get_ksym_desc of gen_loader.c function for loop initial declarations cause compile problems

[liminwanga]

I compiled the bcc application from https://github.com/iovisor/bcc. When I compiled it I got a error as fllows:

/root/bcc/src/cc/libbpf/src/gen_loader.c: In function get_ksym_desc:
/root/bcc/src/cc/libbpf/src/gen_loader.c:585:2: error: ‘for’ loop initial declarations are only allowed in C99 mode
  for (int i = 0; i < gen->nr_ksyms; i++) {

so I search the other funtion in gen_loader.c file. For example ,the function bpf_gen__finish use loop is for (i = 0; i < gen->nr_progs; i++)

I modify function get_ksym_desc for loop as same as bpf_gen__finish and compiled ok!

[anakryiko]

Yeah, that's unfortunate. I'll fix it upstream. Would you mind running BCC build in verbose mode and pasting here exact compiler flags that are passed. I'll try to make sure we match relevant parts to catch this early on. Thanks!

[liminwanga]

Yeah, that's unfortunate. I'll fix it upstream. Would you mind running BCC build in verbose mode and pasting here exact compiler flags that are passed. I'll try to make sure we match relevant parts to catch this early on. Thanks!

OK, I compiled bcc use make VERBOSE and get info as fllows:

make VERBOSE=1
/usr/bin/cmake3 -S/root/bcc -B/root/bcc/build --check-build-system CMakeFiles/Makefile.cmake 0
/usr/bin/cmake3 -E cmake_progress_start /root/bcc/build/CMakeFiles /root/bcc/build/CMakeFiles/progress.marks
make  -f CMakeFiles/Makefile2 all
make[1]: Entering directory `/root/bcc/build'
make  -f src/cc/frontends/clang/CMakeFiles/clang_frontend.dir/build.make src/cc/frontends/clang/CMakeFiles/clang_frontend.dir/depend
make[2]: Entering directory `/root/bcc/build'
cd /root/bcc/build && /usr/bin/cmake3 -E cmake_depends "Unix Makefiles" /root/bcc /root/bcc/src/cc/frontends/clang /root/bcc/build /root/bcc/build/src/cc/frontends/clang /root/bcc/build/src/cc/frontends/clang/CMakeFiles/clang_frontend.dir/DependInfo.cmake --color=
make[2]: Leaving directory `/root/bcc/build'
make  -f src/cc/frontends/clang/CMakeFiles/clang_frontend.dir/build.make src/cc/frontends/clang/CMakeFiles/clang_frontend.dir/build
make[2]: Entering directory `/root/bcc/build'
make[2]: Nothing to be done for `src/cc/frontends/clang/CMakeFiles/clang_frontend.dir/build'.
make[2]: Leaving directory `/root/bcc/build'
[  2%] Built target clang_frontend
make  -f src/cc/CMakeFiles/bpf-static.dir/build.make src/cc/CMakeFiles/bpf-static.dir/depend
make[2]: Entering directory `/root/bcc/build'
cd /root/bcc/build && /usr/bin/cmake3 -E cmake_depends "Unix Makefiles" /root/bcc /root/bcc/src/cc /root/bcc/build /root/bcc/build/src/cc /root/bcc/build/src/cc/CMakeFiles/bpf-static.dir/DependInfo.cmake --color=
make[2]: Leaving directory `/root/bcc/build'
make  -f src/cc/CMakeFiles/bpf-static.dir/build.make src/cc/CMakeFiles/bpf-static.dir/build
make[2]: Entering directory `/root/bcc/build'
[  2%] Building C object src/cc/CMakeFiles/bpf-static.dir/libbpf/src/gen_loader.c.o
cd /root/bcc/build/src/cc && /usr/bin/cc -DEXPORT_USDT -I/opt/rh/llvm-toolset-7/root/usr/include/../tools/clang/include -I/root/bcc/src -I/root/bcc/build/src -I/root/bcc/build/src/cc -I/root/bcc/src/cc -I/root/bcc/build/src/cc/frontends/b -I/root/bcc/src/cc/frontends/b -I/root/bcc/src/cc/frontends/clang -I/opt/rh/llvm-toolset-7/root/usr/include -I/root/bcc/src/cc/libbpf/include -I/root/bcc/src/cc/libbpf/include/uapi  -Wall -fPIC -Wno-unused-result -DCOMPAT_NEED_REALLOCARRAY -O2 -DNDEBUG   -DLLVM_BUILD_GLOBAL_ISEL -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -o CMakeFiles/bpf-static.dir/libbpf/src/gen_loader.c.o   -c /root/bcc/src/cc/libbpf/src/gen_loader.c
/root/bcc/src/cc/libbpf/src/gen_loader.c: In function ‘get_ksym_desc’:
/root/bcc/src/cc/libbpf/src/gen_loader.c:585:2: error: ‘for’ loop initial declarations are only allowed in C99 mode
  for (int i = 0; i < gen->nr_ksyms; i++) {
  ^
/root/bcc/src/cc/libbpf/src/gen_loader.c:585:2: note: use option -std=c99 or -std=gnu99 to compile your code
make[2]: *** [src/cc/CMakeFiles/bpf-static.dir/libbpf/src/gen_loader.c.o] Error 1
make[2]: Leaving directory `/root/bcc/build'
make[1]: *** [src/cc/CMakeFiles/bpf-static.dir/all] Error 2
make[1]: Leaving directory `/root/bcc/build'
make: *** [all] Error 2

[anakryiko]

Interesting, there is no -std=c89 or -std=gnu89 specified, yet compiler complains about this. While libbpf code was complied without -std=c89/-std=gnu89 and there was no warning.

Either way, this has been fixed already and synced into Github. See 2ab2615. You'll need to pull the latest libbpf into BCC repo, though.