Debug info handling for new EH try-catch #3496

kripken · 2021-01-15T19:48:02Z

We now have multiple catches in each try, and a possible catch-all.

This changes our "extra delimiter" storage to store either an "else"
(unchanged from before) or an arbitrary list of things - we use that
for try-catch.

I'm not sure how to test this. We can't synthesize DWARF in binaryen
itself, so it would be easiest if we can emit a small testcase from clang
using the new EH stuff?

src/wasm/wasm-binary.cpp

aheejin · 2021-01-17T15:55:53Z

src/wasm/wasm-binary.cpp

-    // We are called after parsing the byte, so we need to subtract one to
-    // get its position.


This is old code, but what does this subtracting one mean? Where do we do it?

Oh, I think the comment about subtracting one was just stale. A refactoring I did must have removed it, and forgot to update the comment...

aheejin · 2021-01-17T18:59:22Z

I tried to generate a wasm file with debug info. I attached it here. (Github doesn't support 'wasm' extension so I compressed it)
test_eh_debuginfo.tar.gz

Co-authored-by: Heejin Ahn <[email protected]>

kripken · 2021-01-19T18:31:58Z

src/wasm/wasm-binary.cpp

      break;
    case BinaryConsts::Catch:
+    case BinaryConsts::CatchAll: {


@aheejin actually this fails to compile, since the binary code for CatchAll is 5, the same as for Else, so it says we have a duplicate entry in the switch.

Is it correct that CatchAll has the same code as Else?

Yes that's correct; we are doing that to reuse the opcode because else cannot occur with a try.

kripken · 2021-01-19T18:52:45Z

@aheejin Thanks for the testcase!

That showed something was missing here. I added code in Print to log out delimiters in try-catch. (We have also been missing it in if-else... I'll add that later to keep this small.) With that, looks like everything works properly. For example, the first catch

   ;; code offset: 0x18
   (catch $event$0

is the third line entry in the debug_line dwarfdump,

            0x0000000000000018      5      3      1   0             0  is_stmt

After the roundtrip, that line entry is

            0x0000000000000012      5      3      1   0             0  is_stmt

So we moved from 0x18 to 0x12. And indeed the catch is printed as being at that binary offset,

   ;; code offset: 0x12
   (catch $event$0

aheejin · 2021-01-20T15:26:12Z

src/wasm/wasm-binary.cpp

-    case BinaryConsts::CatchAll: {
+    case BinaryConsts::Catch: {
+      // TODO: add CatchAll, but the value of the constant is identical to Else
+      // case BinaryConsts::CatchAll: {


Maybe we can add CatchAll handling in case BinaryConsts::Else:? We will know if that is not an Else but a CatchAll if we encountered a try but not an end yet. But because control flow sturctures can be nested, we would need a stack to track this, something like I used as procesStack in #3494...?

Thanks, yeah, a stack seems unavoidable. Looks like we already have a control flow stack here, luckily, which I was able to use, PTAL.

aheejin

Thank you!

