Release overlay GCC build fails with "aliased to external symbol" #60481

liam-clink · 2023-02-02T15:08:30Z

CMake invocation: (C/C++ compilers set to GCC/G++)

cmake -S ../llvm -B . -G Ninja -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=$HOME/llvm-15_temp -DLLVM_TARGETS_TO_BUILD="X86" -DLLVM_ENABLE_PROJECTS="all"

[1/7688] Building CXX object projects/libc/src/stdlib/CMakeFiles/libc.src.stdlib.bsearch.dir/bsearch.cpp.o
FAILED: projects/libc/src/stdlib/CMakeFiles/libc.src.stdlib.bsearch.dir/bsearch.cpp.o 
/home/liam/gcc-12.2.0/bin/g++ -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/home/liam/Documents/GitHub/llvm-project/build/projects/libc/src/stdlib -I/home/liam/Documents/GitHub/llvm-project/libc/src/stdlib -I/home/liam/Documents/GitHub/llvm-project/build/include -I/home/liam/Documents/GitHub/llvm-project/llvm/include -I/home/liam/Documents/GitHub/llvm-project/build/projects/libc/include -I/home/liam/Documents/GitHub/llvm-project/libc -I/home/liam/Documents/GitHub/llvm-project/build/projects/libc -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror=date-time -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wno-missing-field-initializers -pedantic -Wno-long-long -Wimplicit-fallthrough -Wno-maybe-uninitialized -Wno-class-memaccess -Wno-redundant-move -Wno-pessimizing-move -Wno-noexcept-type -Wdelete-non-virtual-dtor -Wsuggest-override -Wno-comment -Wmisleading-indentation -fdiagnostics-color -ffunction-sections -fdata-sections -O3 -DNDEBUG -fpie -ffreestanding -fno-builtin -fno-exceptions -fno-unwind-tables -fno-asynchronous-unwind-tables -fno-rtti -DLLVM_LIBC_PUBLIC_PACKAGING -std=c++17 -MD -MT projects/libc/src/stdlib/CMakeFiles/libc.src.stdlib.bsearch.dir/bsearch.cpp.o -MF projects/libc/src/stdlib/CMakeFiles/libc.src.stdlib.bsearch.dir/bsearch.cpp.o.d -o projects/libc/src/stdlib/CMakeFiles/libc.src.stdlib.bsearch.dir/bsearch.cpp.o -c /home/liam/Documents/GitHub/llvm-project/libc/src/stdlib/bsearch.cpp
In file included from /home/liam/Documents/GitHub/llvm-project/libc/src/stdlib/bsearch.cpp:10:
/home/liam/Documents/GitHub/llvm-project/libc/src/stdlib/bsearch.cpp:16:28: error: 'void* __llvm_libc::bsearch(const void*, const void*, size_t, size_t, int (*)(const void*, const void*))' aliased to external symbol 'bsearch'
   16 | LLVM_LIBC_FUNCTION(void *, bsearch,
      |                            ^~~~~~~
/home/liam/Documents/GitHub/llvm-project/libc/src/__support/common.h:33:31: note: in definition of macro 'LLVM_LIBC_FUNCTION'
   33 |   decltype(__llvm_libc::name) name [[gnu::alias(#name)]];                      \
      |                               ^~~~
/home/liam/Documents/GitHub/llvm-project/libc/src/stdlib/bsearch.cpp:16:28: warning: 'void* __llvm_libc::bsearch(const void*, const void*, size_t, size_t, int (*)(const void*, const void*))' specifies less restrictive attribute than its target 'void* bsearch(const void*, const void*, size_t, size_t, __compar_fn_t)': 'nonnull' [-Wmissing-attributes]
   16 | LLVM_LIBC_FUNCTION(void *, bsearch,
      |                            ^~~~~~~
/home/liam/Documents/GitHub/llvm-project/libc/src/__support/common.h:33:31: note: in definition of macro 'LLVM_LIBC_FUNCTION'
   33 |   decltype(__llvm_libc::name) name [[gnu::alias(#name)]];                      \
      |                               ^~~~
In file included from /usr/include/stdlib.h:833,
                 from /home/liam/gcc-12.2.0/include/c++/12.2.0/cstdlib:75,
                 from /home/liam/gcc-12.2.0/include/c++/12.2.0/stdlib.h:36,
                 from /home/liam/Documents/GitHub/llvm-project/libc/src/stdlib/bsearch.h:9,
                 from /home/liam/Documents/GitHub/llvm-project/libc/src/stdlib/bsearch.cpp:9:
/usr/include/x86_64-linux-gnu/bits/stdlib-bsearch.h:20:1: note: 'void* __llvm_libc::bsearch(const void*, const void*, size_t, size_t, int (*)(const void*, const void*))' target declared here
   20 | bsearch (const void *__key, const void *__base, size_t __nmemb, size_t __size,
      | ^~~~~~~

