[ELF] Support placing .lbss/.lrodata/.ldata after .bss

https://reviews.llvm.org/D150510 places .lrodata before .rodata to
minimize the number of permission transitions in the memory image.
However, this layout is less ideal for -fno-pic code (which is still
important).

Small code model -fno-pic code has R_X86_64_32S relocations with a range
of `[0,2**31)` (if we ignore the negative area). Placing `.lrodata`
earlier exerts relocation pressure on such code. Non-x86 64-bit
architectures generally have a similar `[0,2**31)` limitation if they
don't use PC-relative relocations.

If we place .lrodata later, we will need one extra PT_LOAD. Two layouts
are appealing:

* .bss/.lbss/.lrodata/.ldata (GNU ld)
* .bss/.ldata/.lbss/.lrodata

The GNU ld layout has the nice property that there is only one BSS
(except .tbss/.relro_padding). Add -z lrodata-after-bss to support
this layout.

Since a read-only PT_LOAD segment (for large data sections) may appear
after RW PT_LOAD segments. The placement of `_etext` has to be adjusted.

Pull Request: https://github.com/llvm/llvm-project/pull/81224

2 files changed, 41 insertions, 5 deletions

diff --git a/lld/test/ELF/lto/codemodel.ll b/lld/test/ELF/lto/codemodel.ll
index a35f877..cf7d0e4 100644
--- a/lld/test/ELF/lto/codemodel.ll
+++ b/lld/test/ELF/lto/codemodel.ll
@@ -2,8 +2,8 @@
 ; RUN: llvm-as %s -o %t.o
 ; RUN: ld.lld %t.o -o %ts -mllvm -code-model=small
 ; RUN: ld.lld %t.o -o %tl -mllvm -code-model=large
-; RUN: llvm-objdump --no-print-imm-hex -d %ts | FileCheck %s --check-prefix=CHECK-SMALL
-; RUN: llvm-objdump --no-print-imm-hex -d %tl | FileCheck %s --check-prefix=CHECK-LARGE
+; RUN: llvm-objdump -d %ts | FileCheck %s --check-prefix=CHECK-SMALL
+; RUN: llvm-objdump -d %tl | FileCheck %s --check-prefix=CHECK-LARGE
 
 target triple = "x86_64-unknown-linux-gnu"
 target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
@@ -13,8 +13,8 @@ target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16
 define ptr @_start() nounwind readonly {
 entry:
 ; CHECK-SMALL-LABEL:  <_start>:
-; CHECK-SMALL: movl    $2097440, %eax
+; CHECK-SMALL: movl    ${{.*}}, %eax
 ; CHECK-LARGE-LABEL: <_start>:
-; CHECK-LARGE: movabsq $2097440, %rax
+; CHECK-LARGE: movabsq ${{.*}}, %rax
     ret ptr @data
 }
diff --git a/lld/test/ELF/x86-64-section-layout.s b/lld/test/ELF/x86-64-section-layout.s
index 0ba605393..b03d3e6 100644
--- a/lld/test/ELF/x86-64-section-layout.s
+++ b/lld/test/ELF/x86-64-section-layout.s
@@ -12,9 +12,12 @@
 # RUN: ld.lld --section-start=.note=0x200300 a1.o -o a1
 # RUN: llvm-readelf -S -sX a1 | FileCheck %s --check-prefix=CHECK1
 
-# RUN: ld.lld -T b.lds -z norelro a.o -o b
+# RUN: ld.lld -T b.lds -z norelro a.o -z lrodata-after-bss -z nolrodata-after-bss -o b --fatal-warnings
 # RUN: llvm-readelf -S -l b | FileCheck %s --check-prefix=CHECK2
 
+# RUN: ld.lld --section-start=.note=0x200300 a.o -z lrodata-after-bss -o a3
+# RUN: llvm-readelf -S -l -sX a3 | FileCheck %s --check-prefix=CHECK3
+
 # CHECK:       Name              Type            Address          Off    Size   ES Flg Lk Inf Al
 # CHECK-NEXT:                    NULL            0000000000000000 000000 000000 00      0   0  0
 # CHECK-NEXT:  .note             NOTE            0000000000200300 000300 000001 00   A  0   0  1
@@ -80,6 +83,39 @@
 # CHECK2-NEXT:   LOAD  0x000305 0x0000000000200305 0x0000000000200305 0x001805 0x002a06 RW  0x1000
 # CHECK2-NEXT:   TLS   0x000305 0x0000000000200305 0x0000000000200305 0x000001 0x000003 R   0x1
 