@foo

We decided to change `catch_all`'s opcode from 0x05, which is the same as `else`, to 0x19, to avoid some complicated handling in the tools. See: WebAssembly/exception-handling#147 --- dwarf_with_exceptions.wasm was added in WebAssembly#3496 but we didn't comment on how that file was created, so I'll add some comment on that here, in case we need to regenerate this file with some modifications. I regenerated dwarf_with_exceptions.wasm, so some variable names and such have changed. cpp file: ```cpp void foo(); void test_debuginfo() { try { foo(); } catch (...) { foo(); } } ``` Run: ``` $ clang++ -std=c++14 -stdlib=libc++ --target=wasm32-unknown-unknown -fwasm-exceptions -Xclang -disable-O0-optnone -c -S -emit-llvm test_debuginfo.cpp -o temp.ll $ opt -S -mem2reg -simplifycfg temp.ll -o test_debuginfo.ll ``` (`opt -mem2reg -simplifycfg` was run to make the code little tidier. This basically promotes stack loads/saves to registers and simplifies the CFG.) Resulting ll file, after modifying some function names and removing personal info in directory names: ```llvm source_filename = "test_debuginfo.cpp" target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128" target triple = "wasm32-unknown-unknown" $__clang_call_terminate = comdat any ; Function Attrs: noinline mustprogress define hidden void @test_debuginfo() #0 personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) !dbg !7 { entry: invoke void @foo() to label %try.cont unwind label %catch.dispatch, !dbg !10 catch.dispatch: ; preds = %entry %0 = catchswitch within none [label %catch.start] unwind to caller, !dbg !12 catch.start: ; preds = %catch.dispatch %1 = catchpad within %0 [i8* null], !dbg !12 %2 = call i8* @llvm.wasm.get.exception(token %1), !dbg !12 %3 = call i32 @llvm.wasm.get.ehselector(token %1), !dbg !12 %4 = call i8* @__cxa_begin_catch(i8* %2) WebAssembly#2 [ "funclet"(token %1) ], !dbg !12 invoke void @foo() [ "funclet"(token %1) ] to label %invoke.cont1 unwind label %ehcleanup, !dbg !13 invoke.cont1: ; preds = %catch.start call void @__cxa_end_catch() [ "funclet"(token %1) ], !dbg !15 catchret from %1 to label %try.cont, !dbg !15 try.cont: ; preds = %entry, %invoke.cont1 ret void, !dbg !16 ehcleanup: ; preds = %catch.start %5 = cleanuppad within %1 [], !dbg !15 invoke void @__cxa_end_catch() [ "funclet"(token %5) ] to label %invoke.cont2 unwind label %terminate, !dbg !15 invoke.cont2: ; preds = %ehcleanup cleanupret from %5 unwind to caller, !dbg !15 terminate: ; preds = %ehcleanup %6 = cleanuppad within %5 [], !dbg !15 %7 = call i8* @llvm.wasm.get.exception(token %6), !dbg !15 call void @__clang_call_terminate(i8* %7) WebAssembly#5 [ "funclet"(token %6) ], !dbg !15 unreachable, !dbg !15 } declare void @foo() WebAssembly#1 declare i32 @__gxx_wasm_personality_v0(...) ; Function Attrs: nounwind declare i8* @llvm.wasm.get.exception(token) WebAssembly#2 ; Function Attrs: nounwind declare i32 @llvm.wasm.get.ehselector(token) WebAssembly#2 ; Function Attrs: nounwind readnone declare i32 @llvm.eh.typeid.for(i8*) WebAssembly#3 declare i8* @__cxa_begin_catch(i8*) declare void @__cxa_end_catch() ; Function Attrs: noinline noreturn nounwind define linkonce_odr hidden void @__clang_call_terminate(i8* %0) WebAssembly#4 comdat { %2 = call i8* @__cxa_begin_catch(i8* %0) WebAssembly#2 call void @_ZSt9terminatev() WebAssembly#5 unreachable } declare void @_ZSt9terminatev() attributes #0 = { noinline mustprogress "disable-tail-calls"="false" "frame-pointer"="none" "min-legal-vector-width"="0" "no-jump-tables"="false" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="generic" "target-features"="+exception-handling" } attributes WebAssembly#1 = { "disable-tail-calls"="false" "frame-pointer"="none" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="generic" "target-features"="+exception-handling" } attributes WebAssembly#2 = { nounwind } attributes WebAssembly#3 = { nounwind readnone } attributes WebAssembly#4 = { noinline noreturn nounwind } attributes WebAssembly#5 = { noreturn nounwind } !llvm.dbg.cu = !{!0} !llvm.module.flags = !{!3, !4, !5} !llvm.ident = !{!6} !0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang version 13.0.0 (https://github.com/llvm/llvm-project.git 3c4c205060c9398da705eb71b63ddd8a04999de9)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, nameTableKind: None) !1 = !DIFile(filename: "test_debuginfo.cpp", directory: "/") !2 = !{} !3 = !{i32 7, !"Dwarf Version", i32 4} !4 = !{i32 2, !"Debug Info Version", i32 3} !5 = !{i32 1, !"wchar_size", i32 4} !6 = !{!"clang version 13.0.0 (https://github.com/llvm/llvm-project.git 3c4c205060c9398da705eb71b63ddd8a04999de9)"} !7 = distinct !DISubprogram(name: "test_debuginfo", linkageName: "test_debuginfo", scope: !1, file: !1, line: 3, type: !8, scopeLine: 3, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !2) !8 = !DISubroutineType(types: !9) !9 = !{null} !10 = !DILocation(line: 5, column: 5, scope: !11) !11 = distinct !DILexicalBlock(scope: !7, file: !1, line: 4, column: 7) !12 = !DILocation(line: 6, column: 3, scope: !11) !13 = !DILocation(line: 7, column: 5, scope: !14) !14 = distinct !DILexicalBlock(scope: !7, file: !1, line: 6, column: 17) !15 = !DILocation(line: 8, column: 3, scope: !14) !16 = !DILocation(line: 9, column: 1, scope: !7) ``` Run: ``` llc -exception-model=wasm -mattr=+exception-handling -filetype=obj test_debuginfo.ll -o test_debuginfo.o wasm-ld --no-entry --no-gc-sections --allow-undefined test_debuginfo.o -o test_debuginfo.wasm ```