llvmbot · 2023-02-02T15:13:29Z

@llvm/issue-subscribers-libc

DavidSpickett · 2023-02-03T12:25:40Z

Just been looking at this myself, this only happens for overlay mode. It's the overlaying mechanism that leads to this error I think.

Reading the gcc docs:
https://gcc.gnu.org/onlinedocs/gcc-4.7.2/gcc/Function-Attributes.html

"It is an error if `__f' is not defined in the same translation unit."

clang does not document it so I don't know if clang allows this on purpose or not.

I also found https://stackoverflow.com/questions/7649979/gcc-alias-to-function-outside-of-translation-unit-aka-is-this-even-the-right-t asking about this with another project. No obvious solution from C, but some ideas with linker scripts and such.

I should note that the libc project only officially supports clang at this time. The gcc buildbots they have build the full mode so they won't have hit this.

sivachandra · 2023-02-03T15:41:53Z

Interestingly, this seems to happen only for release mode builds with -DCMAKE_BUILD_TYPE=Release. I am not able to reproduce this for debug builds.

sivachandra · 2023-02-03T15:50:23Z

Ah, looks like bsearch gets defined as an extern inline function in glibc's stdlib.h under release build and so the alias here is conflicting with that extern inline function.

mikhailramalho · 2023-02-28T19:44:53Z

I also started to get the same error for readlinkat in RelWithDebInfo mode:

In file included from /home/mgadelha/tools/llvm-project/libc/src/__support/OSUtil/linux/syscall.h:12,
                 from /home/mgadelha/tools/llvm-project/libc/src/__support/OSUtil/syscall.h:13,
                 from /home/mgadelha/tools/llvm-project/libc/src/unistd/linux/readlinkat.cpp:11:
/home/mgadelha/tools/llvm-project/libc/src/unistd/linux/readlinkat.cpp:20:29: error: ‘ssize_t __llvm_libc::readlinkat(int, const char*, char*, size_t)’ aliased to external symbol ‘readlinkat’
   20 | LLVM_LIBC_FUNCTION(ssize_t, readlinkat,
      |                             ^~~~~~~~~~
/home/mgadelha/tools/llvm-project/libc/src/__support/common.h:30:31: note: in definition of macro ‘LLVM_LIBC_FUNCTION’
   30 |   decltype(__llvm_libc::name) name [[gnu::alias(#name)]];                      \
      |                               ^~~~
/home/mgadelha/tools/llvm-project/libc/src/unistd/linux/readlinkat.cpp:20:29: warning: ‘ssize_t __llvm_libc::readlinkat(int, const char*, char*, size_t)’ specifies less restrictive attributes than its target ‘ssize_t readlinkat(int, const char*, char*, size_t)’: ‘leaf’, ‘nonnull’, ‘nothrow’ [-Wmissing-attributes]
   20 | LLVM_LIBC_FUNCTION(ssize_t, readlinkat,
      |                             ^~~~~~~~~~
/home/mgadelha/tools/llvm-project/libc/src/__support/common.h:30:31: note: in definition of macro ‘LLVM_LIBC_FUNCTION’
   30 |   decltype(__llvm_libc::name) name [[gnu::alias(#name)]];                      \
      |                               ^~~~
In file included from /usr/include/features.h:486,
                 from /usr/include/unistd.h:25,
                 from /home/mgadelha/tools/llvm-project/libc/src/unistd/readlinkat.h:12,
                 from /home/mgadelha/tools/llvm-project/libc/src/unistd/linux/readlinkat.cpp:9:
/usr/include/x86_64-linux-gnu/bits/unistd.h:144:1: note: ‘ssize_t __llvm_libc::readlinkat(int, const char*, char*, size_t)’ target declared here
  144 | __NTH (readlinkat (int __fd, const char *__restrict __path,
      | ^~~~~

