[PATCH v3] ld.so: Decorate BSS mappings
Petr Malat
oss@malat.biz
Tue Jan 28 10:08:20 GMT 2025
Decorate BSS mappings with [anon: glibc: .bss <file>], for example
[anon: glibc: .bss /lib/libc.so.6]. The string ".bss" is already used
by bionic so use the same, but add the filename as well. If the name
would be longer than what the kernel allows, drop the directory part
of the path.
Refactor glibc.mem.decorate_maps check to a separate function and use
it to avoid assembling a name, which would not be used later.
Signed-off-by: Petr Malat <oss@malat.biz>
---
elf/dl-map-segments.h | 30 +++++++++++++++++++
nptl/allocatestack.c | 4 ---
sysdeps/generic/setvmaname.h | 12 ++++++++
sysdeps/unix/sysv/linux/setvmaname.c | 45 ++++++++++++++++++++--------
sysdeps/unix/sysv/linux/setvmaname.h | 8 +++++
5 files changed, 83 insertions(+), 16 deletions(-)
diff --git a/elf/dl-map-segments.h b/elf/dl-map-segments.h
index 203b6c7b0b..ee68dda550 100644
--- a/elf/dl-map-segments.h
+++ b/elf/dl-map-segments.h
@@ -18,6 +18,7 @@
<https://www.gnu.org/licenses/>. */
#include <dl-load.h>
+#include <setvmaname.h>
/* Map a segment and align it properly. */
@@ -182,12 +183,41 @@ _dl_map_segments (struct link_map *l, int fd,
if (zeroend > zeropage)
{
/* Map the remaining zero pages in from the zero fill FD. */
+ char bssname[ANON_VMA_NAME_MAX_LEN] = " glibc: .bss";
+
caddr_t mapat;
mapat = __mmap ((caddr_t) zeropage, zeroend - zeropage,
c->prot, MAP_ANON|MAP_PRIVATE|MAP_FIXED,
-1, 0);
if (__glibc_unlikely (mapat == MAP_FAILED))
return DL_MAP_SEGMENTS_ERROR_MAP_ZERO_FILL;
+ if (__is_decorate_maps_enabled ())
+ {
+ if (l->l_name != NULL && *l->l_name != '\0')
+ {
+ int i = strlen (bssname), j = 0;
+ int namelen = strlen (l->l_name);
+
+ bssname[i++] = ' ';
+ if (namelen > sizeof (bssname) - i - 1)
+ for (j = namelen - 1; j > 0; j--)
+ if (l->l_name[j - 1] == '/')
+ break;
+
+ for (; l->l_name[j] != '\0' && i < sizeof (bssname) - 1;
+ i++, j++)
+ {
+ char ch = l->l_name[j];
+ /* Replace non-printable characters and
+ \, `, $, [ and ]. */
+ if (ch <= 0x1f || ch >= 0x7f || strchr("\\`$[]", ch))
+ ch = '!';
+ bssname[i] = ch;
+ }
+ bssname[i] = 0;
+ }
+ __set_vma_name ((void*)zeropage, zeroend - zeropage, bssname);
+ }
}
}
diff --git a/nptl/allocatestack.c b/nptl/allocatestack.c
index 9c1a72bcf0..622c22f050 100644
--- a/nptl/allocatestack.c
+++ b/nptl/allocatestack.c
@@ -549,10 +549,6 @@ allocate_stack (const struct pthread_attr *attr, struct pthread **pdp,
return 0;
}
-/* Maximum supported name from initial kernel support, not exported
- by user API. */
-#define ANON_VMA_NAME_MAX_LEN 80
-
#define SET_STACK_NAME(__prefix, __stack, __stacksize, __tid) \
({ \
char __stack_name[sizeof (__prefix) + \
diff --git a/sysdeps/generic/setvmaname.h b/sysdeps/generic/setvmaname.h
index baca984a54..496fcca33b 100644
--- a/sysdeps/generic/setvmaname.h
+++ b/sysdeps/generic/setvmaname.h
@@ -19,6 +19,18 @@
