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Diffstat (limited to 'meta/recipes-core/glibc/glibc/0010-Quote-from-bug-1443-which-explains-what-the-patch-do.patch')
-rw-r--r-- | meta/recipes-core/glibc/glibc/0010-Quote-from-bug-1443-which-explains-what-the-patch-do.patch | 62 |
1 files changed, 62 insertions, 0 deletions
diff --git a/meta/recipes-core/glibc/glibc/0010-Quote-from-bug-1443-which-explains-what-the-patch-do.patch b/meta/recipes-core/glibc/glibc/0010-Quote-from-bug-1443-which-explains-what-the-patch-do.patch new file mode 100644 index 0000000000..6b2bf65cac --- /dev/null +++ b/meta/recipes-core/glibc/glibc/0010-Quote-from-bug-1443-which-explains-what-the-patch-do.patch | |||
@@ -0,0 +1,62 @@ | |||
1 | From f6581da98bef982c888061fa06092c03f3c6c708 Mon Sep 17 00:00:00 2001 | ||
2 | From: Khem Raj <raj.khem@gmail.com> | ||
3 | Date: Wed, 18 Mar 2015 00:20:09 +0000 | ||
4 | Subject: [PATCH 10/30] Quote from bug 1443 which explains what the patch does | ||
5 | : | ||
6 | |||
7 | We build some random program and link it with -lust. When we run it, | ||
8 | it dies with a SIGSEGV before reaching main(). | ||
9 | |||
10 | Libust.so depends on liburcu-bp.so from the usermode-rcu package. | ||
11 | Although libust.so is not prelinked, liburcu-bp.so IS prelinked; this | ||
12 | is critical. | ||
13 | |||
14 | Libust.so uses a TLS / __thread variable that is defined in liburcu- | ||
15 | bp.so. There are special ARM-specific relocation types that allow two | ||
16 | shared libraries to share thread-specific data. This is critical too. | ||
17 | |||
18 | One more critical issue: although liburcu-bp.so is prelinked, we can't | ||
19 | load it at its prelinked address, because we also link against | ||
20 | librt.so, and librt.so uses that address. | ||
21 | |||
22 | The dynamic linker is forced to relink liburcu-bp.so at a different | ||
23 | address. In the course of relinking, it processes the special ARM | ||
24 | relocation record mentioned above. The prelinker has already filled | ||
25 | in the information, which is a short offset into a table of thread- | ||
26 | specific data that is allocated per-thread for each library that uses | ||
27 | TLS. Because the normal behavior of a relocation is to add the symbol | ||
28 | value to an addend stored at the address being relocated, we end up | ||
29 | adding the short offset to itself, doubling it. | ||
30 | |||
31 | Now we have an awkward situation. The libust.so library doesn't know | ||
32 | about the addend, so its TLS data for this element is correct. The | ||
33 | liburcu-bp.so library has a different offset for the element. When we | ||
34 | go to initialize the element for the first time in liburcu-bp.so, we | ||
35 | write the address of the result at the doubled (broken) offset. | ||
36 | Later, when we refer to the address from libust.so, we check the value | ||
37 | at the correct offset, but it's NULL, so we eat hot SIGSEGV. | ||
38 | |||
39 | Upstream-Status: Pending | ||
40 | |||
41 | Signed-off-by: Andrei Dinu <andrei.adrianx.dinu@intel.com> | ||
42 | Signed-off-by: Khem Raj <raj.khem@gmail.com> | ||
43 | --- | ||
44 | sysdeps/arm/dl-machine.h | 2 +- | ||
45 | 1 file changed, 1 insertion(+), 1 deletion(-) | ||
46 | |||
47 | diff --git a/sysdeps/arm/dl-machine.h b/sysdeps/arm/dl-machine.h | ||
48 | index 1a4fd3f17b..a02c47571a 100644 | ||
49 | --- a/sysdeps/arm/dl-machine.h | ||
50 | +++ b/sysdeps/arm/dl-machine.h | ||
51 | @@ -510,7 +510,7 @@ elf_machine_rel (struct link_map *map, const Elf32_Rel *reloc, | ||
52 | |||
53 | case R_ARM_TLS_DTPOFF32: | ||
54 | if (sym != NULL) | ||
55 | - *reloc_addr += sym->st_value; | ||
56 | + *reloc_addr = sym->st_value; | ||
57 | break; | ||
58 | |||
59 | case R_ARM_TLS_TPOFF32: | ||
60 | -- | ||
61 | 2.18.0 | ||
62 | |||