Compile from i386 host fails: 'ct_assert_0' declared as an array with a negative size

[lrvick]

Building from i386 based live-bootstrap environment as follows:

	cmake \
		-B build \
		-S llvm \
		-Wno-dev \
		-DCMAKE_INSTALL_PREFIX=/usr/ \
		-DCMAKE_BUILD_TYPE=Release \
		-DLLVM_TARGETS_TO_BUILD="X86;AArch64" \
		-DLLVM_ENABLE_PROJECTS="clang;clang-tools-extra;lld" \
		-DLLVM_ENABLE_RUNTIMES="compiler-rt;libcxx;libcxxabi;libunwind" \
		-DLLVM_BUILD_DOCS=OFF
	cmake --build build --parallel $(nproc)

Failure output:

1225.8 [ 82%] Building ASM object CMakeFiles/clang_rt.builtins-i386.dir/i386/floatundixf.S.o
1225.8 [ 83%] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/divtf3.c.o
1225.8 [ 83%] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/divtc3.c.o
1225.8 [ 83%] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/extenddftf2.c.o
1225.8 [ 83%] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/extendhftf2.c.o
1225.8 [ 83%] Building C object CMakeFiles/clang_rt.builtins-i386.dir/extendbfsf2.c.o
1225.8 [ 84%] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/extendsftf2.c.o
1225.8 [ 85%] Building C object CMakeFiles/clang_rt.builtins-i386.dir/truncdfbf2.c.o
1225.8 [ 85%] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/fixtfdi.c.o
1225.8 [ 85%] Building C object CMakeFiles/clang_rt.builtins-i386.dir/truncxfbf2.c.o
1225.8 [ 85%] Building C object CMakeFiles/clang_rt.builtins-i386.dir/truncsfbf2.c.o
1225.8 [ 86%] Building C object CMakeFiles/clang_rt.builtins-i386.dir/trunctfbf2.c.o
1225.8 [ 86%] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/fixtfsi.c.o
1225.8 [ 87%] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/fixtfti.c.o
1225.8 [ 87%] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/fixunstfdi.c.o
1225.8 [ 87%] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/fixunstfsi.c.o
1225.8 [ 88%] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/fixunstfti.c.o
1225.8 [ 88%] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/floatditf.c.o
1225.8 [ 88%] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/floatsitf.c.o
1225.8 /llvm-project-20.1.0.src/compiler-rt/lib/builtins/enable_execute_stack.c:60:17: warning: cast to smaller integer type 'uintptr_t' (aka 'unsigned int') from 'void *' [-Wvoid-pointer-to-int-cast]
1225.8    60 |   uintptr_t p = (uintptr_t)addr;
1225.8       |                 ^~~~~~~~~~~~~~~
1225.8 /llvm-project-20.1.0.src/compiler-rt/lib/builtins/enable_execute_stack.c:61:30: warning: cast to 'unsigned char *' from smaller integer type 'uintptr_t' (aka 'unsigned int') [-Wint-to-pointer-cast]
1225.8    61 |   unsigned char *startPage = (unsigned char *)(p & pageAlignMask);
1225.8       |                              ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1225.8 /llvm-project-20.1.0.src/compiler-rt/lib/builtins/enable_execute_stack.c:63:7: warning: cast to 'unsigned char *' from smaller integer type 'uintptr_t' (aka 'unsigned int') [-Wint-to-pointer-cast]
1225.8    63 |       (unsigned char *)((p + TRAMPOLINE_SIZE + pageSize) & pageAlignMask);
1225.8       |       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1225.9 /llvm-project-20.1.0.src/compiler-rt/lib/builtins/gcc_personality_v0.c:124:15: warning: cast to smaller integer type 'uintptr_t' (aka 'unsigned int') from 'const uint8_t *' (aka 'const unsigned char *') [-Wpointer-to-int-cast]
