Here's what's to be done for maintaining LLVM.

Apart from the target-specific configuration machinery, there shouldn't be any major differences within LLVM between the GNU/Hurd and GNU/Linux ports, for example. Especially all the compiler magic is all the same.

General information
1. Rebuild of the Debian archive with clang
Sources
Configuration
Build
1. Analysis
Install
1. Analysis
Testsuite
1. Analysis

General information

Rebuild of the Debian archive with clang

From id:"20120305195308.GA1904@zouish.org": http://sylvestre.ledru.info/blog/sylvestre/2012/02/29/rebuild_of_the_debian_archive_with_clang, http://clang.debian.net/.

Sources

Configuration

Last reviewed up to the Git mirror's sources: llvm 6f7becfe23f38e8c28e9422d883263974058aeed (2013-03-24), clang 495cfa46300979642acde8d93a1f21c9291dac98 (2013-03-23), compiler-rt a06fe9183fbffb78798a444da9bc3040fdd444aa (2013-03-23), test-suite 5a05572d268568fb15b48f374f9fc9f882adecd2 (2013-03-23).

http://anonscm.debian.org/viewvc/pkg-llvm/llvm/trunk/debian/patches/.
[low] Some more PATH_MAX/MAXPATHLEN things.

gs: usage

lib/Target/X86/, test/CodeGen/X86/, test/MC/X86/.

tools/clang/

tools/clang/docs/LanguageExtensions.rst:          movl    %gs:(%eax), %eax
tools/clang/test/Sema/asm.c:  asm volatile ("movb %%gs:%P2,%b0" : "=q"(b) : "0"(0), "i"(5L));

compiler-rt and test-suite not yet examined.

[low] Linuxisms
- In some CMake files (CMakeLists.txt, for example).
- test/, unittests, tools/clang/test/, tools/clang/unittests/ not yet examined.
  - In clang's test/Driver/ a lot of testing can be generalized from Linux to GNU environment, adding GNU/Hurd testing, too.
- LLVM commit 98fbe27ac8f0766ea94b89b8c03418131b72bea4 Support for HiPE-compatible code emission
  
  Only relevant for CallingConv::HiPE.
```
+  assert(ST->isTargetLinux() &&
+         "HiPE prologue is only supported on Linux operating systems.");
```
- compiler-rt and test-suite not yet examined.
/proc usage
- compiler-rt and test-suite not yet examined.
libc++ (not currently using)

Some Hurd-porting work is said to have been done as Google Summer of Code 2012 Debian project, http://wiki.debian.org/SummerOfCode2012/StudentApplications/AndrejBelym.
sanitizers

A lot of Linux-specific things.

IRC, OFTC, #debian-hurd, 2013-09-05:

<gg0> how can this fix it on {kf,hurd}-i386?
  http://anonscm.debian.org/viewvc/pkg-llvm/llvm-toolchain/branches/3.3/debian/patches/libstdc%2B%2B-header-i386.diff?view=markup&sortby=date&pathrev=830
<pinotree> what makes you think it does?
<pinotree> it fixes #714890, which has nothing to do with hurd or
  kfreebsd
<gg0> i simple wouldn't add a patch that fixes it on one i386 arch
  only, being aware there are others
<pinotree> meet sylvestre

IRC, freenode, #hurd, 2013-09-05:

<pinotree> tschwinge: iirc you were working on llvm/clang, weren't you?
<tschwinge> pinotree: That's right.  I have patches to
  follow-up/rework.  Stalled at the moment, as you probably already
  guessed...  %-)
<pinotree> tschwinge: <Sylvestre> by the way, pinotree if you have time
  for hurd stuff, I would be glad to have your help to port
  llvm-toolchain-3.3 to hurd. I am having some issues with threading
  aspects https://paste.debian.net/35466/
<pinotree> he's the debian packager of llvm
<tschwinge> That paste is for LLDB -- which I'd not assume to be in a
  shape usable for Hurd.
<tschwinge> (I didn't look at it at all.)
<pinotree> tschwinge: if you look at the latest llvm-toolchain-3.3
  debian source, there's a lldb-hurd.diff patch, which starts some
  include header dance

Build

Here's a log of a LLVM build run; this is from our Git repository's sources, llvm dc218fb6ae3241f4b66e9bf2c9d6352efecc0a14 (2013-03-24), clang 744290b5ecd48bddb4a6cf96d68cdc4a57e24e36 (2013-03-24), compiler-rt a06fe9183fbffb78798a444da9bc3040fdd444aa (2013-03-23), test-suite 1821ab0ef1c73430705356fdfde3769460092382 (2013-03-24), run on kepler.SCHWINGE and coulomb.SCHWINGE.

