[PATCH] D77021: [Hexagon] R_HEX_GD_PLT_B22_PCREL cannot be relaxed.

[Sid Manning via Phabricator via llvm-commits]

sidneym updated this revision to Diff 253617.
sidneym added a comment.

Update and add more context to the testcase.

call a at GDPLT is transformed to call __tls_get_addr I added some more context to the testcase to show the sequence.  I'm not sure just saying call a at GDPLT is just an alias for call __tls_get_addr is 100% correct but that is basically how I think of it.   Section 16.10 of the Hexagon ABI discusses this and the link is here:
http://lists.llvm.org/pipermail/llvm-dev/attachments/20190916/21516a52/attachment-0001.pdf


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D77021/new/

https://reviews.llvm.org/D77021

Files:
  lld/ELF/Relocations.cpp
  lld/test/ELF/hexagon-tls-gd-symbolic.s


Index: lld/test/ELF/hexagon-tls-gd-symbolic.s
===================================================================
--- /dev/null
+++ lld/test/ELF/hexagon-tls-gd-symbolic.s
@@ -0,0 +1,50 @@
+# REQUIRES: hexagon
+# RUN: llvm-mc -filetype=obj -triple=hexagon-unknown-elf %s -o %t.o
+# RUN: ld.lld -Bsymbolic -shared %t.o -o %t.so
+# RUN: llvm-objdump -d --no-show-raw-insn --print-imm-hex %t.so | FileCheck -check-prefix DISASM %s
+# RUN: llvm-readobj -d %t.so | FileCheck %s
+# RUN: llvm-readobj -r %t.so | FileCheck -check-prefix RELOC %s
+
+## Prior to change associated with this test lld for the Hexagon target would
+## error out with something like:
+## ld.lld: error: relocation R_HEX_GD_PLT_B22_PCREL cannot refer to absolute symbol: a
+## Binding to the internal symbol doesn't apply in this particular case
+## since Hexagon will transform the call a at GDPLT to call __tls_get_addr
+##
+## The following produces the code sequence similar to the test:
+##   __thread int a=1;
+##   int get() {
+##     return a;
+##   }
+## When built -fpic and linked with -Bsymbolic the above mentioned
+## error surfaced.
+
+.globl _start
+.type _start, @function
+
+_start:
+                r2 = add(pc,##_GLOBAL_OFFSET_TABLE_ at PCREL)
+                r0 = add(r2,##a at GDGOT)
+                call a at GDPLT
+                r0 = memw(r0+#0)
+# DISASM:     { immext(#{{.*}})
+# DISASM-NEXT:  r2 = add(pc,##{{.*}}) }
+# DISASM-NEXT:{ immext(#{{.*}})
+# DISASM-NEXT:  r0 = add(r2,##-{{.*}}) }
+# DISASM-NEXT:{ call {{.*}} }
+# DISASM-NEXT:{ r0 = memw(r0+#0x0) }
+
+
+# CHECK: DynamicSection
+# CHECK:   0x0000001E FLAGS    SYMBOLIC
+
+# RELOC: Relocations [
+# RELOC:        {{.*}}R_HEX_JMP_SLOT
+# RELOC-NEXT:   {{.*}}R_HEX_JMP_SLOT __tls_get_addr
+# RELOC-NEXT: }
+# RELOC-NEXT: ]
+
+.section        .tdata,"awT", at progbits
+.globl  a
+a:
+.word 1
Index: lld/ELF/Relocations.cpp
===================================================================
--- lld/ELF/Relocations.cpp
+++ lld/ELF/Relocations.cpp
@@ -1333,7 +1333,10 @@
       // 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 in the same module.
+      if (!(config->emachine == EM_HEXAGON && type == R_HEX_GD_PLT_B22_PCREL))
+        expr = fromPlt(expr);
     }
   }
 


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