Build failure with armv7m/m68k uClibc-ng-1.0.50

[kadambininema]

I did this

Build libcurl under the following environment:
curl version: 8.14.0
Arch - armv7m and m68k
libc - uClibc-ng-1.0.50
Compiler - gcc-13.3.0
OS - Ubuntu

Build fails with the following error:
cf-socket.c: In function 'cf_tcp_accept_connect': cf-socket.c:2141:18: error: implicit declaration of function 'accept4'; did you mean 'accept'? [-Werror=implicit-function-declaration] 2141 | s_accepted = accept4(ctx->sock, (struct sockaddr *) &add, &size,

Additional info:
https://gitlab.com/jolivain/buildroot/-/pipelines/1846597109
https://patchwork.ozlabs.org/project/buildroot/patch/20250530213904.465152-1-kadambini.nema@gmail.com/
3d02872

I expected the following

Successful build

curl/libcurl version

8.14.0

operating system

Ubuntu-24

[bagder]

So how do you build curl and using which options?

[kadambininema]

This error was seen with buildroot test-pkg
$ ./utils/test-pkg -k -c curl.config -p libcurl
bootlin-armv5-uclibc [1/6]: OK
bootlin-armv7-glibc [2/6]: OK
bootlin-armv7m-uclibc [3/6]: FAILED
bootlin-x86-64-musl [4/6]: OK
br-arm-full-static [5/6]: OK
arm-aarch64 [6/6]: OK
6 builds, 0 skipped, 1 build failed, 0 legal-info failed, 0 show-info failed

libcurl configure options
AR="/br-test-pkg/bootlin-armv7m-uclibc/host/bin/arm-linux-gcc-ar" AS="/br-test-pkg/bootlin-armv7m-uclibc/host/bin/arm-linux-as" LD="/br-test-pkg/bootlin-armv7m-uclibc/host/bin/arm-linux-ld" NM="/br-test-pkg/bootlin-armv7m-uclibc/host/bin/arm-linux-gcc-nm" CC="/br-test-pkg/bootlin-armv7m-uclibc/host/bin/arm-linux-gcc" GCC="/br-test-pkg/bootlin-armv7m-uclibc/host/bin/arm-linux-gcc" CPP="/br-test-pkg/bootlin-armv7m-uclibc/host/bin/arm-linux-cpp" CXX="/br-test-pkg/bootlin-armv7m-uclibc/host/bin/arm-linux-g++" FC="/br-test-pkg/bootlin-armv7m-uclibc/host/bin/arm-linux-gfortran" F77="/br-test-pkg/bootlin-armv7m-uclibc/host/bin/arm-linux-gfortran" RANLIB="/br-test-pkg/bootlin-armv7m-uclibc/host/bin/arm-linux-gcc-ranlib" READELF="/br-test-pkg/bootlin-armv7m-uclibc/host/bin/arm-linux-readelf" STRIP="/bin/true" OBJCOPY="/br-test-pkg/bootlin-armv7m-uclibc/host/bin/arm-linux-objcopy" OBJDUMP="/br-test-pkg/bootlin-armv7m-uclibc/host/bin/arm-linux-objdump" AR_FOR_BUILD="/usr/bin/ar" AS_FOR_BUILD="/usr/bin/as" CC_FOR_BUILD="/usr/bin/gcc" GCC_FOR_BUILD="/usr/bin/gcc" CXX_FOR_BUILD="/usr/bin/g++" LD_FOR_BUILD="/usr/bin/ld" CPPFLAGS_FOR_BUILD="-I/br-test-pkg/bootlin-armv7m-uclibc/host/include" CFLAGS_FOR_BUILD="-O2 -I/br-test-pkg/bootlin-armv7m-uclibc/host/include" CXXFLAGS_FOR_BUILD="-O2 -I/br-test-pkg/bootlin-armv7m-uclibc/host/include" LDFLAGS_FOR_BUILD="-L/br-test-pkg/bootlin-armv7m-uclibc/host/lib -Wl,-rpath,/br-test-pkg/bootlin-armv7m-uclibc/host/lib" FCFLAGS_FOR_BUILD="" DEFAULT_ASSEMBLER="/br-test-pkg/bootlin-armv7m-uclibc/host/bin/arm-linux-as" DEFAULT_LINKER="/br-test-pkg/bootlin-armv7m-uclibc/host/bin/arm-linux-ld" CPPFLAGS="-D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64" CFLAGS="-D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -O2 -g0 -Wl,-elf2flt=-r -static" CXXFLAGS="-D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -O2 -g0 -Wl,-elf2flt=-r -static -Wl,-elf2flt=-r -static" LDFLAGS=" -Wl,-elf2flt=-r -static" FCFLAGS=" -O2 -g0 -Wl,-elf2flt=-r -static" FFLAGS=" -O2 -g0 -Wl,-elf2flt=-r -static" PKG_CONFIG="/br-test-pkg/bootlin-armv7m-uclibc/host/bin/pkg-config" STAGING_DIR="/br-test-pkg/bootlin-armv7m-uclibc/host/arm-buildroot-uclinux-uclibcgnueabi/sysroot" INTLTOOL_PERL=/usr/bin/perl ac_cv_lbl_unaligned_fail=yes ac_cv_func_mmap_fixed_mapped=yes ac_cv_func_memcmp_working=yes ac_cv_have_decl_malloc=yes gl_cv_func_malloc_0_nonnull=yes ac_cv_func_malloc_0_nonnull=yes ac_cv_func_calloc_0_nonnull=yes ac_cv_func_realloc_0_nonnull=yes lt_cv_sys_lib_search_path_spec="" ac_cv_c_bigendian=no CONFIG_SITE=/dev/null ./configure --target=arm-buildroot-uclinux-uclibcgnueabi --host=arm-buildroot-uclinux-uclibcgnueabi --build=x86_64-pc-linux-gnu --prefix=/usr --exec-prefix=/usr --sysconfdir=/etc --localstatedir=/var --program-prefix="" --disable-gtk-doc --disable-gtk-doc-html --disable-doc --disable-docs --disable-documentation --with-xmlto=no --with-fop=no --disable-dependency-tracking --enable-ipv6 --disable-nls --enable-static --disable-shared --disable-manual --disable-ntlm --disable-ntlm-wb --with-random=/dev/urandom --disable-curldebug --disable-libcurl-option --disable-ldap --disable-ldaps --enable-threaded-resolver LIBS=-latomic --enable-verbose --without-ssl --without-openssl --without-bearssl --without-gnutls --without-mbedtls --without-wolfssl --disable-ares --without-libidn2 --without-libpsl --without-libssh2 --without-brotli --without-nghttp2 --without-libgsasl --enable-cookies --enable-proxy --enable-websockets --enable-dict --enable-gopher --enable-imap --enable-pop3 --enable-rtsp --enable-smb --enable-smtp --enable-telnet --enable-tftp `

