On 24/10/23 12:32, Alejandro Colomar wrote: > Hi Vincent, > > On Tue, Oct 24, 2023 at 04:31:17PM +0200, Vincent Lefevre wrote: >> The glibc 2.34 NEWS file says that mtrace() and mcheck() have now been >> disabled in the main C library, and preloading libc_malloc_debug.so is > > Can you please clarify "disabled"? What is the behavior if that library > is not preloaded? My attempt to run this program is that mcheck(3) > returns -1. So, the preload interposes the dummy function that only > returns -1 with an actual mcheck(3) implementation? The libc mcheck and mcheck_pedantic now return -1, while mprobe returns MCHECK_DISABLED. All the implementation that used to live in libc.so were moved to libc_malloc_debug.so. > > Are these functions deprecated by glibc? If so, we should probably use > [[deprecated]] in the SYNOPSIS. Or did they just move the functionality > for other reasons but without deprecating? There is no deprecation because the functionality is still fully supported, albeit in a different library. Setting to deprecated would require to move the prototypes to a different header. > > Should we document the need for LD_PRELOAD in the LIBRARY section? Yes, I think it would be better. > > Thanks, > Alex > >> needed to get this functionality back. >> >> So the examples now need a "LD_PRELOAD=libc_malloc_debug.so". >> >> Signed-off-by: Vincent Lefevre <vincent@xxxxxxxxxx> >> --- >> man3/mcheck.3 | 2 +- >> man3/mtrace.3 | 2 +- >> 2 files changed, 2 insertions(+), 2 deletions(-) >> >> diff --git a/man3/mcheck.3 b/man3/mcheck.3 >> index 285ea946c..e17650a4c 100644 >> --- a/man3/mcheck.3 >> +++ b/man3/mcheck.3 >> @@ -169,7 +169,7 @@ when running the program: >> .PP >> .in +4n >> .EX >> -.RB "$" " ./a.out" >> +.RB "$ " "LD_PRELOAD=libc_malloc_debug.so ./a.out" >> About to free >> \& >> About to free a second time >> diff --git a/man3/mtrace.3 b/man3/mtrace.3 >> index f30511cd0..d0cde42c9 100644 >> --- a/man3/mtrace.3 >> +++ b/man3/mtrace.3 >> @@ -153,7 +153,7 @@ diagnosed memory leaks at two different locations in the program: >> .EX >> .RB "$ " "cc \-g t_mtrace.c \-o t_mtrace" >> .RB "$ " "export MALLOC_TRACE=/tmp/t" >> -.RB "$ " "./t_mtrace" >> +.RB "$ " "LD_PRELOAD=libc_malloc_debug.so ./t_mtrace" >> .RB "$ " "mtrace ./t_mtrace $MALLOC_TRACE" >> Memory not freed: >> -\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\- >> -- >> 2.42.0 >> >
