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Debug info for function argument missing DW_AT_location #23266

Open llvmbot opened 9 years ago

llvmbot commented 9 years ago
Bugzilla Link 22892
Version unspecified
OS All
Attachments Example C code that demonstrates the issue, llvm-dwarfdump output, llvm-dwarfdump output from a 64 bit build
Reporter LLVM Bugzilla Contributor
CC @adrian-prantl,@dwblaikie

Extended Description

When I compile the attached code, the "args_" argument to "Khandle_missed_dispatchVKgI" is missing a DW_AT_location.

This is a test case isolated from a much larger body of code (where this happens more often). This code is also generated from our C back-end. It is interesting (to me at least) that the code generated by our LLVM back-end has the same problem.

I compile with clang 3.5, 3.6 or the most recent release from Apple:

clang -arch i386 -g -O -c -o bad-debug-info.o bad-debug-info.c

and then I run dwarfdump (or llvm-dwarfdump) and see:

0x000005f4: DW_TAG_subprogram [18] * DW_AT_low_pc [DW_FORM_addr] (0x0000000000000030) DW_AT_high_pc [DW_FORM_addr] (0x000000000000028e) DW_AT_frame_base [DW_FORM_block1] (<0x01> 55 ) DW_AT_name [DW_FORM_strp] ( .debug_str[0x00000447] = "Khandle_missed_dispatchVKgI") DW_AT_decl_file [DW_FORM_data1] ("/Users/bruce/Development/dylan/missing-debug-location/new-dispatch.c") DW_AT_decl_line [DW_FORM_data1] (105) DW_AT_prototyped [DW_FORM_flag] (0x01) DW_AT_type [DW_FORM_ref4] (cu + 0x0127 => {0x00000127}) DW_AT_external [DW_FORM_flag] (0x01) DW_AT_APPLE_optimized [DW_FORM_flag] (0x01)

0x0000060c: DW_TAG_formal_parameter [24] DW_AT_location [DW_FORM_data4] (0x00000000) DW_AT_name [DW_FORM_strp] ( .debugstr[0x00000480] = "d") DW_AT_decl_file [DW_FORM_data1] ("/Users/bruce/Development/dylan/missing-debug-location/new-dispatch.c") DW_AT_decl_line [DW_FORM_data1] (105) DW_AT_type [DW_FORM_ref4] (cu + 0x0127 => {0x00000127})

0x0000061b: DW_TAG_formal_parameter [24] DW_AT_location [DW_FORM_data4] (0x000000fc) DW_AT_name [DW_FORM_strp] ( .debugstr[0x0000046f] = "parent") DW_AT_decl_file [DW_FORM_data1] ("/Users/bruce/Development/dylan/missing-debug-location/new-dispatch.c") DW_AT_decl_line [DW_FORM_data1] (105) DW_AT_type [DW_FORM_ref4] (cu + 0x0127 => {0x00000127})

0x0000062a: DW_TAG_formal_parameter [25] DW_AT_name [DW_FORM_strp] ( .debugstr[0x0000047a] = "args") DW_AT_decl_file [DW_FORM_data1] ("/Users/bruce/Development/dylan/missing-debug-location/new-dispatch.c") DW_AT_decl_line [DW_FORM_data1] (105) DW_AT_type [DW_FORM_ref4] (cu + 0x0127 => {0x00000127})

When I use llvm-dwarfdump, I get a bunch of error messages (and more on 3.6 than on 3.5). I don't get any messages when using the system dwarfdump.

I believe that gcc is generating correct debug info for this code.

llvmbot commented 9 years ago

echristo suggest pinging on this bug again. Any ideas?

llvmbot commented 9 years ago

Any further thoughts on this since it happens with PIC codegen?

llvmbot commented 9 years ago

Under the theory that perhaps this is register-pressure induced due to PIC and x86, I wondered if my original test case would reproduce this issue since it has a lot more variables.

