PAGE_SIZE is not portable

[vext01]

After working around #10, I get the following compilation error on OpenBSD:

[  3%] Building C object libipt/CMakeFiles/libipt.dir/src/posix/pt_section_posix.c.o
cd /home/edd/research/hwt_experiment/processor-trace/build/libipt && /usr/bin/cc  -DFEATURE_THREADS -DPT_VERSION_BUILD=0 -DPT_VERSION_EXT=\"\" -DPT_VERSION_MAJOR=1 -DPT_VERSION_MINOR=6 -Dlibipt_EXPORTS -I/home/edd/research/hwt_experiment/processor-trace/include -I/home/edd/research/hwt_experiment/processor-trace/build/libipt/include -I/home/edd/research/hwt_experiment/processor-trace/include/posix -I/home/edd/research/hwt_experiment/processor-trace/libipt/internal/include -I/home/edd/research/hwt_experiment/processor-trace/libipt/internal/include/posix  -std=c99 -fvisibility=hidden -fPIC   -o CMakeFiles/libipt.dir/src/posix/pt_section_posix.c.o   -c /home/edd/research/hwt_experiment/processor-trace/libipt/src/posix/pt_section_posix.c
/home/edd/research/hwt_experiment/processor-trace/libipt/src/posix/pt_section_posix.c: In function 'pt_sec_posix_map':
/home/edd/research/hwt_experiment/processor-trace/libipt/src/posix/pt_section_posix.c:114: error: 'PAGE_SIZE' undeclared (first use in this function)
/home/edd/research/hwt_experiment/processor-trace/libipt/src/posix/pt_section_posix.c:114: error: (Each undeclared identifier is reported only once
/home/edd/research/hwt_experiment/processor-trace/libipt/src/posix/pt_section_posix.c:114: error: for each function it appears in.)

Arguably the page size should not be a compile time constant, as this means traces from different machines with different page sizes can not be decoded.

[markus-metzger]

Thanks for reporting this.

The PAGE_SIZE macro is defined in <sys/user.h> on Linux - but apparently not on OpenBSD. A more portable version should be sysconf(_SC_PAGESIZE). I hope this is available on OpenBSD, as well.

Let me set up an OpenBSD system to check.

[vext01]

Hi Markus,

On my OpenBSD amd64 laptop:

unistd.h
180:#define     _SC_PAGESIZE            28
181:#define     _SC_PAGE_SIZE           _SC_PAGESIZE    /* 1170 compatibility */

So you could probably fix the compilation error in this way, yes. But is the page-size baked into the PT trace somehow? If so, you'd probably want a runtime switch?

Thanks

[markus-metzger]

Hi Edd,

The page size is used to align mmap() mapped memory. Libipt maps code sections from binary files to decode instructions. This should be OK; sysconf(_SC_PAGESIZE) is also used in the example on the mmap(2) man page.

[vext01]

Hi Markus, just found that unistd.h defines getpagesize() on both Linux and OpenBSD.

[vext01]

Thanks!