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[RISCV][MC] Adjust conditions to emit R_RISCV_ADD*/R_RISCV_SUB* pairs

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D132262 tried to simplify `IsMetadataOrEHFrameSection` originally introduced in
D127549 but caused a regression as `.quad` directives in

```
.section .note,"a",@note; note:
.quad extern-note    # extern is undefined

.section .rodata,"a",@progbits; rodata:
.quad extern-rodata  # extern is undefined

.section .nonalloc,"",@progbits; nw:
.quad extern-nw
```

are incorrectly rejected: these differences may be link-time constants and
are allowed in GNU assembler and LLVM MC's non-RISC-V ports.

Relax the conditions to allow these cases. For A-B, A may be defined later, but
this requiresFixups call has to eagerly make a decision. For now, emit ADD/SUB
unless A is `.L*`. This euristic handles many temporary label differences for
.debug_* and .apple_types sections. Ideally we should delay the decision of
PC-relative vs ADD/SUB until A is defined.

Reviewed By: compnerd

Differential Revision: https://reviews.llvm.org/D145474
This commit is contained in:
Fangrui Song
2023-03-14 15:17:38 -07:00
parent 0ddc283a29
commit 2f5fe16e6d
2 changed files with 27 additions and 9 deletions
Download Patch File Download Diff File Expand all files Collapse all files

10
llvm/lib/Target/RISCV/MCTargetDesc/RISCVELFStreamer.cpp
View File

@@ -156,6 +156,16 @@ bool RISCVELFStreamer::requiresFixups(MCContext &C, const MCExpr *Value,
if (B.isInSection() && B.getSection().getKind().isText())
return true;
// If A is undefined and B is defined, we should emit ADD/SUB for A-B.
// Unfortunately, A may be defined later, but this requiresFixups call has to
// eagerly make a decision. For now, emit ADD/SUB unless A is .L*. This
// heuristic handles many temporary label differences for .debug_* and
// .apple_types sections.
//
// TODO Implement delayed relocation decision.
if (!A.isInSection() && !A.isTemporary() && B.isInSection())
return true;
// Support cross-section symbolic differences ...
return A.isInSection() && B.isInSection() &&
A.getSection().getName() != B.getSection().getName();

26
llvm/test/MC/RISCV/riscv64-64b-pcrel.s
View File

@@ -4,6 +4,14 @@
# RUN: | FileCheck %s --check-prefix=ERROR
# CHECK: Relocations [
# CHECK-NEXT: Section ({{.*}}) .rela.note {
# CHECK-NEXT: 0x0 R_RISCV_ADD64 extern 0x0
# CHECK-NEXT: 0x0 R_RISCV_SUB64 note 0x0
# CHECK-NEXT: }
# CHECK-NEXT: Section ({{.*}}) .rela.rodata {
# CHECK-NEXT: 0x0 R_RISCV_ADD64 extern 0x0
# CHECK-NEXT: 0x0 R_RISCV_SUB64 rodata 0x0
# CHECK-NEXT: }
# CHECK-NEXT: Section ({{.*}}) .rela.alloc_w {
# CHECK-NEXT: 0x0 R_RISCV_ADD64 extern 0x0
# CHECK-NEXT: 0x0 R_RISCV_SUB64 w 0x0
@@ -24,20 +32,24 @@
# CHECK-NEXT: 0x0 R_RISCV_ADD64 x 0x0
# CHECK-NEXT: 0x0 R_RISCV_SUB64 y 0x0
# CHECK-NEXT: }
# CHECK-NEXT: Section ({{.*}}) .rela.nonalloc_w {
# CHECK-NEXT: 0x0 R_RISCV_ADD64 extern 0x0
# CHECK-NEXT: 0x0 R_RISCV_SUB64 nw 0x0
# CHECK-NEXT: }
# CHECK-NEXT: Section ({{.*}}) .rela.nonalloc_x {
# CHECK-NEXT: 0x0 R_RISCV_ADD64 ny 0x0
# CHECK-NEXT: 0x0 R_RISCV_SUB64 nx 0x0
# CHECK-NEXT: }
# CHECK-NEXT: Section ({{.*}}) .rela.nonalloc_y {
# CHECK-NEXT: 0x0 R_RISCV_ADD64 nx 0x0
# CHECK-NEXT: 0x0 R_RISCV_SUB64 ny 0x0
# CHECK-NEXT: }
# CHECK-NEXT: ]
.ifdef ERR
.section .note,"a",@note; note:
# ERROR: :[[#@LINE+1]]:7: error: unsupported relocation type
.quad extern-note
.section .rodata,"a",@progbits; rodata:
# ERROR: :[[#@LINE+1]]:7: error: unsupported relocation type
.quad extern-rodata
.endif
.section .alloc_w,"aw",@progbits; w:
.quad extern-w # extern is undefined
@@ -53,17 +65,13 @@ w1:
.quad x-y
.section .nonalloc_w; nw:
.ifdef ERR
# ERROR: :[[#@LINE+1]]:7: error: unsupported relocation type
.quad extern-nw
.ifdef ERR
# ERROR: :[[#@LINE+1]]:7: error: symbol 'extern' can not be undefined in a subtraction expression
.quad nw-extern
.endif
.section .nonalloc_x; nx:
.ifdef ERR
# ERROR: :[[#@LINE+1]]:7: error: unsupported relocation type
.quad ny-nx
.endif
.section .nonalloc_y; ny:
.quad nx-ny