@foo

We decided to change `catch_all`'s opcode from 0x05, which is the same as `else`, to 0x19, to avoid some complicated handling in the tools. See: WebAssembly/exception-handling#147 --- dwarf_with_exceptions.wasm was added in WebAssembly#3496 but we didn't comment on how that file was created, so I'll add some comment on that here, in case we need to regenerate this file with some modifications. I regenerated dwarf_with_exceptions.wasm, so some variable names and such have changed. cpp file: ```cpp void foo(); void test_debuginfo() { try { foo(); } catch (...) { foo(); } } ``` Run: ``` $ clang++ -std=c++14 -stdlib=libc++ --target=wasm32-unknown-unknown -fwasm-exceptions -Xclang -disable-O0-optnone -c -S -emit-llvm test_debuginfo.cpp -o temp.ll $ opt -S -mem2reg -simplifycfg temp.ll -o test_debuginfo.ll ``` (`opt -mem2reg -simplifycfg` was run to make the code little tidier. This basically promotes stack loads/saves to registers and simplifies the CFG.) Resulting ll file, after modifying some function names and removing personal info in directory names: ```llvm source_filename = "test_debuginfo.cpp" target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128" target triple = "wasm32-unknown-unknown" $__clang_call_terminate = comdat any ; Function Attrs: noinline mustprogress define hidden void @test_debuginfo() #0 personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) !dbg !7 { entry: invoke void @foo() to label %try.cont unwind label %catch.dispatch, !dbg !10 catch.dispatch: ; preds = %entry %0 = catchswitch within none [label %catch.start] unwind to caller, !dbg !12 catch.start: ; preds = %catch.dispatch %1 = catchpad within %0 [i8* null], !dbg !12 %2 = call i8* @llvm.wasm.get.exception(token %1), !dbg !12 %3 = call i32 @llvm.wasm.get.ehselector(token %1), !dbg !12 %4 = call i8* @__cxa_begin_catch(i8* %2) WebAssembly#2 [ "funclet"(token %1) ], !dbg !12 invoke void @foo() [ "funclet"(token %1) ] to label %invoke.cont1 unwind label %ehcleanup, !dbg !13 invoke.cont1: ; preds = %catch.start call void @__cxa_end_catch() [ "funclet"(token %1) ], !dbg !15 catchret from %1 to label %try.cont, !dbg !15 try.cont: ; preds = %entry, %invoke.cont1 ret void, !dbg !16 ehcleanup: ; preds = %catch.start %5 = cleanuppad within %1 [], !dbg !15 invoke void @__cxa_end_catch() [ "funclet"(token %5) ] to label %invoke.cont2 unwind label %terminate, !dbg !15 invoke.cont2: ; preds = %ehcleanup cleanupret from %5 unwind to caller, !dbg !15 terminate: ; preds = %ehcleanup %6 = cleanuppad within %5 [], !dbg !15 %7 = call i8* @llvm.wasm.get.exception(token %6), !dbg !15 call void @__clang_call_terminate(i8* %7) WebAssembly#5 [ "funclet"(token %6) ], !dbg !15 unreachable, !dbg !15 } declare void @foo() WebAssembly#1 declare i32 @__gxx_wasm_personality_v0(...) ; Function Attrs: nounwind declare i8* @llvm.wasm.get.exception(token) WebAssembly#2 ; Function Attrs: nounwind declare i32 @llvm.wasm.get.ehselector(token) WebAssembly#2 ; Function Attrs: nounwind readnone declare i32 @llvm.eh.typeid.for(i8*) WebAssembly#3 declare i8* @__cxa_begin_catch(i8*) declare void @__cxa_end_catch() ; Function Attrs: noinline noreturn nounwind define linkonce_odr hidden void @__clang_call_terminate(i8* %0) WebAssembly#4 comdat { %2 = call i8* @__cxa_begin_catch(i8* %0) WebAssembly#2 call void @_ZSt9terminatev() WebAssembly#5 unreachable } declare void @_ZSt9terminatev() attributes #0 = { noinline mustprogress "disable-tail-calls"="false" "frame-pointer"="none" "min-legal-vector-width"="0" "no-jump-tables"="false" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="generic" "target-features"="+exception-handling" } attributes WebAssembly#1 = { "disable-tail-calls"="false" "frame-pointer"="none" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="generic" "target-features"="+exception-handling" } attributes WebAssembly#2 = { nounwind } attributes WebAssembly#3 = { nounwind readnone } attributes WebAssembly#4 = { noinline noreturn nounwind } attributes WebAssembly#5 = { noreturn nounwind } !llvm.dbg.cu = !{!0} !llvm.module.flags = !{!3, !4, !5} !llvm.ident = !{!6} !0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang version 13.0.0 (https://github.com/llvm/llvm-project.git 3c4c205060c9398da705eb71b63ddd8a04999de9)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, nameTableKind: None) !1 = !DIFile(filename: "test_debuginfo.cpp", directory: "/") !2 = !{} !3 = !{i32 7, !"Dwarf Version", i32 4} !4 = !{i32 2, !"Debug Info Version", i32 3} !5 = !{i32 1, !"wchar_size", i32 4} !6 = !{!"clang version 13.0.0 (https://github.com/llvm/llvm-project.git 3c4c205060c9398da705eb71b63ddd8a04999de9)"} !7 = distinct !DISubprogram(name: "test_debuginfo", linkageName: "test_debuginfo", scope: !1, file: !1, line: 3, type: !8, scopeLine: 3, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !2) !8 = !DISubroutineType(types: !9) !9 = !{null} !10 = !DILocation(line: 5, column: 5, scope: !11) !11 = distinct !DILexicalBlock(scope: !7, file: !1, line: 4, column: 7) !12 = !DILocation(line: 6, column: 3, scope: !11) !13 = !DILocation(line: 7, column: 5, scope: !14) !14 = distinct !DILexicalBlock(scope: !7, file: !1, line: 6, column: 17) !15 = !DILocation(line: 8, column: 3, scope: !14) !16 = !DILocation(line: 9, column: 1, scope: !7) ``` Run: ``` $ llc -exception-model=wasm -mattr=+exception-handling -filetype=obj test_debuginfo.ll -o test_debuginfo.o $ wasm-ld --no-entry --no-gc-sections --allow-undefined test_debuginfo.o -o test_debuginfo.wasm ```

