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authorAndrew Burgess <aburgess@redhat.com>2022-01-10 17:17:23 +0000
committerAndrew Burgess <aburgess@redhat.com>2022-01-13 10:25:45 +0000
commit4b74833d1a27478968e4179a8217521315fa9331 (patch)
treee25bad83e99d2a93846dd366494930469f961127 /gdbsupport/acinclude.m4
parent993248f4439271d7d5d3b504b851043af7495c25 (diff)
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gdb: don't use -Wmissing-prototypes with g++
This commit aims to not make use of -Wmissing-prototypes when compiling with g++. Use of -Wmissing-prototypes was added with this commit: commit a0761e34f054767de6d6389929d27e9015fb299b Date: Wed Mar 11 15:15:12 2020 -0400 gdb: enable -Wmissing-prototypes warning Because clang can provide helpful warnings with this flag. Unfortunately, g++ doesn't accept this flag, and will give this warning: cc1plus: warning: command line option ‘-Wmissing-prototypes’ is valid for C/ObjC but not for C++ In theory the fact that this flag is not supported should be detected by the configure check in gdbsupport/warning.m4, but for users of ccache, this check doesn't work due to a long standing ccache issue: https://github.com/ccache/ccache/issues/738 The ccache problem is that -W... options are reordered on the command line, and so -Wmissing-prototypes is seen before -Werror. Usually this doesn't matter, but the above warning (about the flag not being valid) is issued before the -Werror flag is processed, and so is not fatal. There have been two previous attempts to fix this that I'm aware of. The first is: https://sourceware.org/pipermail/gdb-patches/2021-September/182148.html In this attempt, instead of just relying on a compile to check if a flag is valid, the proposal was to both compile and link. As linking doesn't go through ccache, we don't suffer from the argument reordering problem, and the link phase will correctly fail when using -Wmissing-prototypes with g++. The configure script will then disable the use of this flag. This approach was rejected, and the suggestion was to only add the -Wmissing-prototypes flag if we are compiling with gcc. The second attempt, attempts this approach, and can be found here: https://sourceware.org/pipermail/gdb-patches/2021-November/183076.html This attempt only adds the -Wmissing-prototypes flag is the value of GCC is not 'yes'. This feels like it is doing the right thing, unfortunately, the GCC flag is really a 'is gcc like' flag, not a strict, is gcc check. As such, GCC is set to 'yes' for clang, which would mean the flag was not included for clang or gcc. The entire point of the original commit was to add this flag for clang, so clearly the second attempt is not sufficient either. In this new attempt I have added gdbsupport/compiler-type.m4, this file defines AM_GDB_COMPILER_TYPE. This macro sets the variable GDB_COMPILER_TYPE to either 'gcc', 'clang', or 'unknown'. In future the list of values might be extended to cover other compilers, if this is ever useful. I've then modified gdbsupport/warning.m4 to only add the problematic -Wmissing-prototypes flag if GDB_COMPILER_TYPE is not 'gcc'. I've tested this with both gcc and clang and see the expected results, gcc no longer attempts to use the -Wmissing-prototypes flag, while clang continues to use it. When compiling using ccache, I am no longer seeing the warning.
Diffstat (limited to 'gdbsupport/acinclude.m4')
-rw-r--r--gdbsupport/acinclude.m43
1 files changed, 3 insertions, 0 deletions
diff --git a/gdbsupport/acinclude.m4 b/gdbsupport/acinclude.m4
index cc9c2dc..c627614 100644
--- a/gdbsupport/acinclude.m4
+++ b/gdbsupport/acinclude.m4
@@ -6,5 +6,8 @@ m4_include([../gdb/libiberty.m4])
m4_include([selftest.m4])
m4_include([ptrace.m4])
+dnl This gets AM_GDB_COMPILER_TYPE.
+m4_include(compiler-type.m4)
+
dnl This gets AM_GDB_WARNINGS.
m4_include(warning.m4)