Add cppdemangle in druntime #3002

ErnyTech · 2020-03-24T18:23:54Z

Add cppdemangle in druntime

Having a C++ symbol demangler is very useful, with this it will
be possible to implement the C++ symbol demangle in the stacktrace.

The demangling is done in Posix platform by function __cxa_demangle
presents in Itanium C++ ABI (https://itanium-cxx-abi.github.io/cxx-abi/abi.html#demangler).

Itanium C++ ABI is used practically in all modern C++ compilers on Posix,
however old compilers (like GCC < 3.0) used a different name mangling,
this is not a problem because DMD in fact only supports Itanium C++ ABI on Posix.

For Windows instead the implementation it is provided by the UnDecorateSymbolName
function present in the Debug Help Library.
(https://docs.microsoft.com/en-us/windows/win32/api/dbghelp/nf-dbghelp-undecoratesymbolname)

dlang-bot · 2020-03-25T15:55:57Z

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Testing this PR locally

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ErnyTech · 2020-04-01T12:35:37Z

It is now ready for review.

Geod24

Did a first round of review

src/core/internal/cppdemangle.d

Geod24 · 2020-04-01T17:03:50Z

src/core/internal/cppdemangle.d

+        version (Posix)
+        {
+            int result;
+            auto demangledNamePtr = _instance.__cxa_demangle(mangledName, null, null, &result);


I don't see the point of copying the result when you could just pass the pointer to the array here ?

ErnyTech · 2020-04-01T17:37:39Z

Thanks for the extensive review!

ErnyTech · 2020-04-12T20:34:25Z

@Geod24, this is ready for second round ;-)

Having a C++ symbol demangler is very useful, with this it will be possible to implement the C++ symbol demangle in the stacktrace. The demangling is done in Posix platform by function __cxa_demangle presents in Itanium C++ ABI (https://itanium-cxx-abi.github.io/cxx-abi/abi.html#demangler). Itanium C++ ABI is used practically in all modern C++ compilers on Posix, however old compilers (like GCC < 3.0) used a different name mangling, this is not a problem because DMD in fact only supports Itanium C++ ABI on Posix. For Windows instead the implementation it is provided by the UnDecorateSymbolName function present in the Debug Help Library. (https://docs.microsoft.com/en-us/windows/win32/api/dbghelp/nf-dbghelp-undecoratesymbolname) Signed-off-by: Ernesto Castellotti <mail@ernestocastellotti.it>

MoonlightSentinel · 2020-06-11T13:09:38Z

src/core/internal/cppdemangle.d

+/**
+* Demangles C++ mangled names.
+*
+* The output buffer and return will be contains the demangled name of C++ symbol if the demangling is successful.


Suggested change

* The output buffer and return will be contains the demangled name of C++ symbol if the demangling is successful.

* The output buffer and return value will contain the demangled name of C++ symbol if the demangling is successful.

MoonlightSentinel · 2020-06-11T13:12:10Z

src/core/internal/cppdemangle.d

+*
+* The output buffer and return will be contains the demangled name of C++ symbol if the demangling is successful.
+*
+* This function will fail and the mangled name in input will be returned if:


I think the "return input on failure" part should be mentioned in the previous sentence as it describes the general function contract

MoonlightSentinel · 2020-06-11T13:16:19Z

src/core/internal/cppdemangle.d

+*
+ * Params:
+ *  mangledName = The string to demangle.
+ *  outputBuffer = The destination buffer, if the size of the destination buffer is <= the size of cppdemangle output the return string would be incomplete.


Redundant size requirement, it's already mentioned above

MoonlightSentinel · 2020-06-11T13:21:12Z

src/core/internal/cppdemangle.d

+ * Returns:
+ *  The demangled name or the original string if the name is not a mangled C++ name.
+ */
+char[] cppdemangle(const(char)[] mangledName, char[] outputBuffer, string prefix = "") @trusted


Don't think this function should accept a prefix, it's an unrelated complication and a user can always do that manually:

buffer[0..prefix.length] = prefix; cppdemangle(mangling, buffer[prefix.length .. $]);

MoonlightSentinel · 2020-06-11T13:21:56Z

src/core/internal/cppdemangle.d

+ * Returns:
+ *  The demangled name or the original string if the name is not a mangled C++ name.
+ */
+char[] cppdemangle(const(char)[] mangledName, char[] outputBuffer, string prefix = "") @trusted


The symbol should be in camelCase: cppDemangle

@trusted should probably be used in smaller scope(s).