$ export LC_ALL=C
$ (cd ../Horace_Silver/ && ln -sfn ../../../clang/tschwinge/Hank_Mobley tools/clang)
$ (cd ../Horace_Silver/ && ln -sfn ../../../compiler-rt/tschwinge/Doug_Watkins projects/compiler-rt)
$ (cd ../Horace_Silver/ && ln -sfn ../../../test-suite/tschwinge/Art_Blakey projects/test-suite)
$ ../Horace_Silver/configure --prefix="$PWD".install --enable-optimized SHELL=/bin/dash CC=gcc-4.7 CXX=g++-4.7 2>&1 | tee log_build
$ make VERBOSE=1 2>&1 | tee log_build_

Different hosts may default to different shells and compiler versions; thus harmonized.

Passing --enable-debug-symbols, the GNU/Hurd build on coulomb.SCHWINGE terminates with a SIGBUS when linking Release+Debug+Asserts/bin/clang (which is bigger than 500 MiB for the corresponding GNU/Linux build). Using --enable-debug-symbols --enable-shared, the GNU/Hurd build hang after make[1]: Leaving directory [...]/tools/llvm-shlib, after (successfully) linking Release+Debug+Asserts/lib/libLLVM-3.3svn.so (which is bigger than 250 MiB for the corresponding GNU/Linux build). Also there is a separate --enable-debug-runtime.

This takes up around 3.2 GiB, and needs roughly 1.5 h on kepler.SCHWINGE and 5.25 h on coulomb.SCHWINGE.

Configuring without --enable-optimized even crashes mighty darnassus, probably because of too-big files when linking. Configuring with --enable-optimized --enable-expensive-checks --disable-threads --enable-debug-symbols --enable-debug-runtime is fine.

Analysis

$ toolchain/logs/process llvm build

    -checking for mmap of files... yes
    +checking for mmap of files... no
     checking if /dev/zero is needed for mmap... no
    +configure: WARNING: mmap() of files required but not found

Due to mmap write-only.

    +In file included from [...]/lib/Support/Process.cpp:85:0:
    +[...]/lib/Support/Unix/Process.inc: In function 'unsigned int getColumns(int)':
    +[...]/lib/Support/Unix/Process.inc:227:21: warning: enumeral and non-enumeral type in conditional expression [enabled by default]

       225    // Try to determine the width of the terminal.
       226    struct winsize ws;
       227    if (ioctl(FileID, TIOCGWINSZ, &ws) == 0)

    include/llvm/Config/*
    Makefile.config

TODO

Install

$ make VERBOSE=1 install 2>&1 | tee log_install

This takes up around 400 MiB, and needs roughly 1 min on kepler.SCHWINGE and 12 min on coulomb.SCHWINGE.

Analysis

$ toolchain/logs/process llvm install

TODO

Testsuite

$ make -k VERBOSE=1 LIT_ARGS='-v --threads=1' check-all 2>&1 | tee log_test_check-all
$ make -k -C projects/test-suite/ 2>&1 | tee log_test_test-suite

LIT_ARGS=-v is default for VERBOSE=1, but we want only one worker thread, for stable order and usable test output log.

This needs roughly 10 min (check-all) + 150 min (test-suite) = 160 min on kepler.SCHWINGE and 45 min (check-all) + 165 min (test-suite) = 210 min on coulomb.SCHWINGE.

Analysis

$ toolchain/logs/process llvm test

LLVM :: CodeGen/X86/mult-alt-generic-i686.ll

This one, as well as a really large set of test from the test-suite fail on coulomb.SCHWINGE no matter whether a GNU/Hurd or GNU/Linux system is booted -- so all these are specific to the Athlon XP processor, hopefully.
Clang :: Index/crash-recovery-modules.m

Also fails on GNU/Linux. Tested --enable-optimized --enable-expensive-checks --disable-threads --enable-debug-symbols --enable-debug-runtime. LLVM bug #11974.

Clang :: Misc/dev-fd-fs.c

$ cat < [...]/test/Misc/dev-fd-fs.c | Release+Debug+Asserts+Checks/bin/clang -x c /dev/fd/0 -E
clang: error: no such file or directory: '/dev/fd/0'
clang: error: no input files

Compare to:

$ cat < [...]/test/Misc/dev-fd-fs.c | gcc -x c /dev/fd/0 -E
gcc: error: /dev/fd/0: (ipc/mig) bad request message ID
gcc: warning: '-x c' after last input file has no effect
gcc: fatal error: no input files
compilation terminated.

