Hex-encode defmt symbols to avoid compatibility issues. #878
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I've pinged the team internally so we can work out how to fix those tests. We're on version 4 of the wire format already, so we must have a process for bumping it. |
decoder/src/elf2table/symbol.rs
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| @@ -38,7 +41,11 @@ pub(super) enum SymbolTag { | |||
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| impl Symbol { | |||
| pub fn demangle(raw: &str) -> anyhow::Result<Self> { | |||
| serde_json::from_str(raw) | |||
| let mut raw = Cow::from(raw); | |||
| if let Some(s) = raw.strip_prefix("__defmt_") { | |||
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This magic string exists twice (once here, once in the macro), and it doesn't say a lot about the encoding used.
- Perhaps it should be
__defmt_hex_, allowing for some future__defmt_base64_or similar. - Is there somewhere it can be defined once and imported in the other place? If not, we should document the canonical form in a third place (like the book) and have the other two places refer to it.
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Perhaps it should be _defmt_hex, allowing for some future _defmt_base64 or similar.
changed!
Is there somewhere it can be defined once and imported in the other place? If not, we should document the canonical form in a third place (like the book) and have the other two places refer to it.
there's no crate that's a shared dep of the macro and the decoder. I've added a section to the book.
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there's no crate that's a shared dep of the macro and the decoder. I've added a section to the book.
There is! It's the defmt-parser. I think it makes sense to put the magic string there.
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Huh.
➜ defmt git:(main) cargo tree -p defmt-macros | grep parser
├── defmt-parser v0.3.4 (/Users/jonathan/Documents/knurling-rs/defmt/parser)
➜ defmt git:(main) cargo tree -p defmt-decoder | grep parser
├── defmt-parser v0.3.4 (/Users/jonathan/Documents/knurling-rs/defmt/parser)
defmt currently puts json as-is in symbol names, which can contain special
characters not normally found in symbol names like quotes `"`, braces `{}`
and spaces ` `.
This can cause compatibility issues with language features or tools that don't
expect this. For example it breaks `sym` in `asm!`.
This is a *breaking change* of the wire format, so this PR increases the
format numbre. `defmt-decoder` is updated to be able to decode the new format,
while keeping ability to decode older formats.
Urhengulas
added
the
breaking change
Yes, that's a known problem. I marked the PR as breaking change, which is not true, but skips the check.
Just bump the commit hash Line 47 in 7d74e8b |
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One nit, and one thought.
By hex encoding the symbols, you stop people from scanning the output of objdump -t and seeing the log strings, modules, etc.
Is there some other encoding which would solve the problem of invalid characters (", {, @, etc), but which retains the ability for a human to read the text? I'm thinking of something like C trigraphs perhaps. Or (shudder) C++/Rust symbol mangling.
| - The double-quote character `'"'` causes issues with escaping if you use it with `sym` inside an `asm!()` call. | ||
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| To deal with this, as of Wire Format Version 5, strings are encoded to bytes as UTF-8, and then the bytes are hex-encoded. | ||
| The symbol is prefixed with `__defmt_hex_` to denote it's is hex-encoded, and to allow for future expansion. |
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| The symbol is prefixed with `__defmt_hex_` to denote it's is hex-encoded, and to allow for future expansion. | |
| The symbol is prefixed with `__defmt_hex_` to denote that it's hex-encoded, and to allow for future expansion. |
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We should probably fix the input section name at the same time (i.e. the |
Hex-encode defmt symbols to avoid compatibility issues.
defmt currently puts json as-is in symbol names, which can contain special
characters not normally found in symbol names like quotes
", braces{}and spaces
This can cause compatibility issues with language features or tools that don't
expect this. For example it breaks
syminasm!.This is a breaking change of the wire format, so this PR increases the
format numbre.
defmt-decoderis updated to be able to decode the new format,while keeping ability to decode older formats.