Re: Compile error on the aarch64 platform: Missing asm/hwcap.h - Mailing list pgsql-hackers

Hi, John,  Thomas, 

IvorySQL team found the same build issue on our building machine when we built IvorySQL code which is based on PG 18.0. 

pg_crc32c_armv8_choose.c:58:32:error:'HWCAP CRC32' undeclared(first use in this function)

    58 | return (getauxval(AT_HWCAP) & HWCAP_CRC32) != θ;

          |                                                                     ^~~~~~~~~~~

Then we tried to build source code of PG 18.1 and got the same failure result. 

 I made some investigation to test the following code in src/port/pg_crc32c_armv8_choose.c

+#if defined(HAVE_ELF_AUX_INFO) || defined(HAVE_GETAUXVAL)

+#include <sys/auxv.h>

+#if defined(__linux__) && !defined(__aarch64__) && !defined(HWCAP2_CRC32)

+#include <asm/hwcap.h>

+#endif

// 1. Test defined(HAVE_ELF_AUX_INFO) || defined(HAVE_GETAUXVAL)

// Got #warning "CONDITION IS FALSE"

echo '#if defined(HAVE_ELF_AUX_INFO) || defined(HAVE_GETAUXVAL)

    #warning "CONDITION IS TRUE"

    #else

    #warning "CONDITION IS FALSE"

    #endif' | gcc -E -x c - -o -

// 2. Test defined(__linux__) 

// Got true

echo '#if defined(__linux__)

    #warning "CONDITION IS TRUE"

    #else

    #warning "CONDITION IS FALSE"

    #endif' | gcc -E -x c - -o -

// 3. Test !defined(__aarch64__) 

// Got false

echo '#if !defined(__aarch64__)

    #warning "CONDITION IS TRUE"

    #else

    #warning "CONDITION IS FALSE"

    #endif' | gcc -E -x c - -o -

// Test  !defined(HWCAP2_CRC32)

// Got true 

echo '#if !defined(HWCAP2_CRC32)

    #warning "CONDITION IS TRUE"

    #else

    #warning "CONDITION IS FALSE"

    #endif' | gcc -E -x c - -o -

So, my question is, why we exclude __aarch64__ in the second #if condition? 

Thanks,

Steven

On Fri, Nov 14, 2025 at 11:02 AM 高增琦 <pgf00a@gmail.com> wrote:
> Compile error on CentOS Linux release 7.6.1810 (AltArch) with the message “‘HWCAP_CRC32’ undeclared”.

We still have at least one CentOS 7 aarch64 machine that gets regular
testing (not sure of the reason, since it's been EOL for a year and a
half IIUC), and it builds fine:

https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=arowana&dt=2025-11-04%2004%3A56%3A57

> After modifying the code to add `include <asm/hwcap.h>`, the compilation succeeded.

We already have the following, so I'm not sure what you mean (or even
what architecture you're running on):

#if defined(HAVE_ELF_AUX_INFO) || defined(HAVE_GETAUXVAL)
#include <sys/auxv.h>
#if defined(__linux__) && !defined(__aarch64__) && !defined(HWCAP2_CRC32)
#include <asm/hwcap.h>
#endif
#endif

--
John Naylor
Amazon Web Services