[PATCH] D54489: Implement -frecord-command-line (-frecord-gcc-switches)

[John McCall via Phabricator via cfe-commits]

rjmccall added inline comments.


================
Comment at: docs/ClangCommandLineReference.rst:797
+
+Generate a section .LLVM.command.line containing the clang driver command line.
+
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scott.linder wrote:
> rjmccall wrote:
> > 1. Is this section always called `.LLVM.command.line`, or does it differ by target object-file format?
> > 2. For that matter, is this actually supported by all object-file formats?
> > 3. Please describe the format of the section.  Is it just a flat C string?  Is it nul-terminated?  Are different options combined with spaces, and if so, does that mean that interior spaces in command line arguments are impossible to distinguish?  If the latter, I assume that this is required behavior for backward compatibility; please at least apologize for that in the documentation. :)
> For (1) I think the answer should be that we emit `.LLVM.command.line` (or whatever name we land on) for every object-file format with the concept of names for sections.
> 
> For (2), I have only implemented this for ELF so far in LLVM. I don't know how reasonable that is, and if it isn't I can look at adding it to other common object-file formats that LLVM supports.
> 
> For (3), my current proposal for the format is the same as the `.comment` section for idents: null-surrounded strings. Interior spaces are escaped, in the same manner as for the -g variant. There may still be more thought to put into the format, as the GCC version null-terminates each individual option; the reason I avoided this is that during object linking the options of many command-lines simply get mixed together, which seems less than useful.
> 
> As an example, for ELF `clang -frecord-command-line -S "foo .c"` produces the ASM:
> 
> ```
> .section        .LLVM.command.line,"MS", at progbits,1
> .zero   1
> .ascii  "/usr/local/bin/clang-8 -frecord-command-line -S foo\\ .c"
> .zero   1
> ```
> 
> And for multiple command-lines in a single object (e.g. linking three objects with recorded command-lines) this would be:
> 
> ```
> .section        .LLVM.command.line,"MS", at progbits,1
> .zero   1
> .ascii  "/usr/local/bin/clang-8 -frecord-command-line -c foo\\ .c"
> .zero   1
> .ascii  "/usr/local/bin/clang-8 -frecord-command-line -some -unique -options -c bar.c"
> .zero   1
> .ascii  "/usr/local/bin/clang-8 -frecord-command-line -something -else -c baz.c"
> .zero   1
> ```
> 
> I will try to capture more of this in the documentation.
Okay.  I don't particularly need you to implement this on additional targets, but yes, please capture all this layout information in the documentation and make sure that the driver enforces any meaningful restrictions about which targets support it.


https://reviews.llvm.org/D54489