generic-sandbox: Fix signal handling on macOS

ucontext_t is different on macOS and Linux. On macOS, SIGSEGV is not
sent for page faults, instead SIGBUS is sent. This commit updates the
signal handler to check for SIGBUS on macOS.

Finally, we also fix the page fault address extraction on macOS.

Signed-off-by: Aman <[email protected]>

Author: aman4150

crates/polkavm/src/sandbox/generic.rs

@@ -325,6 +325,61 @@ unsafe extern "C" fn signal_handler(signal: c_int, info: &sys::siginfo_t, contex
 
     let vmctx = THREAD_VMCTX.with(|thread_ctx| *thread_ctx.get());
     if !vmctx.is_null() {
+        #[cfg(target_os = "macos")]
+        macro_rules! macos_reg_field {
+            (rax) => {
+                (*context.uc_mcontext).__ss.__rax
+            };
+            (rbx) => {
+                (*context.uc_mcontext).__ss.__rbx
+            };
+            (rcx) => {
+                (*context.uc_mcontext).__ss.__rcx
+            };
+            (rdx) => {
+                (*context.uc_mcontext).__ss.__rdx
+            };
+            (rdi) => {
+                (*context.uc_mcontext).__ss.__rdi
+            };
+            (rsi) => {
+                (*context.uc_mcontext).__ss.__rsi
+            };
+            (rbp) => {
+                (*context.uc_mcontext).__ss.__rbp
+            };
+            (rsp) => {
+                (*context.uc_mcontext).__ss.__rsp
+            };
+            (r8) => {
+                (*context.uc_mcontext).__ss.__r8
+            };
+            (r9) => {
+                (*context.uc_mcontext).__ss.__r9
+            };
+            (r10) => {
+                (*context.uc_mcontext).__ss.__r10
+            };
+            (r11) => {
+                (*context.uc_mcontext).__ss.__r11
+            };
+            (r12) => {
+                (*context.uc_mcontext).__ss.__r12
+            };
+            (r13) => {
+                (*context.uc_mcontext).__ss.__r13
+            };
+            (r14) => {
+                (*context.uc_mcontext).__ss.__r14
+            };
+            (r15) => {
+                (*context.uc_mcontext).__ss.__r15
+            };
+            (rip) => {
+                (*context.uc_mcontext).__ss.__rip
+            };
+        }
+
         macro_rules! fetch_reg {
             ($reg:ident) => {{
                 #[cfg(target_os = "linux")]
@@ -333,7 +388,7 @@ unsafe extern "C" fn signal_handler(signal: c_int, info: &sys::siginfo_t, contex
                 }
                 #[cfg(target_os = "macos")]
                 {
-                    (*context.uc_mcontext).__ss.$reg as u64
+                    macos_reg_field!($reg) as u64
                 }
                 #[cfg(target_os = "freebsd")]
                 {
@@ -343,19 +398,19 @@ unsafe extern "C" fn signal_handler(signal: c_int, info: &sys::siginfo_t, contex
         }
 
         const X86_TRAP_PF: u64 = 14;
-        let is_page_fault = signal == sys::SIGSEGV && {
+        let is_page_fault = {
             #[cfg(target_os = "linux")]
             {
-                context.uc_mcontext.trapno == X86_TRAP_PF
+                signal == sys::SIGSEGV && context.uc_mcontext.trapno == X86_TRAP_PF
+            }
+            #[cfg(target_os = "macos")]
+            {
+                signal == sys::SIGBUS && (*context.uc_mcontext).__es.__trapno as u64 == X86_TRAP_PF
+            }
+            #[cfg(target_os = "freebsd")]
+            {
+                signal == sys::SIGBUS && context.uc_mcontext.mc_trapno == X86_TRAP_PF
             }
-            // #[cfg(target_os = "macos")]
-            // {
-            //     (*context.uc_mcontext).__ss.trapno == X86_TRAP_PF
-            // }
-            // #[cfg(target_os = "freebsd")]
-            // {
-            //     context.uc_mcontext.mc_trapno == X86_TRAP_PF
-            // }
         };
 
         let rip = fetch_reg!(rip);
@@ -401,14 +456,14 @@ unsafe extern "C" fn signal_handler(signal: c_int, info: &sys::siginfo_t, contex
                     {
                         info.__bindgen_anon_1.__bindgen_anon_1._sifields._sigfault._addr as u64
                     }
-                    // #[cfg(target_os = "macos")]
-                    // {
-                    //     info.si_addr as u64
-                    // }
-                    // #[cfg(target_os = "freebsd")]
-                    // {
-                    //     info.si_addr as u64
-                    // }
+                    #[cfg(target_os = "macos")]
+                    {
+                        info.si_addr as u64
+                    }
+                    #[cfg(target_os = "freebsd")]
+                    {
+                        info.si_addr as u64
+                    }
                 };
 
                 log::trace!("Page fault at 0x{fault_address:x} (rip: 0x{rip:x})");