1 files changed, 53 insertions, 0 deletions
diff --git a/third_party/rust/crash-context/src/linux/getcontext/arm.rs b/third_party/rust/crash-context/src/linux/getcontext/arm.rs
new file mode 100644
index 0000000000..0734634a3e
--- /dev/null
+++ b/third_party/rust/crash-context/src/linux/getcontext/arm.rs
@@ -0,0 +1,53 @@
+std::arch::global_asm! {
+    ".text",
+    ".global crash_context_getcontext",
+    ".hidden crash_context_getcontext",
+    ".type crash_context_getcontext, #function",
+    ".align 0",
+    ".fnstart",
+"crash_context_getcontext:",
+
+    // First, save r4-r11
+    "add   r1, r0, #(32 + 4 * 4)",
+    "stm   r1, {{r4-r11}}",
+
+    // r12 is a scratch register, don't save it
+
+    // Save sp and lr explicitly.
+    // - sp can't be stored with stmia in Thumb-2
+    // - STM instructions that store sp and pc are deprecated in ARM
+    "str   sp, [r0, #(32 + 13 * 4)]",
+    "str   lr, [r0, #(32 + 14 * 4)]",
+
+    // Save the caller's address in 'pc'
+    "str   lr, [r0, #(32 + 15 * 4)]",
+
+    // Save ucontext_t* pointer across next call
+    "mov   r4, r0",
+
+    // Call sigprocmask(SIG_BLOCK, NULL, &(ucontext->uc_sigmask))
+    "mov   r0, #0",  // SIG_BLOCK
+    "mov   r1, #0",  // NULL
+    "add   r2, r4, #104", // UCONTEXT_SIGMASK_OFFSET
+    "bl    sigprocmask(PLT)",
+
+    /* Intentionally do not save the FPU state here. This is because on
+    * Linux/ARM, one should instead use ptrace(PTRACE_GETFPREGS) or
+    * ptrace(PTRACE_GETVFPREGS) to get it.
+    *
+    * Note that a real implementation of getcontext() would need to save
+    * this here to allow setcontext()/swapcontext() to work correctly.
+    */
+
+    // Restore the values of r4 and lr
+    "mov   r0, r4",
+    "ldr   lr, [r0, #(32 + 14 * 4)]",
+    "ldr   r4, [r0, #(32 +  4 * 4)]",
+
+    // Return 0
+    "mov   r0, #0",
+    "bx    lr",
+
+    ".fnend",
+    ".size crash_context_getcontext, . - crash_context_getcontext",
+}