https://github.com/wzssyqa created https://github.com/llvm/llvm-project/pull/120526
The limits.h of glibc, aka /usr/include/limits.h file of *-linux-gnu systems, has `#include_next <limits.h>`, so the limits.h from clang is included. And in the limits.h for clang, `#include_next <limits.h>` is also used. Normally it won't be a problem as the headers is protected by something like _LIBC_LIMITS_H_, while it may be a problem when we cross-build glibc on a none glibc platform. For example if we build glibc for x86_64-linux-gnu on a x86_64-linux-musl platform. To test it, we can do ``` echo "#include </usr/include/limits.h>" | bin/clang -E -O2 -xc - -MM -H ``` We can see there is ``` . /usr/include/limits.h .. /usr/lib/llvm-19/lib/clang/19/include/limits.h ... /usr/include/limits.h ``` >From a7e475b01b73c66965403330f6ad377b32e13e74 Mon Sep 17 00:00:00 2001 From: YunQiang Su <yunqi...@isrc.iscas.ac.cn> Date: Thu, 19 Dec 2024 14:09:04 +0800 Subject: [PATCH] clang/limits.h: Avoid including limits.h twice The limits.h of glibc, aka /usr/include/limits.h file of *-linux-gnu systems, has `#include_next <limits.h>`, so the limits.h from clang is included. And in the limits.h for clang, `#include_next <limits.h>` is also used. Normally it won't be a problem as the headers is protected by something like _LIBC_LIMITS_H_, while it may be a problem when we cross-build glibc on a none glibc platform. For example if we build glibc for x86_64-linux-gnu on a x86_64-linux-musl platform. To test it, we can do ``` echo "#include </usr/include/limits.h>" | bin/clang -E -O2 -xc - -MM -H ``` We can see there is ``` . /usr/include/limits.h .. /usr/lib/llvm-19/lib/clang/19/include/limits.h ... /usr/include/limits.h ``` --- clang/lib/Headers/limits.h | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/clang/lib/Headers/limits.h b/clang/lib/Headers/limits.h index d08227fe4d3d48..90f01791f857ee 100644 --- a/clang/lib/Headers/limits.h +++ b/clang/lib/Headers/limits.h @@ -20,8 +20,9 @@ #endif /* System headers include a number of constants from POSIX in <limits.h>. - Include it if we're hosted. */ -#if __STDC_HOSTED__ && __has_include_next(<limits.h>) + Include it if we're hosted. The limits.h of glibc uses include_next to + include us, we shouldn't include it again. */ +#if __STDC_HOSTED__ && __has_include_next(<limits.h>) && !defined(_LIBC_LIMITS_H_) #include_next <limits.h> #endif _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
