* [PATCH 0/3] Forced ordering for DFS ELF dependency sorting (bug 28937)
@ 2022-08-15 14:30 Florian Weimer
2022-08-15 14:30 ` [PATCH 1/3] scripts/dso-ordering-test.py: Generate program run-time dependencies Florian Weimer
` (2 more replies)
0 siblings, 3 replies; 10+ messages in thread
From: Florian Weimer @ 2022-08-15 14:30 UTC (permalink / raw)
To: libc-alpha
An Arch Linux test case showed that in some cases, dlclose could unload
mappings that are still in use. Triggering this requires dependency
cycles, which is why I think this is somewhat rare.
Tested on i686-linux-gnu and x86_64-linux-gnu.
Thanks,
Florian
Florian Weimer (3):
scripts/dso-ordering-test.py: Generate program run-time dependencies
elf: Rename _dl_sort_maps parameter from skip to force_first
elf: Implement force_first handling in _dl_sort_maps_dfs
elf/dl-sort-maps.c | 47 ++++++++++++++++++++++++------------
elf/dso-sort-tests-1.def | 7 ++++++
scripts/dso-ordering-test.py | 14 +++++------
sysdeps/generic/ldsodefs.h | 6 +++--
4 files changed, 50 insertions(+), 24 deletions(-)
base-commit: 453b88efe6fa79f5c7c6fccc3a520c75fdd43074
--
2.37.1
^ permalink raw reply [flat|nested] 10+ messages in thread
* [PATCH 1/3] scripts/dso-ordering-test.py: Generate program run-time dependencies
2022-08-15 14:30 [PATCH 0/3] Forced ordering for DFS ELF dependency sorting (bug 28937) Florian Weimer
@ 2022-08-15 14:30 ` Florian Weimer
2022-08-15 14:35 ` Florian Weimer
2022-08-29 14:30 ` Adhemerval Zanella Netto
2022-08-15 14:30 ` [PATCH 2/3] elf: Rename _dl_sort_maps parameter from skip to force_first Florian Weimer
2022-08-15 14:30 ` [PATCH 3/3] elf: Implement force_first handling in _dl_sort_maps_dfs Florian Weimer
2 siblings, 2 replies; 10+ messages in thread
From: Florian Weimer @ 2022-08-15 14:30 UTC (permalink / raw)
To: libc-alpha
The main program needs to depend on all shared objects, even objects
that have link-time dependencies among shared objects. Filtering
out shared objects that already have an link-time dependencies is not
necessary here; make will do this automatically.
---
scripts/dso-ordering-test.py | 14 +++++++-------
1 file changed, 7 insertions(+), 7 deletions(-)
diff --git a/scripts/dso-ordering-test.py b/scripts/dso-ordering-test.py
index 2dd6bfda18..f6d22aa00e 100644
--- a/scripts/dso-ordering-test.py
+++ b/scripts/dso-ordering-test.py
@@ -707,13 +707,12 @@ def process_testcase(t):
"\t$(compile.c) $(OUTPUT_OPTION)\n")
makefile.write (rule)
- not_depended_objs = find_objs_not_depended_on(test_descr)
- if not_depended_objs:
- depstr = ""
- for dep in not_depended_objs:
- depstr += (" $(objpfx)" + test_subdir + "/"
- + test_name + "-" + dep + ".so")
- makefile.write("$(objpfx)%s.out:%s\n" % (base_test_name, depstr))
+ # Ensure that all shared objects are built before running the
+ # test, whether there link-time dependencies or not.
+ depobjs = ["$(objpfx){}/{}-{}.so".format(test_subdir, test_name, dep)
+ for dep in test_descr.objs]
+ makefile.write("$(objpfx){}.out: {}\n".format(
+ base_test_name, " ".join(depobjs)))
# Add main executable to test-srcs
makefile.write("test-srcs += %s/%s\n" % (test_subdir, test_name))
@@ -779,6 +778,7 @@ def process_testcase(t):
# description string.
for obj in test_descr.objs:
src_name = test_name + "-" + obj + ".c"
+ print('Generating {}...'.format(src_name))
f = open(testpfx_src + src_name, "w")
if obj in test_descr.callrefs:
called_objs = test_descr.callrefs[obj]
--
2.37.1
^ permalink raw reply [flat|nested] 10+ messages in thread
* [PATCH 2/3] elf: Rename _dl_sort_maps parameter from skip to force_first
2022-08-15 14:30 [PATCH 0/3] Forced ordering for DFS ELF dependency sorting (bug 28937) Florian Weimer
2022-08-15 14:30 ` [PATCH 1/3] scripts/dso-ordering-test.py: Generate program run-time dependencies Florian Weimer
@ 2022-08-15 14:30 ` Florian Weimer
2022-08-29 16:40 ` Adhemerval Zanella Netto
2022-08-15 14:30 ` [PATCH 3/3] elf: Implement force_first handling in _dl_sort_maps_dfs Florian Weimer
2 siblings, 1 reply; 10+ messages in thread
From: Florian Weimer @ 2022-08-15 14:30 UTC (permalink / raw)
To: libc-alpha
The new implementation will not be able to skip an arbitrary number
of objects.
