Hardcoded path name for asm.S

[noppej]

Binary files using this crate ends up with a hardcoded path for asmS file, as per the following dwarfdump output ...

0x00001f41: DW_TAG_compile_unit
              DW_AT_stmt_list   (0x00000a88)
              DW_AT_ranges      (0x0000000c
                 [0x00003648, 0x0000365c)
                 [0x00000400, 0x00000460))
              DW_AT_name        ("asm.S")
              DW_AT_comp_dir    ("/home/jonas/dev/cortex-m-rt")
              DW_AT_producer    ("GNU AS 2.37")
              DW_AT_language    (DW_LANG_Mips_Assembler)

The impact of this is that debuggers that step through the code will fail to find the source code for the particular file. I don't know how this can be fixed, but it would be great if somehow we can encode the DW_AT_comp_dir value so that debuggers can discover this file from the .cargo/registry/src location.

[TDHolmes]

This will soon be irrelevant as I believe this path for making assembly will be eliminated

[noppej]

Excellent. Do you have a reference to a discussion that I can follow for this please?

[TDHolmes]

I'm not aware of one yet. Once 1.59 releases with stable support for global asm the feature inline-asm will be made the default / only option. You could switch to using that feature in the meantime

[adamgreig]

At the moment the inline-asm feature doesn't change how the cortex-m-rt asm is generated, but the plan is indeed to move it to use global_asm!() for Rust 1.59, at which point asm.S can be deleted entirely.

If there was some easy fix we could apply now, I'd be happy to merge it, but I don't want to spend too long investigating when we plan to change the approach entirely once the next Rust release is out.

[noppej]

Totally understand, and I can easily wait for Rust 1.59. Thanks for the info.

[adamgreig]

See #420 for progress.