From 2d005827b874f27535cda72c80b6558d9d4cd30c Mon Sep 17 00:00:00 2001
From: Andrew Kelley <andrew@ziglang.org>
Date: Mon, 9 Sep 2024 21:16:06 -0700
Subject: [PATCH] make lowest stack an internal libfuzzer detail

This value is useful to help determine run uniqueness in the face of
recursion, however it is not valuable to expose to the fuzzing UI.
---
 lib/fuzzer.zig                   | 6 +++---
 lib/fuzzer/web/index.html        | 1 -
 lib/fuzzer/web/main.js           | 2 --
 lib/fuzzer/web/main.zig          | 7 -------
 lib/std/Build/Fuzz/WebServer.zig | 2 --
 lib/std/Build/Fuzz/abi.zig       | 2 --
 6 files changed, 3 insertions(+), 17 deletions(-)

diff --git a/lib/fuzzer.zig b/lib/fuzzer.zig
index 6cc8f9cc28..3f8a991148 100644
--- a/lib/fuzzer.zig
+++ b/lib/fuzzer.zig
@@ -28,7 +28,8 @@ fn logOverride(
     f.writer().print(prefix1 ++ prefix2 ++ format ++ "\n", args) catch @panic("failed to write to fuzzer log");
 }
 
-export threadlocal var __sancov_lowest_stack: usize = std.math.maxInt(usize);
+/// Helps determine run uniqueness in the face of recursion.
+export threadlocal var __sancov_lowest_stack: usize = 0;
 
 export fn __sanitizer_cov_trace_const_cmp1(arg1: u8, arg2: u8) void {
     handleCmp(@returnAddress(), arg1, arg2);
@@ -220,7 +221,6 @@ const Fuzzer = struct {
                 .n_runs = 0,
                 .unique_runs = 0,
                 .pcs_len = pcs.len,
-                .lowest_stack = std.math.maxInt(usize),
             };
             f.seen_pcs.appendSliceAssumeCapacity(std.mem.asBytes(&header));
             f.seen_pcs.appendNTimesAssumeCapacity(0, n_bitset_elems * @sizeOf(usize));
@@ -261,8 +261,8 @@ const Fuzzer = struct {
             f.input.appendSliceAssumeCapacity(run.input);
             try f.mutate();
 
-            _ = @atomicRmw(usize, &header.lowest_stack, .Min, __sancov_lowest_stack, .monotonic);
             @memset(f.pc_counters, 0);
+            __sancov_lowest_stack = std.math.maxInt(usize);
             f.coverage.reset();
 
             fuzzer_one(f.input.items.ptr, f.input.items.len);
diff --git a/lib/fuzzer/web/index.html b/lib/fuzzer/web/index.html
index 16fa879913..0addd9f882 100644
--- a/lib/fuzzer/web/index.html
+++ b/lib/fuzzer/web/index.html
@@ -147,7 +147,6 @@
         <li>Total Runs: <span id="statTotalRuns"></span></li>
         <li>Unique Runs: <span id="statUniqueRuns"></span></li>
         <li>Coverage: <span id="statCoverage"></span></li>
-        <li>Lowest Stack: <span id="statLowestStack"></span></li>
         <li>Entry Points: <ul id="entryPointsList"></ul></li>
       </ul>
     </div>
diff --git a/lib/fuzzer/web/main.js b/lib/fuzzer/web/main.js
index ce02276f98..9ee6b445e2 100644
--- a/lib/fuzzer/web/main.js
+++ b/lib/fuzzer/web/main.js
@@ -6,7 +6,6 @@
   const domStatTotalRuns = document.getElementById("statTotalRuns");
   const domStatUniqueRuns = document.getElementById("statUniqueRuns");
   const domStatCoverage = document.getElementById("statCoverage");
-  const domStatLowestStack = document.getElementById("statLowestStack");
   const domEntryPointsList = document.getElementById("entryPointsList");
 
   let wasm_promise = fetch("main.wasm");
@@ -158,7 +157,6 @@
     domStatTotalRuns.innerText = totalRuns;
     domStatUniqueRuns.innerText = uniqueRuns + " (" + percent(uniqueRuns, totalRuns) + "%)";
     domStatCoverage.innerText = coveredSourceLocations + " / " + totalSourceLocations + " (" + percent(coveredSourceLocations, totalSourceLocations) + "%)";
-    domStatLowestStack.innerText = unwrapString(wasm_exports.lowestStack());
 
     const entryPoints = unwrapInt32Array(wasm_exports.entryPoints());
     resizeDomList(domEntryPointsList, entryPoints.length, "<li></li>");
diff --git a/lib/fuzzer/web/main.zig b/lib/fuzzer/web/main.zig
index 342adc3b56..94ea8cc92f 100644
--- a/lib/fuzzer/web/main.zig
+++ b/lib/fuzzer/web/main.zig
@@ -106,13 +106,6 @@ export fn decl_source_html(decl_index: Decl.Index) String {
     return String.init(string_result.items);
 }
 
-export fn lowestStack() String {
-    const header: *abi.CoverageUpdateHeader = @ptrCast(recent_coverage_update.items[0..@sizeOf(abi.CoverageUpdateHeader)]);
-    string_result.clearRetainingCapacity();
-    string_result.writer(gpa).print("0x{d}", .{header.lowest_stack}) catch @panic("OOM");
-    return String.init(string_result.items);
-}
-
 export fn totalSourceLocations() usize {
     return coverage_source_locations.items.len;
 }
diff --git a/lib/std/Build/Fuzz/WebServer.zig b/lib/std/Build/Fuzz/WebServer.zig
index b5ad86af15..391f67e823 100644
--- a/lib/std/Build/Fuzz/WebServer.zig
+++ b/lib/std/Build/Fuzz/WebServer.zig
@@ -406,7 +406,6 @@ fn sendCoverageContext(
     const seen_pcs = cov_header.seenBits();
     const n_runs = @atomicLoad(usize, &cov_header.n_runs, .monotonic);
     const unique_runs = @atomicLoad(usize, &cov_header.unique_runs, .monotonic);
-    const lowest_stack = @atomicLoad(usize, &cov_header.lowest_stack, .monotonic);
     if (prev_unique_runs.* != unique_runs) {
         // There has been an update.
         if (prev_unique_runs.* == 0) {
@@ -431,7 +430,6 @@ fn sendCoverageContext(
         const header: abi.CoverageUpdateHeader = .{
             .n_runs = n_runs,
             .unique_runs = unique_runs,
-            .lowest_stack = lowest_stack,
         };
         const iovecs: [2]std.posix.iovec_const = .{
             makeIov(std.mem.asBytes(&header)),
diff --git a/lib/std/Build/Fuzz/abi.zig b/lib/std/Build/Fuzz/abi.zig
index 0e16f0d5fa..c3f32d309b 100644
--- a/lib/std/Build/Fuzz/abi.zig
+++ b/lib/std/Build/Fuzz/abi.zig
@@ -13,7 +13,6 @@ pub const SeenPcsHeader = extern struct {
     n_runs: usize,
     unique_runs: usize,
     pcs_len: usize,
-    lowest_stack: usize,
 
     /// Used for comptime assertions. Provides a mechanism for strategically
     /// causing compile errors.
@@ -79,7 +78,6 @@ pub const CoverageUpdateHeader = extern struct {
     flags: Flags = .{},
     n_runs: u64,
     unique_runs: u64,
-    lowest_stack: u64,
 
     pub const Flags = packed struct(u64) {
         tag: ToClientTag = .coverage_update,