---
elf/dl-sort-maps.c | 14 +++++++-------
sysdeps/generic/ldsodefs.h | 6 ++++--
2 files changed, 11 insertions(+), 9 deletions(-)
diff --git a/elf/dl-sort-maps.c b/elf/dl-sort-maps.c
index 96638d7ed1..5b550b1e94 100644
--- a/elf/dl-sort-maps.c
+++ b/elf/dl-sort-maps.c
@@ -27,12 +27,12 @@
If FOR_FINI is true, this is called for finishing an object. */
static void
_dl_sort_maps_original (struct link_map **maps, unsigned int nmaps,
- unsigned int skip, bool for_fini)
+ bool force_first, bool for_fini)
{
/* Allows caller to do the common optimization of skipping the first map,
usually the main binary. */
- maps += skip;
- nmaps -= skip;
+ maps += force_first;
+ nmaps -= force_first;
/* A list of one element need not be sorted. */
if (nmaps <= 1)
@@ -182,7 +182,7 @@ dfs_traversal (struct link_map ***rpo, struct link_map *map,
static void
_dl_sort_maps_dfs (struct link_map **maps, unsigned int nmaps,
- unsigned int skip __attribute__ ((unused)), bool for_fini)
+ bool force_first __attribute__ ((unused)), bool for_fini)
{
for (int i = nmaps - 1; i >= 0; i--)
maps[i]->l_visited = 0;
@@ -286,7 +286,7 @@ _dl_sort_maps_init (void)
void
_dl_sort_maps (struct link_map **maps, unsigned int nmaps,
- unsigned int skip, bool for_fini)
+ bool force_first, bool for_fini)
{
/* It can be tempting to use a static function pointer to store and call
the current selected sorting algorithm routine, but experimentation
@@ -296,9 +296,9 @@ _dl_sort_maps (struct link_map **maps, unsigned int nmaps,
input cases. A simple if-case with direct function calls appears to
be the fastest. */
if (__glibc_likely (GLRO(dl_dso_sort_algo) == dso_sort_algorithm_original))
- _dl_sort_maps_original (maps, nmaps, skip, for_fini);
+ _dl_sort_maps_original (maps, nmaps, force_first, for_fini);
else
- _dl_sort_maps_dfs (maps, nmaps, skip, for_fini);
+ _dl_sort_maps_dfs (maps, nmaps, force_first, for_fini);
}
#endif /* HAVE_TUNABLES. */
diff --git a/sysdeps/generic/ldsodefs.h b/sysdeps/generic/ldsodefs.h
index 050a3032de..6b256b8388 100644
--- a/sysdeps/generic/ldsodefs.h
+++ b/sysdeps/generic/ldsodefs.h
@@ -1048,9 +1048,11 @@ extern void _dl_init (struct link_map *main_map, int argc, char **argv,
initializer functions have completed. */
extern void _dl_fini (void) attribute_hidden;
-/* Sort array MAPS according to dependencies of the contained objects. */
+/* Sort array MAPS according to dependencies of the contained objects.
+ If FORCE_FIRST, MAPS[0] keeps its place even if the dependencies
+ say otherwise. */
extern void _dl_sort_maps (struct link_map **maps, unsigned int nmaps,
- unsigned int skip, bool for_fini) attribute_hidden;
+ bool force_first, bool for_fini) attribute_hidden;
/* The dynamic linker calls this function before and having changing
any shared object mappings. The `r_state' member of `struct r_debug'
--
2.37.1
^ permalink raw reply [flat|nested] 10+ messages in thread
* [PATCH 3/3] elf: Implement force_first handling in _dl_sort_maps_dfs
2022-08-15 14:30 [PATCH 0/3] Forced ordering for DFS ELF dependency sorting (bug 28937) Florian Weimer
2022-08-15 14:30 ` [PATCH 1/3] scripts/dso-ordering-test.py: Generate program run-time dependencies Florian Weimer
2022-08-15 14:30 ` [PATCH 2/3] elf: Rename _dl_sort_maps parameter from skip to force_first Florian Weimer
@ 2022-08-15 14:30 ` Florian Weimer
2022-08-31 16:37 ` Adhemerval Zanella Netto
2 siblings, 1 reply; 10+ messages in thread
From: Florian Weimer @ 2022-08-15 14:30 UTC (permalink / raw)
To: libc-alpha
As documented in a comment _dl_close_worker, the skipping is actually
needed for correctness. It also seems less surprising if the
just-opened object is always initialized last, even in the presence
of cycles.