It builds fine in Debug mode.

erkinalp · 2023-05-29T18:05:19Z

Suggested re-title: "Standard library re-aliasing issues in overlay mode builds only in the release configuration"

nickdesaulniers · 2024-04-17T21:12:39Z

Looks like gcc will error for aliases created with the alias attributes, but not asm aliases.

https://godbolt.org/z/xsxrTavnx

nickdesaulniers · 2024-04-19T22:03:35Z

Simpler reproducer:

$ cd <new build dir>
$ cmake ../llvm -DLLVM_ENABLE_PROJECTS="libc" -DCMAKE_BUILD_TYPE=Release -G Ninja
$ ninja libc.src.stdlib.bsearch

When building overlay mode with GCC in release mode, glibc's stdlib.h contains an extern inline declaration of bsearch. This breaks our use of the gnu::alias function attribute in LLVM_LIBC_FUNCTION with GCC because GCC checks that the aliasee is defined in the same TU (clang does not). We're looking at also potentially updating our definition of LLVM_LIBC_FUNCTION from libc/src/__support/common.h. Upon testing, I was able to get -Wnonnull-compare diagnostics from GCC in our definition of bsearch because glibc declares bsearch with the fugly nonnull function attribute. There's more we can do here though to improve our implementation of bsearch. 7.24.5.1 says: Pointer arguments on such a call shall still have valid values, as described in 7.1.4. We could also use either function attributes or parameter attributes to denote these should not be null (for users/callers) and perhaps still check for non-null explicitly under some yet to be discussed hardening configurations in the future. Fixes: llvm#60481 Link: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-nonnull-function-attribute

nickdesaulniers · 2024-04-19T23:50:45Z

Looks like gcc will error for aliases created with the alias attributes, but not asm aliases.

https://godbolt.org/z/xsxrTavnx

So clang can diagnose this, but seemingly only at -O0. I hit asserts in LLVM when I try to build that test case with optimizations enabled though.

I have a fix for the immediate issue of bsearch, but it won't close out this issue because we hit similar but slightly trickier to fix cases for 3 other functions (wctob, vprintf, and atof).

When building overlay mode with GCC in release mode, glibc's stdlib.h contains an extern inline declaration of bsearch. This breaks our use of the gnu::alias function attribute in LLVM_LIBC_FUNCTION with GCC because GCC checks that the aliasee is defined in the same TU (clang does not). We're looking at also potentially updating our definition of LLVM_LIBC_FUNCTION from libc/src/__support/common.h. Upon testing, I was able to get -Wnonnull-compare diagnostics from GCC in our definition of bsearch because glibc declares bsearch with the fugly nonnull function attribute. There's more we can do here though to improve our implementation of bsearch. 7.24.5.1 says: Pointer arguments on such a call shall still have valid values, as described in 7.1.4. We could also use either function attributes or parameter attributes to denote these should not be null (for users/callers) and perhaps still check for non-null explicitly under some yet to be discussed hardening configurations in the future. Link: #60481 Link: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-nonnull-function-attribute

lntue · 2024-09-19T20:56:22Z

Turns out the problems are from extra extern inline definitions of libc functions in the system headers when building with gcc. Those inclusions are guarded by __USE_FORTIFY_LEVEL and __USE_EXTERN_INLINES, which are in turn guarded by: _FORTIFY_SOURCE and __NO_INLINE__ / __OPTIMIZE__.