1225.9   124 |     result += (uintptr_t)(*data);
1225.9       |               ^~~~~~~~~~~~~~~~~~
1225.9 /llvm-project-20.1.0.src/compiler-rt/lib/builtins/gcc_personality_v0.c:138:16: warning: cast to 'const uintptr_t *' (aka 'const unsigned int *') from smaller integer type 'uintptr_t' (aka 'unsigned int') [-Wint-to-pointer-cast]
1225.9   138 |     result = *((const uint[ 89%] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/floattitf.c.o
1225.9 ptr_t *)result);
1225.9       |                ^~~~~~~~~~~~~~~~~~~~~~~~~
1225.9 [ 89%] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/floatunsitf.c.o
1225.9 [ 89%] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/floatunditf.c.o
1225.9 /llvm-project-20.1.0.src/compiler-rt/lib/builtins/gcc_personality_v0.c:239:21: warning: cast to smaller integer type 'uintptr_t' (aka 'unsigned int') from 'struct _Unwind_Exception *' [-Wpointer-to-int-cast]
1225.9   239 |     /llvm-project-20.1.0.src/compiler-rt/lib/builtins/emutls.c:75:20: warning: cast to smaller integer type 'uintptr_t' (aka 'unsigned int') from 'char *' [-Wpointer-to-int-cast]
1225.9      75 |   base = (void *)(((uintptr_t)(object + EXTRA_ALIGN_PTR_BYTES)) &
1225.9       |                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1225.9      /llvm-project-20.1.0.src/compiler-rt/lib/builtins/emutls.c:75:10: warning: cast to 'void *' from smaller integer type 'uintptr_t' (aka 'unsigned int') [-Wint-to-void-pointer-cast]
1225.9             (uintptr_t)exceptionObject);
1225.9       |                     ^~~~~~~~~~~~~~~~~~~~~~~~~~
1225.9 75 |   base = (void *)(((uintptr_t)(object + EXTRA_ALIGN_PTR_BYTES)) &
1225.9       |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1225.9    76 |                   ~(uintptr_t)(align - 1));
1225.9       |                   ~~~~~~~~~~~~~~~~~~~~~~~~
1225.9 /llvm-project-20.1.0.src/compiler-rt/lib/builtins/emutls.c:291:3: error: 'ct_assert_0' declared as an array with a negative size
1225.9   291 |   COMPILE_[ 89%] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/floatuntitf.c.o
1225.9 TIME_ASSERT(sizeof(uintptr_t) == sizeof(gcc_pointer));
1225.9       |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1225.9 /llvm-project-20.1.0.src/compiler-rt/lib/builtins/int_util.h:26:35: note: expanded from macro 'COMPILE_TIME_ASSERT'
1225.9    26 | #define COMPILE_TIME_ASSERT(expr) COMPILE_TIME_ASSERT1(expr, __COUNTER__)
1225.9       |                                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1225.9 /llvm-project-20.1.0.src/compiler-rt/lib/builtins/int_util.h:27:41: note: expanded from macro 'COMPILE_TIME_ASSERT1'
1225.9    27 | #define COMPILE_TIME_ASSERT1(expr, cnt) COMPILE_TIME_ASSERT2(expr, cnt)
1225.9       |                                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1225.9 /llvm-project-20.1.0.src/compiler-rt/lib/builtins/int_util.h:29:32: note: expanded from macro 'COMPILE_TIME_ASSERT2'
1225.9    29 |   typedef char ct_assert_##cnt[(expr) ? 1 : -1] UNUSED
1225.9       |                                ^~~~~~~~~~~~~~~
1225.9 /llvm-project-20.1.0.src/compiler-rt/lib/builtins/emutls.c:292:3: error: 'ct_assert_1' declared as an array with a negative size
1225.9   292 |   COMPILE_TIME_ASSERT(sizeof(uintptr_t) == si[ 90%] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/multc3.c.o
1225.9 zeof(void *));
