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Trap handler changes to support s390x #2871

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May 3, 2021
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Trap handler changes to support s390x #2871

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25 changes: 21 additions & 4 deletions crates/runtime/src/traphandlers/unix.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -47,8 +47,8 @@ pub unsafe fn platform_init() {
// Handle `unreachable` instructions which execute `ud2` right now
register(&mut PREV_SIGILL, libc::SIGILL);

// x86 uses SIGFPE to report division by zero
if cfg!(target_arch = "x86") || cfg!(target_arch = "x86_64") {
// x86 and s390x use SIGFPE to report division by zero
if cfg!(target_arch = "x86") || cfg!(target_arch = "x86_64") || cfg!(target_arch = "s390x") {
register(&mut PREV_SIGFPE, libc::SIGFPE);
}

Expand Down Expand Up @@ -85,7 +85,7 @@ unsafe extern "C" fn trap_handler(
// Otherwise flag ourselves as handling a trap, do the trap
// handling, and reset our trap handling flag. Then we figure
// out what to do based on the result of the trap handling.
let pc = get_pc(context);
let pc = get_pc(context, signum);
let jmp_buf = info.jmp_buf_if_trap(pc, |handler| handler(signum, siginfo, context));

// Figure out what to do based on the result of this handling of
Expand Down Expand Up @@ -127,7 +127,7 @@ unsafe extern "C" fn trap_handler(
}
}

unsafe fn get_pc(cx: *mut libc::c_void) -> *const u8 {
unsafe fn get_pc(cx: *mut libc::c_void, _signum: libc::c_int) -> *const u8 {
cfg_if::cfg_if! {
if #[cfg(all(target_os = "linux", target_arch = "x86_64"))] {
let cx = &*(cx as *const libc::ucontext_t);
Expand All @@ -138,6 +138,23 @@ unsafe fn get_pc(cx: *mut libc::c_void) -> *const u8 {
} else if #[cfg(all(any(target_os = "linux", target_os = "android"), target_arch = "aarch64"))] {
let cx = &*(cx as *const libc::ucontext_t);
cx.uc_mcontext.pc as *const u8
} else if #[cfg(all(target_os = "linux", target_arch = "s390x"))] {
// On s390x, SIGILL and SIGFPE are delivered with the PSW address
// pointing *after* the faulting instruction, while SIGSEGV and
// SIGBUS are delivered with the PSW address pointing *to* the
// faulting instruction. To handle this, the code generator registers
// any trap that results in one of "late" signals on the last byte
// of the instruction, and any trap that results in one of the "early"
// signals on the first byte of the instruction (as usual). This
// means we simply need to decrement the reported PSW address by
// one in the case of a "late" signal here to ensure we always
// correctly find the associated trap handler.
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Is there an online link to gist here which goes into some more detail? I'm mostly just curious for my own edification!

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That's a good question. Right now, I don't think this is documented anywhere but by reading the Linux kernel sources. This should probably be added to the ABI document. I've added an issue there as a reminder: IBM/s390x-abi#2

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Ok, sounds reasonable to me!

let trap_offset = match _signum {
libc::SIGILL | libc::SIGFPE => 1,
_ => 0,
};
let cx = &*(cx as *const libc::ucontext_t);
(cx.uc_mcontext.psw.addr - trap_offset) as *const u8
} else if #[cfg(all(target_os = "freebsd", target_arch = "x86_64"))] {
let cx = &*(cx as *const libc::ucontext_t);
cx.uc_mcontext.mc_rip as *const u8
Expand Down