These work:

$ Release+Debug+Asserts+Checks/bin/clang -x c /dev/fd/0 -E < [...]/test/Misc/dev-fd-fs.c
[...]
int x;
$ gcc -x c /dev/fd/0 -E < [...]/test/Misc/dev-fd-fs.c
[...]
int x;


#include <stdio.h>
#include <unistd.h>


int main(int argc, char *argv[])
{   
  while (argc > 0)
    {
      int err;
      char *f = argv[argc -1];


  err = access(f, F_OK);
  if (err &lt; 0)
    printf("%s: %m\n", f);


  argc--;
}


  return 0;
}


$ ./a.out /dev/fd/0 < /dev/null
$ cat < /dev/null | ./a.out /dev/fd/0
/dev/fd/0: (ipc/mig) bad request message ID

file_check_access fails with MIG_BAD_ID, meaning this RPC is not implemented.

The difference is that the former directly refers to the /dev/null instance, whereas the latter goes through an intermediate pflocal instance.

Similarly:

$ stat /dev/fd/0 < /dev/null
  File: `/dev/fd/0'
  Size: 0               Blocks: 0          IO Block: 1048576 character special file
Device: 17h/23d Inode: 342820      Links: 1     Device type: 0,0
Access: (0666/crw-rw-rw-)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2012-11-27 16:03:19.000000000 +0100
Modify: 2012-11-27 16:03:19.000000000 +0100
Change: 2012-11-27 16:03:19.000000000 +0100
 Birth: -
$ cat < /dev/null | stat /dev/fd/0
  File: `/dev/fd/0'
  Size: 0               Blocks: 0          IO Block: 65536  fifo
Device: 9h/9d   Inode: 0           Links: 0
Access: (0000/p---------)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 1970-01-01 01:00:00.000000000 +0100
Modify: 1970-01-01 01:00:00.000000000 +0100
Change: 1970-01-01 01:00:00.000000000 +0100
 Birth: -

io_stat_request fills in these values.

Clang :: Tooling/clang-check-builtin-headers.cpp

Fails: fatal error: 'stddef.h' file not found; succeeds when ran manually.
With --enable-optimized --enable-expensive-checks --disable-threads --enable-debug-symbols --enable-debug-runtime, there are a few new FAILs for both GNU/Linux and GNU/Hurd:
- Clang :: Tooling/auto-detect-from-source-parent-of-cwd.cpp
- Clang :: Tooling/auto-detect-from-source-parent.cpp
- Clang :: Tooling/clang-check-autodetect-dir.cpp
For all three, the clang-check invocation fails. LLVM bug #15194.

Several tests are not considered on GNU/Hurd.

-PASS: Clang-Unit :: ASTMatchers/[...]/tschwinge/Horace_Silver.build/tools/clang/unittests/ASTMatchers/Release+Asserts/ASTMatchersTests/HasNameDeathTest.DiesOnEmptyName
-PASS: Clang-Unit :: ASTMatchers/[...]/tschwinge/Horace_Silver.build/tools/clang/unittests/ASTMatchers/Release+Asserts/ASTMatchersTests/HasNameDeathTest.DiesOnEmptyPattern
-PASS: Clang-Unit :: ASTMatchers/[...]/tschwinge/Horace_Silver.build/tools/clang/unittests/ASTMatchers/Release+Asserts/ASTMatchersTests/IsDerivedFromDeathTest.DiesOnEmptyBaseName
-PASS: LLVM-Unit :: ADT/[...]/tschwinge/Horace_Silver.build/unittests/ADT/Release+Asserts/ADTTests/APFloatTest.SemanticsDeath
-PASS: LLVM-Unit :: ADT/[...]/tschwinge/Horace_Silver.build/unittests/ADT/Release+Asserts/ADTTests/APFloatTest.StringDecimalDeath
-PASS: LLVM-Unit :: ADT/[...]/tschwinge/Horace_Silver.build/unittests/ADT/Release+Asserts/ADTTests/APFloatTest.StringDecimalExponentDeath
-PASS: LLVM-Unit :: ADT/[...]/tschwinge/Horace_Silver.build/unittests/ADT/Release+Asserts/ADTTests/APFloatTest.StringDecimalSignificandDeath
-PASS: LLVM-Unit :: ADT/[...]/tschwinge/Horace_Silver.build/unittests/ADT/Release+Asserts/ADTTests/APFloatTest.StringHexadecimalDeath
-PASS: LLVM-Unit :: ADT/[...]/tschwinge/Horace_Silver.build/unittests/ADT/Release+Asserts/ADTTests/APFloatTest.StringHexadecimalExponentDeath
-PASS: LLVM-Unit :: ADT/[...]/tschwinge/Horace_Silver.build/unittests/ADT/Release+Asserts/ADTTests/APFloatTest.StringHexadecimalSignificandDeath
-PASS: LLVM-Unit :: ADT/[...]/tschwinge/Horace_Silver.build/unittests/ADT/Release+Asserts/ADTTests/APIntTest.StringDeath
-PASS: LLVM-Unit :: Support/[...]/tschwinge/Horace_Silver.build/unittests/Support/Release+Asserts/SupportTests/LeakDetector.Death1
-PASS: LLVM-Unit :: Support/[...]/tschwinge/Horace_Silver.build/unittests/Support/Release+Asserts/SupportTests/ValueHandle.AssertingVH_Asserts


