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4d3a0cade2
Simplify the logic of handling sections in BOLT. This change brings more
direct and predictable mapping of BinarySection instances to sections in
the input and output files.
* Only sections from the input binary will have a non-null SectionRef.
When a new section is created as a copy of the input section,
its SectionRef is reset to null.
* RewriteInstance::getOutputSectionName() is removed as the section name
in the output file is now defined by BinarySection::getOutputName().
* Querying BinaryContext for sections by name uses their original name.
E.g., getUniqueSectionByName(".rodata") will return the original
section even if the new .rodata section was created.
* Input file sections (with relocations applied) are emitted via MC with
".bolt.org" prefix. However, their name in the output binary is
unchanged unless a new section with the same name is created.
* New sections are emitted internally with ".bolt.new" prefix if there's
a name conflict with an input file section. Their original name is
preserved in the output file.
* Section header string table is properly populated with section names
that are actually used. Previously we used to include discarded
section names as well.
* Fix the problem when dynamic relocations were propagated to a new
section with a name that matched a section in the input binary.
E.g., the new .rodata with jump tables had dynamic relocations from
the original .rodata.
Reviewed By: rafauler
Differential Revision: https://reviews.llvm.org/D135494
80 lines
3.1 KiB
ArmAsm
80 lines
3.1 KiB
ArmAsm
# This reproduces a bug when rewriting dynamic relocations in X86 as
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# BOLT incorrectly attributes R_X86_64_64 dynamic relocations
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# to the wrong section when the -jump-tables=move flag is used. We
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# expect the relocations to belong to the .bolt.org.rodata section but
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# it is attributed to a new .rodata section that only contains jump
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# table entries, created by BOLT. BOLT will only create this new .rodata
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# section if both -jump-tables=move is used and a hot function with
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# jt is present in the input binary, triggering a scenario where the
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# dynamic relocs rewriting gets confused on where to put .rodata relocs.
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# It is uncommon to end up with dynamic relocations against .rodata,
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# but it can happen. In these cases we cannot corrupt the
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# output binary by writing out dynamic relocs incorrectly. The linker
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# avoids emitting relocs against read-only sections but we override
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# this behvior with the -z notext flag. During runtime, these pages
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# are mapped with write permission and then changed to read-only after
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# the dynamic linker finishes processing the dynamic relocs.
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# In this test, we create a reference to a dynamic object that will
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# imply in R_X86_64_64 being used for .rodata. Now BOLT, when creating
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# a new .rodata to hold jump table entries, needs to remember to emit
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# these dynamic relocs against the original .rodata, and not the new
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# one it just created.
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# REQUIRES: system-linux
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# RUN: llvm-mc -filetype=obj -triple x86_64-unknown-linux \
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# RUN: %s -o %t.o
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# RUN: link_fdata %s %t.o %t.fdata
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# RUN: llvm-mc -filetype=obj -triple x86_64-unknown-linux \
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# RUN: %p/Inputs/define_bar.s -o %t.2.o
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# RUN: llvm-strip --strip-unneeded %t.o
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# RUN: ld.lld %t.2.o -o %t.so -shared
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# RUN: ld.lld -z notext %t.o -o %t.exe -q %t.so
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# RUN: llvm-bolt -data %t.fdata %t.exe -relocs -o %t.out -lite=0 \
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# RUN: -jump-tables=move
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# RUN: llvm-readobj -rs %t.out | FileCheck --check-prefix=READOBJ %s
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# Verify that BOLT outputs the dynamic reloc at the correct address,
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# which is the start of the .bolt.org.rodata section.
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# READOBJ: Relocations [
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# READOBJ: Section ([[#]]) .rela.dyn {
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# READOBJ-NEXT: 0x[[#%X,ADDR:]] R_X86_64_64 bar 0x10
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# READOBJ: Symbols [
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# READOBJ: Name: .bolt.org.rodata
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# READOBJ-NEXT: Value: 0x[[#ADDR]]
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# Create a hot function with jump table
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.text
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.globl _start
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.type _start, %function
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_start:
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.cfi_startproc
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# FDATA: 0 [unknown] 0 1 _start 0 0 6
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movq .LJUMPTABLE(,%rdi,8), %rax
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b: jmpq *%rax
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# FDATA: 1 _start #b# 1 _start #c# 0 3
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c:
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mov $1, %rax
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d:
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xorq %rax, %rax
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ret
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.cfi_endproc
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.size _start, .-_start
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# This is the section that needs to be tested.
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.section .rodata
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.align 4
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# We will have a R_X86_64_64 here or R_X86_64_COPY if this section
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# is non-writable. We use -z notext to force the linker to accept dynamic
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# relocations in read-only sections and make it a R_X86_64_64.
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.quad bar + 16 # Reference a dynamic object (such as a vtable ref)
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# Add other contents to this section: a hot jump table that will be
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# copied by BOLT into a new section.
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.LJUMPTABLE:
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.quad c
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.quad c
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.quad d
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.quad d
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