Configuration Report
`configure: Configured to build curl/libcurl:

Host setup: arm-buildroot-uclinux-uclibcgnueabi
Install prefix: /usr
Compiler: /br-test-pkg/bootlin-armv7m-uclibc/host/bin/arm-linux-gcc
CFLAGS: -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -O2 -g0 -Wl,-elf2flt=-r -static -Werror-implicit-function-declaration -Wno-system-headers
CFLAGS extras:
CPPFLAGS: -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64
LDFLAGS: -Wl,-elf2flt=-r -static -L/br-test-pkg/bootlin-armv7m-uclibc/host/bin/../arm-buildroot-uclinux-uclibcgnueabi/sysroot/usr/lib
curl-config:
LIBS: -lz -latomic

curl version: 8.14.0
SSL: no (--with-{openssl,gnutls,mbedtls,wolfssl,schannel,secure-transport,amissl,bearssl,rustls} )
SSH: no (--with-{libssh,libssh2})
zlib: enabled
brotli: no (--with-brotli)
zstd: no (--with-zstd)
GSS-API: no (--with-gssapi)
GSASL: no (--with-gsasl)
TLS-SRP: no (--enable-tls-srp)
resolver: POSIX threaded
IPv6: enabled
Unix sockets: enabled
IDN: no (--with-{libidn2,winidn})
Build docs: no
Build libcurl: Shared=no, Static=yes
Built-in manual: no (--enable-manual)
--libcurl option: no
Verbose errors: enabled (--disable-verbose)
Code coverage: disabled
SSPI: no (--enable-sspi)
ca cert bundle: no
ca cert path:
ca cert embed: no
ca fallback:
LDAP: no (--enable-ldap / --with-ldap-lib / --with-lber-lib)
LDAPS: no (--enable-ldaps)
IPFS/IPNS: enabled
RTSP: enabled
RTMP: no (--with-librtmp)
PSL: no (--with-libpsl)
Alt-svc: enabled (--disable-alt-svc)
Headers API: enabled (--disable-headers-api)
HSTS: no (--enable-hsts)
HTTP1: enabled (internal)
HTTP2: no (--with-nghttp2)
HTTP3: no (--with-ngtcp2 --with-nghttp3, --with-quiche, --with-openssl-quic, --with-msh3)
ECH: no (--enable-ech)
HTTPS RR: no (--enable-httpsrr)
SSLS-EXPORT: no (--enable-ssls-export)
Protocols: dict file ftp gopher http imap ipfs ipns mqtt pop3 rtsp smtp telnet tftp ws
Features: alt-svc AsynchDNS IPv6 Largefile libz threadsafe UnixSockets
`

[bagder]

configure checks for accept4 and curl uses it only if detected and a quick google seems to indicate that uClibc-ng supports it.

