a40f651a06
For an output section with no input section, GNU ld eliminates the
output section when there are only symbol assignments (e.g.
`.foo : { symbol = 42; }`) but not for `.foo : { . += 42; }`
(`SHF_ALLOC|SHF_WRITE`).
We choose to retain such an output section with a symbol assignment
(unless unreferenced `PROVIDE`). We copy the previous section flag (see
https://reviews.llvm.org/D37736) to hopefully make the current PT_LOAD
segment extend to the current output section:
* decrease the number of PT_LOAD segments
* If a new PT_LOAD segment is introduced without a page-size
alignment as a separator, there may be a run-time crash.
However, this `flags` copying behavior is not suitable for
`.foo : { . += 42; }` when `flags` contains `SHF_EXECINSTR`. The
executable bit is surprising
(https://discourse.llvm.org/t/lld-output-section-flag-assignment-behavior/74359).
I think we should drop SHF_EXECINSTR when copying `flags`. The risk is a
code section followed by `.foo : { symbol = 42; }` will be broken, which
I believe is unrelated as such uses are almost always related to data
sections.
For data-command-only output sections (e.g. `.foo : { QUAD(42) }`), we
keep allowing copyable SHF_WRITE.
Some tests are updated to drop the SHF_EXECINSTR flag. GNU ld doesn't
set SHF_EXECINSTR as well, though it sets SHF_WRITE for some tests while
we don't.
32 lines
1.3 KiB
Plaintext
32 lines
1.3 KiB
Plaintext
# REQUIRES: x86
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# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %p/Inputs/extend-pt-load.s -o %t.o
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# RUN: ld.lld --hash-style=sysv -o %t2 --script %s %t.o -shared
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# RUN: llvm-readelf -S -l %t2 | FileCheck %s
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# Then add the section bar. Note how bar is given AX flags, which causes the PT_LOAD to now
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# cover the padding bits created by ALIGN.
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SECTIONS {
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. = SIZEOF_HEADERS;
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.dynsym : {}
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.hash : {}
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.dynstr : {}
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.rodata : { *(.rodata) }
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foo : { sym = .; }
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.text : { *(.text) }
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bar : { . = ALIGN(0x1000); }
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.data.rel.ro : { *(.data.rel.ro) }
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}
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# CHECK: .rodata PROGBITS 000000000000024d 00024d 000001 00 A 0
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# CHECK-NEXT: foo PROGBITS 000000000000024e 00024e 000000 00 A 0
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# CHECK-NEXT: .text PROGBITS 0000000000000250 000250 000001 00 AX 0
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# CHECK-NEXT: bar PROGBITS 0000000000000251 000251 000daf 00 A 0
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# CHECK-NEXT: .data.rel.ro PROGBITS 0000000000001000 001000 000001 00 WA 0
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# CHECK: LOAD 0x000000 0x0000000000000000 0x0000000000000000 0x00024e 0x00024e R 0x1000
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# CHECK-NEXT: LOAD 0x000250 0x0000000000000250 0x0000000000000250 0x000001 0x000001 R E 0x1000
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# CHECK-NEXT: LOAD 0x000251 0x0000000000000251 0x0000000000000251 0x000daf 0x000daf R 0x1000
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# CHECK-NEXT: LOAD 0x001000 0x0000000000001000 0x0000000000001000 0x000068 0x000068 RW 0x1000
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