---
elf/dl-sort-maps.c | 35 ++++++++++++++++++++++++++---------
elf/dso-sort-tests-1.def | 7 +++++++
2 files changed, 33 insertions(+), 9 deletions(-)
diff --git a/elf/dl-sort-maps.c b/elf/dl-sort-maps.c
index 5b550b1e94..cd2d9c93fc 100644
--- a/elf/dl-sort-maps.c
+++ b/elf/dl-sort-maps.c
@@ -182,8 +182,9 @@ dfs_traversal (struct link_map ***rpo, struct link_map *map,
static void
_dl_sort_maps_dfs (struct link_map **maps, unsigned int nmaps,
- bool force_first __attribute__ ((unused)), bool for_fini)
+ bool force_first, bool for_fini)
{
+ struct link_map *first_map = maps[0];
for (int i = nmaps - 1; i >= 0; i--)
maps[i]->l_visited = 0;
@@ -208,14 +209,6 @@ _dl_sort_maps_dfs (struct link_map **maps, unsigned int nmaps,
Adjusting the order so that maps[0] is last traversed naturally avoids
this problem.
- Further, the old "optimization" of skipping the main object at maps[0]
- from the call-site (i.e. _dl_sort_maps(maps+1,nmaps-1)) is in general
- no longer valid, since traversing along object dependency-links
- may "find" the main object even when it is not included in the initial
- order (e.g. a dlopen()'ed shared object can have circular dependencies
- linked back to itself). In such a case, traversing N-1 objects will
- create a N-object result, and raise problems.
-
To summarize, just passing in the full list, and iterating from back
to front makes things much more straightforward. */
@@ -274,6 +267,30 @@ _dl_sort_maps_dfs (struct link_map **maps, unsigned int nmaps,
}
memcpy (maps, rpo, sizeof (struct link_map *) * nmaps);
+
+ /* Skipping the first object at maps[0] is not valid in general,
+ since traversing along object dependency-links may "find" that
+ first object even when it is not included in the initial order
+ (e.g. a dlopen()'ed shared object can have circular dependencies
+ linked back to itself). In such a case, traversing N-1 objects
+ will create a N-object result, and raise problems. Instead,
+ force the object back into first place after sorting. */
+ if (force_first && maps[0] != first_map)
+ {
+ struct link_map *saved = maps[0];
+ maps[0] = first_map;
+ int i = 1;
+ while (true)
+ {
+ assert (i < nmaps);
+ struct link_map *current = maps[i];
+ maps[i] = saved;
+ if (current == first_map)
+ break;
+ saved = current;
+ ++i;
+ }
+ }
}
void
diff --git a/elf/dso-sort-tests-1.def b/elf/dso-sort-tests-1.def
index 5f7f18ef27..4bf9052db1 100644
--- a/elf/dso-sort-tests-1.def
+++ b/elf/dso-sort-tests-1.def
@@ -64,3 +64,10 @@ output: b>a>{}<a<b
tst-bz15311: {+a;+e;+f;+g;+d;%d;-d;-g;-f;-e;-a};a->b->c->d;d=>[ba];c=>a;b=>e=>a;c=>f=>b;d=>g=>c
output(glibc.rtld.dynamic_sort=1): {+a[d>c>b>a>];+e[e>];+f[f>];+g[g>];+d[];%d(b(e(a()))a()g(c(a()f(b(e(a()))))));-d[];-g[];-f[];-e[];-a[<a<c<d<g<f<b<e];}
output(glibc.rtld.dynamic_sort=2): {+a[d>c>b>a>];+e[e>];+f[f>];+g[g>];+d[];%d(b(e(a()))a()g(c(a()f(b(e(a()))))));-d[];-g[];-f[];-e[];-a[<g<f<a<b<c<d<e];}
+
+# Test that even in the presence of dependency loops involving dlopen'ed
+# object, that object is initialized last (and not unloaded prematurely).
+# Final destructor order is indeterminate due to the cycle.
+tst-bz28937: {+a;+b;-b;+c;%c};a->a1;a->a2;a2->a;b->b1;c->a1;c=>a1
+output(glibc.rtld.dynamic_sort=1): {+a[a2>a1>a>];+b[b1>b>];-b[<b<b1];+c[c>];%c(a1());}<a<a2<c<a1
+output(glibc.rtld.dynamic_sort=2): {+a[a2>a1>a>];+b[b1>b>];-b[<b<b1];+c[c>];%c(a1());}<a2<a<c<a1
--
2.37.1
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH 1/3] scripts/dso-ordering-test.py: Generate program run-time dependencies
2022-08-15 14:30 ` [PATCH 1/3] scripts/dso-ordering-test.py: Generate program run-time dependencies Florian Weimer
@ 2022-08-15 14:35 ` Florian Weimer
2022-08-29 14:30 ` Adhemerval Zanella Netto
1 sibling, 0 replies; 10+ messages in thread
From: Florian Weimer @ 2022-08-15 14:35 UTC (permalink / raw)
To: Florian Weimer via Libc-alpha
* Florian Weimer via Libc-alpha:
> The main program needs to depend on all shared objects, even objects
> that have link-time dependencies among shared objects. Filtering
> out shared objects that already have an link-time dependencies is not
> necessary here; make will do this automatically.
