[llvm-dev] RFC: Add a preprocessor to yaml2obj (and other YAML tools) (original) (raw)

George Rimar via llvm-dev llvm-dev at lists.llvm.org
Tue Feb 4 01:20:07 PST 2020

?The idea itself is indeed good.

Regarding to escaping: I think we should have it.

Imagine the following example (I've took it from D73828).

--- !ELF FileHeader: Class: ELFCLASS[[BITS]] Data: ELFDATA2LSB Type: ET_EXEC Machine: EM_386

RUN: yaml2obj %s --docnum=4 -D BITS=32 -o %t-32bit.o

RUN: yaml2obj %s --docnum=4 -D BITS=64 -o %t-64bit.o

Without escaping it would be: Class: ELFCLASSBITS

What does not look so clear as a version with escaping IMO.

Best regards, George | Developer | Access Softek, Inc

От: James Henderson <jh7370.2008 at my.bristol.ac.uk> Отправлено: 4 февраля 2020 г. 12:09 Кому: Fangrui Song Копия: llvm-dev; George Rimar Тема: Re: RFC: Add a preprocessor to yaml2obj (and other YAML tools)

CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you recognize the sender and know the content is safe. If you suspect potential phishing or spam email, report it to ReportSpam at accesssoftek.com As someone who suggested this kind of functionality in a review earlier, this will certainly be useful, I think. I think the syntax makes sense to me, if we allow for unrecognised macros to just be treated as part of the input string. This means we don't have to worry about complexities like escaping "[[" etc. In the (unlikely) event that somebody's YAML needs to include the literal "[[FOO]]", they simply should not also use -DFOO - use a different name instead, e.g. -DBAR.

On Mon, 3 Feb 2020 at 22:04, Fangrui Song <maskray at google.com<mailto:maskray at google.com>> wrote: I am adding -D k=v to yaml2obj, similar to clang -D. This makes it easy to generate {32-bit,64-bit} x {big-endian,little-endian} tests.

--- !ELF FileHeader: Class: ELFCLASS[[BITS]] Data: ELFDATA2[[ENCODE]] Type: ET_DYN Machine: EM_X86_64

RUN: yaml2obj -D BITS=32 -D ENCODE=LSB %s -o %t.32le

RUN: yaml2obj -D BITS=32 -D ENCODE=MSB %s -o %t.32le

RUN: yaml2obj -D BITS=64 -D ENCODE=LSB %s -o %t.64le

RUN: yaml2obj -D BITS=64 -D ENCODE=MSB %s -o %t.64be

See https://reviews.llvm.org/D73828 for examples how -D simplifies tests.

Do people think it may be useful in other YAML tools? If yes, I'll move the yaml2obj implementation (https://reviews.llvm.org/D73821 ) to include/llvm/Support/YAMLTraits.h llvm::yaml::Input so that other YAML tools can use the feature.

Do people prefer a different syntax? I think [[PATTERN]] is nice because it is what FileCheck -DFILE=... uses:

CHECK: ... [[FILE]]

FileCheck only preprocesses patterns in CHECK lines. D73821 preprocesses both comment lines (which include CHECK lines) and non-comment lines (which include YAML). It is not a problem that the YAML preprocessor also processes CHECK lines, because tokens on a comment line will be ignored.

If -D UNDEF= is not specified, should [[UNDEF]] in the source be considered an error? I think it is fine not to treat it as an error because there can be legitimate use cases of unterminated [[, for example, [[ in a string literal. YAML parsing is complex. I don't expect the preprocessor to be smart enough to recognize string literals. (llvm/lib/Support/YAMLParser.cpp does not seem to provide raw strings of spaces and comments. Hooking a preprocessor into the scanner does not seem to be simple.)

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