| Message ID | 1306859269-21304-1-git-send-email-dave.martin@linaro.org |
|---|---|
| State | Accepted |
| Headers | show |
On 31 May 2011 17:27, Dave Martin <dave.martin@linaro.org> wrote: > The "Thumb bit" of a symbol is only really meaningful for function > symbols (STT_FUNC). > > However, sometimes a branch is relocated against a non-function > symbol; for example, PC-relative branches to anonymous assembler > local symbols are typically fixed up against the start-of-section > symbol, which is not a function symbol. Some inline assembler > generates references of this type, such as fixup code generated by > macros in <asm/uaccess.h>. > > The existing relocation code for R_ARM_THM_CALL/R_ARM_THM_JUMP24 > interprets this case as an error, because the target symbol appears > to be an ARM symbol; but this is really not the case, since the > target symbol is just a base in these cases. The addend defines > the precise offset to the target location, but since the addend is > encoded in a non-interworking Thumb branch instruction, there is no > explicit Thumb bit in the addend. Because these instructions never > interwork, the implied Thumb bit in the addend is 1, and the > destination is Thumb by definition. > > This patch removes the extraneous Thumb bit check for non-function > symbols, enabling modules containing the affected relocation types > to be loaded. No modification to the actual relocation code is > required, since this code does not take bit[0] of the > location->destination offset into account in any case. > > Function symbols are always checked for interworking conflicts, as > before. > > Signed-off-by: Dave Martin <dave.martin@linaro.org> Acked-by: Catalin Marinas <catalin.marinas@arm.com>
On Wed, Jun 01, 2011 at 10:27:14AM +0100, Catalin Marinas wrote: > On 31 May 2011 17:27, Dave Martin <dave.martin@linaro.org> wrote: > > The "Thumb bit" of a symbol is only really meaningful for function > > symbols (STT_FUNC). > > > > However, sometimes a branch is relocated against a non-function > > symbol; for example, PC-relative branches to anonymous assembler > > local symbols are typically fixed up against the start-of-section > > symbol, which is not a function symbol. Some inline assembler > > generates references of this type, such as fixup code generated by > > macros in <asm/uaccess.h>. > > > > The existing relocation code for R_ARM_THM_CALL/R_ARM_THM_JUMP24 > > interprets this case as an error, because the target symbol appears > > to be an ARM symbol; but this is really not the case, since the > > target symbol is just a base in these cases. The addend defines > > the precise offset to the target location, but since the addend is > > encoded in a non-interworking Thumb branch instruction, there is no > > explicit Thumb bit in the addend. Because these instructions never > > interwork, the implied Thumb bit in the addend is 1, and the > > destination is Thumb by definition. > > > > This patch removes the extraneous Thumb bit check for non-function > > symbols, enabling modules containing the affected relocation types > > to be loaded. No modification to the actual relocation code is > > required, since this code does not take bit[0] of the > > location->destination offset into account in any case. > > > > Function symbols are always checked for interworking conflicts, as > > before. > > > > Signed-off-by: Dave Martin <dave.martin@linaro.org> > > Acked-by: Catalin Marinas <catalin.marinas@arm.com> Thanks ---Dave
diff --git a/arch/arm/kernel/module.c b/arch/arm/kernel/module.c index fee7c36..016d6a0 100644 --- a/arch/arm/kernel/module.c +++ b/arch/arm/kernel/module.c @@ -193,8 +193,17 @@ apply_relocate(Elf32_Shdr *sechdrs, const char *strtab, unsigned int symindex, offset -= 0x02000000; offset += sym->st_value - loc; - /* only Thumb addresses allowed (no interworking) */ - if (!(offset & 1) || + /* + * For function symbols, only Thumb addresses are + * allowed (no interworking). + * + * For non-function symbols, the destination + * has no specific ARM/Thumb disposition, so + * the branch is resolved under the assumption + * that interworking is not required. + */ + if ((ELF32_ST_TYPE(sym->st_info) == STT_FUNC && + !(offset & 1)) || offset <= (s32)0xff000000 || offset >= (s32)0x01000000) { pr_err("%s: section %u reloc %u sym '%s': relocation %u out of range (%#lx -> %#x)\n",
The "Thumb bit" of a symbol is only really meaningful for function symbols (STT_FUNC). However, sometimes a branch is relocated against a non-function symbol; for example, PC-relative branches to anonymous assembler local symbols are typically fixed up against the start-of-section symbol, which is not a function symbol. Some inline assembler generates references of this type, such as fixup code generated by macros in <asm/uaccess.h>. The existing relocation code for R_ARM_THM_CALL/R_ARM_THM_JUMP24 interprets this case as an error, because the target symbol appears to be an ARM symbol; but this is really not the case, since the target symbol is just a base in these cases. The addend defines the precise offset to the target location, but since the addend is encoded in a non-interworking Thumb branch instruction, there is no explicit Thumb bit in the addend. Because these instructions never interwork, the implied Thumb bit in the addend is 1, and the destination is Thumb by definition. This patch removes the extraneous Thumb bit check for non-function symbols, enabling modules containing the affected relocation types to be loaded. No modification to the actual relocation code is required, since this code does not take bit[0] of the location->destination offset into account in any case. Function symbols are always checked for interworking conflicts, as before. Signed-off-by: Dave Martin <dave.martin@linaro.org> --- [Reposting to give people a chance to comment.] arch/arm/kernel/module.c | 13 +++++++++++-- 1 files changed, 11 insertions(+), 2 deletions(-)