> ---
> scripts/dso-ordering-test.py | 14 +++++++-------
> 1 file changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/scripts/dso-ordering-test.py b/scripts/dso-ordering-test.py
> index 2dd6bfda18..f6d22aa00e 100644
> --- a/scripts/dso-ordering-test.py
> +++ b/scripts/dso-ordering-test.py
> @@ -707,13 +707,12 @@ def process_testcase(t):
> "\t$(compile.c) $(OUTPUT_OPTION)\n")
> makefile.write (rule)
>
> - not_depended_objs = find_objs_not_depended_on(test_descr)
> - if not_depended_objs:
> - depstr = ""
> - for dep in not_depended_objs:
> - depstr += (" $(objpfx)" + test_subdir + "/"
> - + test_name + "-" + dep + ".so")
> - makefile.write("$(objpfx)%s.out:%s\n" % (base_test_name, depstr))
> + # Ensure that all shared objects are built before running the
> + # test, whether there link-time dependencies or not.
> + depobjs = ["$(objpfx){}/{}-{}.so".format(test_subdir, test_name, dep)
> + for dep in test_descr.objs]
> + makefile.write("$(objpfx){}.out: {}\n".format(
> + base_test_name, " ".join(depobjs)))
>
> # Add main executable to test-srcs
> makefile.write("test-srcs += %s/%s\n" % (test_subdir, test_name))
> @@ -779,6 +778,7 @@ def process_testcase(t):
> # description string.
> for obj in test_descr.objs:
> src_name = test_name + "-" + obj + ".c"
> + print('Generating {}...'.format(src_name))
> f = open(testpfx_src + src_name, "w")
> if obj in test_descr.callrefs:
> called_objs = test_descr.callrefs[obj]
Ugh, I'm going to remove that debugging leftover before committing.
Thanks,
Florian
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH 1/3] scripts/dso-ordering-test.py: Generate program run-time dependencies
2022-08-15 14:30 ` [PATCH 1/3] scripts/dso-ordering-test.py: Generate program run-time dependencies Florian Weimer
2022-08-15 14:35 ` Florian Weimer
@ 2022-08-29 14:30 ` Adhemerval Zanella Netto
1 sibling, 0 replies; 10+ messages in thread
From: Adhemerval Zanella Netto @ 2022-08-29 14:30 UTC (permalink / raw)
To: Florian Weimer, libc-alpha
On 15/08/22 11:30, Florian Weimer via Libc-alpha wrote:
> The main program needs to depend on all shared objects, even objects
> that have link-time dependencies among shared objects. Filtering
> out shared objects that already have an link-time dependencies is not
> necessary here; make will do this automatically.
LGTM with the print debug leftover removed.
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
> ---
> scripts/dso-ordering-test.py | 14 +++++++-------
> 1 file changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/scripts/dso-ordering-test.py b/scripts/dso-ordering-test.py
> index 2dd6bfda18..f6d22aa00e 100644
> --- a/scripts/dso-ordering-test.py
> +++ b/scripts/dso-ordering-test.py
> @@ -707,13 +707,12 @@ def process_testcase(t):
> "\t$(compile.c) $(OUTPUT_OPTION)\n")
> makefile.write (rule)
>
> - not_depended_objs = find_objs_not_depended_on(test_descr)
> - if not_depended_objs:
> - depstr = ""
> - for dep in not_depended_objs:
> - depstr += (" $(objpfx)" + test_subdir + "/"
> - + test_name + "-" + dep + ".so")
> - makefile.write("$(objpfx)%s.out:%s\n" % (base_test_name, depstr))
> + # Ensure that all shared objects are built before running the
> + # test, whether there link-time dependencies or not.
> + depobjs = ["$(objpfx){}/{}-{}.so".format(test_subdir, test_name, dep)
> + for dep in test_descr.objs]
> + makefile.write("$(objpfx){}.out: {}\n".format(
> + base_test_name, " ".join(depobjs)))
>
> # Add main executable to test-srcs
> makefile.write("test-srcs += %s/%s\n" % (test_subdir, test_name))
> @@ -779,6 +778,7 @@ def process_testcase(t):
> # description string.
> for obj in test_descr.objs:
> src_name = test_name + "-" + obj + ".c"
> + print('Generating {}...'.format(src_name))
> f = open(testpfx_src + src_name, "w")
> if obj in test_descr.callrefs:
> called_objs = test_descr.callrefs[obj]
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH 2/3] elf: Rename _dl_sort_maps parameter from skip to force_first
2022-08-15 14:30 ` [PATCH 2/3] elf: Rename _dl_sort_maps parameter from skip to force_first Florian Weimer
@ 2022-08-29 16:40 ` Adhemerval Zanella Netto
0 siblings, 0 replies; 10+ messages in thread
From: Adhemerval Zanella Netto @ 2022-08-29 16:40 UTC (permalink / raw)
To: Florian Weimer, libc-alpha
On 15/08/22 11:30, Florian Weimer via Libc-alpha wrote:
> The new implementation will not be able to skip an arbitrary number
> of objects.
LGTM, thanks.
