Re: [PATCH v7 3/8] Move malloc hooks into a compat DSO

[Florian Weimer via Libc-alpha <libc-alpha@sourceware.org>]

* Siddhesh Poyarekar:

> Remove all malloc hook uses from core malloc functions and move it
> into a new library libc_malloc_debug.so.  With this, the hooks now no
> longer have any effect on the core library.
>
> libc_malloc_debug.so is a malloc interposer that needs to be preloaded
> to get hooks functionality back so that the debugging features that
> depend on the hooks, i.e. malloc-check, mcheck and mtrace work again.
> Without the preloaded DSO these debugging features will be nops.
> These features will be ported away from hooks in subsequent patches.
>
> Similarly, legacy applications that need hooks functionality need to
> preload libc_malloc_debug.so.
>
> The symbols exported by libc_malloc_debug.so are maintained at exactly
> the same version as libc.so.
>
> Finally, static binaries will no longer be able to use malloc
> debugging features since they cannot preload the debugging DSO.

Commit subject could be adjusted because the DSO contains more than just
the hooks.

This patch needs to update the shlib-versions file on architectures
which do not use DEFAULT.  For example, on ia64-linux-gnu, there is a
malloc/check-abi-libc_malloc_debug failure that looks like this:

--- ../sysdeps/unix/sysv/linux/ia64/libc_malloc_debug.abilist   2021-07-09 02:20:33.198770372 -0400
+++ /home/bmg/build/glibcs/ia64-linux-gnu/glibc/malloc/libc_malloc_debug.symlist        2021-07-09 02:41:48.575228929 -0400
@@ -0,0 +1,20 @@
+GLIBC_2.0 __free_hook D 0x8
+GLIBC_2.0 __malloc_hook D 0x8
+GLIBC_2.0 __memalign_hook D 0x8
+GLIBC_2.0 __realloc_hook D 0x8
+GLIBC_2.0 calloc F
+GLIBC_2.0 free F
+GLIBC_2.0 mallinfo F
+GLIBC_2.0 malloc F
+GLIBC_2.0 malloc_stats F
+GLIBC_2.0 malloc_trim F
+GLIBC_2.0 malloc_usable_size F
+GLIBC_2.0 mallopt F
+GLIBC_2.0 mcheck F
+GLIBC_2.0 memalign F
+GLIBC_2.0 mprobe F
+GLIBC_2.0 mtrace F
+GLIBC_2.0 muntrace F
+GLIBC_2.0 pvalloc F
+GLIBC_2.0 realloc F
+GLIBC_2.0 valloc F
@@ -3,13 +22,0 @@ GLIBC_2.16 aligned_alloc F
-GLIBC_2.2 __free_hook D 0x8
-GLIBC_2.2 __malloc_hook D 0x8
-GLIBC_2.2 __memalign_hook D 0x8
-GLIBC_2.2 __realloc_hook D 0x8
-GLIBC_2.2 calloc F
-GLIBC_2.2 free F
-GLIBC_2.2 mallinfo F
-GLIBC_2.2 malloc F
-GLIBC_2.2 malloc_stats F
-GLIBC_2.2 malloc_trim F
-GLIBC_2.2 malloc_usable_size F
-GLIBC_2.2 mallopt F
-GLIBC_2.2 mcheck F
@@ -18,4 +24,0 @@ GLIBC_2.2 mcheck_pedantic F
-GLIBC_2.2 memalign F
-GLIBC_2.2 mprobe F
-GLIBC_2.2 mtrace F
-GLIBC_2.2 muntrace F
@@ -23,3 +25,0 @@ GLIBC_2.2 posix_memalign F
-GLIBC_2.2 pvalloc F
-GLIBC_2.2 realloc F
-GLIBC_2.2 valloc F

I expect this to fix ia64-linux-gnu:

diff --git a/sysdeps/unix/sysv/linux/ia64/shlib-versions b/sysdeps/unix/sysv/linux/ia64/shlib-versions
index 37374c0e20..c6d06480a1 100644
--- a/sysdeps/unix/sysv/linux/ia64/shlib-versions
+++ b/sysdeps/unix/sysv/linux/ia64/shlib-versions
@@ -1,4 +1,5 @@
 libc=6.1		GLIBC_2.2
+libc_malloc_debug=0	GLIBC_2.2
 libm=6.1		GLIBC_2.2
 
 ld=ld-linux-ia64.so.2	GLIBC_2.2

The other targets affected by this are:

hppa-linux-gnu
sh3eb-linux-gnu
sh3-linux-gnu
sh4eb-linux-gnu
sh4eb-linux-gnu-soft
sh4-linux-gnu
sh4-linux-gnu-soft
sparc64-linux-gnu
sparc64-linux-gnu-disable-multi-arch

Thanks,
Florian