1225.9       |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1225.9 /llvm-project-20.1.0.src/compiler-rt/lib/builtins/int_util.h:26:35: note: expanded from macro 'COMPILE_TIME_ASSERT'
1225.9    26 | #define COMPILE_TIME_ASSERT(expr) COMPILE_TIME_ASSERT1(expr, __COUNTER__)
1225.9       |                                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1225.9 /llvm-project-20.1.0.src/compiler-rt/lib/builtins/int_util.h:27:41: note: expanded from macro 'COMPILE_TIME_ASSERT1'
1225.9    27 | #define COMPILE_TIME_ASSERT1(expr, cnt) COMPILE_TIME_ASSERT2(expr, cnt)
1225.9       |                                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1225.9 /llvm-project-20.1.0.src/compiler-rt/lib/builtins/int_util.h:29:32: note: expanded from macro 'COMPILE_TIME_ASSERT2'
1225.9    29 |   typedef char ct_assert_##cnt[(expr) ? 1 : -1] UNUSED
1225.9       |                                ^~~~~~~~~~~~~~~
1225.9 3 warnings generated.
1225.9 2 warnings and 2 errors generated.
1225.9 [ 90%] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/multf3.c.o
1225.9 [ 90%] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/powitf2.c.o
1225.9 [ 91%] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/trunctfdf2.c.o
1225.9 [ 91%] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/subtf3.c.o
1225.9 make[5]: *** [CMakeFiles/clang_rt.builtins-x86_64.dir/build.make:1675: CMakeFiles/clang_rt.builtins-x86_64.dir/emutls.c.o] Error 1
1225.9 make[5]: *** Waiting for unfinished jobs....
1225.9 [ 91%] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/trunctfhf2.c.o
1225.9 [ 92%] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/trunctfsf2.c.o
1225.9 [ 92%] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/cpu_model/x86.c.o
1225.9 [ 93%] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/x86_64/floatdidf.c.o
1225.9 [ 93%] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/i386/fp_mode.c.o
1225.9 [ 93%] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/x86_64/floatdisf.c.o
1225.9 [ 93%] Building ASM object CMakeFiles/clang_rt.builtins-x86_64.dir/x86_64/floatundidf.S.o
1225.9 [ 93%] Building ASM object CMakeFiles/clang_rt.builtins-x86_64.dir/x86_64/floatundisf.S.o
1225.9 [ 94%] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/divxc3.c.o
1225.9 3 warnings generated.
1226.1 [ 94%] Linking C static library /llvm-project-20.1.0.src/build/lib/clang/20/lib/i386-unknown-linux-gnu/libclang_rt.builtins.a
1226.1 [ 94%] Built target clang_rt.builtins-i386
1226.1 make[4]: *** [CMakeFiles/Makefile2:652: CMakeFiles/clang_rt.builtins-x86_64.dir/all] Error 2
1226.1 make[3]: *** [Makefile:136: all] Error 2
1226.1 make[2]: *** [runtimes/CMakeFiles/builtins-build.dir/build.make:76: runtimes/builtins-stamps/builtins-build] Error 2
1226.1 make[1]: *** [CMakeFiles/Makefile2:168455: runtimes/CMakeFiles/builtins-build.dir/all] Error 2
1226.1 make[1]: *** Waiting for unfinished jobs....
1226.6 [100%] Built target lli
1231.3 [100%] Linking CXX executable ../../../../bin/c-index-test
1232.8 [100%] Linking CXX executable ../../bin/llvm-jitlink
1232.9 [100%] Built target clang-repl
1234.2 [100%] Built target llvm-jitlink
1234.3 [100%] Built target c-index-test
1235.7 [100%] Linking CXX executable ../../bin/llvm-exegesis
1236.7 [100%] Built target obj.clangDaemon
1237.7 [100%] Built target llvm-exegesis
1237.7 make: *** [Makefile:156: all] Error 2