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
> ---
> elf/dl-sort-maps.c | 14 +++++++-------
> sysdeps/generic/ldsodefs.h | 6 ++++--
> 2 files changed, 11 insertions(+), 9 deletions(-)
>
> diff --git a/elf/dl-sort-maps.c b/elf/dl-sort-maps.c
> index 96638d7ed1..5b550b1e94 100644
> --- a/elf/dl-sort-maps.c
> +++ b/elf/dl-sort-maps.c
> @@ -27,12 +27,12 @@
> If FOR_FINI is true, this is called for finishing an object. */
> static void
> _dl_sort_maps_original (struct link_map **maps, unsigned int nmaps,
> - unsigned int skip, bool for_fini)
> + bool force_first, bool for_fini)
> {
> /* Allows caller to do the common optimization of skipping the first map,
> usually the main binary. */
> - maps += skip;
> - nmaps -= skip;
> + maps += force_first;
> + nmaps -= force_first;
>
> /* A list of one element need not be sorted. */
> if (nmaps <= 1)
> @@ -182,7 +182,7 @@ dfs_traversal (struct link_map ***rpo, struct link_map *map,
>
> static void
> _dl_sort_maps_dfs (struct link_map **maps, unsigned int nmaps,
> - unsigned int skip __attribute__ ((unused)), bool for_fini)
> + bool force_first __attribute__ ((unused)), bool for_fini)
> {
> for (int i = nmaps - 1; i >= 0; i--)
> maps[i]->l_visited = 0;
> @@ -286,7 +286,7 @@ _dl_sort_maps_init (void)
>
> void
> _dl_sort_maps (struct link_map **maps, unsigned int nmaps,
> - unsigned int skip, bool for_fini)
> + bool force_first, bool for_fini)
> {
> /* It can be tempting to use a static function pointer to store and call
> the current selected sorting algorithm routine, but experimentation
> @@ -296,9 +296,9 @@ _dl_sort_maps (struct link_map **maps, unsigned int nmaps,
> input cases. A simple if-case with direct function calls appears to
> be the fastest. */
> if (__glibc_likely (GLRO(dl_dso_sort_algo) == dso_sort_algorithm_original))
> - _dl_sort_maps_original (maps, nmaps, skip, for_fini);
> + _dl_sort_maps_original (maps, nmaps, force_first, for_fini);
> else
> - _dl_sort_maps_dfs (maps, nmaps, skip, for_fini);
> + _dl_sort_maps_dfs (maps, nmaps, force_first, for_fini);
> }
>
> #endif /* HAVE_TUNABLES. */
> diff --git a/sysdeps/generic/ldsodefs.h b/sysdeps/generic/ldsodefs.h
> index 050a3032de..6b256b8388 100644
> --- a/sysdeps/generic/ldsodefs.h
> +++ b/sysdeps/generic/ldsodefs.h
> @@ -1048,9 +1048,11 @@ extern void _dl_init (struct link_map *main_map, int argc, char **argv,
> initializer functions have completed. */
> extern void _dl_fini (void) attribute_hidden;
>
> -/* Sort array MAPS according to dependencies of the contained objects. */
> +/* Sort array MAPS according to dependencies of the contained objects.
> + If FORCE_FIRST, MAPS[0] keeps its place even if the dependencies
> + say otherwise. */
> extern void _dl_sort_maps (struct link_map **maps, unsigned int nmaps,
> - unsigned int skip, bool for_fini) attribute_hidden;
> + bool force_first, bool for_fini) attribute_hidden;
>
> /* The dynamic linker calls this function before and having changing
> any shared object mappings. The `r_state' member of `struct r_debug'
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH 3/3] elf: Implement force_first handling in _dl_sort_maps_dfs
2022-08-15 14:30 ` [PATCH 3/3] elf: Implement force_first handling in _dl_sort_maps_dfs Florian Weimer
@ 2022-08-31 16:37 ` Adhemerval Zanella Netto
2022-08-31 16:37 ` Adhemerval Zanella Netto
2022-09-06 6:39 ` Florian Weimer
0 siblings, 2 replies; 10+ messages in thread
From: Adhemerval Zanella Netto @ 2022-08-31 16:37 UTC (permalink / raw)
To: libc-alpha, Florian Weimer
On 15/08/22 11:30, Florian Weimer via Libc-alpha wrote:
> As documented in a comment _dl_close_worker, the skipping is actually
> needed for correctness. It also seems less surprising if the
> just-opened object is always initialized last, even in the presence
> of cycles.
