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Commit adca6dc2 authored by Catalin Marinas's avatar Catalin Marinas
Browse files

Thumb-2: Add support for loadable modules 



Modules compiled to Thumb-2 have two additional relocations needing to
be resolved at load time, R_ARM_THM_CALL and R_ARM_THM_JUMP24, for BL
and B.W instructions. The maximum Thumb-2 addressing range is +/-2^24
(+/-16MB) therefore the MODULES_VADDR macro in asm/memory.h is set to
(MODULES_END - 8MB) for the Thumb-2 compiled kernel.

Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent 0e056f20

arch/arm/include/asm/elf.h

+3 −0
Original line number Diff line number Diff line
@@ -55,6 +55,9 @@ typedef struct user_fp elf_fpregset_t; 
#define R_ARM_MOVW_ABS_NC	43

#define R_ARM_MOVT_ABS		44



#define R_ARM_THM_CALL		10

#define R_ARM_THM_JUMP24	30



/*

 * These are used to set parameters in the core dumps.

 */

arch/arm/include/asm/memory.h

+6 −0
Original line number Diff line number Diff line
@@ -44,7 +44,13 @@ 
 * The module space lives between the addresses given by TASK_SIZE

 * and PAGE_OFFSET - it must be within 32MB of the kernel text.

 */

#ifndef CONFIG_THUMB2_KERNEL

#define MODULES_VADDR		(PAGE_OFFSET - 16*1024*1024)

#else

/* smaller range for Thumb-2 symbols relocation (2^24)*/

#define MODULES_VADDR		(PAGE_OFFSET - 8*1024*1024)

#endif



#if TASK_SIZE > MODULES_VADDR

#error Top of user space clashes with start of module space

#endif

arch/arm/kernel/module.c

+53 −0
Original line number Diff line number Diff line
@@ -102,6 +102,7 @@ apply_relocate(Elf32_Shdr *sechdrs, const char *strtab, unsigned int symindex, 
		unsigned long loc;

		Elf32_Sym *sym;

		s32 offset;

		u32 upper, lower, sign, j1, j2;



		offset = ELF32_R_SYM(rel->r_info);

		if (offset < 0 || offset > (symsec->sh_size / sizeof(Elf32_Sym))) {
@@ -184,6 +185,58 @@ apply_relocate(Elf32_Shdr *sechdrs, const char *strtab, unsigned int symindex, 
					(offset & 0x0fff);

			break;



		case R_ARM_THM_CALL:

		case R_ARM_THM_JUMP24:

			upper = *(u16 *)loc;

			lower = *(u16 *)(loc + 2);



			/*

			 * 25 bit signed address range (Thumb-2 BL and B.W

			 * instructions):

			 *   S:I1:I2:imm10:imm11:0

			 * where:

			 *   S     = upper[10]   = offset[24]

			 *   I1    = ~(J1 ^ S)   = offset[23]

			 *   I2    = ~(J2 ^ S)   = offset[22]

			 *   imm10 = upper[9:0]  = offset[21:12]

			 *   imm11 = lower[10:0] = offset[11:1]

			 *   J1    = lower[13]

			 *   J2    = lower[11]

			 */

			sign = (upper >> 10) & 1;

			j1 = (lower >> 13) & 1;

			j2 = (lower >> 11) & 1;

			offset = (sign << 24) | ((~(j1 ^ sign) & 1) << 23) |

				((~(j2 ^ sign) & 1) << 22) |

				((upper & 0x03ff) << 12) |

				((lower & 0x07ff) << 1);

			if (offset & 0x01000000)

				offset -= 0x02000000;

			offset += sym->st_value - loc;



			/* only Thumb addresses allowed (no interworking) */

			if (!(offset & 1) ||

			    offset <= (s32)0xff000000 ||

			    offset >= (s32)0x01000000) {

				printk(KERN_ERR

				       "%s: relocation out of range, section "

				       "%d reloc %d sym '%s'\n", module->name,

				       relindex, i, strtab + sym->st_name);

				return -ENOEXEC;

			}



			sign = (offset >> 24) & 1;

			j1 = sign ^ (~(offset >> 23) & 1);

			j2 = sign ^ (~(offset >> 22) & 1);

			*(u16 *)loc = (u16)((upper & 0xf800) | (sign << 10) |

					    ((offset >> 12) & 0x03ff));

			*(u16 *)(loc + 2) = (u16)((lower & 0xd000) |

						  (j1 << 13) | (j2 << 11) |

						  ((offset >> 1) & 0x07ff));

			upper = *(u16 *)loc;

			lower = *(u16 *)(loc + 2);

			break;



		default:

			printk(KERN_ERR "%s: unknown relocation: %u\n",

			       module->name, ELF32_R_TYPE(rel->r_info));