fix(walltime): extract unwind data for binaries without eh_frame_hdr

unwind_data_from_elf bailed when .eh_frame_hdr was absent, leaving
modules like Valgrind's statically-linked tools without any unwind
data. Samples passing through their code could not be unwound,
producing broken stacks in the flamegraph.

Only require .eh_frame and emit the hdr fields as None when the
section is missing.

Author: not-matthias

src/executor/wall_time/profiler/perf/jit_dump.rs

@@ -82,8 +82,8 @@ impl JitDump {
                     let unwind_data = UnwindData {
                         path,
                         base_svma: 0,
-                        eh_frame_hdr,
-                        eh_frame_hdr_svma: 0..0,
+                        eh_frame_hdr: Some(eh_frame_hdr),
+                        eh_frame_hdr_svma: Some(0..0),
                         eh_frame,
                         eh_frame_svma: 0..0,
                     };

src/executor/wall_time/profiler/perf/snapshots/codspeed_runner__executor__wall_time__profiler__perf__unwind_data__tests__cpp_unwind_data.snap

@@ -1,14 +1,14 @@
 ---
-source: src/executor/wall_time/perf/unwind_data.rs
-expression: "unwind_data_from_elf(MODULE_PATH.as_bytes(), start_addr, end_addr, None,\nload_bias,)"
+source: src/executor/wall_time/profiler/perf/unwind_data.rs
+expression: "unwind_data_from_elf(module_path.as_bytes(), start_addr, end_addr, None,\nexpected_load_bias,)"
 ---
 Ok(
     (
         UnwindData {
             path: "testdata/perf_map/cpp_my_benchmark.bin",
             base_svma: 400000,
-            eh_frame_hdr_svma: 4577bc..458b30,
-            eh_frame_hdr_hash: 4b4eac90f7f5e60d,
+            eh_frame_hdr_svma: Some(4577bc..458b30),
+            eh_frame_hdr_hash: Some(4b4eac90f7f5e60d),
             eh_frame_hash: 233bdd4ae9fe4ba4,
             eh_frame_svma: 451098..4577bc,
         },

src/executor/wall_time/profiler/perf/snapshots/codspeed_runner__executor__wall_time__profiler__perf__unwind_data__tests__golang_unwind_data.snap

@@ -1,14 +1,14 @@
 ---
-source: src/executor/wall_time/perf/unwind_data.rs
-expression: "unwind_data_from_elf(MODULE_PATH.as_bytes(), start_addr, end_addr, None,\nload_bias,)"
+source: src/executor/wall_time/profiler/perf/unwind_data.rs
+expression: "unwind_data_from_elf(module_path.as_bytes(), start_addr, end_addr, None,\nexpected_load_bias,)"
 ---
 Ok(
     (
         UnwindData {
             path: "testdata/perf_map/go_fib.bin",
             base_svma: 400000,
-            eh_frame_hdr_svma: 6498b0..649b94,
-            eh_frame_hdr_hash: f1f69beb959a08d7,
+            eh_frame_hdr_svma: Some(6498b0..649b94),
+            eh_frame_hdr_hash: Some(f1f69beb959a08d7),
             eh_frame_hash: a8727039dd21b51c,
             eh_frame_svma: 649b98..64aa70,
         },

src/executor/wall_time/profiler/perf/snapshots/codspeed_runner__executor__wall_time__profiler__perf__unwind_data__tests__ruff_unwind_data.snap

@@ -1,14 +1,14 @@
 ---
-source: src/executor/wall_time/perf/unwind_data.rs
-expression: "unwind_data_from_elf(MODULE_PATH.as_bytes(), start_addr, end_addr, None,\nload_bias,)"
+source: src/executor/wall_time/profiler/perf/unwind_data.rs
+expression: "unwind_data_from_elf(module_path.as_bytes(), start_addr, end_addr, None,\nexpected_load_bias,)"
 ---
 Ok(
     (
         UnwindData {
             path: "testdata/perf_map/ty_walltime",
             base_svma: 0,
-            eh_frame_hdr_svma: 7ec298..80f67c,
-            eh_frame_hdr_hash: 6d6dd1e2c782318a,
+            eh_frame_hdr_svma: Some(7ec298..80f67c),
+            eh_frame_hdr_hash: Some(6d6dd1e2c782318a),
             eh_frame_hash: ee27244db791265a,
             eh_frame_svma: 80f680..918a9c,
         },

src/executor/wall_time/profiler/perf/snapshots/codspeed_runner__executor__wall_time__profiler__perf__unwind_data__tests__rust_divan_unwind_data.snap

