Provide an easy way to view AOT disassembly

[vsmenon]

Today:

dart -disassemble foo.dart

provides a convenient way to view disassembled code, but only for JIT mode.

AFAIK, you need a checked SDK to view AOT disassembled code (which is more useful) - e.g.,:

.../dart/sdk/pkg/vm/tool/precompiler2 --disassemble foo.dart foo.aot

Is there a way to integrate that into the Dart cli?

@jefflim-google

[vsmenon]

FYI - @mraleph - @jefflim-google was asking.

[vsmenon]

Also, is there an easy way to show ARM code from an x86 machine?

[bkonyi]

cc @alexmarkov

[mraleph]

Currently, you can't get disassembly with --disassemble from dart compile exe or flutter build apk --release because they use PRODUCT build of gen_snapshot which exclude disassembler. There is actually no good reason for why it excludes it (it historical). I have recently (see d7a57a5) fixed it to include IL printer into PRODUCT gen_snapshot and I think we can similarly include disassembler as well.

That said you can do the following today:

• flutter build apk --profile --extra-gen-snapshot-options=--disassemble would work and dump disassembly
• flutter build apk --release --extra-gen-snapshot-options=--print-flow-graph or dart compile exe --extra-gen-snapshot-options=--print-flow-graph would work and dump IL graphs (which are much easier to read than assembly anyway).
• flutter build apk --release --extra-gen-snapshot-options=--no-strip,--code-comments,--write-code-comments-as-synthetic-source-to=/tmp/comments.txt after which you can use the right objdump to disassemble ./build/app/intermediates/merged_native_libs/release/out/lib/arm64-v8a/libapp.so and see IL instructions along with disassembly, e.g.

$ aarch64-linux-gnu-nm ./build/app/intermediates/merged_native_libs/release/out/lib/arm64-v8a/libapp.so | grep main
0000000000034334 t Precompiled__IntegerImplementation_0150898_remainder_584
00000000000e7204 t Precompiled____main_3795
00000000000e7234 t Precompiled____main_main_3796
0000000000083df0 t Precompiled_ReadBuffer_get_hasRemaining_1949
$ aarch64-linux-gnu-objdump --source --disassemble=Precompiled____main_3795 ./build/app/intermediates/merged_native_libs/release/out/lib/arm64-v8a/libapp.so

./build/app/intermediates/merged_native_libs/release/out/lib/arm64-v8a/libapp.so:     file format elf64-littleaarch64


Disassembly of section .text:

Disassembly of section .text:

00000000000e7204 <Precompiled____main_3795>:
EnterCallRuntimeFrame
EnterCallRuntimeFrame
EnterCallRuntimeFrame
B0
B1
Enter frame
   e7204:	a9bf79fd 	stp	x29, x30, [x15, #-16]!
   e7208:	aa0f03fd 	mov	x29, x15
CheckStackOverflow:8(stack=0, loop=0)
   e720c:	f9402350 	ldr	x16, [x26, #64]
   e7210:	eb1001ff 	cmp	x15, x16
   e7214:	540000c9 	b.ls	e722c <Precompiled____main_3795+0x28>  // b.plast
StaticCall:10( runApp<0> , result_type = T{Null?})
   e7218:	97fef350 	bl	a3f58 <Precompiled____runApp_2550>
ParallelMove r0 <- C
   e721c:	aa1603e0 	mov	x0, x22
Return:12(v0)
   e7220:	aa1d03ef 	mov	x15, x29
   e7224:	a8c179fd 	ldp	x29, x30, [x15], #16
   e7228:	d65f03c0 	ret
CheckStackOverflowSlowPath
   e722c:	97fffd11 	bl	e6670 <Precompiled_Stub__iso_stub_StackOverflowSharedWithoutFPURegsStub>
   e7230:	54ffff4e 	b.al	e7218 <Precompiled____main_3795+0x14>

This is on Linux using aarch64 binutils (available via sudo apt-get install binutils-aarch64-linux-gnu, similarly you can install binutils for ARM).

Alternatively if you have Android NDK installed (which you often do), you can look for llvm-objdump there. It has slightly different flags and format of the output, but the idea is the same (you can replace linux below with darwin on Mac).

$ ${ANDROID_NDK}/toolchains/llvm/prebuilt/linux-x86_64/bin/llvm-objdump --source --disassemble-symbols=Precompiled____main_3795 ./build/app/intermediates/merged_native_libs/release/out/lib/arm64-v8a/libapp.so

./build/app/intermediates/merged_native_libs/release/out/lib/arm64-v8a/libapp.so:	file format elf64-littleaarch64


Disassembly of section .text:

00000000000e7204 <Precompiled____main_3795>:
; Enter frame
   e7204: fd 79 bf a9  	stp	x29, x30, [x15, #-16]!
   e7208: fd 03 0f aa  	mov	x29, x15
; CheckStackOverflow:8(stack=0, loop=0)
   e720c: 50 23 40 f9  	ldr	x16, [x26, #64]
   e7210: ff 01 10 eb  	cmp	x15, x16
   e7214: c9 00 00 54  	b.ls	0xe722c <Precompiled____main_3795+0x28>
; StaticCall:10( runApp<0> , result_type = T{Null?})
   e7218: 50 f3 fe 97  	bl	0xa3f58 <Precompiled____runApp_2550>
; ParallelMove r0 <- C
   e721c: e0 03 16 aa  	mov	x0, x22
; Return:12(v0)
   e7220: ef 03 1d aa  	mov	x15, x29
   e7224: fd 79 c1 a8  	ldp	x29, x30, [x15], #16
   e7228: c0 03 5f d6  	ret
; CheckStackOverflowSlowPath
   e722c: 11 fd ff 97  	bl	0xe6670 <Precompiled_Stub__iso_stub_StackOverflowSharedWithoutFPURegsStub>
   e7230: 4e ff ff 54  	b.al	0xe7218 <Precompiled____main_3795+0x14>

[SpamixOfficial]

I know this issue is fairly stale but would love to see this happen since we have disassembly for other snapshots already

[mraleph]

FWIW: dart compile exe -v --extra-gen-snapshot-options=--disassemble,--print-flow-graph,--code-comments should work these days.

[SpamixOfficial]

The thing is I want to get the disassembly from an already built AOT snapshot. Is that possible? @mraleph

[mraleph]

Then you can objdump/otool it. It's just a native ELF/Mach-O file.

[SpamixOfficial]

Fair. Thanks a lot!