#ifndef __SETVMANAME_H
#define __SETVMANAME_H
+#include <stdbool.h>
+
+/* Set this to small value to not waste memory on systems, which do
+ * not support VMA name. */
+#define ANON_VMA_NAME_MAX_LEN 16
+
+static inline bool
+__is_decorate_maps_enabled (void)
+{
+ return false;
+}
+
static inline
void __set_vma_name (void *start, size_t len, const char *name)
{
diff --git a/sysdeps/unix/sysv/linux/setvmaname.c b/sysdeps/unix/sysv/linux/setvmaname.c
index 749c587f12..ea93a5ffbe 100644
--- a/sysdeps/unix/sysv/linux/setvmaname.c
+++ b/sysdeps/unix/sysv/linux/setvmaname.c
@@ -22,6 +22,33 @@
#include <sysdep.h>
#include <elf/dl-tunables.h>
+static enum {
+ decorate_unknown = -1,
+ decorate_off,
+ decorate_on
+} decorate_maps = decorate_unknown;
+
+bool
+__is_decorate_maps_enabled (void)
+{
+ switch (atomic_load_relaxed (&decorate_maps))
+ {
+ case decorate_unknown:
+ if (TUNABLE_GET (glibc, mem, decorate_maps, int32_t, NULL) != 0)
+ {
+ atomic_store_relaxed (&decorate_maps, decorate_on);
+ return true;
+ }
+ atomic_store_relaxed (&decorate_maps, decorate_off);
+ return false;
+ case decorate_off:
+ return false;
+ case decorate_on:
+ return true;
+ }
+ __builtin_unreachable ();
+}
+
/* If PR_SET_VMA_ANON_NAME is not supported by the kernel, prctl returns
EINVAL. However, it also returns the same error for invalid argument.
Since it is an internal-only API, it assumes well formatted input:
@@ -31,19 +58,13 @@
void
__set_vma_name (void *start, size_t len, const char *name)
{
- static int prctl_supported = 1;
- if (atomic_load_relaxed (&prctl_supported) == 0)
- return;
-
- /* Set the prctl as not supported to avoid checking the tunable on every
- call. */
- if (TUNABLE_GET (glibc, mem, decorate_maps, int32_t, NULL) != 0)
+ if (__is_decorate_maps_enabled ())
{
int r = INTERNAL_SYSCALL_CALL (prctl, PR_SET_VMA, PR_SET_VMA_ANON_NAME,
- start, len, name);
- if (r == 0 || r != -EINVAL)
- return;
+ start, len, name);
+
+ /* Disable further attempts if not supported by the kernel. */
+ if (r == -EINVAL)
+ atomic_store_relaxed (&decorate_maps, decorate_off);
}
- atomic_store_relaxed (&prctl_supported, 0);
- return;
}
diff --git a/sysdeps/unix/sysv/linux/setvmaname.h b/sysdeps/unix/sysv/linux/setvmaname.h
index 715b096799..48643d0dad 100644
--- a/sysdeps/unix/sysv/linux/setvmaname.h
+++ b/sysdeps/unix/sysv/linux/setvmaname.h
@@ -19,9 +19,17 @@
#ifndef __SETVMANAME_H
#define __SETVMANAME_H
+/* Maximum supported name from initial kernel support, not exported
+ by user API. */
+#define ANON_VMA_NAME_MAX_LEN 80
+
/* Set the NAME to the anonymous memory map START with size of LEN.
It assumes well-formatted input. */
#if IS_IN(libc) || IS_IN(rtld)
+#include <stdbool.h>
+
+bool __is_decorate_maps_enabled (void) attribute_hidden;
+
void __set_vma_name (void *start, size_t len, const char *name)
attribute_hidden;
#else
--
2.39.5
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