Build failure with GCC 10 ('alloca' bound is unknown)

[ebourg]

Hi,

When building JNA 5.6 on Debian (sid) the build failed with the following error:

native:
     [exec] make[2]: Entering directory '/build/libjna-java-5.6.0/native'
     [exec] gcc -m64 -W -Wall -Wno-unused -Wno-parentheses -fPIC  -O2 -fno-omit-frame-pointer -fno-strict-aliasing  -D_REENTRANT -DHAVE_PROTECTION -I"/usr/lib/jvm/java-11-openjdk-amd64/include" -I"/usr/lib/jvm/java-11-openjdk-amd64/include/linux" -I"/build/libjna-java-5.6.0/build/headers" -I/include -DJNA_JNI_VERSION='"6.1.0"' -DCHECKSUM='""'  -Wno-unknown-warning-option -Werror -Wno-clobbered -Wno-unused-variable -c dispatch.c -o /build/libjna-java-5.6.0/build/native-linux-x86-64/dispatch.o
     [exec] In file included from dispatch.h:33,
     [exec]                  from dispatch.c:30:
     [exec] dispatch.c: In function 'dispatch_direct':
     [exec] dispatch.c:1770:23: error: 'alloca' bound is unknown [-Werror=alloca-larger-than=]
     [exec]  1770 |             args[i] = alloca(data->cif.arg_types[i]->size);
     [exec]       |                       ^~~~~~
     [exec] dispatch.c:1796:23: error: 'alloca' bound is unknown [-Werror=alloca-larger-than=]
     [exec]  1796 |             args[i] = alloca(data->cif.arg_types[i]->size);
     [exec]       |                       ^~~~~~
     [exec] make[2]: Leaving directory '/build/libjna-java-5.6.0/native'
     [exec] dispatch.c: At top level:
     [exec] cc1: note: unrecognized command-line option '-Wno-unknown-warning-option' may have been intended to silence earlier diagnostics
     [exec] cc1: all warnings being treated as errors
     [exec] make[2]: *** [Makefile:430: /build/libjna-java-5.6.0/build/native-linux-x86-64/dispatch.o] Error 1

I'm not sure but I suspect the error appeared when switching to GCC 10.

[matthiasblaesing]

You are right. I checked debian testing vs. unstable and indeed gcc is the core component, that was updated and caused the test failure. While the release notes of gcc10 do not report a change in the -Wall behaviour, I assume alloca-larger-than was added to the list of warnings activated by default.

The patch in #1245 surpresses the warning on GCC.

[matthiasblaesing]

Fix was merged to master - the patch itself should apply cleanly to 5.6.0 so feel free to extract it to fix the FTBS bug on debian.