Does it work if you just do this?

diff --git a/lib/curl_setup_once.h b/lib/curl_setup_once.h
index c1051e0fae..379d41f09c 100644
--- a/lib/curl_setup_once.h
+++ b/lib/curl_setup_once.h
@@ -95,10 +95,11 @@
 #    endif
 #  endif
 #endif
 
 #ifdef HAVE_SYS_SOCKET_H
+#define _GNU_SOURCE
 #include <sys/socket.h>
 #endif
 
 #include "functypes.h"
 

[vszakats]

@kadambininema Can you post your full ./configure output, and the output of make V=1? Seeing lib/curl_config.h and config.log would also give useful clues.

It's curious that other uclibc jobs pass, e.g. bootlin-m68k-68040-uclibc:
https://gitlab.com/jolivain/buildroot/-/jobs/10212653614

[kadambininema]

configure checks for accept4 and curl uses it only if detected and a quick google seems to indicate that uClibc-ng supports it.

Does it work if you just do this?

diff --git a/lib/curl_setup_once.h b/lib/curl_setup_once.h
index c1051e0fae..379d41f09c 100644
--- a/lib/curl_setup_once.h
+++ b/lib/curl_setup_once.h
@@ -95,10 +95,11 @@

endif

endif

#endif

#ifdef HAVE_SYS_SOCKET_H
+#define _GNU_SOURCE
#include <sys/socket.h>
#endif

#include "functypes.h"

The build failure on bootlin-armv7m-uclibc persists even after applying this patch.
Please see the attached log file.
logfile.txt

[bagder]

@kadambininema so what do you need to do on your platform to use accept4() ? configure detects it fine and documentation seems to say it exists in your libc.

[kadambininema]

curl_config.h

config.log

curl_config.h.txt

[bagder]

Yes, those files show how curl detects accep4 and deems it should use it.

The remaining question is why it doesn't work.

[vszakats]

@kadambininema According to the configure output, CPPFLAGS is missing -D_GNU_SOURCE,
which would be required by uglibc's sys/socket.h to declare accept4(). make V=1 output could
confirm it by showing the compiler command-line.

accept4 detection doesn't rely on the header and this macro, which may cause a build error like this.

But, this should have been fixed by @bagder's patch above.

One more thing to try is passing -D_GNU_SOURCE explicitly via CPPFLAGS, or possibly tweaking
this condition to detect this host platform as Linux:

curl/configure.ac

Lines 595 to 596 in 700b544

	linux*|cygwin*|msys*)
	CPPFLAGS="$CPPFLAGS -D_GNU_SOURCE"

(Another option is to swap AC_CHECK_FUNCS()-based detection to something more comprehensive
and replace check_function_exists() with check_symbol_exists() for CMake. Though this one
can make detection fragile.)

[kadambininema]

@kadambininema According to the configure output, CPPFLAGS is missing -D_GNU_SOURCE, which would be required by uglibc's sys/socket.h to declare accept4(). make V=1 output could confirm it by showing the compiler command-line.

accept4 detection doesn't rely on the header and this macro, which may cause a build error like this.

But, this should have been fixed by @bagder's patch above.

One more thing to try is passing -D_GNU_SOURCE explicitly via CPPFLAGS, or possibly tweaking this condition to detect this host platform as Linux:

curl/configure.ac

Lines 595 to 596 in 700b544
linux*|cygwin*|msys*)
CPPFLAGS="$CPPFLAGS -D_GNU_SOURCE"

(Another option is to swap AC_CHECK_FUNCS()-based detection to something more comprehensive and replace check_function_exists() with check_symbol_exists() for CMake. Though this one can make detection fragile.)

Thank you @vszakats and @bagder . The build is successful after adding -D_GNU_SOURCE in the CFLAGS during configure step.

[vszakats]

If we could figure out where the condition fails, we may merge a fix to make the manual workaround unnecessary.

Does this patch work for you, after dropping the CFLAGS workaround?:

--- a/configure.ac
+++ b/configure.ac
@@ -592,7 +592,7 @@ AM_CONDITIONAL(BUILD_UNITTESTS, test x$supports_unittests = xyes)
 # In order to detect support of sendmmsg() and accept4(), we need to escape the POSIX
 # jail by defining _GNU_SOURCE or <sys/socket.h> will not expose it.
 case $host_os in
-  linux*|cygwin*|msys*)
+  *linux*|cygwin*|msys*)
     CPPFLAGS="$CPPFLAGS -D_GNU_SOURCE"
     ;;
 esac

host_os should be uclinux-uclibcgnueabi in this case.