MoonlightSentinel · 2020-06-11T13:30:38Z

src/core/internal/cppdemangle.d

+        @nogc nothrow extern(System)
+        {
+            private UnDecorateSymbolNameFunc UnDecorateSymbolName;
+        }


@nogc nothrow extern(System) doesn't affect the type of UnDecorateSymbolName and extern(System) is redundant anyway

MoonlightSentinel · 2020-06-11T13:31:02Z

src/core/internal/cppdemangle.d

+        }
+    }
+
+    version (Windows)


Suggested change

version (Windows)

else version (Windows)

ErnyTech · 2020-06-24T16:21:50Z

Now that my exams are over I can continue with this!
Thanks for the review @MoonlightSentinel

MoonlightSentinel · 2021-12-06T19:14:27Z

Ping @ErnyTech

ljmf00

Just a note to tick later: Missing tests.

ljmf00 · 2021-12-06T19:39:51Z

src/core/internal/cppdemangle.d

+            private static immutable names = ["libc++abi.dylib", "libstdc++.dylib"];
+        else
+        {
+            private static immutable names = ["libstdc++.so", "libstdc++.so.6", "libstdc++.so.5",


What about fallbacks to other major versions of libstdc++? It shouldn't be required for new systems but could be good for compatibility.

ljmf00 · 2021-12-06T19:47:11Z

src/core/internal/cppdemangle.d

+
+        @nogc nothrow extern(System)
+        {
+            private UnDecorateSymbolNameFunc UnDecorateSymbolName;


UnDecorateSymbolName is a symbol from dbghelp.dll and that doesn't come with a Windows stock installation, being instead, part of Windows Debugging Kit (WDK). Also, considering MinGW systems, aren't libstdc++ shipped anyway? Notwithstanding, we should have fallbacks for those too, just in case.

ljmf00 · 2021-12-06T19:49:42Z

src/core/internal/cppdemangle.d

+        {
+            import core.sys.posix.dlfcn : dlsym, dlopen, dlclose, RTLD_LAZY;
+
+            auto handle = dlopen(null, RTLD_LAZY);


Why not add null to the fallback list instead of doing code duplication? Is there any additional logic I'm missing here?

ljmf00 · 2021-12-06T19:56:31Z

src/core/internal/cppdemangle.d

+            return null;
+        }
+
+        auto mangledNamePtr = cast(char*) pureCalloc(mangledName.length + 1, char.sizeof);


Please check if the allocation succeed.

ljmf00 · 2021-12-06T19:59:10Z

src/core/internal/cppdemangle.d

+                }
+            }
+
+            return copyResult(demangledName[0..strlen(demangledName)], outputBuffer);


Please don't do strlen. __cxa_demangle is capable of returning the length. See https://gcc.gnu.org/onlinedocs/libstdc++/libstdc++-html-USERS-4.3/a01696.html

Why do we use a copyResult function in the first place? We shouldn't hang if the buffer is not large enough, and could return the allocated buffer directly if the provided output buffer is null.

ljmf00 · 2021-12-06T20:04:42Z

src/core/internal/cppdemangle.d

+        version (Posix)
+        {
+            int status;
+            auto demangledName = _instance.__cxa_demangle(mangledNamePtr, null, null, &status);


Please feed the output buffer to __cxa_demangle since a preallocated buffer can help avoid unnecessary reallocations.

This was referenced Mar 24, 2020

Add cppdemangle in druntime #2803

Closed

[WIP] [DONT MERGE] Enable demangling of C++ symbols in the stacktrace #3003

Draft

ErnyTech marked this pull request as ready for review March 24, 2020 21:46

ErnyTech requested review from andralex, MartinNowak, schveiguy and wilzbach as code owners March 24, 2020 21:46

ErnyTech force-pushed the cppdemangle branch from 79e7a7c to 115ff06 Compare March 25, 2020 15:55

ErnyTech force-pushed the cppdemangle branch 2 times, most recently from 36d80f7 to 1be511b Compare March 26, 2020 14:30

ErnyTech changed the title ~~Add cppdemangle in druntime~~ [WIP] Add cppdemangle in druntime Mar 27, 2020

dlang-bot added the WIP Work In Progress - not ready for review or pulling label Mar 27, 2020

ErnyTech force-pushed the cppdemangle branch 6 times, most recently from cb69e57 to 0de39b0 Compare April 1, 2020 11:15

ErnyTech changed the title ~~[WIP] Add cppdemangle in druntime~~ Add cppdemangle in druntime Apr 1, 2020

Geod24 suggested changes Apr 1, 2020

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Geod24 removed the WIP Work In Progress - not ready for review or pulling label Apr 1, 2020

ErnyTech force-pushed the cppdemangle branch 6 times, most recently from bbe2da0 to f7e3b10 Compare April 12, 2020 19:33

ErnyTech requested a review from Geod24 April 12, 2020 20:38

ErnyTech force-pushed the cppdemangle branch from f7e3b10 to 2e92b4a Compare April 22, 2020 14:37

MoonlightSentinel suggested changes Jun 11, 2020

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Add cppdemangle in druntime #3002

Add cppdemangle in druntime #3002

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	* The output buffer and return will be contains the demangled name of C++ symbol if the demangling is successful.
	* The output buffer and return value will contain the demangled name of C++ symbol if the demangling is successful.

Add cppdemangle in druntime #3002

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Add cppdemangle in druntime #3002

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Bugzilla references

Testing this PR locally

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