All compilers are expected to be able to compile to the C99 language standard, +as some C99 features are used in the source code. Microsoft Visual Studio +doesn't fully support C99 so in practice shared code is limited to using C99 +features that it does support.
The minimum accepted version of gcc is 4.8. Older versions will generate a warning by configure and are unlikely to work.
The JDK is currently known to be able to compile with at least version 7.4 of gcc.
diff -r dc343eb0fcf0 -r 98ed47cd114a doc/building.md --- a/doc/building.md Thu May 23 02:36:15 2019 +0200 +++ b/doc/building.md Wed May 22 21:50:16 2019 -0400 @@ -328,6 +328,11 @@ Solaris Oracle Solaris Studio 12.6 (with compiler version 5.15) Windows Microsoft Visual Studio 2017 update 15.9.6 +All compilers are expected to be able to compile to the C99 language standard, +as some C99 features are used in the source code. Microsoft Visual Studio +doesn't fully support C99 so in practice shared code is limited to using C99 +features that it does support. + ### gcc The minimum accepted version of gcc is 4.8. Older versions will generate a warning diff -r dc343eb0fcf0 -r 98ed47cd114a make/autoconf/flags-cflags.m4 --- a/make/autoconf/flags-cflags.m4 Thu May 23 02:36:15 2019 +0200 +++ b/make/autoconf/flags-cflags.m4 Wed May 22 21:50:16 2019 -0400 @@ -564,7 +564,7 @@ TOOLCHAIN_CFLAGS="-errshort=tags" TOOLCHAIN_CFLAGS_JDK="-mt $TOOLCHAIN_FLAGS" - TOOLCHAIN_CFLAGS_JDK_CONLY="-xCC -Xa -W0,-noglobal $TOOLCHAIN_CFLAGS" # C only + TOOLCHAIN_CFLAGS_JDK_CONLY="-W0,-noglobal $TOOLCHAIN_CFLAGS" # C only TOOLCHAIN_CFLAGS_JDK_CXXONLY="-features=no%except -norunpath -xnolib" # CXX only TOOLCHAIN_CFLAGS_JVM="-template=no%extdef -features=no%split_init \ -library=stlport4 -mt -features=no%except $TOOLCHAIN_FLAGS" @@ -585,6 +585,30 @@ TOOLCHAIN_CFLAGS_JDK="-nologo -MD -Zc:wchar_t-" fi + # CFLAGS C language level for JDK sources (hotspot only uses C++) + # Ideally we would have a common level across all toolchains so that all sources + # are sure to conform to the same standard. Unfortunately neither our sources nor + # our toolchains are in a condition to support that. But what we loosely aim for is + # C99 level. + if test "x$TOOLCHAIN_TYPE" = xgcc || test "x$TOOLCHAIN_TYPE" = xclang || test "x$TOOLCHAIN_TYPE" = xxlc; then + # This raises the language level for older 4.8 gcc, while lowering it for later + # versions. clang and xlclang support the same flag. + LANGSTD_CFLAGS="-std=c99" + elif test "x$TOOLCHAIN_TYPE" = xsolstudio; then + # We can't turn on -std=c99 without breaking compilation of the splashscreen/png + # utilities. But we can enable c99 as below (previously achieved by using -Xa). + # It is the no_lib that makes the difference. + LANGSTD_CFLAGS="-xc99=all,no_lib" + elif test "x$TOOLCHAIN_TYPE" = xmicrosoft; then + # MSVC doesn't support C99/C11 explicitly, unless you compile as C++: + # LANGSTD_CFLAGS="/TP" + # but that requires numerous changes to the sources files. So we are limited + # to C89/C90 plus whatever extensions Visual Studio has decided to implement. + # This is the lowest bar for shared code. + LANGSTD_CFLAGS="" + fi + TOOLCHAIN_CFLAGS_JDK_CONLY="$LANGSTD_CFLAGS $TOOLCHAIN_CFLAGS_JDK_CONLY" + # CFLAGS WARNINGS STUFF # Set JVM_CFLAGS warning handling if test "x$TOOLCHAIN_TYPE" = xgcc; then diff -r dc343eb0fcf0 -r 98ed47cd114a make/lib/Awt2dLibraries.gmk --- a/make/lib/Awt2dLibraries.gmk Thu May 23 02:36:15 2019 +0200 +++ b/make/lib/Awt2dLibraries.gmk Wed May 22 21:50:16 2019 -0400 @@ -378,7 +378,6 @@ OPTIMIZATION := HIGHEST, \ CFLAGS := $(CFLAGS_JDKLIB) \ $(LCMS_CFLAGS), \ - CFLAGS_solaris := -xc99=no_lib, \ CFLAGS_windows := -DCMS_IS_WINDOWS_, \ EXTRA_HEADER_DIRS := \ common/awt/debug \