"--sysroot /" mess up overlaid VFS

[llvmbot]

Bugzilla Link	27909
Version	unspecified
OS	Linux
Reporter	LLVM Bugzilla Contributor
CC	@benlangmuir,@bcardosolopes,@zygoloid

Extended Description

Virtual file system cannot find overlaid file if "--sysroot /" is specified.

Way to reproduce:
$ cat overlay.yml
{
"version": 0,
"use-external-names": false,
"roots": [
{
"type": "file",
"name": "/usr/include/stdio_vfs.h",
"external-contents": "/usr/include/stdio.h"
}
]
}
$ cat foo.c
#include <stdio_vfs.h>
int main() {
printf("foo");
}
$ clang -ivfsoverlay overlay.yml foo.c # NO PROBLEM
$ clang --sysroot / -ivfsoverlay overlay.yml foo.c
foo.c:1:10: fatal error: 'stdio_vfs.h' file not found
#include <stdio_vfs.h>
^
1 error generated.
$

[bcardosolopes]

Thanks for reporting this! Which version of LLVM did you use?

Did you tests this on ToT? There were lots of VFS changes in the past month and I wonder whether they fix this.

Thanks,

[llvmbot]

I tested with

Ubuntu 15.10 clang
Ubuntu clang version 3.6.2-1 (tags/RELEASE_362/final) (based on LLVM 3.6.2)

and

https://github.com/apple/swift-llvm stable branch
https://github.com/apple/swift-clang stable branch
build.

I will try official trunk/trunk from now.

[llvmbot]

Reproduced with trunk

$ ~/Documents/repos/build/bin/clang -v --sysroot / -ivfsoverlay overlay.yml foo.c
clang version 3.9.0 (trunk 271088) (llvm/trunk 271087)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/rintaro/Documents/repos/build/bin
Found candidate GCC installation: //usr/lib/gcc/i686-linux-gnu/5.2.1
Found candidate GCC installation: //usr/lib/gcc/x86_64-linux-gnu/5.2.1
Selected GCC installation: //usr/lib/gcc/x86_64-linux-gnu/5.2.1
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Candidate multilib: x32;@MX32
Selected multilib: .;@m64
"/home/rintaro/Documents/repos/build/bin/clang-3.9" -cc1 -triple x86_64-unknown-linux-gnu -emit-obj -mrelax-all -disable-free -main-file-name foo.c -mrelocation-model static -mthread-model posix -mdisable-fp-elim -fmath-errno -masm-verbose -mconstructor-aliases -munwind-tables -fuse-init-array -target-cpu x86-64 -v -dwarf-column-info -debugger-tuning=gdb -resource-dir /home/rintaro/Documents/repos/build/bin/../lib/clang/3.9.0 -ivfsoverlay overlay.yml -isysroot / -internal-isystem //usr/local/include -internal-isystem /home/rintaro/Documents/repos/build/bin/../lib/clang/3.9.0/include -internal-externc-isystem //usr/include/x86_64-linux-gnu -internal-externc-isystem //include -internal-externc-isystem //usr/include -fdebug-compilation-dir /home/rintaro -ferror-limit 19 -fmessage-length 191 -fobjc-runtime=gcc -fdiagnostics-show-option -fcolor-diagnostics -o /tmp/foo-1cae04.o -x c foo.c
clang -cc1 version 3.9.0 based upon LLVM 3.9.0svn default target x86_64-unknown-linux-gnu
ignoring nonexistent directory "//include"
#include "..." search starts here:
#include <...> search starts here:
//usr/local/include
/home/rintaro/Documents/repos/build/bin/../lib/clang/3.9.0/include
//usr/include/x86_64-linux-gnu
//usr/include
End of search list.
foo.c:1:10: fatal error: 'stdio_vfs.h' file not found
#include <stdio_vfs.h>
^
1 error generated.

[llvmbot]

This is because:
llvm::sys::path splits "//usr/include/vfs_stdio.h" as:
{ "//usr", "/", "include", "vfs_stdio.h" }
It doesn't match the path components in the YAML:
{ "/", "usr", "include", "vfs_stdio.h" }

Now, I'm not sure which we should fix, Driver or RedirectingFileSystem.

The really quick fix would be:

===================================================================
--- lib/Driver/Driver.cpp (revision 271112)
+++ lib/Driver/Driver.cpp (working copy)
@@ -490,6 +490,9 @@
}
if (const Arg *A = Args.getLastArg(options::OPT__sysroot_EQ))
SysRoot = A->getValue();

• // If specified value is just a root directory, set empty SysRoot.
• if (llvm::sys::path::relative_path(SysRoot).empty())

•  SysRoot = llvm::sys::path::root_name(SysRoot);
  

  if (const Arg *A = Args.getLastArg(options::OPT__dyld_prefix_EQ))
  DyldPrefix = A->getValue();
  if (Args.hasArg(options::OPT_nostdlib))

But maybe, we should replace every SysRoot + ... in lib/Driver/Toolchain.cpp
with llvm::sys::path::append or such.

[benlangmuir]

We may want to explicitly teach the VFS that if it gets a root that is a net name (like //foo) and it doesn't find it, it should try treating it as "/foo".

[llvmbot]

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