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[lld][LoongArch] Support the R_LARCH_{ADD,SUB}_ULEB128 relocation types (#81133)
For a label difference like `.uleb128 A-B`, MC generates a pair of R_LARCH_{ADD,SUB}_ULEB128 if A-B cannot be folded as a constant. GNU assembler generates a pair of relocations in more cases (when A or B is in a code section with linker relaxation). It is similar to RISCV. R_LARCH_{ADD,SUB}_ULEB128 relocations are created by Clang and GCC in `.gcc_except_table` and other debug sections with linker relaxation enabled. On LoongArch, first read the buf and count the available space. Then add or sub the value. Finally truncate the expected value and fill it into the available space.
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‎lld/ELF/Arch/LoongArch.cpp

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@@ -11,6 +11,7 @@
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#include "Symbols.h"
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#include "SyntheticSections.h"
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#include "Target.h"
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#include "llvm/Support/LEB128.h"
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using namespace llvm;
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using namespace llvm::object;
@@ -155,6 +156,16 @@ static bool isJirl(uint32_t insn) {
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return (insn & 0xfc000000) == JIRL;
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}
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static void handleUleb128(uint8_t *loc, uint64_t val) {
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const uint32_t maxcount = 1 + 64 / 7;
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uint32_t count;
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uint64_t orig = decodeULEB128(loc, &count);
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if (count > maxcount)
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errorOrWarn(getErrorLocation(loc) + "extra space for uleb128");
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uint64_t mask = count < maxcount ? (1ULL << 7 * count) - 1 : -1ULL;
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encodeULEB128((orig + val) & mask, loc, count);
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}
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LoongArch::LoongArch() {
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// The LoongArch ISA itself does not have a limit on page sizes. According to
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// the ISA manual, the PS (page size) field in MTLB entries and CSR.STLBPS is
@@ -396,11 +407,13 @@ RelExpr LoongArch::getRelExpr(const RelType type, const Symbol &s,
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case R_LARCH_ADD16:
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case R_LARCH_ADD32:
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case R_LARCH_ADD64:
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case R_LARCH_ADD_ULEB128:
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case R_LARCH_SUB6:
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case R_LARCH_SUB8:
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case R_LARCH_SUB16:
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case R_LARCH_SUB32:
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case R_LARCH_SUB64:
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case R_LARCH_SUB_ULEB128:
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// The LoongArch add/sub relocs behave like the RISCV counterparts; reuse
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// the RelExpr to avoid code duplication.
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return R_RISCV_ADD;
@@ -635,6 +648,9 @@ void LoongArch::relocate(uint8_t *loc, const Relocation &rel,
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case R_LARCH_ADD64:
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write64le(loc, read64le(loc) + val);
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return;
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case R_LARCH_ADD_ULEB128:
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handleUleb128(loc, val);
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return;
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case R_LARCH_SUB6:
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*loc = (*loc & 0xc0) | ((*loc - val) & 0x3f);
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return;
@@ -650,6 +666,9 @@ void LoongArch::relocate(uint8_t *loc, const Relocation &rel,
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case R_LARCH_SUB64:
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write64le(loc, read64le(loc) - val);
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return;
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case R_LARCH_SUB_ULEB128:
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handleUleb128(loc, -val);
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return;
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case R_LARCH_MARK_LA:
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case R_LARCH_MARK_PCREL:

‎lld/test/ELF/loongarch-reloc-leb128.s

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# REQUIRES: loongarch
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# RUN: rm -rf %t && split-file %s %t && cd %t
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# RUN: llvm-mc --filetype=obj --triple=loongarch64 --mattr=+relax a.s -o a.o
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# RUN: llvm-readobj -r -x .gcc_except_table -x .debug_rnglists -x .debug_loclists a.o | FileCheck %s --check-prefix=REL
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# RUN: ld.lld -shared --gc-sections a.o -o a.so
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# RUN: llvm-readelf -x .gcc_except_table -x .debug_rnglists -x .debug_loclists a.so | FileCheck %s
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# RUN: llvm-mc --filetype=obj --triple=loongarch32 --mattr=+relax a.s -o a32.o
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# RUN: llvm-readobj -r -x .gcc_except_table -x .debug_rnglists -x .debug_loclists a32.o | FileCheck %s --check-prefix=REL
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# RUN: ld.lld -shared --gc-sections a32.o -o a32.so
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# RUN: llvm-readelf -x .gcc_except_table -x .debug_rnglists -x .debug_loclists a32.so | FileCheck %s
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# RUN: llvm-mc --filetype=obj --triple=loongarch32 --mattr=+relax extraspace.s -o extraspace32.o
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# RUN: llvm-mc --filetype=obj --triple=loongarch64 --mattr=+relax extraspace.s -o extraspace64.o
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# RUN: not ld.lld -shared extraspace32.o 2>&1 | FileCheck %s --check-prefix=ERROR
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# RUN: not ld.lld -shared extraspace64.o 2>&1 | FileCheck %s --check-prefix=ERROR
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# ERROR: error: extraspace{{.*}}.o:(.rodata+0x0): extra space for uleb128
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#--- a.s
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.cfi_startproc
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.cfi_lsda 0x1b,.LLSDA0
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.cfi_endproc
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.section .text.w,"axR"
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break 0; break 0; break 0; w1:
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.p2align 4 # 4 bytes after relaxation
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w2: break 0
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.section .text.x,"ax"
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break 0; break 0; break 0; x1:
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.p2align 4 # 4 bytes after relaxation
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x2: break 0
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.section .gcc_except_table,"a"
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.LLSDA0:
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.uleb128 w2-w1+116 # initial value: 0x0080
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.uleb128 w1-w2+141 # initial value: 0x0080
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.uleb128 w2-w1+16372 # initial value: 0x008080
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.uleb128 w1-w2+16397 # initial value: 0x008080
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.uleb128 w2-w1+2097140 # initial value: 0x00808080
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.uleb128 w1-w2+2097165 # initial value: 0x00808080
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.section .debug_rnglists
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.uleb128 w2-w1+116 # initial value: 0x0080
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.uleb128 w1-w2+141 # initial value: 0x0080
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.uleb128 w2-w1+16372 # initial value: 0x008080
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.uleb128 w1-w2+16397 # initial value: 0x008080
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.uleb128 w2-w1+2097140 # initial value: 0x00808080
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.uleb128 w1-w2+2097165 # initial value: 0x00808080
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.section .debug_loclists
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.uleb128 x2-x1 # references discarded symbols
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# REL: Section ({{.*}}) .rela.debug_rnglists {
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# REL-NEXT: 0x0 R_LARCH_ADD_ULEB128 w2 0x74
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# REL-NEXT: 0x0 R_LARCH_SUB_ULEB128 w1 0x0
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# REL-NEXT: 0x2 R_LARCH_ADD_ULEB128 w1 0x8D
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# REL-NEXT: 0x2 R_LARCH_SUB_ULEB128 w2 0x0
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# REL-NEXT: 0x4 R_LARCH_ADD_ULEB128 w2 0x3FF4
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# REL-NEXT: 0x4 R_LARCH_SUB_ULEB128 w1 0x0
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# REL-NEXT: 0x7 R_LARCH_ADD_ULEB128 w1 0x400D
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# REL-NEXT: 0x7 R_LARCH_SUB_ULEB128 w2 0x0
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# REL-NEXT: 0xA R_LARCH_ADD_ULEB128 w2 0x1FFFF4
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# REL-NEXT: 0xA R_LARCH_SUB_ULEB128 w1 0x0
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# REL-NEXT: 0xE R_LARCH_ADD_ULEB128 w1 0x20000D
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# REL-NEXT: 0xE R_LARCH_SUB_ULEB128 w2 0x0
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# REL-NEXT: }
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# REL: Section ({{.*}}) .rela.debug_loclists {
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# REL-NEXT: 0x0 R_LARCH_ADD_ULEB128 x2 0x0
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# REL-NEXT: 0x0 R_LARCH_SUB_ULEB128 x1 0x0
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# REL-NEXT: }
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# REL: Hex dump of section '.gcc_except_table':
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# REL-NEXT: 0x00000000 80008000 80800080 80008080 80008080 .
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# REL-NEXT: 0x00000010 8000 .
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# REL: Hex dump of section '.debug_rnglists':
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# REL-NEXT: 0x00000000 80008000 80800080 80008080 80008080 .
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# REL-NEXT: 0x00000010 8000 .
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# REL: Hex dump of section '.debug_loclists':
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# REL-NEXT: 0x00000000 00 .
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# CHECK: Hex dump of section '.gcc_except_table':
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# CHECK-NEXT: 0x[[#%x,]] f8008901 f8ff0089 8001f8ff ff008980 .
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# CHECK-NEXT: 0x[[#%x,]] 8001 .
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# CHECK: Hex dump of section '.debug_rnglists':
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# CHECK-NEXT: 0x00000000 f8008901 f8ff0089 8001f8ff ff008980 .
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# CHECK-NEXT: 0x00000010 8001 .
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# CHECK: Hex dump of section '.debug_loclists':
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# CHECK-NEXT: 0x00000000 00 .
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#--- extraspace.s
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.text
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w1:
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la.pcrel $t0, w1
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w2:
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.rodata
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.reloc ., R_LARCH_ADD_ULEB128, w2
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.reloc ., R_LARCH_SUB_ULEB128, w1
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.fill 10, 1, 0x80
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.byte 0

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