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LLD: Fix getFdePC with sdata2 or sdata4 #92228

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LLD: Fix getFdePC with sdata2 or sdata4 #92228

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21 changes: 17 additions & 4 deletions lld/ELF/SyntheticSections.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -612,10 +612,23 @@ uint64_t EhFrameSection::getFdePc(uint8_t *buf, size_t fdeOff,
// the .eh_frame section.
size_t off = fdeOff + 8;
uint64_t addr = readFdeAddr(buf + off, enc & 0xf);
if ((enc & 0x70) == DW_EH_PE_absptr)
return addr;
if ((enc & 0x70) == DW_EH_PE_pcrel)
return addr + getParent()->addr + off + outSecOff;
if ((enc & 0x70) == DW_EH_PE_absptr) {
if ((enc & 0xf) == DW_EH_PE_sdata2)
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This is probably not desired for ELFCLASS64.

See the alternative fix: #92438 , but thanks for investigation.

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Ohh, yes. we won't support any platform with 16bit absptr with ELF.

return (uint64_t)(uint16_t)addr;
else if ((enc & 0xf) == DW_EH_PE_sdata4)
return (uint64_t)(uint32_t)addr;
else
return addr;
}
if ((enc & 0x70) == DW_EH_PE_pcrel) {
uint64_t addr_base = getParent()->addr + off + outSecOff;
if ((enc & 0xf) == DW_EH_PE_sdata2)
return (int16_t)addr + addr_base;
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This is unnecessary.

else if ((enc & 0xf) == DW_EH_PE_sdata4)
return (int32_t)addr + addr_base;
else
return addr + addr_base;
}
fatal("unknown FDE size relative encoding");
}

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8 changes: 8 additions & 0 deletions lld/test/ELF/Inputs/mips32-kseg0.lds
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@@ -0,0 +1,8 @@
OUTPUT_ARCH(mips)
SECTIONS
{
. = 0x80000000;
.text : { *(.text) }
.data : { *(.data) }
.bss : { *(.bss) }
}
5 changes: 5 additions & 0 deletions lld/test/ELF/mips-eh_frame-pic.s
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Expand Up @@ -23,15 +23,20 @@
# RUN: llvm-dwarfdump --eh-frame %t-nopic32.o | FileCheck %s --check-prefix=ABS32-EH-FRAME
# RUN: llvm-readobj -r %t-nopic32.o | FileCheck %s --check-prefixes=RELOCS,ABS32-RELOCS
# RUN: not ld.lld -shared %t-nopic32.o -o /dev/null 2>&1 | FileCheck %s --check-prefix=NOPIC32-ERR
# RUN: ld.lld %t-nopic32.o -T %p/Inputs/mips32-kseg0.lds -eh-frame-hdr -static -o /dev/null 2>&1 \
# RUN: | FileCheck %s --check-prefix=NOPIC32-ABSPTR
## Note: ld.bfd can link this file because it rewrites the .eh_frame section to use
## relative addressing.
# NOPIC32-ERR: ld.lld: error: relocation R_MIPS_32 cannot be used against local symbol
# NOPIC32-ABSPTR: cannot find entry symbol __start

## For -fPIC, .eh_frame should contain DW_EH_PE_pcrel | DW_EH_PE_sdata4 values:
# RUN: llvm-mc -filetype=obj -triple=mips-unknown-linux --position-independent %s -o %t-pic32.o
# RUN: llvm-readobj -r %t-pic32.o | FileCheck %s --check-prefixes=RELOCS,PIC32-RELOCS
# RUN: ld.lld -shared %t-pic32.o -o %t-pic32.so
# RUN: ld.lld -shared -T %p/Inputs/mips32-kseg0.lds %t-pic32.o -o %t-pic32-kseg0.so
# RUN: llvm-dwarfdump --eh-frame %t-pic32.so | FileCheck %s --check-prefix=PIC32-EH-FRAME
# RUN: llvm-dwarfdump --eh-frame %t-pic32-kseg0.so | FileCheck %s --check-prefix=PIC32-EH-FRAME

# RELOCS: .rel{{a?}}.eh_frame {
# ABS32-RELOCS-NEXT: 0x1C R_MIPS_32 .text
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