(Was: Re: [PATCH] wc: Add AVX2 optimization when counting only lines)
So, it looks like the check for avx2 support is broken - the build broke for me after the update. Seems it is doing a compile check when a link check is necessary.
I was seeing this in my build: src/wc.c: In function 'avx2_supported': src/wc.c:153:13: warning: implicit declaration of function '__get_cpuid_count' [-Wimplicit-function-declaration] if (! __get_cpuid_count (7, 0, &eax, &ebx, &ecx, &edx)) ^ ... src/wc.o: In function `avx2_supported': /.../coreutils/src/wc.c:153: undefined reference to `__get_cpuid_count' collect2: error: ld returned 1 exit status Makefile:9415: recipe for target 'src/wc' failed My config.h has: #define USE_AVX2_WC_LINECOUNT 1 My config.log has: configure:77113: checking if __get_cpuid_count exists configure:77129: gcc -c -g -O2 conftest.c >&5 conftest.c: In function 'main': conftest.c:842:7: warning: implicit declaration of function '__get_cpuid_count' [-Wimplicit-function-declaration] __get_cpuid_count(7, 0, &eax, &ebx, &ecx, &edx); ^ configure:77129: $? = 0 configure:77131: result: yes... So it looks like '__get_cpuid_count' not being declared is just treated as a warning, and so the compile test succeeds. The actual failure happens at link time. Would it be more appropriate to use AC_LINK_IFELSE instead of AC_COMPILE_IFELSE ?
I tried swapping this out (as in the attached patch), and now it correctly omits the #define for USE_AVX2_WC_LINECOUNT, and wc compiles & links properly.
Thanks, Carl
From 4f7e27ae1745331772a835564f868e25ecae070c Mon Sep 17 00:00:00 2001 From: Carl Edquist <edqu...@cs.wisc.edu> Date: Mon, 10 May 2021 05:22:11 -0500 Subject: [PATCH] configure.ac: fix __get_cpuid_count check to catch link failure The test program will compile successfully even if __get_cpuid_count is not declared. The error for the missing symbol will only show up at link time. Thus, use AC_LINK_IFELSE instead of AC_COMPILE_IFELSE. * configure.ac: (__get_cpuid_count check) use C_LINK_IFELSE instead of AC_COMPILE_IFELSE. --- configure.ac | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/configure.ac b/configure.ac index f0fbbd9..f826a4b 100644 --- a/configure.ac +++ b/configure.ac @@ -576,7 +576,7 @@ AM_CONDITIONAL([USE_PCLMUL_CRC32], CFLAGS=$ac_save_CFLAGS AC_MSG_CHECKING([if __get_cpuid_count exists]) -AC_COMPILE_IFELSE( +AC_LINK_IFELSE( [AC_LANG_SOURCE([[ #include <cpuid.h> -- 2.9.0