Preserve the __debug_line section on macOS in the final executable

[jacob-carlborg]

The linker on macOS will remove any debug info, i.e. every section with the S_ATTR_DEBUG flag, this includes everything in the __DWARF section. By using the S_REGULAR flag the linker will not remove this section. This allows to get the filenames and line numbers for backtraces from the executable.

Normally the linker removes all the debug info but adds a reference to the object files. The debugger can then read the object files to get filename and line number information. It's also possible to use an additional tool that generates a separate .dSYM file. This file can then later be deployed with the application if debug info is needed when the application is deployed.

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[jacob-carlborg]

I've not included a changelog entry here because it's not a user facing change.

[WalterBright]

Please add your opening comment in as a comment in the code.

[jacob-carlborg]

Please add your opening comment in as a comment in the code.

It's already in the commit message, do you want it in the code as well?

[jacob-carlborg]

Please add your opening comment in as a comment in the code.

@WalterBright added comment to the code and added a test as well.

[jacob-carlborg]

Is the failing DAutoTest related to this change? Nothing else fails.

[wilzbach]

Yeah the error is

Test the D Language specification
../dmd/generated/linux/release/64/dmd -run tools/dspec_tester.d --compiler=../dmd/generated/linux/release/64/dmd
---
void main() {
import std.stdio;
        struct S { int x; float y; }

        int foo(S s) { return s.x; }

        foo( S(1, 2) ); // set field x to 1, field y to 2
        
}
---
/usr/bin/ld: error in __stdin.o(.eh_frame); no .eh_frame_hdr table will be created.
/usr/bin/ld: __stdin.o: invalid string offset 1096055152 >= 528 for section `.strtab'
/usr/bin/ld: unknown operator '(' in complex symbol
/usr/bin/ld: final link failed: Invalid operation
collect2: error: ld returned 1 exit status
Error: linker exited with status 1

But it's unrelated to this PR.

[wilzbach]

Is the failing DAutoTest related to this change? Nothing else fails.

-> dlang/dlang.org#2345

[jacob-carlborg]

Everything is green.

[jacob-carlborg]

Ping, this is pretty trivial.

[jacob-carlborg]

@wilzbach @JinShil ping

[WalterBright]

Suggestion to revert this:

https://www.digitalmars.com/d/archives/digitalmars/D/Not_Working_on_the_Mac_369782.html#N369787

[jacob-carlborg]

@WalterBright

There are a couple of options:

• You can choose to revert this. Then filenames and line numbers will not be available in stack traces of exceptions (unless LDC has upstreamed its changes in druntime. The changes require an external tool, shipped with Xcode, which might not be available when an application is deployed)
• Try to fix the alignment (don't know if that's possible)
• Revert this change but duplicate the debug info in a custom section. I don't know if the linker will strip custom sections with the S_ATTR_DEBUG attribute

[WalterBright]

@jacob-carlborg I'd prefer to fix the problem rather than revert this. Except nobody seems to know what to do about it.

[WalterBright]

Can you try fixing the alignment and see if it works?

[jacob-carlborg]

Can you try fixing the alignment and see if it works?

Unfortunately that's out of my league. It would be more suitable for someone that actually knows the compiler.