v8/tools/debug_helper/README.md

# V8 debug helper

This library is for debugging V8 itself, not debugging JavaScript running within
V8. It is designed to be called from a debugger extension running within a
native debugger such as WinDbg or LLDB. It can be used on live processes or
crash dumps, and cannot assume that all memory is available in a dump.
Reland "Add postmortem debugging helper library" This is a reland of 517ab73fd7e3fdb70220b9699bca4c69a32e212e Updates since original: now compressed pointers passed to the function GetObjectProperties are required to be sign-extended. Previously, the function allowed zero-extended values, but that led to ambiguity on pointers like 0x88044919: is it compressed or is the heap range actually centered on 0x100000000? Original change's description: > Add postmortem debugging helper library > > This change begins to implement the functionality described in > https://docs.google.com/document/d/1evHnb1uLlSbvHAAsmOXyc25x3uh1DjgNa8u1RHvwVhk/edit# > for investigating V8 state in crash dumps. > > This change adds a new library, v8_debug_helper, for providing platform- > agnostic assistance with postmortem debugging. This library can be used > by extensions built for debuggers such as WinDbg or lldb. Its public API > is described by debug-helper.h; currently the only method it exposes is > GetObjectProperties, but we'd like to add more functionality over time. > The API surface is restricted to plain C-style structs and pointers, so > that it's easy to link from a debugger extension built with a different > toolchain. > > This change also adds a new cctest file to exercise some basic > interaction with the new library. > > The API function GetObjectProperties takes an object pointer (which > could be compressed, or weak, or a SMI), and returns a string > description of the object and a list of properties the object contains. > For now, the list of properties is entirely based on Torque object > definitions, but we expect to add custom properties in future updates so > that it can be easier to make sense of complex data structures such as > dictionaries. > > GetObjectProperties does several things that are intended to generate > somewhat useful results even in cases where memory may be corrupt or > unavailable: > - The caller may optionally provide a type string which will be used if > the memory for the object's Map is inaccessible. > - All object pointers are compared against the list of known objects > generated by mkgrokdump. The caller may optionally provide the > pointers for the first pages of various heap spaces, to avoid spurious > matches. If those pointers are not provided, then any matches are > prefixed with "maybe" in the resulting description string, such as > "maybe UndefinedValue (0x4288000341 <Oddball>)". > > Bug: v8:9376 > > Change-Id: Iebf3cc2dea3133c7811bcefcdf38d9458b02fded > Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1628012 > Commit-Queue: Seth Brenith <seth.brenith@microsoft.com> > Reviewed-by: Yang Guo <yangguo@chromium.org> > Reviewed-by: Michael Stanton <mvstanton@chromium.org> > Cr-Commit-Position: refs/heads/master@{#62882} Bug: v8:9376 Change-Id: I866a1cc9d4c34bfe10c7b98462451fe69763cf3f Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1717090 Reviewed-by: Michael Achenbach <machenbach@chromium.org> Reviewed-by: Michael Stanton <mvstanton@chromium.org> Commit-Queue: Seth Brenith <seth.brenith@microsoft.com> Cr-Commit-Position: refs/heads/master@{#63008} 2019-07-30 14:38:15 +00:00			`# V8 debug helper`

			`This library is for debugging V8 itself, not debugging JavaScript running within`
			`V8. It is designed to be called from a debugger extension running within a`
			`native debugger such as WinDbg or LLDB. It can be used on live processes or`
			`crash dumps, and cannot assume that all memory is available in a dump.`