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https://sourceware.org/ml/binutils/2009-04/msg00426.html

Detect ARM MOVW/MOVT relocations in shared library links

• From: "Joseph S. Myers" <joseph at codesourcery dot com>
• To: binutils at sourceware dot org
• Date: Mon, 27 Apr 2009 22:06:39 +0000 (UTC)
• Subject: Detect ARM MOVW/MOVT relocations in shared library links

---

ARMv7 has MOVW and MOVT instructions for loading constants withoutneeding a constant pool, and associated relocations for when thoseconstants are symbol addresses.Of course PIC code can't use these instructions to load absolutesymbol addresses.  This patch adds linker checks for linking objectsusing the relevant relocations into shared libraries, to detect thecommon mistake (for people coming from x86) of building objectswithout -fPIC and linking them into a shared library; the previousbehavior was silently dropping the relocations and so generating abroken shared library, which is obviously undesirable.Tested with no regressions with cross to arm-none-eabi.  OK to commit?This certainly does not fix every case of ARM relocations that areeither always unsafe for objects linked into shared libraries, orunsafe for such objects if the symbol referenced might not be resolvedwithin the library at runtime; there are many other cases that mayhave similar issues, but these are the ones observed to cause problemsin practice.  ("Unsafe" means not fully resolved at static link timeand not converted to a dynamic relocation or no suitable dynamicrelocation available to which to convert the relocation.)bfd:2009-04-27  Joseph Myers  <[e-mail]>* elf32-arm.c (elf32_arm_check_relocs): Give errors for absoluteMOVW and MOVT relocations in a shared library linkld/testsuite:2009-04-27  Joseph Myers  <[e-mail]>* ld-arm/movw-shared-1.d, ld-arm/movw-shared-1.s,ld-arm/movw-shared-2.d, ld-arm/movw-shared-2.s,ld-arm/movw-shared-3.d, ld-arm/movw-shared-3.s,ld-arm/movw-shared-4.d, ld-arm/movw-shared-4.s: New tests.* ld-arm/arm-elf.exp: Run these new tests.Index: bfd/elf32-arm.c===================================================================RCS file: /cvs/src/src/bfd/elf32-arm.c,vretrieving revision 1.189diff -u -r1.189 elf32-arm.c--- bfd/elf32-arm.c22 Apr 2009 14:01:30 -00001.189+++ bfd/elf32-arm.c27 Apr 2009 21:45:11 -0000@@ -9808,16 +9808,27 @@     needs_plt = 1;     goto normal_reloc; +  case R_ARM_MOVW_ABS_NC:+  case R_ARM_MOVT_ABS:+  case R_ARM_THM_MOVW_ABS_NC:+  case R_ARM_THM_MOVT_ABS:+    if (info->shared)+      {+(*_bfd_error_handler)+  (_("%B: relocation %s against `%s' can not be used when making a shared object; recompile with -fPIC"),+   abfd, elf32_arm_howto_table_1[r_type].name,+   (h) ? h->root.root.string : "a local symbol");+bfd_set_error (bfd_error_bad_value);+return FALSE;+      }++    /* Fall through.  */   case R_ARM_ABS32:   case R_ARM_ABS32_NOI:   case R_ARM_REL32:   case R_ARM_REL32_NOI:-  case R_ARM_MOVW_ABS_NC:-  case R_ARM_MOVT_ABS:   case R_ARM_MOVW_PREL_NC:   case R_ARM_MOVT_PREL:-  case R_ARM_THM_MOVW_ABS_NC:-  case R_ARM_THM_MOVT_ABS:   case R_ARM_THM_MOVW_PREL_NC:   case R_ARM_THM_MOVT_PREL:     needs_plt = 0;Index: ld/testsuite/ld-arm/arm-elf.exp===================================================================RCS file: /cvs/src/src/ld/testsuite/ld-arm/arm-elf.exp,vretrieving revision 1.54diff -u -r1.54 arm-elf.exp--- ld/testsuite/ld-arm/arm-elf.exp17 Apr 2009 13:04:41 -00001.54+++ ld/testsuite/ld-arm/arm-elf.exp27 Apr 2009 21:45:11 -0000@@ -187,6 +187,10 @@ run_dump_test "thumb2-bl-undefweak" run_dump_test "thumb2-bl-undefweak1" run_dump_test "emit-relocs1"+run_dump_test "movw-shared-1"+run_dump_test "movw-shared-2"+run_dump_test "movw-shared-3"+run_dump_test "movw-shared-4"  # Exclude non-ARM-EABI targets. Index: ld/testsuite/ld-arm/movw-shared-1.d===================================================================RCS file: ld/testsuite/ld-arm/movw-shared-1.ddiff -N ld/testsuite/ld-arm/movw-shared-1.d--- /dev/null1 Jan 1970 00:00:00 -0000+++ ld/testsuite/ld-arm/movw-shared-1.d27 Apr 2009 21:45:11 -0000@@ -0,0 +1,4 @@+#name: MOVW/MOVT shared libraries test 1+#source: movw-shared-1.s+#ld: -shared+#error: .