Unfortunately, compiling it with -fno-PIC results in a working DW_AT_location:

0x0000062a: DW_TAG_formal_parameter [24] DW_AT_location [DW_FORM_data4] (0x00000000) DW_AT_name [DW_FORM_strp] ( .debugstr[0x0000049b] = "args") DW_AT_decl_file [DW_FORM_data1] ("/Users/bruce/Development/dylan/missing-debug-location/new-dispatch.c") DW_AT_decl_line [DW_FORM_data1] (105) DW_AT_type [DW_FORM_ref4] (cu + 0x0127 => {0x00000127})

Does that make it any clearer for anyone why this is happening in PIC mode?

dwblaikie commented 9 years ago

I still see this on a recent build:

batavia:missing-debug-location bruce $ ~/Development/build-llvm/bin/clang -### -W -Wall -arch i386 -g -O -c -o bad-debug-info.o bad-debug-info.c clang version 3.7.0 (trunk 231926) (llvm/trunk 231925) Target: i386-apple-darwin14.1.0 Thread model: posix "/Users/bruce/Development/build-llvm/bin/clang-3.7" "-cc1" "-triple" "i386-apple-macosx10.10.0" "-emit-obj" "-disable-free" "-disable-llvm-verifier" "-main-file-name" "bad-debug-info.c" "-mrelocation-model" "pic" "-pic-level" "2" "-mthread-model" "posix" "-mdisable-fp-elim" "-masm-verbose" "-target-cpu" "yonah" "-target-linker-version" "241.9" "-gdwarf-2" "-dwarf-column-info" "-coverage-file" "/Users/bruce/Development/dylan/missing-debug-location/bad-debug-info.o" "-resource-dir" "/Users/bruce/Development/build-llvm/bin/../lib/clang/3.7.0" "-O2" "-W" "-Wall" "-fdebug-compilation-dir" "/Users/bruce/Development/dylan/missing-debug-location" "-ferror-limit" "19" "-fmessage-length" "204" "-stack-protector" "1" "-mstackrealign" "-fblocks" "-fobjc-runtime=macosx-fragile-10.10.0" "-fobjc-subscripting-legacy-runtime" "-fencode-extended-block-signature" "-fmax-type-align=16" "-fdiagnostics-show-option" "-fcolor-diagnostics" "-vectorize-loops" "-vectorize-slp" "-o" "bad-debug-info.o" "-x" "c" "bad-debug-info.c"

Seems something in particular to do with -mrelocation-model pic, doesn't reproduce with -mrelocation-model static.

llvmbot commented 9 years ago

I still see this on a recent build:

batavia:missing-debug-location bruce $ ~/Development/build-llvm/bin/clang -### -W -Wall -arch i386 -g -O -c -o bad-debug-info.o bad-debug-info.c clang version 3.7.0 (trunk 231926) (llvm/trunk 231925) Target: i386-apple-darwin14.1.0 Thread model: posix "/Users/bruce/Development/build-llvm/bin/clang-3.7" "-cc1" "-triple" "i386-apple-macosx10.10.0" "-emit-obj" "-disable-free" "-disable-llvm-verifier" "-main-file-name" "bad-debug-info.c" "-mrelocation-model" "pic" "-pic-level" "2" "-mthread-model" "posix" "-mdisable-fp-elim" "-masm-verbose" "-target-cpu" "yonah" "-target-linker-version" "241.9" "-gdwarf-2" "-dwarf-column-info" "-coverage-file" "/Users/bruce/Development/dylan/missing-debug-location/bad-debug-info.o" "-resource-dir" "/Users/bruce/Development/build-llvm/bin/../lib/clang/3.7.0" "-O2" "-W" "-Wall" "-fdebug-compilation-dir" "/Users/bruce/Development/dylan/missing-debug-location" "-ferror-limit" "19" "-fmessage-length" "204" "-stack-protector" "1" "-mstackrealign" "-fblocks" "-fobjc-runtime=macosx-fragile-10.10.0" "-fobjc-subscripting-legacy-runtime" "-fencode-extended-block-signature" "-fmax-type-align=16" "-fdiagnostics-show-option" "-fcolor-diagnostics" "-vectorize-loops" "-vectorize-slp" "-o" "bad-debug-info.o" "-x" "c" "bad-debug-info.c"

dwblaikie commented 9 years ago

(works on trunk, fixed some time ago)

adrian-prantl commented 9 years ago

This was fixed somewhere between r209773 and r211143, which is around June last year. FYI it also works with the version of clang that is in the latest Xcode 6.3 beta.

dwblaikie commented 9 years ago

I don't think I can reproduce this with ToT clang on Linux:

$ clang -target i386 -g -O -c -o bad-debug-info.o bad-debug-info.c && llvm-dwarfdump-tot -debug-dump=info bad-debug-info.o | grep -B 2 args_ 0x00000065: DW_TAG_formal_parameter [5]
DW_AT_location [DW_FORM_sec_offset] (0x00000000) DW_AT_name [DW_FORM_strp] ( .debugstr[0x0000007d] = "args")

So perhaps this is fixed, or only reproduces on Apple? Not sure.

llvmbot commented 9 years ago

llvm-dwarfdump output from a 64 bit build

llvmbot commented 9 years ago

llvm-dwarfdump output

llvmbot commented 9 years ago

Example C code that demonstrates the issue Much more minimized code that reproduces this issue.

dwblaikie commented 9 years ago

A further simplified (as much as possible, really) test case would be helpful.

