[musl] Questions on commit 98e688a9da5e7b2925dda17a2d6820dddf1fb287

[musl] Questions on commit 98e688a9da5e7b2925dda17a2d6820dddf1fb287

[puwenxu]

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Dear maintainer,
       As you can see in the pictures, the commit 98e688a9da5e7b2925dda17a2d6820dddf1fb287 modified the codes related to macro __cpluscplus.
[cid:image005.png@01D8EB1B.83A5DFC0]
During my usage of musl, I found that if the macro __cplusplus had not been defined, the compilation will fail, and report error on __cplusplus. I am very puzzled about this commit, I think this modification doesn't take the condition that the __cplusplus hasn't been defined into consideration. I'm eager to know why.
       In order to continue my job immediately, I modify the codes like the picture below. As far as I'm concerned, before using __cpluscplus, we should judge whether it has been defined. Attached is my full patch.
[cid:image006.png@01D8EB1B.83A5DFC0]
I'm looking forward to your reply.

Wish Pu
OS kernel lab

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From debcca71d9c19481abdb54b58b4e4de70e6c2cd0 Mon Sep 17 00:00:00 2001
From: p00670060 <puwenxu1@huawei.com>
Date: Fri, 28 Oct 2022 12:08:07 +0800
Subject: [PATCH] musl: Upgrade musl

HongMeng inclusion
DTS/AR: AR.SR.IREQ02850018.001.002
TestPolicyOwner: Wu Wenguo <wuwenguo@huawei.com>
CVE: NA
TestCase: This is a commit no need test

--------

Signed-off-by: Pu Wenxu <puwenxu1@huawei.com>
---
 include/locale.h | 2 +-
 include/stddef.h | 2 +-
 include/stdio.h  | 2 +-
 include/stdlib.h | 2 +-
 include/string.h | 2 +-
 include/time.h   | 2 +-
 include/unistd.h | 2 +-
 include/wchar.h  | 2 +-
 8 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/include/locale.h b/include/locale.h
index 959d0605..9b1b3054 100644
--- a/include/locale.h
+++ b/include/locale.h
@@ -8,7 +8,7 @@ extern "C" {
 #include <features.h>
 
 #ifndef NULL
-#if __cplusplus >= 201103L
+#if defined(__cplusplus) &&  __cplusplus >= 201103L
 #define NULL nullptr
 #elif defined(__cplusplus)
 #define NULL 0L
diff --git a/include/stddef.h b/include/stddef.h
index 7aeed3f7..30876221 100644
--- a/include/stddef.h
+++ b/include/stddef.h
@@ -2,7 +2,7 @@
 #define _STDDEF_H
 
 #ifndef NULL
-#if __cplusplus >= 201103L
+#if defined(__cplusplus) && __cplusplus >= 201103L
 #define NULL nullptr
 #elif defined(__cplusplus)
 #define NULL 0L
diff --git a/include/stdio.h b/include/stdio.h
index cf0980c8..fc761038 100644
--- a/include/stdio.h
+++ b/include/stdio.h
@@ -26,7 +26,7 @@ extern "C" {
 #include <bits/alltypes.h>
 
 #ifndef NULL
-#if __cplusplus >= 201103L
+#if defined(__cplusplus) && __cplusplus >= 201103L
 #define NULL nullptr
 #elif defined(__cplusplus)
 #define NULL 0L
diff --git a/include/stdlib.h b/include/stdlib.h
index 3fc5f58d..f50dee40 100644
--- a/include/stdlib.h
+++ b/include/stdlib.h
@@ -8,7 +8,7 @@ extern "C" {
 #include <features.h>
 
 #ifndef NULL
-#if __cplusplus >= 201103L
+#if defined(__cplusplus) && __cplusplus >= 201103L
 #define NULL nullptr
 #elif defined(__cplusplus)
 #define NULL 0L
diff --git a/include/string.h b/include/string.h
index 0f0ef4b4..0701d728 100644
--- a/include/string.h
+++ b/include/string.h
@@ -8,7 +8,7 @@ extern "C" {
 #include <features.h>
 
 #ifndef NULL
-#if __cplusplus >= 201103L
+#if defined(__cplusplus) && __cplusplus >= 201103L
 #define NULL nullptr
 #elif defined(__cplusplus)
 #define NULL 0L
diff --git a/include/time.h b/include/time.h
index a76a3962..d08f568a 100644
--- a/include/time.h
+++ b/include/time.h
@@ -8,7 +8,7 @@ extern "C" {
 #include <features.h>
 
 #ifndef NULL
-#if __cplusplus >= 201103L
+#if defined(__cplusplus) && __cplusplus >= 201103L
 #define NULL nullptr
 #elif defined(__cplusplus)
 #define NULL 0L
diff --git a/include/unistd.h b/include/unistd.h
index 25016c64..53099349 100755
--- a/include/unistd.h
+++ b/include/unistd.h
@@ -18,7 +18,7 @@ extern "C" {
 #define SEEK_HOLE 4
 
 #ifndef NULL
-#if __cplusplus >= 201103L
+#if defined(__cplusplus) && __cplusplus >= 201103L
 #define NULL nullptr
 #elif defined(__cplusplus)
 #define NULL 0L
diff --git a/include/wchar.h b/include/wchar.h
index 31aa7d1d..115993d1 100644
--- a/include/wchar.h
+++ b/include/wchar.h
@@ -39,7 +39,7 @@ extern "C" {
 #endif
 
 #ifndef NULL
-#if __cplusplus >= 201103L
+#if defined(__cplusplus) && __cplusplus >= 201103L
 #define NULL nullptr
 #elif defined(__cplusplus)
 #define NULL 0L
-- 
2.22.0

Re: [musl] Questions on commit 98e688a9da5e7b2925dda17a2d6820dddf1fb287

[Rich Felker]

On Fri, Oct 28, 2022 at 02:20:50PM +0000, puwenxu wrote:
> Dear maintainer,
>        As you can see in the pictures, the commit 98e688a9da5e7b2925dda17a2d6820dddf1fb287 modified the codes related to macro __cpluscplus.
> [cid:image005.png@01D8EB1B.83A5DFC0]
> During my usage of musl, I found that if the macro __cplusplus had
> not been defined, the compilation will fail, and report error on
> __cplusplus. I am very puzzled about this commit, I think this
> modification doesn't take the condition that the __cplusplus hasn't
> been defined into consideration. I'm eager to know why.

Because the definition of how the preprocessor works is that
identifiers without definitions expand to the token 0.

You didn't include any information about your compilation environment,
so it sounds like either:

- you have a buggy compiler that doesn't honor the language spec
  (unlikely), or

- you have enabled a warning that doesn't like this expansion, have
  told the compiler to treat warnings as errors, and are using a weird
  compiler invocation where it's not aware that this is a system
  header (since normally compilers suppress such warnings for system
  headers).

Since it's probably the latter, I would recommend trying to figure out
what's wrong with your compiler invocation, since it could indicate
that you're trying to use musl with a compiler toolchain targeting a
different libc, which could have all sorts of other hidden problems
you haven't seen yet.

Rich