[musl] Question about flexible array

[樊鹏 <fanpeng@loongson.cn>]

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hi,

In arch/loongarch64/bits/signal.h, I got some compiling errors about flexible array:

In file included from /usr/include/signal.h:48,
                 from /usr/include/ucontext.h:9,
                 from /home/alpine/aports/community/onetbb/src/oneTBB-2021.12.0/python/rml/../../src/tbb/co_context.h:52,
                 from /home/alpine/aports/community/onetbb/src/oneTBB-2021.12.0/python/rml/../../src/tbb/scheduler_common.h:27,
                 from /home/alpine/aports/community/onetbb/src/oneTBB-2021.12.0/python/rml/ipc_server.cpp:23:
/usr/include/bits/signal.h:35:23: error: flexible array member 'mcontext_t::__extcontext' not at end of 'struct tbb::detail::r1::coroutine_type'
   35 |         unsigned long __extcontext[] __attribute__((__aligned__(16)));
      |                       ^~~~~~~~~~~~
compilation terminated due to -Wfatal-errors.
ninja: subcommand failed
>>> ERROR: onetbb: build failed


The reason is a difference between gcc and g++:

Flexible array members are not officially part of C++.
Flexible array members were officially standardized in C99.

If *.cpp includes this header file, it may result in an error. I suggest to change it to size-zero array format.

Meanwhile, you can also consider the patch I attached.
Your opinions are welcome.

Thanks.

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diff --git a/arch/loongarch64/bits/signal.h b/arch/loongarch64/bits/signal.h
index 5a9ed8c9..cefa9a61 100644
--- a/arch/loongarch64/bits/signal.h
+++ b/arch/loongarch64/bits/signal.h
@@ -24,7 +24,7 @@ struct sigcontext {
 	unsigned long sc_pc;
 	unsigned long sc_regs[32];
 	unsigned sc_flags;
-	unsigned long sc_extcontext[] __attribute__((__aligned__(16)));
+	unsigned long sc_extcontext[0] __attribute__((__aligned__(16)));
 };
 #endif
 
@@ -32,7 +32,7 @@ typedef struct {
 	unsigned long __pc;
 	unsigned long __gregs[32];
 	unsigned __flags;
-	unsigned long __extcontext[] __attribute__((__aligned__(16)));
+	unsigned long __extcontext[0] __attribute__((__aligned__(16)));
 } mcontext_t;
 
 struct sigaltstack {