*: relocation R_ARM_MOVW_ABS_NC against `a' can not be used when making a shared object; recompile with -fPICIndex: ld/testsuite/ld-arm/movw-shared-1.s===================================================================RCS file: ld/testsuite/ld-arm/movw-shared-1.sdiff -N ld/testsuite/ld-arm/movw-shared-1.s--- /dev/null1 Jan 1970 00:00:00 -0000+++ ld/testsuite/ld-arm/movw-shared-1.s27 Apr 2009 21:45:11 -0000@@ -0,0 +1,5 @@+.arch armv7-a+.text+.syntax unified+f:+movw r0, #:lower16:aIndex: ld/testsuite/ld-arm/movw-shared-2.d===================================================================RCS file: ld/testsuite/ld-arm/movw-shared-2.ddiff -N ld/testsuite/ld-arm/movw-shared-2.d--- /dev/null1 Jan 1970 00:00:00 -0000+++ ld/testsuite/ld-arm/movw-shared-2.d27 Apr 2009 21:45:11 -0000@@ -0,0 +1,4 @@+#name: MOVW/MOVT shared libraries test 2+#source: movw-shared-2.s+#ld: -shared+#error: .*: relocation R_ARM_MOVT_ABS against `b' can not be used when making a shared object; recompile with -fPICIndex: ld/testsuite/ld-arm/movw-shared-2.s===================================================================RCS file: ld/testsuite/ld-arm/movw-shared-2.sdiff -N ld/testsuite/ld-arm/movw-shared-2.s--- /dev/null1 Jan 1970 00:00:00 -0000+++ ld/testsuite/ld-arm/movw-shared-2.s27 Apr 2009 21:45:11 -0000@@ -0,0 +1,5 @@+.arch armv7-a+.text+.syntax unified+f:+movt r0, #:upper16:bIndex: ld/testsuite/ld-arm/movw-shared-3.d===================================================================RCS file: ld/testsuite/ld-arm/movw-shared-3.ddiff -N ld/testsuite/ld-arm/movw-shared-3.d--- /dev/null1 Jan 1970 00:00:00 -0000+++ ld/testsuite/ld-arm/movw-shared-3.d27 Apr 2009 21:45:11 -0000@@ -0,0 +1,4 @@+#name: MOVW/MOVT shared libraries test 3+#source: movw-shared-3.s+#ld: -shared+#error: .*: relocation R_ARM_THM_MOVW_ABS_NC against `c' can not be used when making a shared object; recompile with -fPICIndex: ld/testsuite/ld-arm/movw-shared-3.s===================================================================RCS file: ld/testsuite/ld-arm/movw-shared-3.sdiff -N ld/testsuite/ld-arm/movw-shared-3.s--- /dev/null1 Jan 1970 00:00:00 -0000+++ ld/testsuite/ld-arm/movw-shared-3.s27 Apr 2009 21:45:11 -0000@@ -0,0 +1,6 @@+.arch armv7-a+.text+.syntax unified+f:+.thumb+movw r0, #:lower16:cIndex: ld/testsuite/ld-arm/movw-shared-4.d===================================================================RCS file: ld/testsuite/ld-arm/movw-shared-4.ddiff -N ld/testsuite/ld-arm/movw-shared-4.d--- /dev/null1 Jan 1970 00:00:00 -0000+++ ld/testsuite/ld-arm/movw-shared-4.d27 Apr 2009 21:45:11 -0000@@ -0,0 +1,4 @@+#name: MOVW/MOVT shared libraries test 4+#source: movw-shared-4.s+#ld: -shared+#error: .*: relocation R_ARM_THM_MOVT_ABS against `d' can not be used when making a shared object; recompile with -fPICIndex: ld/testsuite/ld-arm/movw-shared-4.s===================================================================RCS file: ld/testsuite/ld-arm/movw-shared-4.sdiff -N ld/testsuite/ld-arm/movw-shared-4.s--- /dev/null1 Jan 1970 00:00:00 -0000+++ ld/testsuite/ld-arm/movw-shared-4.s27 Apr 2009 21:45:11 -0000@@ -0,0 +1,6 @@+.arch armv7-a+.text+.syntax unified+f:+.thumb+movt r0, #:upper16:d-- Joseph S. 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