004be4037e
tl;dr See D81784 for the 'tombstone value' concept. This patch changes our behavior to be almost the same as GNU ld (except that we also use 1 for .debug_loc): * .debug_ranges & .debug_loc: 1 (LLD<11: 0+addend; GNU ld uses 1 for .debug_ranges) * .debug_*: 0 (LLD<11: 0+addend; GNU ld uses 0; future LLD: -1) We make the tweaks because: 1) The new tombstone is novel and needs more time to be adopted by consumers before it's the default. 2) The old (gold) strategy had problems with zero-length functions - so rather than going back that, we're going to the GNU ld strategy which doesn't have that problem. 3) One slight tweak to (2) is to apply the .debug_ranges workaround to .debug_loc for the same reasons it applies to debug_ranges - to avoid terminating lists early. ----- http://lists.llvm.org/pipermail/llvm-dev/2020-July/143482.html The tombstone value -1 in .debug_line caused problems to lldb (fixed by D83957; will be included in 11.0.0) and breakpad (fixed by https://crrev.com/c/2321300). It may potentially affects other DWARF consumers. For .debug_ranges & .debug_loc: 1, an argument preferring 1 (GNU ld for .debug_ranges) over -2 is that: ``` {-1, -2} <<< base address selection entry {0, length} <<< address range ``` may create a situation where low_pc is greater than high_pc. So we use 1, the GNU ld behavior for .debug_ranges For other .debug_* sections, there haven't been many reports. One issue is that bloaty (src/dwarf.cc) can incorrectly count address ranges in .debug_ranges . To reduce similar disruption, this patch changes the tombstone values to be similar to GNU ld. This does mean another behavior change to the default trunk behavior. Sorry about it. The default trunk behavior will be similar to release/11.x while we work on a transition plan for LLD users. Reviewed By: dblaikie, echristo Differential Revision: https://reviews.llvm.org/D84825
36 lines
1.2 KiB
ArmAsm
36 lines
1.2 KiB
ArmAsm
# REQUIRES: x86
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## Test we resolve symbolic relocations in .debug_* sections to a tombstone
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## value if the referenced section symbol is folded into another section by ICF.
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## Otherwise, we would leave entries in multiple CUs claiming ownership of the
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## same range of code, which can confuse consumers.
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# RUN: llvm-mc -filetype=obj -triple=x86_64 %s -o %t.o
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# RUN: ld.lld --icf=all %t.o -o %t
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# RUN: llvm-objdump -s %t | FileCheck %s
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# CHECK: Contents of section .debug_info:
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# CHECK-NEXT: 0000 {{[0-9a-f]+}}000 00000000 00000000 00000000
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# CHECK: Contents of section .debug_line:
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# CHECK-NEXT: 0000 [[ADDR:[0-9a-f]+]] 00000000
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# CHECK-SAME: [[ADDR]] 00000000
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.globl _start
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_start:
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ret
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## .text.1 will be folded by ICF.
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.section .text.1,"ax"
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ret
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.section .debug_info
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.quad .text+8
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.quad .text.1+8
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## .debug_line contributions associated with folded-in functions will describe
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## different lines to the canonical function. Leaving a tombstone value would
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## prevent users from setting breakpoints on the folded-in functions.
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## Instead resolve the relocation to the folded .text.1 to .text
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.section .debug_line
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.quad .text
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.quad .text.1
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