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authorRichard Purdie <richard.purdie@linuxfoundation.org>2017-03-07 13:47:03 +0000
committerRichard Purdie <richard.purdie@linuxfoundation.org>2017-03-07 20:05:31 +0000
commitc4901328fe5cf912c0965e5b011b64a95a9bcb9d (patch)
tree0f86e0feb929817fe3b6d21498ffb15a5d0eb01e /meta/recipes-devtools/patchelf
parent4485ea5807dd99b7f140b06b35654a6a70c286e4 (diff)
downloadpoky-c4901328fe5cf912c0965e5b011b64a95a9bcb9d.tar.gz
patchelf: Fix issues with the 'hole' in binaries approach
We're seeing two issues with patchelf, one where it inflates binaries to MBs in size, the other where stripping the resulting binary fails: $ strip fixincl Not enough room for program headers, try linking with -N [.note.ABI-tag]: Bad value The patch header describes more about what the problem is and how the patch fixes it. [YOCTO #11123] [YOCTO #11009] (From OE-Core rev: 39f5a05152aa0c3503735e18dd3b4c066b284107) Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Diffstat (limited to 'meta/recipes-devtools/patchelf')
-rw-r--r--meta/recipes-devtools/patchelf/patchelf/avoidholes.patch163
-rw-r--r--meta/recipes-devtools/patchelf/patchelf_0.9.bb1
2 files changed, 164 insertions, 0 deletions
diff --git a/meta/recipes-devtools/patchelf/patchelf/avoidholes.patch b/meta/recipes-devtools/patchelf/patchelf/avoidholes.patch
new file mode 100644
index 0000000000..a273688b98
--- /dev/null
+++ b/meta/recipes-devtools/patchelf/patchelf/avoidholes.patch
@@ -0,0 +1,163 @@
1Different types of binaries create challenges for patchelf. In order to extend
2sections they need to be moved within the binary. The current approach to
3handling ET_DYN binaries is to move the INTERP section to the end of the file.
4This means changing PT_PHDR to add an extra PT_LOAD section so that the new section
5is mmaped into memory by the elf loader in the kernel. In order to extend PHDR,
6this means moving it to the end of the file.
7
8Its documented in patchelf there is a kernel 'bug' which means that if you have holes
9in memory between the base load address and the PT_LOAD segment that contains PHDR,
10it will pass an incorrect PHDR address to ld.so and fail to load the binary, segfaulting.
11
12To avoid this, the code currently inserts space into the binary to ensure that when
13loaded into memory there are no holes between the PT_LOAD sections. This inflates the
14binaries by many MBs in some cases. Whilst we could make them sparse, there is a second
15issue which is that strip can fail to process these binaries:
16
17$ strip fixincl
18Not enough room for program headers, try linking with -N
19[.note.ABI-tag]: Bad value
20
21This turns out to be due to libbfd not liking the relocated PHDR section either
22(https://github.com/NixOS/patchelf/issues/10).
23
24Instead this patch implements a different approach, leaving PHDR where it is but extending
25it in place to allow addition of a new PT_LOAD section. This overwrites sections in the
26binary but those get moved to the end of the file in the new PT_LOAD section.
27
28This is based on patches linked from the above github issue, however whilst the idea
29was good, the implementation wasn't correct and they've been rewritten here.
30
31RP
322017/3/7
33
34Upstream-Status: Pending
35
36Index: patchelf-0.9/src/patchelf.cc
37===================================================================
38--- patchelf-0.9.orig/src/patchelf.cc
39+++ patchelf-0.9/src/patchelf.cc
40@@ -146,6 +146,8 @@ private:
41 string & replaceSection(const SectionName & sectionName,
42 unsigned int size);
43
44+ bool haveReplacedSection(const SectionName & sectionName);
45+
46 void writeReplacedSections(Elf_Off & curOff,
47 Elf_Addr startAddr, Elf_Off startOffset);
48
49@@ -497,6 +499,16 @@ unsigned int ElfFile<ElfFileParamNames>:
50 return 0;
51 }
52
53+template<ElfFileParams>
54+bool ElfFile<ElfFileParamNames>::haveReplacedSection(const SectionName & sectionName)
55+{
56+ ReplacedSections::iterator i = replacedSections.find(sectionName);
57+
58+ if (i != replacedSections.end())
59+ return true;
60+ return false;
61+}
62+
63
64 template<ElfFileParams>
65 string & ElfFile<ElfFileParamNames>::replaceSection(const SectionName & sectionName,
66@@ -595,52 +607,52 @@ void ElfFile<ElfFileParamNames>::rewrite
67
68 debug("last page is 0x%llx\n", (unsigned long long) startPage);
69
70+ /* Because we're adding a new section header, we're necessarily increasing
71+ the size of the program header table. This can cause the first section
72+ to overlap the program header table in memory; we need to shift the first
73+ few segments to someplace else. */
74+ /* Some sections may already be replaced so account for that */
