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llvm-objcopy: "error: invalid symbol index" with mips64el-linux-gnuabi64 #52647

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nathanchance opened this issue Dec 13, 2021 · 4 comments
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llvm-objcopy: "error: invalid symbol index" with mips64el-linux-gnuabi64 #52647

nathanchance opened this issue Dec 13, 2021 · 4 comments
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tools:llvm-objcopy/strip

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@nathanchance
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Initial reported and triaged at ClangBuiltLinux/linux#1534.

While building the Linux kernel with OBJCOPY=llvm-objcopy, the following error is observed:

llvm-objcopy: error: invalid symbol index: 67108864
make: *** [Makefile:1161: vmlinux] Error 1

This appears to be related to the use of -EL and -mabi=64. A very simple C reproducer:

$ cat test.c
void lkdtm_rodata_do_nothing() {}

$ clang --target=mips64el-linux-gnuabi64 -c test.c

$ llvm-objcopy test.o test_objcopy.o
llvm-objcopy: error: invalid symbol index: 33554432

It does not happen with mips64-linux-gnuabi64 or 32-bit MIPS targets.
@nathanchance nathanchance mentioned this issue Dec 13, 2021
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@jh7370
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jh7370 commented Dec 13, 2021

I think the problem is in initRelocations in the llvm-objcopy code: it has references to Rel.getType(false) and Rel.getSymbol(false). The latter in particular is likely the culprit, but both are probably wrong, based on my reading of this bug: the boolean corresponds to an isMips64EL, which I'd expect to be true for the test case.

The fix will be to pass this information to these functions, and quite possibly other functions in the code (I see a reference to getSymbolAndType in writeRel that also has a suspicious hard-coded false).

Unfortunately, my MIPS knowledge is limited, so I don't know how to get the proper value for the isMips64EL parameter from the object into llvm-objcopy. As such, I cannot provide a fix myself.

@atanasyan
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I will take a look at this bug.

@atanasyan
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The fix is in the https://reviews.llvm.org/D115635.

atanasyan added a commit that referenced this issue Dec 14, 2021
@atanasyan
[llvm-objcopy] Fix handling of MIPS64 little endian files
d5d8b1c 
MIPS64 little endian target has a "special" encoding of `r_info`
relocation record field. Instead of one 64-bit little endian number, it
is a little endian 32-bit number followed by a 32-bit big endian number.
For correct reading and writing such fields we must provide information
about target machine into the corresponding routine. This patch does
this for the `llvm-objcopy` tool and fix handling of MIPS64 little
endian files.

The bug was reported in the issue #52647.

Differential Revision: https://reviews.llvm.org/D115635
@nathanchance
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Thanks Simon!

d5d8b1c

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@asl @atanasyan @nathanchance @jh7370