A solution for this issue is:

Divert all those header inclusions to proxy headers
Update the guards before and after including those system headers in overlay mode with something like:

#ifdef _FORTIFY_SOURCE
#define LIBC_OLD_FORTIFY_SOURCE _FORTIFY_SOURCE
#undef _FORTIFY_SOURCE
#endif

#ifndef __NO_INLINE__
#define __NO_INLINE__ 1
#define LIBC_SET_NO_INLINE
#endif

#include <stdio.h>

#ifdef LIBC_OLD_FORTIFY_SOURCE
#define _FORTIFY_SOURCE LIBC_OLD_FORTIFY_SOURCE
#undef LIBC_OLD_FORTIFY_SOURCE
#endif

#ifdef LIBC_SET_NO_INLINE
#undef __NO_INLINE__
#undef LIBC_SET_NO_INLINE
#endif

List of headers having __USE_FORTIFY_LEVEL:

/usr/include/fcntl.h
/usr/include/mqueue.h
/usr/include/setjmp.h
/usr/include/stdio.h
/usr/include/stdlib.h
/usr/include/string.h
/usr/include/strings.h
/usr/include/unistd.h
/usr/include/wchar.h

List of headers having __USE_EXTERN_INLINES:

/usr/include/argp.h
/usr/include/argz.h
/usr/include/ctype.h
/usr/include/pthread.h
/usr/include/stdio.h
/usr/include/stdlib.h
/usr/include/threads.h
/usr/include/wchar.h

Also protect against extern inline function definitions added when building with gcc: #60481.

…110067) #60481

…#110067) llvm/llvm-project#60481

…lvm#110067) llvm#60481

RossComputerGuy · 2024-12-05T21:24:30Z

I've ran into this same problem recently with a couple different files:

