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Fix segfault on probestack with dynamic alloca. #244

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merged 2 commits into from
May 28, 2018
Merged

Fix segfault on probestack with dynamic alloca. #244

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56293ad
Fix segfault on probestack with dynamic alloca.
qnighy May 27, 2018
1d15be6
Explain why we need extra check in probestack.
qnighy May 28, 2018
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12 changes: 12 additions & 0 deletions src/probestack.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -64,13 +64,21 @@ pub unsafe extern fn __rust_probestack() {
// 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
Expand Down Expand Up @@ -98,13 +106,17 @@ pub unsafe extern fn __rust_probestack() {
asm!("
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)

Expand Down