ld: ELF binaries not compatible with strip #1242
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Owner changed to r...@golang.org. Status changed to LongTerm. |
strip actually emits a bunch of warnings:
max@mahako:~/src/test$ cat hello.go
package main
func main() {
print("Hello world.\n")
}
max@mahako:~/src/test$ 8g hello.go
max@mahako:~/src/test$ 8l -o hello hello.8
max@mahako:~/src/test$ ./hello
Hello world.
max@mahako:~/src/test$ strip hello
BFD: stGWSejb: section .rodata vma 0x8054000 overlaps previous sections
BFD: stGWSejb: section .plt vma 0x8054010 overlaps previous sections
BFD: stGWSejb: section .hash vma 0x8054020 overlaps previous sections
BFD: stGWSejb: section .dynstr vma 0x8054034 overlaps previous sections
BFD: stGWSejb: section .dynamic vma 0x8054050 overlaps previous sections
BFD: stGWSejb: section .gopclntab vma 0x80581a8 overlaps previous sections
BFD: stGWSejb: section .gosymtab vma 0x8059b68 overlaps previous sections
BFD: stGWSejb: section .got.plt vma 0x8069040 overlaps previous sections
BFD: stGWSejb: section .bss vma 0x806a3b8 overlaps previous sections
BFD: stGWSejb: warning: allocated section `.interp' not in segment
max@mahako:~/src/test$ ./hello
Segmentation fault
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> strip actually emits a bunch of warnings: I get similar warnings: $ strip ./main BFD: ./stkhBl0d: section .rodata lma 0x807e000 adjusted to 0x807e010 BFD: ./stkhBl0d: section .plt lma 0x807e010 adjusted to 0x8119fb8 BFD: ./stkhBl0d: section .hash lma 0x807e020 adjusted to 0x8119fc8 BFD: ./stkhBl0d: section .dynstr lma 0x807e034 adjusted to 0x8119fdc BFD: ./stkhBl0d: section .dynamic lma 0x807e064 adjusted to 0x811a00c BFD: ./stkhBl0d: section .gopclntab lma 0x80b29ec adjusted to 0x811a084 BFD: ./stkhBl0d: section .gosymtab lma 0x80b78c0 adjusted to 0x811ef58 BFD: ./stkhBl0d: section .got.plt lma 0x811a098 adjusted to 0x811ba58 BFD: ./stkhBl0d: section .bss lma 0x811ba58 adjusted to 0x811ba64 BFD: ./stkhBl0d: warning: allocated section `.interp' not in segment |
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Issue #1280 has been merged into this issue. |
Comment 7:
I don't think that elfutils is a safe way to determine whether an ELF Binary is
"wellformed".
Consider this C Code:
#include <stdio.h>
int main()
{
printf("Hello World\n");
return 0;
}
Now, after running elflint:
section [10] '.rel.plt': relocation 0: offset out of bounds
section [10] '.rel.plt': relocation 1: offset out of bounds
section [10] '.rel.plt': relocation 2: offset out of bounds
section [27] '.symtab': _GLOBAL_OFFSET_TABLE_ symbol size 0 does not match .got.plt section size 24
section [27] '.symtab': _DYNAMIC symbol size 0 does not match dynamic segment size 200
And now, the same with Go:
package main
import "fmt"
func main() {
fmt.Printf("Hello world\n")
}
And elflint:
PHDR segment not contained in a loaded segment
section [ 1] '.interp': alloc flag set but section not in any loaded segment
section [12] '.rodata' has wrong flags: expected ALLOC and possibly MERGE|STRINGS, is WRITE|ALLOC
I suppose that elflint actually has a hardcoded pattern for ELF Binaries, or some such...
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Issue #1578 has been merged into this issue. |
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Issue #1580 has been merged into this issue. |
I wrote a small program (in python, sry) that will run readelf -S and sort the results
so that the issues might be more visible. It prints out zero sized sections too, but
feel free ignore those.
On tutorial hello world, with 6g pulled in 2011-03-16, the results are as follows (prior
to even running strip):
./parse-sections.py 6.out
SectName VMAddress Size(B) Errors
.interp 0x00400be4 28
.text 0x00400c00 237618
.rela.plt 0x0043b000 0 ZERO SIZED SECTION
.rela 0x0043b000 0 OVERLAPS WITH PREVIOUS, ZERO SIZED SECTION
.dynstr 0x0043b000 4 OVERLAPS WITH PREVIOUS
.rodata 0x0043b000 788232 OVERLAPS WITH PREVIOUS
.plt 0x0043b004 16 OVERLAPS WITH PREVIOUS
.hash 0x0043b014 20
.dynsym 0x0043b028 24
.dynamic 0x0043b040 224
.shstrtab 0x0043b120 340
.gopclntab 0x0048f9a8 21080
.gosymtab 0x00494c00 420616
.got 0x004fc000 0 ZERO SIZED SECTION
.data 0x004fc000 8160 OVERLAPS WITH PREVIOUS
.got.plt 0x004fc118 24 OVERLAPS WITH PREVIOUS
.bss 0x004fdfe0 33647768
Some of the overlaps are quite serious in range. These will certainly trigger the
warnings of libbfd (that strip uses).
The silly little python script I wrote can be found at
http://iohazard.net/pub/go/parse-sections.py .
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Ok, I'll send a couple of initial minors from last night for appraisal. Owner changed to @niemeyer. Status changed to Started. |
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This issue was closed by revision cf143e9. Status changed to Fixed. |
Yes, unfortunately I was testing with a non-dynamic binary. A similar fix will have to be made for dynamic ones, and I'll work on it next. A new bug was opened to track this: https://golang.org/issue/2022 |
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Comment 20 by danderson@google.com: The major issue reported by elflint is not to do with symbol lengths and section alignment, but with the PHDR segment: PHDR segment not contained in a loaded segment This is, as far as I can tell, the only fatal error that the tools I want to use (paxctl notably) report, the others being icky but workaroundable. A quick analysis of a static Go binary suggests that the PHDR section is the last in the section header table, after all the loadable sections containing the executable text/data. However, the ELF specs that I've been looking at specify that the PHDR section entry in the section header table should appear /before/ any sections marked loadable. I'm fairly sure there's more constraints on the PHDR section that I haven't found yet, but that's the braindump of my current attempts to make paxctl work with Go programs, if anyone can beat me to a patch that makes that fatal error go away. |
I have been fixing these other elflint warnings as well, and even though I've not debugged the PHDR issue yet I have a few other in the pipeline which I know the cause and the fix. I've just been a bit slow due to projects at Canonical taking my time. Note that this one bug we're discussing here is about strip working. It will be closed without the PHDR issue being addressed, so feel free to open another one if that's important for you. |
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Comment 22 by danderson@google.com: I did open another one, a long time ago. It was closed as a duplicate of this one. |
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Comment 24 by danderson@google.com: Aha, I see. The bug I reported was slightly different at the time: Go binaries crash on hardened kernels that enforce W^X memory pages, because the runtime needs W+X. Normally, you can disable that enforcement per-binary with tools that tag the ELF with flags, but those tools crash because of ELF malformations. Anyway, you're correct that it's a separate, but related bug. I'll open a new issue and assign it to myself for further poking. |
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This issue was closed by revision ba2e3af. Status changed to Fixed. |
This issue was closed.
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by slairf:
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