[efriedma-quic]

It looks like you're cross-compiling the runtimes from 32-bit to 64-bit. Which should work in theory, but it looks like it isn't supported in your environment. You can override the default by specifying something like -DLLVM_RUNTIME_TARGETS=i686-linux-gnu.

[lrvick]

I get the same error when building i386 -> i386 as an attempted intermediate step.

[efriedma-quic]

To expand a bit:

COMPILE_TIME_ASSERT(sizeof(uintptr_t) == sizeof(void *)); is asserting that uintptr_t is defined correctly. If it's failing, probably your stdint.h is defining uintptr_t as a 32-bit integer.

If you're getting "the same error", you're still building for 64-bit; there's no other way to get that error.

The line CMakeFiles/clang_rt.builtins-x86_64.dir/build.make:1675: CMakeFiles/clang_rt.builtins-x86_64.dir/emutls.c.o] Error 1 in your build log indicates that the error is being produced building a 64-bit compiler-rt.

By default, on x86, 32-bit and 64-bit variants of compiler-rt are built. You should be able to override this using -DLLVM_RUNTIME_TARGETS.

[lrvick]

My ultimate goal is to bootstrap x86_64 hosted llvm/clang from i386 hosted gcc 13.

Assuming I play with the above and I do succeed in compiling i386 llvm by excluding all 64 bit targets, could I then use that to compile an i386 hosted llvm that can target x86_64?

[efriedma-quic]

LLVM is naturally a cross-compiler: if you've built it with x86 support, it supports generating code for all 32-bit and 64-bit x86 variants. The catch is that you need an appropriate sysroot that contains appropriate headers and libraries. https://llvm.org/docs/HowToCrossCompileBuiltinsOnArm.html might be helpful.

[lrvick]

Attempted your suggestion as follows:

  cmake \
    -B build \
    -S llvm \
    -Wno-dev \
    -DCMAKE_INSTALL_PREFIX=/usr/ \
    -DCMAKE_BUILD_TYPE=Release \
    -DLLVM_TARGETS_TO_BUILD="X86" \
    -DLLVM_RUNTIME_TARGETS="i386-linux-musl" \
    -DLLVM_ENABLE_PROJECTS="clang;clang-tools-extra;lld" \
    -DLLVM_ENABLE_RUNTIMES="compiler-rt;libcxx;libcxxabi;libunwind" \
    -DLLVM_BUILD_DOCS=OFF
  cmake --build build --parallel $(nproc)

Still failed similarly:

#21 1232.5 [ 80%] Building ASM object CMakeFiles/clang_rt.builtins-i386.dir/i386/muldi3.S.o
#21 1232.5 /llvm-project-19.1.7.src/compiler-rt/lib/builtins/enable_execute_stack.c:60:17: warning: cast to smaller integer type 'uintptr_t' (aka 'unsigned int') from 'void *' [-Wvoid-pointer-to-int-cast]
#21 1232.5    60 |   uintptr_t p = (uintptr_t)addr;
#21 1232.5       |                 ^~~~~~~~~~~~~~~
#21 1232.5 /llvm-project-19.1.7.src/compiler-rt/lib/builtins/enable_execute_stack.c:61:30: warning: cast to 'unsigned char *' from smaller integer type 'uintptr_t' (aka 'unsigned int') [-Wint-to-pointer-cast]
#21 1232.5    61 |   unsigned [ 81%] Building ASM object CMakeFiles/clang_rt.builtins-i386.dir/i386/udivdi3.S.o
#21 1232.5 char *startPage = (unsigned char [ 81%] Building ASM object CMakeFiles/clang_rt.builtins-i386.dir/i386/umoddi3.S.o
#21 1232.5 */llvm-project-19.1.7.src/compiler-rt/lib/builtins/gcc_personality_v0.c:124:15: warning: cast to smaller integer type 'uintptr_t' (aka 'unsigned int') from 'const uint8_t *' (aka 'const unsigned char *') [-Wpointer-to-int-cast]
#21 1232.5 )(  p & pageAlignMask);
#21 1232.5       |                              ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#21 1232.5 124 |     res/llvm-project-19.1.7.src/compiler-rt/lib/builtins/enable_execute_stack.cult += (uintptr_t)(*data);
#21 1232.5       |               ^~~~~~~~~~~~~~~~~~
#21 1232.5 :63:7: warning: cast to 'unsigned char *' from smaller integer type 'uintptr_t' (aka 'unsigned int') [-Wint-to-pointer-cast]
#21 1232.5    63 |       /llvm-project-19.1.7.src/compiler-rt/lib/builtins/gcc_personality_v0.c:138:16: warning: cast to 'const uintptr_t *' (aka 'const unsigned int *') from smaller integer type 'uintptr_t' (aka 'unsigned int') [-Wint-to-pointer-cast]
#21 1232.5 (  138 |     result = *((const uintptr_t *)result);
#21 1232.5       |                ^~~~~~~~~~~~~~~~~~~~~~~~~
#21 1232.5 unsigned char *)((p + TRAMPOLINE_SIZE + pageSize) &[ 81%] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/fixtfsi.c.o
#21 1232.5  pageAlignMask);
#21 1232.5       |       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#21 1232.5 [ 82%] Building C object CMakeFiles/clang_rt.builtins-i386.dir/extendxftf2.c.o
#21 1232.5 [ 82%] Building C object CMakeFiles/clang_rt.builtins-i386.dir/divxc3.c.o
#21 1232.5 /llvm-project-19.1.7.src/compiler-rt/lib/builtins/emutls.c/llvm-project-19.1.7.src/compiler-rt/lib/builtins/gcc_personality_v0.c:239:21: warning: cast to smaller integer type 'uintptr_t' (aka 'unsigned int') from 'struct _Unwind_Exception *' [-Wpointer-to-int-cast]
#21 1232.5 :  239 |               [ 82%] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/fixunstfdi.c.o
#21 1232.5       (uintptr_t)exceptionObject);
#21 1232.5       |                     ^~~~~~~~~~~~~~~~~~~~~~~~~~
#21 1232.5 75:20: warning: cast to smaller integer type 'uintptr_t' (aka 'unsigned int') from 'char *' [-Wpointer-to-int-cast]
#21 1232.5    75 |   base = (void *)(((uintptr_t)(object + EXTRA_ALIGN_PTR_BYTES)) &
#21 1232.5       |                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#21 1232.5 /llvm-project-19.1.7.src/compiler-rt/lib/builtins/emutls.c:75:10: warning: cast to 'void *' from smaller integer type 'uintptr_t' (aka 'unsigned int') [-Wint-to-void-pointer-cast]
#21 1232.5    75 |   base = (void *)(((uintptr_t)(object + EXTRA_ALIGN_PTR_BYTES)) &
#21 1232.5       |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#21 1232.5    76 |             [ 83%] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/fixtfti.c.o