GTEST_HAS_DEATH_TEST utils/unittest/googletest/include/gtest/internal/gtest-port.h


-PASS: LLVM-Unit :: ADT/[...]/tschwinge/Horace_Silver.build/unittests/ADT/Release+Asserts/ADTTests/PackedVectorTest.SignedValues
-PASS: LLVM-Unit :: ADT/[...]/tschwinge/Horace_Silver.build/unittests/ADT/Release+Asserts/ADTTests/PackedVectorTest.UnsignedValues


EXPECT_DEBUG_DEATH utils/unittest/googletest/include/gtest/gtest-death-test.h

Differences in test-suite, that are not evidently floating-point issues, GNU/Linux vs. GNU/Hurd on coulomb.SCHWINGE:

 gcc-4.6 -I/media/erich/home/thomas/tmp/llvm/tschwinge/Horace_Silver.build/projects/test-suite/SingleSource/UnitTests -I/media/erich/home/thomas/tmp/llvm/test-suite/tschwinge/Art_Blakey/SingleSource/UnitTests -I/home/thomas/tmp/llvm/tschwinge/Horace_Silver.build/projects/test-suite/../../../Horace_Silver/projects/test-suite/include -I../../include -I/home/thomas/tmp/llvm/tschwinge/Horace_Silver.build/include -I/home/thomas/tmp/llvm/tschwinge/Horace_Silver/include -D_GNU_SOURCE -D__STDC_LIMIT_MACROS -DNDEBUG  -O3  /media/erich/home/thomas/tmp/llvm/test-suite/tschwinge/Art_Blakey/SingleSource/UnitTests/2007-04-25-weak.c -lm -o Output/2007-04-25-weak.native  -lstdc++ 
+/media/erich/home/thomas/tmp/llvm/test-suite/tschwinge/Art_Blakey/SingleSource/UnitTests/2007-04-25-weak.c:3:1: warning: 'weak_import' attribute directive ignored [-Wattributes]
+/tmp/ccWGwKvo.o: In function `main':
+2007-04-25-weak.c:(.text.startup+0x7): undefined reference to `test_weak'
+collect2: ld returned 1 exit status
+make[2]: [Output/2007-04-25-weak.native] Error 1 (ignored)

On GNU/Linux, the clamav tests are compiled with -DC_LINUX.

+/media/erich/home/thomas/tmp/llvm/test-suite/tschwinge/Art_Blakey/MultiSource/Applications/lambda-0.1.3/lambda.cc:63:12: error: use of undeclared identifier 'MAXPATHLEN'
+                char buf[MAXPATHLEN+1];

..., with follow-up failures.

projects/test-suite/MultiSource/Applications/obsequi is not at all considered for GNU/Hurd.

+/media/erich/home/thomas/tmp/llvm/test-suite/tschwinge/Art_Blakey/MultiSource/Benchmarks/Olden/voronoi/newvor.c:178:25: warning: implicit declaration of function 'memalign' is invalid in C99 [-Wimplicit-function-declaration]
+    char* base = (char*)memalign(align_size, alloc_size);
+                        ^
+1 warning generated.


+/media/erich/home/thomas/tmp/llvm/test-suite/tschwinge/Art_Blakey/MultiSource/Benchmarks/Prolangs-C/archie-client/get_vdir.c:213:20: error: use of undeclared identifier 'MAXPATHLEN'
+                    char        l_name[MAX_DIR_LINESIZE];
+                                       ^
+/media/erich/home/thomas/tmp/llvm/test-suite/tschwinge/Art_Blakey/MultiSource/Benchmarks/Prolangs-C/archie-client/pprot.h:39:37: note: expanded from macro 'MAX_DIR_LINESIZE'
+#define        MAX_DIR_LINESIZE 160+MAXPATHLEN /* Max linesize in directory */
+                                    ^

..., and several more.