[PATCH] D72819: [ELF] Decrease alignment of ThunkSection on 64-bit targets from 8 to 4

[Fangrui Song via Phabricator via llvm-commits]

MaskRay created this revision.
MaskRay added reviewers: PowerPC, grimar, peter.smith, pcc, ruiu.
Herald added subscribers: llvm-commits, kbarton, arichardson, nemanjai, emaste.
Herald added a reviewer: espindola.
Herald added a project: LLVM.

ThunkSection contains 4-byte instructions on all targets that use
thunks. Thunks should not be used in any performance sensitive places,
and locality/cache line arguments should not apply.

I'll fix the remaining tests (offset change) if the idea does not sound silly.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D72819

Files:
  lld/ELF/SyntheticSections.cpp
  lld/test/ELF/aarch64-call26-thunk.s
  lld/test/ELF/aarch64-jump26-thunk.s
  lld/test/ELF/ppc64-long-branch.s


Index: lld/test/ELF/ppc64-long-branch.s
===================================================================
--- lld/test/ELF/ppc64-long-branch.s
+++ lld/test/ELF/ppc64-long-branch.s
@@ -64,9 +64,9 @@
 # CHECK-NEXT:  2002000:       addis 2, 12, 1
 # CHECK-NEXT:                 addi 2, 2, -32728
 # CHECK-NEXT:                 bl .-33554432
-# CHECK-NEXT:                 bl .+12
+# CHECK-NEXT:                 bl .+8
 # CHECK:      __long_branch_:
-# CHECK-NEXT:  2002018:       addis 12, 2, 0
+# CHECK-NEXT:  2002014:       addis 12, 2, 0
 # CHECK-NEXT:                 ld 12, -32744(12)
 # CHECK-NEXT:                 mtctr 12
 # CHECK-NEXT:                 bctr
Index: lld/test/ELF/aarch64-jump26-thunk.s
===================================================================
--- lld/test/ELF/aarch64-jump26-thunk.s
+++ lld/test/ELF/aarch64-jump26-thunk.s
@@ -12,10 +12,10 @@
 // CHECK: Disassembly of section .text:
 // CHECK-EMPTY:
 // CHECK-NEXT: _start:
-// CHECK-NEXT:    210120:       b       #8
+// CHECK-NEXT:    210120:       b       #4
 // CHECK: __AArch64AbsLongThunk_big:
-// CHECK-NEXT:    210128:       ldr     x16, #8
-// CHECK-NEXT:    21012c:       br      x16
+// CHECK-NEXT:    210124:       ldr     x16, #8
+// CHECK-NEXT:    210128:       br      x16
 // CHECK: $d:
-// CHECK-NEXT:    210130:       00 00 00 00     .word   0x00000000
-// CHECK-NEXT:    210134:       10 00 00 00     .word   0x00000010
+// CHECK-NEXT:    21012c:       00 00 00 00     .word   0x00000000
+// CHECK-NEXT:    210130:       10 00 00 00     .word   0x00000010
Index: lld/test/ELF/aarch64-call26-thunk.s
===================================================================
--- lld/test/ELF/aarch64-call26-thunk.s
+++ lld/test/ELF/aarch64-call26-thunk.s
@@ -12,11 +12,11 @@
 // CHECK: Disassembly of section .text:
 // CHECK-EMPTY:
 // CHECK-NEXT: _start:
-// CHECK-NEXT:    210120:       bl      #8
+// CHECK-NEXT:    210120:       bl      #4
 // CHECK: __AArch64AbsLongThunk_big:
-// CHECK-NEXT:    210128:       ldr     x16, #8
-// CHECK-NEXT:    21012c:       br      x16
+// CHECK-NEXT:    210124:       ldr     x16, #8
+// CHECK-NEXT:    210128:       br      x16
 // CHECK: $d:
-// CHECK-NEXT:    210130:       00 00 00 00     .word   0x00000000
-// CHECK-NEXT:    210134:       10 00 00 00     .word   0x00000010
+// CHECK-NEXT:    21012c:       00 00 00 00     .word   0x00000000
+// CHECK-NEXT:    210130:       10 00 00 00     .word   0x00000010
 
Index: lld/ELF/SyntheticSections.cpp
===================================================================
--- lld/ELF/SyntheticSections.cpp
+++ lld/ELF/SyntheticSections.cpp
@@ -3451,8 +3451,8 @@
 }
 
 ThunkSection::ThunkSection(OutputSection *os, uint64_t off)
-    : SyntheticSection(SHF_ALLOC | SHF_EXECINSTR, SHT_PROGBITS,
-                       config->wordsize, ".text.thunk") {
+    : SyntheticSection(SHF_ALLOC | SHF_EXECINSTR, SHT_PROGBITS, 4,
+                       ".text.thunk") {
   this->parent = os;
   this->outSecOff = off;
 }


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