#21 1232.5       ~(uintptr_t)(alig[ 83%] Building C object CMakeFiles/clang_rt.builtins-i386.dir/fixxfdi.c.o
#21 1232.5 n - 1));
#21 1232.5       |                   ~~~~~~~~~~~~~~~~~~~~~~~~
#21 1232.5 [ 83%] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/fixunstfsi.c.o
#21 1232.5 [ 83%] Building C object CMakeFiles/clang_rt.builtins-i386.dir/fixxfti.c.o
#21 1232.5 /llvm-project-19.1.7.src/compiler-rt/lib/builtins/emutls.c:291:3: error: 'ct_assert_0' declared as an array with a negative size
#21 1232.5   291 |   COMPILE_TIME_ASSERT(sizeof(uintptr_t) == sizeof(gcc_pointer));
#21 1232.5 [ 84%] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/fixunstfti.c.o
#21 1232.5       |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#21 1232.5 /llvm-project-19.1.7.src/compiler-rt/lib/builtins/int_util.h:26:35: note: expanded from macro 'COMPILE_TIME_ASSERT'
#21 1232.5    26 | #define COMPILE_TIME_ASSERT(expr) COMPILE_TIME_ASSERT1(expr, __COUNTER__)
#21 1232.5       |                                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#21 1232.5 /llvm-project-19.1.7.src/compiler-rt/lib/builtins/int_util.h:27:41: note: expanded from macro 'COMPILE_TIME_ASSERT1'
#21 1232.5    27 | #define COMPILE_TIME_ASSERT1(expr, cnt) COM[ 84%] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/floatditf.c.o
#21 1232.5 PILE_TIME_ASSERT2(expr, cnt)[ 84%] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/floatsitf.c.o
#21 1232.5 
#21 1232.5       |                                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#21 1232.5 /llvm-project-19.1.7.src/compiler-rt/lib/builtins/int_util.h:29:32: note: expanded from macro 'COMPILE_TIME_ASSERT2'
#21 1232.5    29 |   typedef char ct_assert_##cnt[(expr) ? 1 : -1] UNUSED
#21 1232.5       |                                ^~~~~~~~~~~~~~~
#21 1232.5 /llvm-project-19.1.7.src/compiler-rt/lib/builtins/emutls.c:292:3: error: 'ct_assert_1' declared as an array with a negative size
#21 1232.5   292 |   COMPILE_TIME_ASSERT(sizeof(uintptr_t) == sizeof(void *));
#21 1232.5       |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#21 1232.5 /llvm-project-19.1.7.src/compiler-rt/lib/builtins/int_util.h:26:35: note: expanded from macro 'COMPILE_TIME_ASSERT'
#21 1232.5    26 | #define COMPILE_TIME_ASSERT(expr) COMPILE_TIME_ASSERT1(expr, __COUNTER__)
#21 1232.5       |                                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#21 1232.5 /llvm-project-19.1.7.src/compiler-rt/lib/builtins/int_util.h:27:41: note: expanded from macro 'COMPILE_TIME_ASSERT1'
#21 1232.5    27 | #define COMPILE_TIME_ASSERT1(expr, cnt) COMPILE_TIME_ASSERT2(expr, cnt)
#21 1232.5       |                                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#21 1232.5 /llvm-project-19.1.7.src/compiler-rt/lib/builtins/int_util.h:29:32: note: expanded from macro 'COMPILE_TIME_ASSERT2'
#21 1232.5    29 |   typedef char ct_assert_##cnt[(expr) ? 1 : -1] UNUSED
#21 1232.5       |                                ^~~~~~~~~~~~~~~
#21 1232.5 [ 84%] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/floattitf.c.o
#21 1232.5 2 warnings and 2 errors generated.
#21 1232.5 3 warnings generated.
#21 1232.5 make[5]: *** [CMakeFiles/clang_rt.builtins-x86_64.dir/build.make:1675: CMakeFiles/clang_rt.builtins-x86_64.dir/emutls.c.o] Error 1
#21 1232.5 make[5]: *** Waiting for unfinished jobs....
#21 1232.5 [ 85%] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/floatunditf.c.o
#21 1232.5 [ 86%] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/floatunsitf.c.o