75+ unsigned int i = 1;
76+ Elf_Addr pht_size = sizeof(Elf_Ehdr) + (phdrs.size() + 1)*sizeof(Elf_Phdr);
77+ while( shdrs[i].sh_addr <= pht_size && i < rdi(hdr->e_shnum) ) {
78+ if (not haveReplacedSection(getSectionName(shdrs[i])))
79+ replaceSection(getSectionName(shdrs[i]), shdrs[i].sh_size);
80+ i++;
81+ }
82
83- /* Compute the total space needed for the replaced sections and
84- the program headers. */
85- off_t neededSpace = (phdrs.size() + 1) * sizeof(Elf_Phdr);
86+ /* Compute the total space needed for the replaced sections */
87+ off_t neededSpace = 0;
88 for (ReplacedSections::iterator i = replacedSections.begin();
89 i != replacedSections.end(); ++i)
90 neededSpace += roundUp(i->second.size(), sectionAlignment);
91 debug("needed space is %d\n", neededSpace);
92
93-
94 size_t startOffset = roundUp(fileSize, getPageSize());
95
96 growFile(startOffset + neededSpace);
97
98-
99 /* Even though this file is of type ET_DYN, it could actually be
100 an executable. For instance, Gold produces executables marked
101- ET_DYN. In that case we can still hit the kernel bug that
102- necessitated rewriteSectionsExecutable(). However, such
103- executables also tend to start at virtual address 0, so
104+ ET_DYN as does LD when linking with pie. If we move PT_PHDR, it
105+ has to stay in the first PT_LOAD segment or any subsequent ones
106+ if they're continuous in memory due to linux kernel constraints
107+ (see BUGS). Since the end of the file would be after bss, we can't
108+ move PHDR there, we therefore choose to leave PT_PHDR where it is but
109+ move enough following sections such that we can add the extra PT_LOAD
110+ section to it. This PT_LOAD segment ensures the sections at the end of
111+ the file are mapped into memory for ld.so to process.
112+ We can't use the approach in rewriteSectionsExecutable()
113+ since DYN executables tend to start at virtual address 0, so
114 rewriteSectionsExecutable() won't work because it doesn't have
115- any virtual address space to grow downwards into. As a
116- workaround, make sure that the virtual address of our new
117- PT_LOAD segment relative to the first PT_LOAD segment is equal
118- to its offset; otherwise we hit the kernel bug. This may
119- require creating a hole in the executable. The bigger the size
120- of the uninitialised data segment, the bigger the hole. */
121+ any virtual address space to grow downwards into. */
122 if (isExecutable) {
123 if (startOffset >= startPage) {
124 debug("shifting new PT_LOAD segment by %d bytes to work around a Linux kernel bug\n", startOffset - startPage);
125- } else {
126- size_t hole = startPage - startOffset;
127- /* Print a warning, because the hole could be very big. */
128- fprintf(stderr, "warning: working around a Linux kernel bug by creating a hole of %zu bytes in ā€˜%sā€™\n", hole, fileName.c_str());
129- assert(hole % getPageSize() == 0);
130- /* !!! We could create an actual hole in the file here,
131- but it's probably not worth the effort. */
132- growFile(fileSize + hole);
133- startOffset += hole;
134 }
135 startPage = startOffset;
136 }
137
138-
139- /* Add a segment that maps the replaced sections and program
140- headers into memory. */
141+ /* Add a segment that maps the replaced sections into memory. */
142 phdrs.resize(rdi(hdr->e_phnum) + 1);
143 wri(hdr->e_phnum, rdi(hdr->e_phnum) + 1);
144 Elf_Phdr & phdr = phdrs[rdi(hdr->e_phnum) - 1];
145@@ -653,15 +665,12 @@ void ElfFile<ElfFileParamNames>::rewrite
146
147
148 /* Write out the replaced sections. */
149- Elf_Off curOff = startOffset + phdrs.size() * sizeof(Elf_Phdr);
150+ Elf_Off curOff = startOffset;
151 writeReplacedSections(curOff, startPage, startOffset);
152 assert(curOff == startOffset + neededSpace);
153
154-
155- /* Move the program header to the start of the new area. */
156- wri(hdr->e_phoff, startOffset);
157-
158- rewriteHeaders(startPage);
159+ /* Write out the updated program and section headers */
160+ rewriteHeaders(hdr->e_phoff);
161 }
162
163
diff --git a/meta/recipes-devtools/patchelf/patchelf_0.9.bb b/meta/recipes-devtools/patchelf/patchelf_0.9.bb
index 54e654bdcb..01f0e62135 100644
--- a/meta/recipes-devtools/patchelf/patchelf_0.9.bb
+++ b/meta/recipes-devtools/patchelf/patchelf_0.9.bb
@@ -2,6 +2,7 @@ SRC_URI = "http://nixos.org/releases/${BPN}/${BPN}-${PV}/${BPN}-${PV}.tar.bz2 \
2 file://Skip-empty-section-fixes-66.patch \ 2 file://Skip-empty-section-fixes-66.patch \
3 file://handle-read-only-files.patch \ 3 file://handle-read-only-files.patch \
4 file://Increase-maxSize-to-64MB.patch \ 4 file://Increase-maxSize-to-64MB.patch \
5 file://avoidholes.patch \
5" 6"
6 7
7LICENSE = "GPLv3" 8LICENSE = "GPLv3"