1 files changed, 161 insertions, 0 deletions
diff --git a/js/src/gdb/mozilla/jitsrc.py b/js/src/gdb/mozilla/jitsrc.py
new file mode 100644
index 0000000000..d986cdae06
--- /dev/null
+++ b/js/src/gdb/mozilla/jitsrc.py
@@ -0,0 +1,161 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this file,
+# You can obtain one at http://mozilla.org/MPL/2.0/.
+
+# This is a gdb extension to automate the process of tracing backwards in rr
+# from a jit instruction to the code that generated that instruction.
+#
+# Usage:
+#  (rr) x/i $pc
+#  => 0x240e954ac13a:	pushq  (%rbx)
+#  (rr) jitsrc 0x240e954ac13a
+
+import re
+
+import gdb
+
+# (base_name, hops, func_name, source_var, dest_var) tuples, such that :
+#   - `base_name`: a regex matching the name of the function that implements
+#       the actual write
+#   - `hops`: the number of stack frames between `base_name` and `func_name`
+#   - `func_name`: a regex matching the name of the function that calls memcpy
+#   - `source_var`: an expression that can be evaluated in the frame
+#       corresponding to `func_name` to get the source of the memcpy
+#   - `dest_var`: an expression that can be evaluated in the frame
+#       corresponding to `func_name` to get the destination of the memcpy
+#
+# If an invocation of `jitsrc` stops in the middle of a memcpy, the solution
+# is normally to add a new pattern here.
+patterns = [
+    (
+        "__memmove",
+        1,
+        "js::jit::X86Encoding::BaseAssembler::executableCopy",
+        "src",
+        "dst",
+    ),
+    (
+        "__memcpy",
+        1,
+        "js::jit::X86Encoding::BaseAssembler::executableCopy",
+        "src",
+        "dst",
+    ),
+    (
+        "__memmove",
+        1,
+        "arena_t::RallocSmallOrLarge",
+        "aPtr",
+        "ret",
+    ),
+    ("__memcpy", 1, "arena_t::RallocSmallOrLarge", "aPtr", "ret"),
+    (
+        "mozilla::detail::VectorImpl<.*>::new_<.*>",
+        3,
+        "mozilla::Vector<.*>::convertToHeapStorage",
+        "beginNoCheck()",
+        "newBuf",
+    ),
+    (
+        "__memmove",
+        1,
+        "js::jit::AssemblerBufferWithConstantPools",
+        "&cur->instructions[0]",
+        "dest",
+    ),
+    (
+        "__memcpy",
+        1,
+        "js::jit::AssemblerBufferWithConstantPools",
+        "&cur->instructions[0]",
+        "dest",
+    ),
+    (
+        "__memcpy",
+        2,
+        "js::jit::AssemblerX86Shared::executableCopy",
+        "masm.m_formatter.m_buffer.m_buffer.mBegin",
+        "buffer",
+    ),
+    ("__memcpy", 1, "arena_t::RallocSmallOrLarge", "aPtr", "ret"),
+    ("js::jit::X86Encoding::SetInt32", 0, "js::jit::X86Encoding::SetInt32", "0", "0"),
+    (
+        "js::jit::X86Encoding::SetPointer",
+        0,
+        "js::jit::X86Encoding::SetPointer",
+        "0",
+        "0",
+    ),
+    (
+        "<unnamed>",
+        1,
+        "js::jit::AssemblerBufferWithConstantPools<.*>::executableCopy",
+        "&cur->instructions[0]",
+        "dest",
+    ),
+    ("std::__copy_move", 4, "CopySpan", "source.data()", "target.data()"),
+    (
+        "__memmove_(avx|evex)_unaligned_erms",
+        1,
+        "mozilla::detail::EndianUtils::copyAndSwapTo<.*0,.*0",
+        "aSrc",
+        "(size_t) aDest",
+    ),
+]
+
+
+class JitSource(gdb.Command):
+    def __init__(self):
+        super(JitSource, self).__init__("jitsrc", gdb.COMMAND_RUNNING)
+        self.dont_repeat()
+
+    def disable_breakpoints(self):
+        self.disabled_breakpoints = [b for b in gdb.breakpoints() if b.enabled]
+        for b in self.disabled_breakpoints:
+            b.enabled = False
+
+    def enable_breakpoints(self):
+        for b in self.disabled_breakpoints:
+            b.enabled = True
+
+    def search_stack(self, base_name, hops, name, src, dst, address):
+        current_frame_name = gdb.newest_frame().name() or "<unnamed>"
+        if not re.match(base_name, current_frame_name):
+            return None
+        f = gdb.newest_frame()
+        for _ in range(hops):
+            f = f.older()
+        if not re.match(name, f.name()):
+            return None
+        f.select()
+        src_val = gdb.parse_and_eval(src)
+        dst_val = gdb.parse_and_eval(dst)
+        return hex(src_val + int(address, 16) - dst_val)
+
+    def next_address(self, old):
+        for pattern in patterns:
+            found = self.search_stack(*pattern, old)
+            if found:
+                return found
+        return None
+
+    def runback(self, address):
+        b = gdb.Breakpoint(
+            "*" + address, type=gdb.BP_WATCHPOINT, wp_class=gdb.WP_WRITE, internal=True
+        )
+        while b.hit_count == 0:
+            gdb.execute("rc", to_string=True)
+        b.delete()
+
+    def invoke(self, arg, from_tty):
+        args = gdb.string_to_argv(arg)
+        address = args[0]
+        self.disable_breakpoints()
+        while address:
+            self.runback(address)
+            address = self.next_address(address)
+        self.enable_breakpoints()
+
+
+# Register to the gdb runtime
+JitSource()