Re: [PATCH] mcheck.3, mtrace.3: update examples for glibc 2.34

[Alejandro Colomar <alx@kernel.org>]

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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?

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?

Should we document the need for LD_PRELOAD in the LIBRARY section?

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@vinc17.net>
> ---
>  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
> 

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