[LLVMdev] Generate .debug_info for asm files?

[Frédéric Riss]

> On May 28, 2015, at 7:36 AM, Alex <alexinbeijing at gmail.com> wrote:
> 
> Dear LLVM devs,
> 
> I've noticed that LLVM's assembler (and hence clang) doesn't generate debug data when assembling, even when run with "-g”.

What are you seeing exactly? because my clang using the integrated as on Darwin definitely produces debug info for assembly input:

$ cat test.s

.globl func
func:
	ret

$ clang -g test.s -c

$ llvm-dwarfdump  test.o 
test.o:	file format Mach-O 64-bit x86-64
[…]

.debug_info contents:
0x00000000: Compile Unit: length = 0x0000008e version = 0x0002 abbr_offset = 0x0000 addr_size = 0x08 (next CU at 0x00000092)

0x0000000b: DW_TAG_compile_unit [1] *
0x0000000c:   DW_AT_stmt_list [DW_FORM_data4]	(0x00000000)
0x00000010:   DW_AT_low_pc [DW_FORM_addr]	(0x0000000000000000)
0x00000018:   DW_AT_high_pc [DW_FORM_addr]	(0x0000000000000001)
0x00000020:   DW_AT_name [DW_FORM_string]	("test.s")
0x00000027:   DW_AT_comp_dir [DW_FORM_string]	("/Users/fred/tmp")
0x00000037:   DW_AT_producer [DW_FORM_string]	("Apple LLVM version 6.0 (clang-600.0.39) (based on LLVM 3.5svn)")
0x00000076:   DW_AT_language [DW_FORM_data2]	(0x8001)

0x00000078:   DW_TAG_label [2] *
0x00000079:     DW_AT_name [DW_FORM_string]	("func")
0x0000007e:     DW_AT_decl_file [DW_FORM_data4]	(0x00000001)
0x00000082:     DW_AT_decl_line [DW_FORM_data4]	(0x00000006)
0x00000086:     DW_AT_low_pc [DW_FORM_addr]	(0x0000000000000000)
0x0000008e:     DW_AT_prototyped [DW_FORM_flag]	(0x00)

0x0000008f:     DW_TAG_unspecified_parameters [3]  

0x00000090:     NULL

0x00000091:   NULL

[…]

.debug_lines contents:
[…]
Address            Line   Column File   ISA Flags
------------------ ------ ------ ------ --- -------------
0x0000000000000000      4      0      1   0  is_stmt
0x0000000000000001      4      0      1   0  is_stmt end_sequence


> Users can add their own CFI/line number data with assembler directives. But GDB ignores the line number data if you don't have a DIE in the .debug_info section which identifies the compilation unit. (I'm not an expert on GDB, but this is the conclusion I have drawn from single-stepping through GDB on some test binaries.)

I’m not sure how that interacts with user supplied debug annotations though.

Fred

> Would you be interested in a patch which makes the assembler generate .debug_info?
> 
> Thanks,
> Alex Dowad
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