ZJIT: Create perf map files for profilers (ruby#13941)

This lets us ZJIT compiled functions show up in the profiles of, say,
perf, or samply.

Fix Shopify#634

Author: tekknolagi

zjit/src/codegen.rs

@@ -154,6 +154,20 @@ fn gen_iseq_entry_point_body(cb: &mut CodeBlock, iseq: IseqPtr) -> *const u8 {
     start_ptr.map(|start_ptr| start_ptr.raw_ptr(cb)).unwrap_or(std::ptr::null())
 }
 
+/// Write an entry to the perf map in /tmp
+fn register_with_perf(iseq_name: String, start_ptr: usize, code_size: usize) {
+    use std::io::Write;
+    let perf_map = format!("/tmp/perf-{}.map", std::process::id());
+    let Ok(mut file) = std::fs::OpenOptions::new().create(true).append(true).open(&perf_map) else {
+        debug!("Failed to open perf map file: {perf_map}");
+        return;
+    };
+    let Ok(_) = writeln!(file, "{:#x} {:#x} zjit::{}", start_ptr, code_size, iseq_name) else {
+        debug!("Failed to write {iseq_name} to perf map file: {perf_map}");
+        return;
+    };
+}
+
 /// Compile a JIT entry
 fn gen_entry(cb: &mut CodeBlock, iseq: IseqPtr, function: &Function, function_ptr: CodePtr, c_stack_bytes: usize) -> Option<CodePtr> {
     // Set up registers for CFP, EC, SP, and basic block arguments
@@ -172,7 +186,17 @@ fn gen_entry(cb: &mut CodeBlock, iseq: IseqPtr, function: &Function, function_pt
     asm.frame_teardown();
     asm.cret(C_RET_OPND);
 
-    asm.compile(cb).map(|(start_ptr, _)| start_ptr)
+    let result = asm.compile(cb).map(|(start_ptr, _)| start_ptr);
+    if let Some(start_addr) = result {
+        if get_option!(perf) {
+            let start_ptr = start_addr.raw_ptr(cb) as usize;
+            let end_ptr = cb.get_write_ptr().raw_ptr(cb) as usize;
+            let code_size = end_ptr - start_ptr;
+            let iseq_name = iseq_get_location(iseq, 0);
+            register_with_perf(format!("entry for {iseq_name}"), start_ptr, code_size);
+        }
+    }
+    result
 }
 
 /// Compile an ISEQ into machine code
@@ -255,7 +279,17 @@ fn gen_function(cb: &mut CodeBlock, iseq: IseqPtr, function: &Function) -> Optio
     }
 
     // Generate code if everything can be compiled
-    asm.compile(cb).map(|(start_ptr, gc_offsets)| (start_ptr, gc_offsets, jit))
+    let result = asm.compile(cb).map(|(start_ptr, gc_offsets)| (start_ptr, gc_offsets, jit));
+    if let Some((start_ptr, _, _)) = result {
+        if get_option!(perf) {
+            let start_usize = start_ptr.raw_ptr(cb) as usize;
+            let end_usize = cb.get_write_ptr().raw_ptr(cb) as usize;
+            let code_size = end_usize - start_usize;
+            let iseq_name = iseq_get_location(iseq, 0);
+            register_with_perf(iseq_name, start_usize, code_size);
+        }
+    }
+    result
 }
 
 /// Compile an instruction

zjit/src/options.rs

@@ -33,6 +33,9 @@ pub struct Options {
 
     /// Dump all compiled machine code.
     pub dump_disasm: bool,
+
+    /// Dump code map to /tmp for performance profilers.
+    pub perf: bool,
 }
 
 /// Return an Options with default values
@@ -44,6 +47,7 @@ pub fn init_options() -> Options {
         dump_hir_opt: None,
         dump_lir: false,
         dump_disasm: false,
+        perf: false,
     }
 }
 
@@ -143,6 +147,8 @@ fn parse_option(options: &mut Options, str_ptr: *const std::os::raw::c_char) ->
 
         ("dump-disasm", "") => options.dump_disasm = true,
 
+        ("perf", "") => options.perf = true,
+
         _ => return None, // Option name not recognized
     }