libc> FAILED: src/fcntl/linux/CMakeFiles/libc.src.fcntl.linux.openat.dir/openat.cpp.o
libc> /nix/store/2r2xi5pbg29bsmqywsm5zgl8l7adky4i-gcc-wrapper-13.3.0/bin/g++ -DLIBC_NAMESPACE=__llvm_libc -D_DEBUG -I/build/libc-src-20.0.0-unstable-2024-12-05/libc -isystem /build/libc-src-20.0.0-unstable-2024-12-05/libc/build/include -g -std=gnu++17 -DLIBC_QSORT_IMPL=LIBC_QSORT_QUICK_SORT -DLIBC_ADD_NULL_CHECKS -DLIBC_COPT_PUBLIC_PACKAGING -MD -MT src/fcntl/linux/CMakeFiles/libc.src.fcntl.linux.openat.dir/openat.cpp.o -MF src/fcntl/linux/CMakeFiles/libc.src.fcntl.linux.openat.dir/openat.cpp.o.d -o src/fcntl/linux/CMakeFiles/libc.src.fcntl.linux.openat.dir/openat.cpp.o -c /build/libc-src-20.0.0-unstable-2024-12-05/libc/src/fcntl/linux/openat.cpp
libc> In file included from /build/libc-src-20.0.0-unstable-2024-12-05/libc/src/__support/OSUtil/linux/syscall.h:13,
libc>                  from /build/libc-src-20.0.0-unstable-2024-12-05/libc/src/__support/OSUtil/syscall.h:15,
libc>                  from /build/libc-src-20.0.0-unstable-2024-12-05/libc/src/fcntl/linux/openat.cpp:11:
libc> /build/libc-src-20.0.0-unstable-2024-12-05/libc/src/fcntl/linux/openat.cpp:22:25: error: 'int __llvm_libc::openat(int, const char*, int, ...)' aliased to external symbol 'openat'
libc>    22 | LLVM_LIBC_FUNCTION(int, openat, (int dfd, const char *path, int flags, ...)) {
libc>       |                         ^~~~~~
libc> /build/libc-src-20.0.0-unstable-2024-12-05/libc/src/__support/common.h:46:34: note: in definition of macro 'LLVM_LIBC_FUNCTION_IMPL'
libc>    46 |   decltype(LIBC_NAMESPACE::name) name [[gnu::alias(#name)]];                   \
libc>       |                                  ^~~~
libc> /build/libc-src-20.0.0-unstable-2024-12-05/libc/src/fcntl/linux/openat.cpp:22:1: note: in expansion of macro 'LLVM_LIBC_FUNCTION'
libc>    22 | LLVM_LIBC_FUNCTION(int, openat, (int dfd, const char *path, int flags, ...)) {
libc>       | ^~~~~~~~~~~~~~~~~~
libc> FAILED: src/fcntl/linux/CMakeFiles/libc.src.fcntl.linux.open.dir/open.cpp.o
libc> /nix/store/2r2xi5pbg29bsmqywsm5zgl8l7adky4i-gcc-wrapper-13.3.0/bin/g++ -DLIBC_NAMESPACE=__llvm_libc -D_DEBUG -I/build/libc-src-20.0.0-unstable-2024-12-05/libc -isystem /build/libc-src-20.0.0-unstable-2024-12-05/libc/build/include -g -std=gnu++17 -DLIBC_QSORT_IMPL=LIBC_QSORT_QUICK_SORT -DLIBC_ADD_NULL_CHECKS -DLIBC_COPT_PUBLIC_PACKAGING -MD -MT src/fcntl/linux/CMakeFiles/libc.src.fcntl.linux.open.dir/open.cpp.o -MF src/fcntl/linux/CMakeFiles/libc.src.fcntl.linux.open.dir/open.cpp.o.d -o src/fcntl/linux/CMakeFiles/libc.src.fcntl.linux.open.dir/open.cpp.o -c /build/libc-src-20.0.0-unstable-2024-12-05/libc/src/fcntl/linux/open.cpp
libc> In file included from /build/libc-src-20.0.0-unstable-2024-12-05/libc/src/__support/OSUtil/linux/syscall.h:13,
libc>                  from /build/libc-src-20.0.0-unstable-2024-12-05/libc/src/__support/OSUtil/syscall.h:15,
libc>                  from /build/libc-src-20.0.0-unstable-2024-12-05/libc/src/fcntl/linux/open.cpp:11:
libc> /build/libc-src-20.0.0-unstable-2024-12-05/libc/src/fcntl/linux/open.cpp:23:25: error: 'int __llvm_libc::open(const char*, int, ...)' aliased to external symbol 'open'
libc>    23 | LLVM_LIBC_FUNCTION(int, open, (const char *path, int flags, ...)) {
libc>       |                         ^~~~
libc> /build/libc-src-20.0.0-unstable-2024-12-05/libc/src/__support/common.h:46:34: note: in definition of macro 'LLVM_LIBC_FUNCTION_IMPL'
libc>    46 |   decltype(LIBC_NAMESPACE::name) name [[gnu::alias(#name)]];                   \
libc>       |                                  ^~~~
libc> /build/libc-src-20.0.0-unstable-2024-12-05/libc/src/fcntl/linux/open.cpp:23:1: note: in expansion of macro 'LLVM_LIBC_FUNCTION'
libc>    23 | LLVM_LIBC_FUNCTION(int, open, (const char *path, int flags, ...)) {
libc>       | ^~~~~~~~~~~~~~~~~~

github-actions bot added the new issue label Feb 2, 2023

EugeneZelenko added build-problem libc and removed new issue labels Feb 2, 2023

DavidSpickett mentioned this issue Feb 6, 2023

Failed to build llvm libc 14.0.5 on Oracle Ampere A1 Arm with GCC 8.5.0 #60473

Closed

sivachandra self-assigned this Feb 28, 2023

erkinalp mentioned this issue May 29, 2023

Standard library function re-aliasing error #62991

Closed

nickdesaulniers unassigned sivachandra Feb 12, 2024

DavidSpickett changed the title ~~__llvm_libc::bsearch() aliased to external symbol 'bsearch'~~ Release overlay GCC build fails with "aliased to external symbol" Apr 17, 2024

nickdesaulniers mentioned this issue Apr 17, 2024

building 18.1.4 with libc issue #89132

Closed

This was referenced Apr 18, 2024

[libc][docs] add note on gcc overlay release build #89314

Closed

[libc] Move from alias(X) to asm(X) for aliasing #89333

Closed

nickdesaulniers mentioned this issue Apr 19, 2024

[libc] don't over include stdlib in the hdr declaring bsearch #89471

Merged

nickdesaulniers mentioned this issue Apr 19, 2024

[clang][alias fn attr] error: alias must point to a defined variable or function false negative when optimizations are enabled #89474