I think it is BZ#28937, isn't? Also could you extend the explanation as you
did in the last comment, the initial phrase sounds confusing. Maybe extend
the comment to say that not _dl_sort_maps_dfs will move the main object to
front, so where previous you have the maps input as:
maps[0].l_name=elf/tst-bz28937-dir/tst-bz28937-a.so
maps[1].l_name=[...]/elf/tst-bz28937-dir/tst-bz28937-a1.so
maps[2].l_name=[...]/elf/tst-bz28937-dir/tst-bz28937-a2.so
maps[3].l_name=./libc.so.6
maps[4].l_name=elf/ld.so
It will not be properly sorted as:
maps[0].l_name=elf/tst-bz28937-dir/tst-bz28937-a.so
maps[1].l_name=[...]/elf/tst-bz28937-dir/tst-bz28937-a1.so
maps[2].l_name=[...]/elf/tst-bz28937-dir/tst-bz28937-a2.so
maps[3].l_name=./libc.so.6
maps[4].l_name=elf/ld.so
Instead of wrongly:
maps[0].l_name=[...]/elf/tst-bz28937-dir/tst-bz28937-a1.so
maps[1].l_name=[...]/elf/tst-bz28937-dir/tst-bz28937-a2.so
maps[2].l_name=elf/tst-bz28937-dir/tst-bz28937-a.so
maps[3].l_name=./libc.so.6
maps[4].l_name=elf/ld.so
> ---
> elf/dl-sort-maps.c | 35 ++++++++++++++++++++++++++---------
> elf/dso-sort-tests-1.def | 7 +++++++
> 2 files changed, 33 insertions(+), 9 deletions(-)
>
> diff --git a/elf/dl-sort-maps.c b/elf/dl-sort-maps.c
> index 5b550b1e94..cd2d9c93fc 100644
> --- a/elf/dl-sort-maps.c
> +++ b/elf/dl-sort-maps.c
> @@ -182,8 +182,9 @@ dfs_traversal (struct link_map ***rpo, struct link_map *map,
>
> static void
> _dl_sort_maps_dfs (struct link_map **maps, unsigned int nmaps,
> - bool force_first __attribute__ ((unused)), bool for_fini)
> + bool force_first, bool for_fini)
> {
> + struct link_map *first_map = maps[0];
Move this to where it is actually used.
> for (int i = nmaps - 1; i >= 0; i--)
> maps[i]->l_visited = 0;
>
> @@ -208,14 +209,6 @@ _dl_sort_maps_dfs (struct link_map **maps, unsigned int nmaps,
> Adjusting the order so that maps[0] is last traversed naturally avoids
> this problem.
>
> - Further, the old "optimization" of skipping the main object at maps[0]
> - from the call-site (i.e. _dl_sort_maps(maps+1,nmaps-1)) is in general
> - no longer valid, since traversing along object dependency-links
> - may "find" the main object even when it is not included in the initial
> - order (e.g. a dlopen()'ed shared object can have circular dependencies> - linked back to itself). In such a case, traversing N-1 objects will
> - create a N-object result, and raise problems.
> -
> To summarize, just passing in the full list, and iterating from back
> to front makes things much more straightforward. */
>
> @@ -274,6 +267,30 @@ _dl_sort_maps_dfs (struct link_map **maps, unsigned int nmaps,
> }
>
> memcpy (maps, rpo, sizeof (struct link_map *) * nmaps);
> +
> + /* Skipping the first object at maps[0] is not valid in general,
> + since traversing along object dependency-links may "find" that
> + first object even when it is not included in the initial order
> + (e.g. a dlopen()'ed shared object can have circular dependencies
> + linked back to itself). In such a case, traversing N-1 objects
Double space after period and think we do not reference symbol using '()'.
> + will create a N-object result, and raise problems. Instead,
> + force the object back into first place after sorting. */
> + if (force_first && maps[0] != first_map)
> + {
> + struct link_map *saved = maps[0];
> + maps[0] = first_map;
> + int i = 1;
> + while (true)
> + {
> + assert (i < nmaps);
> + struct link_map *current = maps[i];
> + maps[i] = saved;
> + if (current == first_map)
> + break;
> + saved = current;
> + ++i;
> + }
> + }
> }
It sounds reasonable to keep the main object as the initial map, although
it would slow down a bit normal dlclose. I think it would be possible
to optimize the memory move with memmove here, although not sure if it is
worth.
>
> void
> diff --git a/elf/dso-sort-tests-1.def b/elf/dso-sort-tests-1.def
> index 5f7f18ef27..4bf9052db1 100644
> --- a/elf/dso-sort-tests-1.def
> +++ b/elf/dso-sort-tests-1.def
> @@ -64,3 +64,10 @@ output: b>a>{}<a<b
> tst-bz15311: {+a;+e;+f;+g;+d;%d;-d;-g;-f;-e;-a};a->b->c->d;d=>[ba];c=>a;b=>e=>a;c=>f=>b;d=>g=>c
> output(glibc.rtld.dynamic_sort=1): {+a[d>c>b>a>];+e[e>];+f[f>];+g[g>];+d[];%d(b(e(a()))a()g(c(a()f(b(e(a()))))));-d[];-g[];-f[];-e[];-a[<a<c<d<g<f<b<e];}
> output(glibc.rtld.dynamic_sort=2): {+a[d>c>b>a>];+e[e>];+f[f>];+g[g>];+d[];%d(b(e(a()))a()g(c(a()f(b(e(a()))))));-d[];-g[];-f[];-e[];-a[<g<f<a<b<c<d<e];}
> +
> +# Test that even in the presence of dependency loops involving dlopen'ed
> +# object, that object is initialized last (and not unloaded prematurely).
> +# Final destructor order is indeterminate due to the cycle.
