fatal error: error in backend: Cannot expand unaligned load of capability type.

[nwf]

While attempting to build CheriBSD (revocation work atop 3158bc6a8e85394177013f0f16d84ff98350464d) with today's llvm (ab53327):

fatal error: error in backend: Cannot expand unaligned load of capability type. Created here: /mnt/mainline/cheribsd/contrib/subrepo-cheri-libunwind/src/DwarfInstructions.hpp:0
clang-9: error: clang frontend command failed with exit code 70 (use -v to see invocation)
clang version 9.0.0 (https://github.com/CTSRD-CHERI/llvm-project.git ab533278223efb5092a57b224b605abf1415d913)
Target: cheri-unknown-freebsd-purecap
Thread model: posix
InstalledDir: /junk/cheri-out/sdk/bin
clang-9: note: diagnostic msg: PLEASE submit a bug report to https://bugs.llvm.org/ and include the crash backtrace, preprocessed source, and associated run script.
clang-9: note: diagnostic msg:

********************
PLEASE ATTACH THE FOLLOWING FILES TO THE BUG REPORT:
Preprocessed source(s) and associated run script(s) are located at:
clang-9: note: diagnostic msg: /tmp/libunwind-a1a176.cpp
clang-9: note: diagnostic msg: /tmp/libunwind-a1a176.sh
clang-9: note: diagnostic msg: 

********************

*** Failed target:  libunwind.o
*** Failed command: /junk/cheri-out/sdk/bin/ccache-clang++ -integrated-as --target=cheri-unknown-freebsd -msoft-float -cheri-uintcap=offset --sysroot=/junk/cheri-build/cheribsd-obj-128/mnt/mainline/cheribsd/mips.mips64/tmp -fpic -cheri=128 -fvisibility=hidden -fPIC -ftls-model=initial-exec -O -pipe -G0 -mcpu=mips4 -EB -mabi=purecap -integrated-as -fpic -cheri-cap-table-abi=pcrel -Wno-deprecated-declarations -cheri=128 -mstack-alignment=16 -D__LP64__=1 -Qunused-arguments -Werror=cheri-bitwise-operations -msoft-float -I/mnt/mainline/cheribsd/contrib/subrepo-cheri-libunwind/include -I/mnt/mainline/cheribsd/lib/libgcc_eh -D_LIBUNWIND_IS_NATIVE_ONLY -cheri-cap-table-abi=pcrel -D__LP64__=1 -O2 -Qunused-arguments -Werror=cheri-bitwise-operations -g -MD -MF.depend.libunwind.o -MTlibunwind.o -nobuiltininc -idirafter /junk/cheri-out/sdk/lib/clang/9.0.0/include -Wsystem-headers -Werror -Wall -Wno-format-y2k -Wno-uninitialized -Wno-empty-body -Wno-string-plus-int -Wno-unused-const-variable -Wno-tautological-compare -Wno-unused-value -Wno-parentheses-equality -Wno-unused-function -Wno-enum-conversion -Wno-unused-local-typedef -Wno-address-of-packed-member -Wno-switch -Wno-switch-enum -Wno-knr-promoted-parameter -Qunused-arguments -std=c++11 -fno-rtti -Qunused-arguments -Werror=cheri-bitwise-operations -stdlib=libc++ -Wno-c++11-extensions -fno-exceptions -funwind-tables -DNDEBUG -c /mnt/mainline/cheribsd/contrib/subrepo-cheri-libunwind/src/libunwind.cpp -o libunwind.o

libunwind-a1a176.zip

[jrtc27]

I assume this is 6bdf026; Jenkins has been reporting this failure over the weekend.

[arichardson]

For now you can just revert 6bdf026 but since that causes webkit to be miscompiled it is not the ideal solution. I'll see if I can come up with a fix.

[arichardson]

We could of course just always emit the CSC/CLC even if LLVM thinks it is unaligned but that might mask some other compiler bugs.

[arichardson]

Minimal test case:

// RUN: %cheri_purecap_cc1 -cheri-uintcap=offset -O2 -std=c++11 -o - -S %s
extern "C" void *memcpy(void *, void *, long);

extern "C" __uintcap_t minimal_test_case(__int128 y) {
  __uintcap_t r;
  memcpy(&r, (void *)(__intcap_t)y, sizeof(r));
  return r;
}

[arichardson]

Casting __int128 to void* is really odd and will crash at runtime, I wonder why this is being generated from the libunwind sources.

[bsdjhb]

I actually want to eventually remove the memcpy and get<> template from libunwind to get us closer to upstream sources and just use a plain uintptr_t read for getP().

[arichardson]

No longer crashes: https://cheri-compiler-explorer.cl.cam.ac.uk/z/9rjEKP