+# CHECK3:       Name              Type            Address          Off    Size   ES Flg Lk Inf Al
+# CHECK3-NEXT:                    NULL            0000000000000000 000000 000000 00      0   0  0
+# CHECK3-NEXT:  .note             NOTE            0000000000200300 000300 000001 00   A  0   0  1
+# CHECK3-NEXT:  .rodata           PROGBITS        0000000000200301 000301 000001 00   A  0   0  1
+# CHECK3-NEXT:  .text             PROGBITS        0000000000201304 000304 000001 00  AX  0   0  4
+# CHECK3-NEXT:  .tdata            PROGBITS        0000000000202305 000305 000001 00 WAT  0   0  1
+# CHECK3-NEXT:  .tbss             NOBITS          0000000000202306 000306 000002 00 WAT  0   0  1
+# CHECK3-NEXT:  .relro_padding    NOBITS          0000000000202306 000306 000cfa 00  WA  0   0  1
+# CHECK3-NEXT:  .data             PROGBITS        0000000000203306 000306 000001 00  WA  0   0  1
+# CHECK3-NEXT:  .bss              NOBITS          0000000000203307 000307 001800 00  WA  0   0  1
+## We spend (size(.bss) + size(.lbss)) % MAXPAGESIZE bytes.
+# CHECK3-NEXT:  .lbss             NOBITS          0000000000204b07 000307 001201 00 WAl  0   0  1
+# CHECK3-NEXT:  .lrodata          PROGBITS        0000000000206d08 000d08 000002 00  Al  0   0  1
+# CHECK3-NEXT:  .ldata            PROGBITS        0000000000207d0a 000d0a 000002 00 WAl  0   0  1
+# CHECK3-NEXT:  .ldata2           PROGBITS        0000000000207d0c 000d0c 000001 00 WAl  0   0  1
+# CHECK3-NEXT:  .comment          PROGBITS        0000000000000000 000d0d {{.*}} 01  MS  0   0  1
+
+# CHECK3:       Program Headers:
+# CHECK3-NEXT:    Type  Offset   VirtAddr           PhysAddr           FileSiz  MemSiz   Flg Align
+# CHECK3-NEXT:    PHDR  0x000040 0x0000000000200040 0x0000000000200040 {{.*}}   {{.*}}   R   0x8
+# CHECK3-NEXT:    LOAD  0x000000 0x0000000000200000 0x0000000000200000 0x000302 0x000302 R   0x1000
+# CHECK3-NEXT:    LOAD  0x000304 0x0000000000201304 0x0000000000201304 0x000001 0x000001 R E 0x1000
+# CHECK3-NEXT:    LOAD  0x000305 0x0000000000202305 0x0000000000202305 0x000001 0x000cfb RW  0x1000
+# CHECK3-NEXT:    LOAD  0x000306 0x0000000000203306 0x0000000000203306 0x000001 0x002a02 RW  0x1000
+# CHECK3-NEXT:    LOAD  0x000d08 0x0000000000206d08 0x0000000000206d08 0x000002 0x000002 R   0x1000
+# CHECK3-NEXT:    LOAD  0x000d0a 0x0000000000207d0a 0x0000000000207d0a 0x000003 0x000003 RW  0x1000
+# CHECK3-NEXT:    TLS   0x000305 0x0000000000202305 0x0000000000202305 0x000001 0x000003 R   0x1
+
+# CHECK3:       0000000000201304     0 NOTYPE  GLOBAL DEFAULT [[#]] (.text)   _start
+# CHECK3-NEXT:  0000000000201305     0 NOTYPE  GLOBAL DEFAULT [[#]] (.text)   _etext
+# CHECK3-NEXT:  0000000000203307     0 NOTYPE  GLOBAL DEFAULT [[#]] (.data)   _edata
+# CHECK3-NEXT:  0000000000207d0d     0 NOTYPE  GLOBAL DEFAULT [[#]] (.ldata2) _end
+
 #--- a.s
 .globl _start, _etext, _edata, _end
 _start: