp, %rbp

mov %rax,%r11 // duplicate %rax as we're clobbering %r11

// Main loop, taken in one page increments. We're decrementing rsp by
// a page each time until there's less than a page remaining. We're
// guaranteed that this function isn't called unless there's more than a
// page needed.
//
// Note that we're also testing against `8(%rsp)` to account for the 8
// bytes pushed on the stack orginally with our return address. Using
// `8(%rsp)` simulates us testing the stack pointer in the caller's
// context.

// It's usually called when %rax >= 0x1000, but that's not always true.
// Dynamic stack allocation, which is needed to implement unsized
// rvalues, triggers stackprobe even if %rax < 0x1000.
// Thus we have to check %r11 first to avoid segfault.
cmp $$0x1000,%r11
jna 3f
2:
sub $$0x1000,%rsp
test %rsp,8(%rsp)
sub $$0x1000,%r11
cmp $$0x1000,%r11
ja 2b

3:
// Finish up the last remaining stack space requested, getting the last
// bits out of r11
sub %r11,%rsp
test %rsp,8(%rsp)

// Restore the stack pointer to what it previously was when entering
// this function. The caller will readjust the stack pointer after we
// return.
add %rax,%rsp

leave
ret
" ::: "memory" : "volatile");
::core::intrinsics::unreachable();
#![cfg(not(feature = "mangled-names"))]
// Windows already has builtins to do this.
#![cfg(not(windows))]
// We only define stack probing for these architectures today.
#![cfg(any(target_arch = "x86_64", target_arch = "x86"))]

extern "C" {
pub fn __rust_probestack();
}

#[naked]
#[no_mangle]
#[cfg(all(target_arch = "x86", not(feature = "mangled-names")))]
pub unsafe extern "C" fn __rust_probestack() {
// This is the same as x86_64 above, only translated for 32-bit sizes. Note
// that on Unix we're expected to restore everything as it was, this
// function basically can't tamper with anything.
//
// The ABI here is the same as x86_64, except everything is 32-bits large.
asm!("
push %ebp
mov %esp, %ebp
push %ecx
mov %eax,%ecx

cmp $$0x1000,%ecx
jna 3f
2:
sub $$0x1000,%esp
test %esp,8(%esp)
sub $$0x1000,%ecx
cmp $$0x1000,%ecx
ja 2b

3:
sub %ecx,%esp
test %esp,8(%esp)

add %eax,%esp
pop %ecx
leave
ret
" ::: "memory" : "volatile");
::core::intrinsics::unreachable();
// A wrapper for our implementation of __rust_probestack, which allows us to
// keep the assembly inline while controlling all CFI directives in the assembly
// emitted for the function.
//
// This is the ELF version.
#[cfg(not(target_vendor = "apple"))]
macro_rules! define_rust_probestack {
($body: expr) => {
concat!(
"
.pushsection .text.__rust_probestack
.globl __rust_probestack
.type __rust_probestack, @function
__rust_probestack:
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I believe on Mach-O the linker would be allowed to move this symbol and following content to another location, as it uses symbols to determine the start and end of every function.

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I think that would be fine. __rust_probestack is the function that gets called, not __rust_probestack_wrapper.

",
$body,
"
.size __rust_probestack, . - __rust_probestack
.popsection
"
)
};
}

// Same as above, but for Mach-O.
#[cfg(target_vendor = "apple")]
macro_rules! define_rust_probestack {
($body: expr) => {
concat!(
"
.globl ___rust_probestack
___rust_probestack:
",
$body
)
};
}

// Our goal here is to touch each page between %rsp+8 and %rsp+8-%rax,
// ensuring that if any pages are unmapped we'll make a page fault.
//
// The ABI here is that the stack frame size is located in `%rax`. Upon
// return we're not supposed to modify `%rsp` or `%rax`.
#[cfg(target_arch = "x86_64")]
global_asm!(define_rust_probestack!(
"
.cfi_startproc
pushq %rbp
.cfi_adjust_cfa_offset 8
.cfi_offset %rbp, -16
movq %rsp, %rbp
.cfi_def_cfa_register %rbp

mov %rax,%r11 // duplicate %rax as we're clobbering %r11

// Main loop, taken in one page increments. We're decrementing rsp by
// a page each time until there's less than a page remaining. We're
// guaranteed that this function isn't called unless there's more than a
// page needed.
//
// Note that we're also testing against `8(%rsp)` to account for the 8
// bytes pushed on the stack orginally with our return address. Using
// `8(%rsp)` simulates us testing the stack pointer in the caller's
// context.

// It's usually called when %rax >= 0x1000, but that's not always true.
// Dynamic stack allocation, which is needed to implement unsized
// rvalues, triggers stackprobe even if %rax < 0x1000.
// Thus we have to check %r11 first to avoid segfault.
cmp $0x1000,%r11
jna 3f
2:
sub $0x1000,%rsp
test %rsp,8(%rsp)
sub $0x1000,%r11
cmp $0x1000,%r11
ja 2b

3:
// Finish up the last remaining stack space requested, getting the last
// bits out of r11
sub %r11,%rsp
test %rsp,8(%rsp)

// Restore the stack pointer to what it previously was when entering
// this function. The caller will readjust the stack pointer after we
// return.
add %rax,%rsp

leave
.cfi_def_cfa_register %rsp
.cfi_adjust_cfa_offset -8
ret
.cfi_endproc
"
));

#[cfg(target_arch = "x86")]
// This is the same as x86_64 above, only translated for 32-bit sizes. Note
// that on Unix we're expected to restore everything as it was, this
// function basically can't tamper with anything.
//
// The ABI here is the same as x86_64, except everything is 32-bits large.
global_asm!(define_rust_probestack!(
"
.cfi_startproc
push %ebp
.cfi_adjust_cfa_offset 4
.cfi_offset %ebp, -8
mov %esp, %ebp
.cfi_def_cfa_register %ebp
push %ecx
mov %eax,%ecx

cmp $0x1000,%ecx
jna 3f
2:
sub $0x1000,%esp
test %esp,8(%esp)
sub $0x1000,%ecx
cmp $0x1000,%ecx
ja 2b

3:
sub %ecx,%esp
test %esp,8(%esp)

add %eax,%esp
pop %ecx
leave
.cfi_def_cfa_register %esp
.cfi_adjust_cfa_offset -4
ret
.cfi_endproc
"
));