clang-cl: Expose -no-canonical-prefixes
ClosedPublic

Authored by thakis on Tue, May 29, 8:02 AM.

Details

Reviewers
rnk
takuto.ikuta
Summary

-no-canonical-prefixes is a weird flag: In gcc, it controls whether realpath() is called on the path of the driver binary. It's needed to support some usecases where gcc is symlinked to, see https://gcc.gnu.org/ml/gcc/2011-01/msg00429.html for some background.

In clang, the resource dir is found relative to the compiler binary, and without -no-canonical-prefixes that's an absolute path. For clang, the main use case for -no-canonical-prefixes is to make the -resource-dir path added by the driver relative instead of absolute. Making it relative seems like the better default, but since neither clang not gcc have -canonical-prefixes without no- which makes changing the default tricky, and since some symlink behaviors do depend on the realpath() call at least for gcc, just expose -no-canonical-prefixes in clang-cl mode.

Alternatively we could default to no-canonical-prefix-mode for clang-cl since it's less likely to be used in symlinked scenarios, but since you already need to about -no-canonical-prefixes for the non-clang-cl bits of your build, not hooking this of driver mode seems better to me.

Diff Detail

thakis created this revision.Tue, May 29, 8:02 AM

Thank you for quick supporting, but this is not sufficient for clang-cl on windows.

llvm::InitLLVM calls windows::GetCommandLineArguments, and argv0 is changed to absolute path.
https://github.com/llvm-project/llvm-project-20170507/blob/7c81daae49eaf7f9681457b46c569c1bc6b80283/llvm/lib/Support/Windows/Process.inc#L229

Then clang's builtin include files are shown in absolute path even we specify -no-canonical-prefixes.
Can we keep using original argv0 when argv0 is not 8.3 filename? Or is there better solution?

I did test this locally before sending it out, and the -resource-dir arg passed to cc1 is relative with this patch:

$ bin/clang-cl -no-canonical-prefixes -c test.cc -###
clang version 7.0.0 
Target: x86_64-pc-windows-msvc
Thread model: posix
InstalledDir: bin
 "bin/clang-cl" "-cc1" "-triple" "x86_64-pc-windows-msvc19.11.0" "-emit-obj" "-mrelax-all" "-mincremental-linker-compatible" "-disable-free" "-main-file-name" "test.cc" "-mrelocation-model" "pic" "-pic-level" "2" "-mthread-model" "posix" "-relaxed-aliasing" "-fmath-errno" "-masm-verbose" "-mconstructor-aliases" "-munwind-tables" "-target-cpu" "x86-64" "-mllvm" "-x86-asm-syntax=intel" "-D_MT" "-flto-visibility-public-std" "--dependent-lib=libcmt" "--dependent-lib=oldnames" "-stack-protector" "2" "-fms-volatile" "-fdiagnostics-format" "msvc" "-dwarf-column-info" "-debugger-tuning=gdb" "-target-linker-version" "305" "-momit-leaf-frame-pointer" "-coverage-notes-file" "/Users/thakis/src/llvm-mono/test.gcno" "-resource-dir" "lib/clang/7.0.0" "-internal-isystem" "lib/clang/7.0.0/include" "-fdeprecated-macro" "-fdebug-compilation-dir" "/Users/thakis/src/llvm-mono" "-ferror-limit" "19" "-fmessage-length" "254" "-fno-use-cxa-atexit" "-fms-extensions" "-fms-compatibility" "-fms-compatibility-version=19.11" "-std=c++14" "-fdelayed-template-parsing" "-fobjc-runtime=gcc" "-fseh-exceptions" "-fdiagnostics-show-option" "-fcolor-diagnostics" "-o" "test.obj" "-x" "c++" "test.cc"

driver.cpp handles this directly here http://llvm-cs.pcc.me.uk/tools/clang/tools/driver/driver.cpp#54 and here http://llvm-cs.pcc.me.uk/tools/clang/tools/driver/driver.cpp#390 -- what's the problem with the InitLLVM call you point at?

thakis added a subscriber: rnk.Tue, May 29, 3:51 PM

But GetExecutablePath isn't called if -no-canonical-prefixes is passed, is
it? (See the first link I pasted above)

GetExecutablePath is called here.
http://llvm-cs.pcc.me.uk/tools/clang/tools/driver/driver.cpp#427

You'll understand what I said if you see the behavior of clang-cl on windows.

test/Driver/cl-options.c
595

Is this related to this change?

rnk accepted this revision.Wed, May 30, 11:32 AM

lgtm

test/Driver/cl-options.c
595

It's a test for a previous change that I made.

This revision is now accepted and ready to land.Wed, May 30, 11:32 AM
takuto.ikuta accepted this revision.Fri, Jun 1, 7:02 AM

I confirmed this CL and https://reviews.llvm.org/D47578 remove absolute path from /showIncludes when include paths are given in relative.

thakis closed this revision.Fri, Jun 1, 8:04 AM

r333761, thanks!

thakis marked 2 inline comments as done.Fri, Jun 1, 8:07 AM
thakis added inline comments.
test/Driver/cl-options.c
595

Sorry, I missed this. It was a mistake, I removed this line again in r333762.