Open

lntue mentioned this issue Sep 19, 2024

[libc][wchar] Move wchar's types to proxy headers. #109334

Merged

lntue added a commit that referenced this issue Sep 20, 2024

[libc][wchar] Move wchar's types to proxy headers. (#109334)

95d4c97

Also protect against extern inline function definitions added when building with gcc: #60481.

lntue mentioned this issue Sep 26, 2024

[libc][stdio] Use proxy headers of stdio.h in src and test folders. #110067

Merged

lntue added a commit that referenced this issue Oct 1, 2024

[libc][stdio] Use proxy headers of stdio.h in src and test folders. (#…

c63112a

…110067) #60481

puja2196 pushed a commit to puja2196/LLVM-tutorial that referenced this issue Oct 2, 2024

[libc][stdio] Use proxy headers of stdio.h in src and test folders. (…

d6c84ef

…#110067) llvm/llvm-project#60481

VitaNuo pushed a commit to VitaNuo/llvm-project that referenced this issue Oct 2, 2024

[libc][stdio] Use proxy headers of stdio.h in src and test folders. (l…

c3f8c57

…lvm#110067) llvm#60481

VitaNuo pushed a commit to VitaNuo/llvm-project that referenced this issue Oct 2, 2024

[libc][stdio] Use proxy headers of stdio.h in src and test folders. (l…

6cf4d4d

…lvm#110067) llvm#60481

Sterling-Augustine pushed a commit to Sterling-Augustine/llvm-project that referenced this issue Oct 3, 2024

[libc][stdio] Use proxy headers of stdio.h in src and test folders. (l…

9e529de

…lvm#110067) llvm#60481

xgupta pushed a commit to xgupta/llvm-project that referenced this issue Oct 4, 2024

[libc][stdio] Use proxy headers of stdio.h in src and test folders. (l…

148f020

…lvm#110067) llvm#60481

nickdesaulniers mentioned this issue Dec 9, 2024

[libc] gcc build failures on github action runners #119266

Closed

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Release overlay GCC build fails with "aliased to external symbol" #60481

Release overlay GCC build fails with "aliased to external symbol" #60481

liam-clink commented Feb 2, 2023 •

edited by VoltrexKeyva

Loading

llvmbot commented Feb 2, 2023

DavidSpickett commented Feb 3, 2023

sivachandra commented Feb 3, 2023

sivachandra commented Feb 3, 2023

mikhailramalho commented Feb 28, 2023

erkinalp commented May 29, 2023 •

edited

Loading

nickdesaulniers commented Apr 17, 2024

nickdesaulniers commented Apr 19, 2024

nickdesaulniers commented Apr 19, 2024

lntue commented Sep 19, 2024

RossComputerGuy commented Dec 5, 2024

Release overlay GCC build fails with "aliased to external symbol" #60481

Release overlay GCC build fails with "aliased to external symbol" #60481

Comments

liam-clink commented Feb 2, 2023 • edited by VoltrexKeyva Loading

llvmbot commented Feb 2, 2023

DavidSpickett commented Feb 3, 2023

sivachandra commented Feb 3, 2023

sivachandra commented Feb 3, 2023

mikhailramalho commented Feb 28, 2023

erkinalp commented May 29, 2023 • edited Loading

nickdesaulniers commented Apr 17, 2024

nickdesaulniers commented Apr 19, 2024

nickdesaulniers commented Apr 19, 2024

lntue commented Sep 19, 2024

RossComputerGuy commented Dec 5, 2024

liam-clink commented Feb 2, 2023 •

edited by VoltrexKeyva

Loading

erkinalp commented May 29, 2023 •

edited

Loading