@@ -1,14 +1,14 @@
 ---
-source: src/executor/wall_time/perf/unwind_data.rs
-expression: "unwind_data_from_elf(MODULE_PATH.as_bytes(), start_addr, end_addr, None,\nload_bias,)"
+source: src/executor/wall_time/profiler/perf/unwind_data.rs
+expression: "unwind_data_from_elf(module_path.as_bytes(), start_addr, end_addr, None,\nexpected_load_bias,)"
 ---
 Ok(
     (
         UnwindData {
             path: "testdata/perf_map/divan_sleep_benches.bin",
             base_svma: 0,
-            eh_frame_hdr_svma: 2ac74..2ea60,
-            eh_frame_hdr_hash: f579da4368e627c1,
+            eh_frame_hdr_svma: Some(2ac74..2ea60),
+            eh_frame_hdr_hash: Some(f579da4368e627c1),
             eh_frame_hash: 791501d5a9c438d,
             eh_frame_svma: 11540..2ac74,
         },

src/executor/wall_time/profiler/perf/snapshots/codspeed_runner__executor__wall_time__profiler__perf__unwind_data__tests__the_algorithms_unwind_data.snap

@@ -1,14 +1,14 @@
 ---
-source: src/executor/wall_time/perf/unwind_data.rs
-expression: "unwind_data_from_elf(MODULE_PATH.as_bytes(), start_addr, end_addr, None,\nload_bias,)"
+source: src/executor/wall_time/profiler/perf/unwind_data.rs
+expression: "unwind_data_from_elf(module_path.as_bytes(), start_addr, end_addr, None,\nexpected_load_bias,)"
 ---
 Ok(
     (
         UnwindData {
             path: "testdata/perf_map/the_algorithms.bin",
             base_svma: 0,
-            eh_frame_hdr_svma: 2f0ec..33590,
-            eh_frame_hdr_hash: 277fbdb59e6decaa,
+            eh_frame_hdr_svma: Some(2f0ec..33590),
+            eh_frame_hdr_hash: Some(277fbdb59e6decaa),
             eh_frame_hash: 21d8b0c8da0d1029,
             eh_frame_svma: 128a8..2f0ec,
         },

src/executor/wall_time/profiler/perf/unwind_data.rs

@@ -62,14 +62,15 @@ pub fn unwind_data_from_elf(
         section.address()..section.address() + section.size()
     }
 
-    let v3 = UnwindData {
+    // `.eh_frame_hdr` is only an optional lookup index into `.eh_frame` — some
+    // binaries (e.g. Valgrind's statically-linked tools) are linked without
+    // `ld --eh-frame-hdr` and don't carry it. The parser rebuilds the index
+    // from `.eh_frame` in that case.
+    let unwind_data = UnwindData {
         path: path.clone(),
         base_svma,
-        eh_frame_hdr: eh_frame_hdr_data.context("Failed to find eh_frame hdr data")?,
-        eh_frame_hdr_svma: eh_frame_hdr
-            .as_ref()
-            .map(svma_range)
-            .context("Failed to find eh_frame hdr section")?,
+        eh_frame_hdr: eh_frame_hdr_data,
+        eh_frame_hdr_svma: eh_frame_hdr.as_ref().map(svma_range),
         eh_frame: eh_frame_data.context("Failed to find eh_frame data")?,
         eh_frame_svma: eh_frame
             .as_ref()
@@ -84,7 +85,7 @@ pub fn unwind_data_from_elf(
         base_avma,
     };
 
-    Ok((v3, mapping))
+    Ok((unwind_data, mapping))
 }
 
 #[cfg(all(test, target_os = "linux"))]
@@ -230,6 +231,20 @@ mod tests {
         ));
     }
 
+    #[test]
+    fn test_valgrind_unwind_data_without_eh_frame_hdr() {
+        // Valgrind's statically-linked tools (here: callgrind-amd64-linux) are
+        // linked with a custom linker script without `ld --eh-frame-hdr`, so
+        // they carry `.eh_frame` but no `.eh_frame_hdr`. Unwind data extraction
+        // must still succeed since the hdr is only an optional lookup index.
+        let module_path = "testdata/perf_map/valgrind";
+        let (unwind_data, _) =
+            unwind_data_from_elf(module_path.as_bytes(), 0x58000000, 0x58292000, None, 0)
+                .expect("unwind data extraction should succeed without .eh_frame_hdr");
+        assert!(unwind_data.eh_frame_hdr.is_none());
+        assert!(!unwind_data.eh_frame.is_empty());
+    }
+
     #[test]
     fn test_ruff_unwind_data() {
         // gdb testdata/perf_map/ty_walltime -ex "break main" -ex "run" -ex "info proc mappings" -ex "continue" -ex "quit" -batch

testdata/perf_map/valgrind

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:5461304de8a1b9242ba3b0b912c50e21d9b28b5423754de13e20cb7c7ff6df05
+size 13298232