> +tst-bz28937: {+a;+b;-b;+c;%c};a->a1;a->a2;a2->a;b->b1;c->a1;c=>a1
So main program:
1. dlopen 'a' and 'b';
2. dclose 'b';
3. dlopen 'c';
4. dlsym 'c' and calls fn_a from 'c';
And we have a circle dependency where a depends of a2 and a2 depends on 'a'.
Do we need to add a test for multiple circles? For instance where you have
either another disjointed circle ({+d};d->d2;d2->d) and/or another circle
in same dependency chain (a1->b;b1->a)?
> +output(glibc.rtld.dynamic_sort=1): {+a[a2>a1>a>];+b[b1>b>];-b[<b<b1];+c[c>];%c(a1());}<a<a2<c<a1
> +output(glibc.rtld.dynamic_sort=2): {+a[a2>a1>a>];+b[b1>b>];-b[<b<b1];+c[c>];%c(a1());}<a2<a<c<a1
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH 3/3] elf: Implement force_first handling in _dl_sort_maps_dfs
2022-08-31 16:37 ` Adhemerval Zanella Netto
@ 2022-08-31 16:37 ` Adhemerval Zanella Netto
2022-09-06 6:39 ` Florian Weimer
1 sibling, 0 replies; 10+ messages in thread
From: Adhemerval Zanella Netto @ 2022-08-31 16:37 UTC (permalink / raw)
To: libc-alpha, Florian Weimer
On 31/08/22 13:37, Adhemerval Zanella Netto wrote:
>
>
> On 15/08/22 11:30, Florian Weimer via Libc-alpha wrote:
>> As documented in a comment _dl_close_worker, the skipping is actually
>> needed for correctness. It also seems less surprising if the
>> just-opened object is always initialized last, even in the presence
>> of cycles.
>
> I think it is BZ#28937, isn't? Also could you extend the explanation as you
> did in the last comment, the initial phrase sounds confusing. Maybe extend
> the comment to say that not _dl_sort_maps_dfs will move the main object to
> front, so where previous you have the maps input as:
>
> maps[0].l_name=elf/tst-bz28937-dir/tst-bz28937-a.so
> maps[1].l_name=[...]/elf/tst-bz28937-dir/tst-bz28937-a1.so
> maps[2].l_name=[...]/elf/tst-bz28937-dir/tst-bz28937-a2.so
> maps[3].l_name=./libc.so.6
> maps[4].l_name=elf/ld.so
>
> It will not be properly sorted as:
It will *now* be ...
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH 3/3] elf: Implement force_first handling in _dl_sort_maps_dfs
2022-08-31 16:37 ` Adhemerval Zanella Netto
2022-08-31 16:37 ` Adhemerval Zanella Netto
@ 2022-09-06 6:39 ` Florian Weimer
1 sibling, 0 replies; 10+ messages in thread
From: Florian Weimer @ 2022-09-06 6:39 UTC (permalink / raw)
To: Adhemerval Zanella Netto; +Cc: libc-alpha
* Adhemerval Zanella Netto:
> On 15/08/22 11:30, Florian Weimer via Libc-alpha wrote:
>> As documented in a comment _dl_close_worker, the skipping is actually
>> needed for correctness. It also seems less surprising if the
>> just-opened object is always initialized last, even in the presence
>> of cycles.
>
> I think it is BZ#28937, isn't? Also could you extend the explanation as you
> did in the last comment, the initial phrase sounds confusing.
I have expanded the commit message.
> Maybe extend the comment to say that not _dl_sort_maps_dfs will move
> the main object to front, so where previous you have the maps input
> as:
>
> maps[0].l_name=elf/tst-bz28937-dir/tst-bz28937-a.so
> maps[1].l_name=[...]/elf/tst-bz28937-dir/tst-bz28937-a1.so
> maps[2].l_name=[...]/elf/tst-bz28937-dir/tst-bz28937-a2.so
> maps[3].l_name=./libc.so.6
> maps[4].l_name=elf/ld.so
>
> It will not be properly sorted as:
>
> maps[0].l_name=elf/tst-bz28937-dir/tst-bz28937-a.so
> maps[1].l_name=[...]/elf/tst-bz28937-dir/tst-bz28937-a1.so
> maps[2].l_name=[...]/elf/tst-bz28937-dir/tst-bz28937-a2.so
> maps[3].l_name=./libc.so.6
> maps[4].l_name=elf/ld.so
>
> Instead of wrongly:
>
> maps[0].l_name=[...]/elf/tst-bz28937-dir/tst-bz28937-a1.so
> maps[1].l_name=[...]/elf/tst-bz28937-dir/tst-bz28937-a2.so
> maps[2].l_name=elf/tst-bz28937-dir/tst-bz28937-a.so
> maps[3].l_name=./libc.so.6
> maps[4].l_name=elf/ld.so
I think with just three elements, it's a bit misleading because a cycle
of this size is rotated correctly by the naive approach.
