Re: Mixing libc with a DEBUG | PROF jemalloc

Le Tue, May 16, 2023 at 11:21:32AM +0200, [email protected] a écrit :
> Since jemalloc is used as the memory allocator, and since it has
> profiling and debugging capacities, I wanted to use such a debug version
> to trace memory allocation for programs.
> 
> The idea was to link the programs with the stub version of the library,
> and then, when needed, to use LD_PRELOAD to load the debug version (I
> have not read the RT dynamic linker src to see if LD_PRELOAD will load
> whatever library and link with the symbols exported even if the library
> is not declared in the executable; hence the link with the stub
> version).
> 
> In src/external/bsd/jemalloc/lib, I have modified the options in
> Makefile.inc (now unused since the bsd.mk includes the inc in the parent
> directory only), simply adding some macro definitions and the path to
> the libc header "extern.h" for jemalloc.c:
> 
> 
> # in the .for loop
> CPPFLAGS.${i}+=-I${JEMALLOC}/include -DJEMALLOC_PROTECT_NOSTD -DJEMALLOC_DEBUG -DJEMALLOC_PROF
> 
> # and for extern.h
> CPPFLAGS.jemalloc.c+=-I${JEMALLOC}/../../../lib/libc/include
> 
> Then, adjusting the Makefile so that defining say a DEBUG_LIB, I can
> include the Makefile.inc and then use its SRCS, it compiles. I can
> indeed substitute the debugging version using
> LD_PRELOAD, but then libc is using calling what is exported from the
> jemalloc debugging version and it doesn't blend well at all.
> 
> Have someone already done something like this? Is a namemangling
> required in order to make only the third party code use the debugging
> version while letting the libc alone?
> 

${JEMALLOC}/lib/Makefile.inc is included from src/lib/libc/Makefile.

And I have a 10 beta src tree while my userland is still 9.3; it
probably doesn't help either to mix a 9.3 libc with a 10 jemalloc.

So I will instead compile a debugging libc, from the correct branch, and
use this one with LD_PRELOAD instead of trying to use a mix of libc with
jemalloc embedded and another jemalloc library.

Note: It seems to be what is done under FreeBSD, with the use of
MALLOC_PRODUCTION macro to switch between a normal (production) version,
and a debugging one.
-- 
        Thierry Laronde <tlaronde +AT+ polynum +dot+ com>
                     http://www.kergis.com/
                    http://kertex.kergis.com/
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