From: Viktor Szakats <commit@vsz.me>
Date: Mon, 13 Nov 2023 00:02:45 +0000 (+0000)
Subject: autotools: avoid passing `LDFLAGS` twice to libcurl
X-Git-Tag: curl-8_5_0~99
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=444f64b3e93bbb0b6a65ffa10c5bb3d1becfc140;p=thirdparty%2Fcurl.git

autotools: avoid passing `LDFLAGS` twice to libcurl

autotools passes `LDFLAGS` automatically linker commands. curl's
`lib/Makefile.am` customizes libcurl linker flags. In that
customization, it added `LDFLAGS` to the custom flags. This resulted in
passing `LDFLAGS` _twice_ to the `libtool` command.

Most of the time this is benign, but some `LDFLAGS` options can break
the build when passed twice. One such example is passing `.o` files,
e.g. `crt*.o` files necessary when customizing the C runtime, e.g. for
MUSL builds.

Passing them twice resulted in duplicate symbol errors:
```
libtool: link:  clang-15 --target=aarch64-unknown-linux-musl [...] /usr/lib/aarch64-linux-musl/crt1.o [...] /usr/lib/aarch64-linux-musl/crt1.o [...]
ld.lld-15: error: duplicate symbol: _start
>>> defined at crt1.c
>>>            /usr/lib/aarch64-linux-musl/crt1.o:(.text+0x0)
>>> defined at crt1.c
>>>            /usr/lib/aarch64-linux-musl/crt1.o:(.text+0x0)
[...]
clang: error: linker command failed with exit code 1 (use -v to see invocation)
```

This behaviour came with commit 1a593191c2769a47b8c3e4d9715ec9f6dddf5e36
(2013-07-23) as a fix for bug https://curl.haxx.se/bug/view.cgi?id=1217.
The patch was a works-for-me hack that ended up merged in curl:
https://sourceforge.net/p/curl/bugs/1217/#06ef
With the root cause remaining unclear.

Perhaps the SUNPro 12 linker was sensitive to `-L` `-l` order, requiring
`-L` first? This would be unusual and suggests a bug in either the
linker or in `libtool`.

The curl build does pass the list of detected libs via its own
`LIBCURL_LIBS` variable, which ends up before `LDFLAGS` on the `libtool`
command line, but it's the job of `libtool` to ensure that even
a peculiar linker gets the options in the expected order. Also because
autotools passes `LDFLAGS` last, making it hardly possible to pass
anything after it.

Perhaps in the 10 years since this issue, this already got a fix
upstream.

This patch deletes `LDFLAGS` from our customized libcurl options,
leaving a single copy of them as passed by autotools automatically.

Reverts 1a593191c2769a47b8c3e4d9715ec9f6dddf5e36
Closes #12310
---

diff --git a/lib/Makefile.am b/lib/Makefile.am
index cae1deceb0..1237c8e997 100644
--- a/lib/Makefile.am
+++ b/lib/Makefile.am
@@ -110,7 +110,7 @@ libcurl_la_CFLAGS_EXTRA += $(CFLAG_CURL_SYMBOL_HIDING)
 endif
 
 libcurl_la_CPPFLAGS = $(AM_CPPFLAGS) $(libcurl_la_CPPFLAGS_EXTRA)
-libcurl_la_LDFLAGS = $(AM_LDFLAGS) $(libcurl_la_LDFLAGS_EXTRA) $(LDFLAGS) $(CURL_LDFLAGS_LIB) $(LIBCURL_LIBS)
+libcurl_la_LDFLAGS = $(AM_LDFLAGS) $(libcurl_la_LDFLAGS_EXTRA) $(CURL_LDFLAGS_LIB) $(LIBCURL_LIBS)
 libcurl_la_CFLAGS = $(AM_CFLAGS) $(libcurl_la_CFLAGS_EXTRA)
 
 libcurlu_la_CPPFLAGS = $(AM_CPPFLAGS) -DCURL_STATICLIB -DUNITTESTS