>> diff --git a/elf/dl-sort-maps.c b/elf/dl-sort-maps.c
>> index 5b550b1e94..cd2d9c93fc 100644
>> --- a/elf/dl-sort-maps.c
>> +++ b/elf/dl-sort-maps.c
>> @@ -182,8 +182,9 @@ dfs_traversal (struct link_map ***rpo, struct link_map *map,
>>
>> static void
>> _dl_sort_maps_dfs (struct link_map **maps, unsigned int nmaps,
>> - bool force_first __attribute__ ((unused)), bool for_fini)
>> + bool force_first, bool for_fini)
>> {
>> + struct link_map *first_map = maps[0];
>
> Move this to where it is actually used.
We need to copy it before it's overwritten by the sort.
>> + /* Skipping the first object at maps[0] is not valid in general,
>> + since traversing along object dependency-links may "find" that
>> + first object even when it is not included in the initial order
>> + (e.g. a dlopen()'ed shared object can have circular dependencies
>> + linked back to itself). In such a case, traversing N-1 objects
>
> Double space after period and think we do not reference symbol using '()'.
Fixed (although I just copied that part of the comment).
>> + will create a N-object result, and raise problems. Instead,
>> + force the object back into first place after sorting. */
>> + if (force_first && maps[0] != first_map)
>> + {
>> + struct link_map *saved = maps[0];
>> + maps[0] = first_map;
>> + int i = 1;
>> + while (true)
>> + {
>> + assert (i < nmaps);
>> + struct link_map *current = maps[i];
>> + maps[i] = saved;
>> + if (current == first_map)
>> + break;
>> + saved = current;
>> + ++i;
>> + }
>> + }
>> }
>
> It sounds reasonable to keep the main object as the initial map, although
> it would slow down a bit normal dlclose. I think it would be possible
> to optimize the memory move with memmove here, although not sure if it is
> worth.
If we make the assert less precise, memmove actually simplifies the
code. I've made the change.
>> void
>> diff --git a/elf/dso-sort-tests-1.def b/elf/dso-sort-tests-1.def
>> index 5f7f18ef27..4bf9052db1 100644
>> --- a/elf/dso-sort-tests-1.def
>> +++ b/elf/dso-sort-tests-1.def
>> @@ -64,3 +64,10 @@ output: b>a>{}<a<b
>> tst-bz15311: {+a;+e;+f;+g;+d;%d;-d;-g;-f;-e;-a};a->b->c->d;d=>[ba];c=>a;b=>e=>a;c=>f=>b;d=>g=>c
>> output(glibc.rtld.dynamic_sort=1): {+a[d>c>b>a>];+e[e>];+f[f>];+g[g>];+d[];%d(b(e(a()))a()g(c(a()f(b(e(a()))))));-d[];-g[];-f[];-e[];-a[<a<c<d<g<f<b<e];}
>> output(glibc.rtld.dynamic_sort=2): {+a[d>c>b>a>];+e[e>];+f[f>];+g[g>];+d[];%d(b(e(a()))a()g(c(a()f(b(e(a()))))));-d[];-g[];-f[];-e[];-a[<g<f<a<b<c<d<e];}
>> +
>> +# Test that even in the presence of dependency loops involving dlopen'ed
>> +# object, that object is initialized last (and not unloaded prematurely).
>> +# Final destructor order is indeterminate due to the cycle.
>> +tst-bz28937: {+a;+b;-b;+c;%c};a->a1;a->a2;a2->a;b->b1;c->a1;c=>a1
>
> So main program:
>
> 1. dlopen 'a' and 'b';
> 2. dclose 'b';
> 3. dlopen 'c';
> 4. dlsym 'c' and calls fn_a from 'c';
>
> And we have a circle dependency where a depends of a2 and a2 depends on 'a'.
>
> Do we need to add a test for multiple circles? For instance where you have
> either another disjointed circle ({+d};d->d2;d2->d) and/or another circle
> in same dependency chain (a1->b;b1->a)?
Could you add this as a follow-up patch? It does not seem strictly
related (and I think we already have other tests for unloading cycles).
Thanks,
Florian
^ permalink raw reply [flat|nested] 10+ messages in thread
end of thread, other threads:[~2022-09-06 6:39 UTC | newest]
Thread overview: 10+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2022-08-15 14:30 [PATCH 0/3] Forced ordering for DFS ELF dependency sorting (bug 28937) Florian Weimer
2022-08-15 14:30 ` [PATCH 1/3] scripts/dso-ordering-test.py: Generate program run-time dependencies Florian Weimer
2022-08-15 14:35 ` Florian Weimer
2022-08-29 14:30 ` Adhemerval Zanella Netto
2022-08-15 14:30 ` [PATCH 2/3] elf: Rename _dl_sort_maps parameter from skip to force_first Florian Weimer
2022-08-29 16:40 ` Adhemerval Zanella Netto
2022-08-15 14:30 ` [PATCH 3/3] elf: Implement force_first handling in _dl_sort_maps_dfs Florian Weimer
2022-08-31 16:37 ` Adhemerval Zanella Netto
2022-08-31 16:37 ` Adhemerval Zanella Netto
2022-09-06 6:39 ` Florian Weimer
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