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gh-127604: Optimize -ldl usage on platforms that use dlopen for libFFI. #133081

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Merged
merged 2 commits into from
Apr 30, 2025
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gh-127604: Optimize -ldl usage on platforms that use dlopen for libFFI. #133081

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297f242
Optimize -ldl usage on platforms that use dlopen for libFFI.
freakboy3742 Apr 28, 2025
f6a117a
Rework addition of -ldl.
freakboy3742 Apr 29, 2025
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213 changes: 112 additions & 101 deletions configure
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25 changes: 16 additions & 9 deletions configure.ac
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Original file line number Diff line number Diff line change
Expand Up @@ -2985,15 +2985,6 @@ AC_CHECK_HEADERS([ \
AC_HEADER_DIRENT
AC_HEADER_MAJOR

# for faulthandler
AC_CHECK_HEADERS([execinfo.h link.h dlfcn.h], [
AC_CHECK_FUNCS([backtrace dladdr1], [
# dladdr1 requires -ldl
ac_cv_require_ldl=yes
])
])
AS_VAR_IF([ac_cv_require_ldl], [yes], [AS_VAR_APPEND([LDFLAGS], [" -ldl"])])

# bluetooth/bluetooth.h has been known to not compile with -std=c99.
# http://permalink.gmane.org/gmane.linux.bluez.kernel/22294
SAVE_CFLAGS=$CFLAGS
Expand Down Expand Up @@ -3715,6 +3706,22 @@ AC_CHECK_LIB([dl], [dlopen]) # Dynamic linking for SunOS/Solaris and SYSV
AC_CHECK_LIB([dld], [shl_load]) # Dynamic linking for HP-UX


dnl for faulthandler
AC_CHECK_HEADERS([execinfo.h link.h dlfcn.h], [
AC_CHECK_FUNCS([backtrace dladdr1], [
# dladdr1 requires -ldl
ac_cv_require_ldl=yes
])
])

dnl only add -ldl to LDFLAGS if it isn't already part of LIBS (GH-133081)
AS_VAR_IF([ac_cv_require_ldl], [yes], [
AS_VAR_IF([ac_cv_lib_dl_dlopen], [yes], [], [
AS_VAR_APPEND([LDFLAGS], [" -ldl"])
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Would autoconf be smart enough if we were to just use AC_CHECK_LIB for dladdr1 as we did for dlopen in that it wouldn't readd the -ldl flag or is it the only way to write these extra checks?

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Honestly, I don't know - I know enough autoconf to get by, but not much more.

Unfortunately, I don't have ready access to a development platform that would use the dladdr1 check (at least, I don't think I do), so it's difficult for me to experiment with this.

My concern would be whether it would add the flag to LIBS or LDFLAGS though - if it's added to LIBS, we'll be back in the same situation as before. Based on what I'm seeing in other AC_CHECK_LIB usage, it looks like it would get added to LIBS by default, and any strategy that got it into LDFLAGS would essentially be no better than AS_VAR_APPEND.

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I see. Let's keep it that way (it works, it's a bit fragile, but we'll manage if there are issues in the future)

])
])


dnl check for uuid dependencies
AH_TEMPLATE([HAVE_UUID_H], [Define to 1 if you have the <uuid.h> header file.])
AH_TEMPLATE([HAVE_UUID_UUID_H], [Define to 1 if you have the <uuid/uuid.h> header file.])
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