[PATCH] D59553: [LLD][ELF][DebugInfo] llvm-symbolizer shows incorrect source line info if --gc-sections used

[James Henderson via Phabricator via llvm-commits]

jhenderson added a comment.

In D59553#1499537 <https://reviews.llvm.org/D59553#1499537>, @MaskRay wrote:

> I want to see a concrete example where 0 is used as a valid DW_AT_low_pc.
>
> I can change `vm.mmap_min_addr` to 0 on my Linux and mmap a fixed page at 0 freely, but that doesn't mean 0 can be a valid DW_AT_low_pc. The 0 page can be mapped but more likely used as file header, irq, etc but unlikely to be used as code.


In Sony executables, the file header is not stored in loadable memory. Our first PT_LOAD has address 0 and sections start from that address. Technically, we don't have any code at that address yet, but we are planning on removing the limitation that stops us from doing so, in which case we will have code at address 0. As mentioned earlier, we have solved the problem for now by using a special value in DW_AT_low_pc, and other techniques, but these all require private patches, so an alternative would be nice.

I do agree that this patching should be limited to debug sections though. Other consumer sections might have other rules regarding special values etc, and be working on the assumption of patching to 0 is the best plan.


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