Error when building from source (Native Build) on Linux Mint: FAILED: ssl/CMakeFiles/ssl.dir/extensions.cc.o

[presentformyfriends]

Followed Native build instructions for Ubuntu (I am running Linux Mint 21.3 Virginia). When I run make chrome-build I get the following:

FAILED: ssl/CMakeFiles/ssl.dir/extensions.cc.o 
/usr/bin/g++ -DBORINGSSL_IMPLEMENTATION -I/home/user/curl-impersonate/build/boringssl/include -Werror -Wformat=2 -Wsign-compare -Wwrite-strings -Wvla -Wshadow -Wtype-limits -ggdb -Wall -fvisibility=hidden -fno-common -Wno-free-nonheap-object -Wimplicit-fallthrough -Wformat-signedness -Wmissing-declarations -fno-exceptions -fno-rtti -O3 -DNDEBUG -fPIC -std=gnu++14 -MD -MT ssl/CMakeFiles/ssl.dir/extensions.cc.o -MF ssl/CMakeFiles/ssl.dir/extensions.cc.o.d -o ssl/CMakeFiles/ssl.dir/extensions.cc.o -c /home/user/curl-impersonate/build/boringssl/ssl/extensions.cc
/home/user/curl-impersonate/build/boringssl/ssl/extensions.cc: In function ‘bool bssl::ssl_set_extension_order(bssl::SSL_HANDSHAKE*)’:
/home/user/curl-impersonate/build/boringssl/ssl/extensions.cc:3374:16: error: ‘ext_index’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
 3374 |     order[idx] = ext_index;
cc1plus: all warnings being treated as errors
[7/56] Building CXX object ssl/CMakeFiles/ssl.dir/ssl_transcript.cc.o
ninja: build stopped: subcommand failed.
make: *** [Makefile:167: /home/user/curl-impersonate/build/boringssl/build/lib/libssl.a] Error 1

Googling the error messages has produced nothing for me.

[sohaib17]

The problem seems to be in the BoringSSL patch

+  while (ext != nullptr) {
+    unsigned ext_index;
+    tls_extension_find(&ext_index, atoi(ext));

unsigned ext_index should be initialized here.

Setting it to unsigned ext_index = 0; in chrome/patches/boringssl.patch:94 worked and build completed successfully but not sure if it is a valid initial value.

[EZaykov]

So it that a correct fix or no? Anyone know?

[Schievel1]

So it that a correct fix or no? Anyone know?

yes it is. -Werror-maybe-initialized is only sometimes a problem. In this case the declared memory for ext_index is only used as a placeholder for tls_extension_find to fill, but the compiler could not figure out if tls_extension_find actually reads the value of ext_index.
Giving it a dummy value just to please the compiler is the correct way to fix this.