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Arm: Fix LSB of GOT for Thumb2 only PLT. 

When you have a Thumb only PLT then the address in the GOT for PLT0 needs to
have the Thumb bit set since the instruction used in PLTn to get there is
`ldr.w	pc` which is an inter-working instruction:

the PLT sequence in question is

00000120 <foo@plt>:
 120:	f240 0c98 	movw	ip, #152	; 0x98
 124:	f2c0 0c01 	movt	ip, #1
 128:	44fc      	add	ip, pc
 12a:	f8dc f000 	ldr.w	pc, [ip]
 12e:	e7fc      	b.n	12a <foo@plt+0xa>

Disassembly of section .text:

00000130 <bar>:
 130:	b580      	push	{r7, lr}
 132:	af00      	add	r7, sp, #0
 134:	f7ff fff4 	bl	120 <foo@plt>

and previously the linker would generate

Hex dump of section '.got':
 ...
  0x000101b8 40010100 00000000 00000000 10010000 @...............

Which would make it jump and transition out of thumb mode and crash since you
only have thumb mode on such cores.

Now it correctly generates

Hex dump of section '.got':
 ...
  0x000101b8 40010100 00000000 00000000 11010000 @...............

Thanks to Amol for testing patch and to rgujju for reporting it.

bfd/ChangeLog:

	PR ld/16017
	* elf32-arm.c (elf32_arm_populate_plt_entry): Set LSB of the PLT0
	address in the GOT if in thumb only mode.

ld/ChangeLog:

	PR ld/16017
	* testsuite/ld-arm/arm-elf.exp (thumb-plt-got): New.
	* testsuite/ld-arm/thumb-plt-got.d: New test.
This commit is contained in:
Tamar Christina 2020-04-01 10:47:18 +01:00
parent 15ccbdd717
commit a7618269b7
5 changed files with 33 additions and 0 deletions
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6
bfd/ChangeLog
View File

@ -1,3 +1,9 @@
2020-04-01 Tamar Christina <tamar.christina@arm.com>
PR ld/16017
* elf32-arm.c (elf32_arm_populate_plt_entry): Set LSB of the PLT0
address in the GOT if in thumb only mode.
2020-04-01 Tamar Christina <tamar.christina@arm.com>
* elf32-arm.c (elf32_thumb2_plt_entry): Fix PC-rel offset.

6
bfd/elf32-arm.c
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@ -10001,6 +10001,12 @@ elf32_arm_populate_plt_entry (bfd *output_bfd, struct bfd_link_info *info,
rel.r_info = ELF32_R_INFO (dynindx, R_ARM_JUMP_SLOT);
initial_got_entry = (splt->output_section->vma
+ splt->output_offset);
/* PR ld/16017
When thumb only we need to set the LSB for any address that
will be used with an interworking branch instruction. */
if (using_thumb_only (htab))
initial_got_entry |= 1;
}
}

6
ld/ChangeLog
View File

@ -1,3 +1,9 @@
2020-04-01 Tamar Christina <tamar.christina@arm.com>
PR ld/16017
* testsuite/ld-arm/arm-elf.exp (thumb-plt-got): New.
* testsuite/ld-arm/thumb-plt-got.d: New test.
2020-04-01 Tamar Christina <tamar.christina@arm.com>
* testsuite/ld-arm/arm-elf.exp (thumb-plt): New.

1
ld/testsuite/ld-arm/arm-elf.exp
View File

@ -1270,3 +1270,4 @@ run_dump_test "non-contiguous-arm5"
run_dump_test "non-contiguous-arm6"
run_dump_test "thumb-plt"
run_dump_test "thumb-plt-got"

14
ld/testsuite/ld-arm/thumb-plt-got.d Normal file
View File

@ -0,0 +1,14 @@
#source: thumb-plt.s
#name: Thumb only PLT and GOT LSB Symbol
#ld: -shared -e0
#readelf: -rx .got
#skip: *-*-pe *-*-wince *-*-vxworks armeb-*-* *-*-gnueabihf
Relocation section '.rel.plt' at offset 0x108 contains 1 entry:
Offset Info Type Sym.Value Sym. Name
000101c4 00000116 R_ARM_JUMP_SLOT 00000000 foo
Hex dump of section '.got':
NOTE: This section has relocations against it, but these have NOT been applied to this dump.
0x000101b8 40010100 00000000 00000000 11010000 @...............