But in general, optimized debug info in LLVM is still pretty hit-or-miss at best. Specific test cases/deficiencies are still good to know about, though.

llvmbot commented 2 months ago

@llvm/issue-subscribers-debuginfo

Author: None (llvmbot)

| | | | --- | --- | | Bugzilla Link | [22892](https://llvm.org/bz22892) | | Version | unspecified | | OS | All | | Attachments | [Example C code that demonstrates the issue](https://user-images.githubusercontent.com/60944935/143751107-fe9d9464-25e1-488a-91de-f254b54d7c0c.gz), [llvm-dwarfdump output](https://user-images.githubusercontent.com/60944935/143751108-4d28bb01-0c68-4e56-802d-6696fa70eb08.gz), [llvm-dwarfdump output from a 64 bit build](https://user-images.githubusercontent.com/60944935/143751109-7bd35e67-97df-4b41-b37d-7df087f238db.gz) | | Reporter | LLVM Bugzilla Contributor | | CC | @adrian-prantl,@dwblaikie | ## Extended Description When I compile the attached code, the "args_" argument to "Khandle_missed_dispatchVKgI" is missing a DW_AT_location. This is a test case isolated from a much larger body of code (where this happens more often). This code is also generated from our C back-end. It is interesting (to me at least) that the code generated by our LLVM back-end has the same problem. I compile with clang 3.5, 3.6 or the most recent release from Apple: clang -arch i386 -g -O -c -o bad-debug-info.o bad-debug-info.c and then I run dwarfdump (or llvm-dwarfdump) and see: 0x000005f4: DW_TAG_subprogram [18] * DW_AT_low_pc [DW_FORM_addr] (0x0000000000000030) DW_AT_high_pc [DW_FORM_addr] (0x000000000000028e) DW_AT_frame_base [DW_FORM_block1] (<0x01> 55 ) DW_AT_name [DW_FORM_strp] ( .debug_str[0x00000447] = "Khandle_missed_dispatchVKgI") DW_AT_decl_file [DW_FORM_data1] ("/Users/bruce/Development/dylan/missing-debug-location/new-dispatch.c") DW_AT_decl_line [DW_FORM_data1] (105) DW_AT_prototyped [DW_FORM_flag] (0x01) DW_AT_type [DW_FORM_ref4] (cu + 0x0127 => {0x00000127}) DW_AT_external [DW_FORM_flag] (0x01) DW_AT_APPLE_optimized [DW_FORM_flag] (0x01) 0x0000060c: DW_TAG_formal_parameter [24] DW_AT_location [DW_FORM_data4] (0x00000000) DW_AT_name [DW_FORM_strp] ( .debug_str[0x00000480] = "d_") DW_AT_decl_file [DW_FORM_data1] ("/Users/bruce/Development/dylan/missing-debug-location/new-dispatch.c") DW_AT_decl_line [DW_FORM_data1] (105) DW_AT_type [DW_FORM_ref4] (cu + 0x0127 => {0x00000127}) 0x0000061b: DW_TAG_formal_parameter [24] DW_AT_location [DW_FORM_data4] (0x000000fc) DW_AT_name [DW_FORM_strp] ( .debug_str[0x0000046f] = "parent_") DW_AT_decl_file [DW_FORM_data1] ("/Users/bruce/Development/dylan/missing-debug-location/new-dispatch.c") DW_AT_decl_line [DW_FORM_data1] (105) DW_AT_type [DW_FORM_ref4] (cu + 0x0127 => {0x00000127}) 0x0000062a: DW_TAG_formal_parameter [25] DW_AT_name [DW_FORM_strp] ( .debug_str[0x0000047a] = "args_") DW_AT_decl_file [DW_FORM_data1] ("/Users/bruce/Development/dylan/missing-debug-location/new-dispatch.c") DW_AT_decl_line [DW_FORM_data1] (105) DW_AT_type [DW_FORM_ref4] (cu + 0x0127 => {0x00000127}) When I use llvm-dwarfdump, I get a bunch of error messages (and more on 3.6 than on 3.5). I don't get any messages when using the system dwarfdump. I believe that gcc is generating correct debug info for this code.