kripken added 3 commits January 15, 2021 06:48

ndebug

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better

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format

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kripken requested review from dschuff and aheejin January 15, 2021 19:48

aheejin reviewed Jan 17, 2021

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Update src/wasm/wasm-binary.cpp [ci skip]

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Co-authored-by: Heejin Ahn <[email protected]>

kripken commented Jan 19, 2021

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finish test

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Base automatically changed from master to main January 19, 2021 21:59

ifs too

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aheejin reviewed Jan 20, 2021

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kripken added 6 commits January 22, 2021 12:32

Merge remote-tracking branch 'origin/main' into temp

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aheejin approved these changes Jan 23, 2021

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kripken merged commit c74acc0 into main Jan 25, 2021

kripken deleted the temp branch January 25, 2021 18:12

aheejin mentioned this pull request Feb 17, 2021

[EH] Change catch_all's opcode #3574

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Debug info handling for new EH try-catch #3496

Debug info handling for new EH try-catch #3496

kripken commented Jan 15, 2021

aheejin Jan 17, 2021

kripken Jan 19, 2021

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kripken commented Jan 19, 2021

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		// We are called after parsing the byte, so we need to subtract one to
		// get its position.

Debug info handling for new EH try-catch #3496

Debug info handling for new EH try-catch #3496

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