From 9178d1cf38f94d132bc6c99321e7a13df3eb5e94 Mon Sep 17 00:00:00 2001
From: Mitchell Hashimoto <m@mitchellh.com>
Date: Sun, 8 Sep 2024 21:25:34 -0700
Subject: [PATCH] crash/minidump: locationReader to read locations in a
 minidump

---
 src/crash/minidump/reader.zig            | 17 ++++++++++++++++-
 src/crash/minidump/stream_threadlist.zig |  6 ++++++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/src/crash/minidump/reader.zig b/src/crash/minidump/reader.zig
index f316e63b0..f792d6670 100644
--- a/src/crash/minidump/reader.zig
+++ b/src/crash/minidump/reader.zig
@@ -54,6 +54,9 @@ pub fn Reader(comptime S: type) type {
         const SourceReader = @typeInfo(@TypeOf(SourceCallable.reader)).Fn.return_type.?;
         const SourceSeeker = @typeInfo(@TypeOf(SourceCallable.seekableStream)).Fn.return_type.?;
 
+        /// A limited reader for reading data from the source.
+        pub const LimitedReader = std.io.LimitedReader(SourceReader);
+
         /// The source type for the reader.
         pub const Source = S;
 
@@ -72,7 +75,6 @@ pub fn Reader(comptime S: type) type {
             /// reader() is called.
             limit_reader: LimitedReader = undefined,
 
-            const LimitedReader = std.io.LimitedReader(SourceReader);
             pub const Reader = LimitedReader.Reader;
 
             /// Returns a Reader implementation that reads the bytes of the
@@ -164,6 +166,19 @@ pub fn Reader(comptime S: type) type {
                 self.endian,
             );
         }
+
+        /// Return a reader for the given location descriptor. This is only
+        /// valid until the reader source is modified in some way.
+        pub fn locationReader(
+            self: *const Self,
+            loc: external.LocationDescriptor,
+        ) !LimitedReader {
+            try self.source.seekableStream().seekTo(loc.rva);
+            return .{
+                .inner_reader = self.source.reader(),
+                .bytes_left = loc.data_size,
+            };
+        }
     };
 }
 
diff --git a/src/crash/minidump/stream_threadlist.zig b/src/crash/minidump/stream_threadlist.zig
index e74d11e3e..51f3f9d4c 100644
--- a/src/crash/minidump/stream_threadlist.zig
+++ b/src/crash/minidump/stream_threadlist.zig
@@ -89,6 +89,7 @@ pub fn ThreadListReader(comptime R: type) type {
 
 test "minidump: threadlist" {
     const testing = std.testing;
+    const alloc = testing.allocator;
 
     var fbs = std.io.fixedBufferStream(@embedFile("../testdata/macos.dmp"));
     const R = Reader(*@TypeOf(fbs));
@@ -107,5 +108,10 @@ test "minidump: threadlist" {
     for (0..v.count) |i| {
         const t = try v.thread(i);
         log.warn("thread i={} thread={}", .{ i, t });
+
+        // Read our stack memory
+        var stack_reader = try r.locationReader(t.stack.memory);
+        const bytes = try stack_reader.reader().readAllAlloc(alloc, t.stack.memory.data_size);
+        defer alloc.free(bytes);
     }
 }