#21 1232.5 [ 86%] Building C object CMakeFiles/clang_rt.builtins-i386.dir/fixunsxfdi.c.o
#21 1232.5 [ 86%] Building C object CMakeFiles/clang_rt.builtins-i386.dir/fixunsxfsi.c.o
#21 1232.5 [ 86%] Building C object CMakeFiles/clang_rt.builtins-i386.dir/fixunsxfti.c.o
#21 1232.5 [ 87%] Building C object CMakeFiles/clang_rt.builtins-i386.dir/floattixf.c.o
#21 1232.5 [ 87%] Building C object CMakeFiles/clang_rt.builtins-i386.dir/floatuntixf.c.o
#21 1232.5 [ 87%] Building C object CMakeFiles/clang_rt.builtins-i386.dir/mulxc3.c.o
#21 1232.5 [ 88%] Building C object CMakeFiles/clang_rt.builtins-i386.dir/powixf2.c.o
#21 1232.5 [ 88%] Building C object CMakeFiles/clang_rt.builtins-i386.dir/trunctfxf2.c.o
#21 1232.5 [ 88%] Building ASM object CMakeFiles/clang_rt.builtins-i386.dir/i386/floatdixf.S.o
#21 1232.5 [ 88%] Building ASM object CMakeFiles/clang_rt.builtins-i386.dir/i386/floatundixf.S.o
#21 1232.5 [ 89%] Building C object CMakeFiles/clang_rt.builtins-i386.dir/extendbfsf2.c.o
#21 1232.5 [ 89%] Building C object CMakeFiles/clang_rt.builtins-i386.dir/truncdfbf2.c.o
#21 1232.5 [ 89%] Building C object CMakeFiles/clang_rt.builtins-i386.dir/truncsfbf2.c.o
#21 1232.6 3 warnings generated.
#21 1232.7 make[4]: *** [CMakeFiles/Makefile2:619: CMakeFiles/clang_rt.builtins-x86_64.dir/all] Error 2
#21 1232.7 make[4]: *** Waiting for unfinished jobs....
#21 1232.7 [ 90%] Linking C static library /llvm-project-19.1.7.src/build/lib/clang/19/lib/i386-unknown-linux-gnu/libclang_rt.builtins.a
#21 1232.8 [ 90%] Built target clang_rt.builtins-i386
#21 1232.8 make[3]: *** [Makefile:136: all] Error 2
#21 1232.8 make[2]: *** [runtimes/CMakeFiles/builtins.dir/build.make:95: runtimes/builtins-stamps/builtins-build] Error 2
#21 1232.8 make[1]: *** [CMakeFiles/Makefile2:167560: runtimes/CMakeFiles/builtins.dir/all] Error 2
#21 1232.8 make[1]: *** Waiting for unfinished jobs....
#21 1233.3 [100%] Built target obj.clangDaemon
#21 1233.3 make: *** [Makefile:156: all] Error 2
#21 ERROR: process "/bin/sh -c set -eux\ncmake \\\n-B build \\\n-S llvm \\\n-Wno-dev \\\n-DCMAKE_INSTALL_PREFIX=/usr/ \\\n-DCMAKE_BUILD_TYPE=Release \\\n-DLLVM_TARGETS_TO_BUILD=\"X86\" \\\n-DLLVM_RUNTIME_TARGETS=\"i386-linux-musl\" \\\n-DLLVM_ENABLE_PROJECTS=\"clang;clang-tools-extra;lld\" \\\n-DLLVM_ENABLE_RUNTIMES=\"compiler-rt;libcxx;libcxxabi;libunwind\" \\\n-DLLVM_BUILD_DOCS=OFF\ncmake --build build --parallel $(nproc)\nDESTDIR=\"/rootfs\" cmake --install build\n" did not complete successfully: exit code: 2
------
 > [linux/386 build 15/16] RUN --network=none <<-EOF (set -eux...):
1232.7 make[4]: *** [CMakeFiles/Makefile2:619: CMakeFiles/clang_rt.builtins-x86_64.dir/all] Error 2
1232.7 make[4]: *** Waiting for unfinished jobs....
1232.7 [ 90%] Linking C static library /llvm-project-19.1.7.src/build/lib/clang/19/lib/i386-unknown-linux-gnu/libclang_rt.builtins.a
1232.8 [ 90%] Built target clang_rt.builtins-i386
1232.8 make[3]: *** [Makefile:136: all] Error 2
1232.8 make[2]: *** [runtimes/CMakeFiles/builtins.dir/build.make:95: runtimes/builtins-stamps/builtins-build] Error 2
1232.8 make[1]: *** [CMakeFiles/Makefile2:167560: runtimes/CMakeFiles/builtins.dir/all] Error 2
1232.8 make[1]: *** Waiting for unfinished jobs....
1233.3 [100%] Built target obj.clangDaemon
1233.3 make: *** [Makefile:156: all] Error 2

[efriedma-quic]

Looking again, you might actually need to set LLVM_BUILTIN_TARGETS? Getting the CMake config right here is sort of complicated.

I don't really have time to dig deeper into this; you might want to look at llvm/runtimes/CMakeLists.txt.