[lld] c484b3e - [Hexagon] Fix issue with non-preemptible STT_TLS symbols

[Sid Manning via llvm-commits]

Author: Sid Manning
Date: 2020-04-03T08:55:23-05:00
New Revision: c484b3e334d3d63841974ba0733311fc812035a1

URL: https://github.com/llvm/llvm-project/commit/c484b3e334d3d63841974ba0733311fc812035a1
DIFF: https://github.com/llvm/llvm-project/commit/c484b3e334d3d63841974ba0733311fc812035a1.diff

LOG: [Hexagon] Fix issue with non-preemptible STT_TLS symbols

A PC-relative relocation referencing a non-preemptible absolute symbol
(due to STT_TLS) is not representable in -pie/-shared mode.

Differential Revision: https://reviews.llvm.org/D77021

Added: 
    lld/test/ELF/hexagon-tls-gd-nonpreemptible.s

Modified: 
    lld/ELF/Relocations.cpp

Removed: 
    


################################################################################
diff  --git a/lld/ELF/Relocations.cpp b/lld/ELF/Relocations.cpp
index 41a0cea96aa1..21fec6e44aa0 100644
--- a/lld/ELF/Relocations.cpp
+++ b/lld/ELF/Relocations.cpp
@@ -1334,7 +1334,10 @@ static void scanReloc(InputSectionBase &sec, OffsetGetter &getOffset, RelTy *&i,
       // stub type. It should be ignored if optimized to R_PC.
       if (config->emachine == EM_PPC && expr == R_PPC32_PLTREL)
         addend &= ~0x8000;
-      expr = fromPlt(expr);
+      // R_HEX_GD_PLT_B22_PCREL (call a at GDPLT) is transformed into
+      // call __tls_get_addr even if the symbol is non-preemptible.
+      if (!(config->emachine == EM_HEXAGON && type == R_HEX_GD_PLT_B22_PCREL))
+        expr = fromPlt(expr);
     }
   }
 

diff  --git a/lld/test/ELF/hexagon-tls-gd-nonpreemptible.s b/lld/test/ELF/hexagon-tls-gd-nonpreemptible.s
new file mode 100644
index 000000000000..ba0eee999c80
--- /dev/null
+++ b/lld/test/ELF/hexagon-tls-gd-nonpreemptible.s
@@ -0,0 +1,39 @@
+
+# REQUIRES: hexagon
+# RUN: llvm-mc -filetype=obj -triple=hexagon-unknown-elf %s -o %t.o
+# RUN: ld.lld -shared %t.o -o %t.so
+# RUN: llvm-readobj -r %t.so | FileCheck --check-prefix=RELOC %s
+# RUN: llvm-objdump -d --no-show-raw-insn --print-imm-hex %t.so | FileCheck %s
+
+## Prior to D77021 lld would error "relocation R_HEX_GD_PLT_B22_PCREL cannot refer to absolute symbol".
+## A PC-relative relocation referencing a non-preemptible absolute symbol (due to STT_TLS) is not representable in -pie/-shared mode.
+## For this case we will actually patch the symbol to the external __tls_get_addr which is preemptible.
+
+.globl _start
+.type _start, @function
+
+# RELOC:      Section ({{.*}}) .rela.plt {
+# RELOC-NEXT:   R_HEX_JMP_SLOT - 0x0
+# RELOC-NEXT:   R_HEX_JMP_SLOT __tls_get_addr 0x0
+# RELOC-NEXT: }
+
+# CHECK:      { immext(#{{.*}})
+# CHECK-NEXT:   r2 = add(pc,##{{.*}}) }
+# CHECK-NEXT: { immext(#{{.*}})
+# CHECK-NEXT:   r0 = add(r2,##-{{.*}}) }
+# CHECK-NEXT: { call {{.*}} }
+# CHECK-NEXT: { r0 = memw(r0+#0x0) }
+
+_start:
+  r2 = add(pc,##_GLOBAL_OFFSET_TABLE_ at PCREL)
+  r0 = add(r2,##a at GDGOT)
+  call a at GDPLT
+  r0 = memw(r0+#0)
+
+## a is non-preemptible due to STV_HIDDEN visibility.
+## We can achieve the same effect with -Bsymbolic.
+.section        .tdata,"awT", at progbits
+.globl  a
+.hidden a
+a:
+.word 1