[PATCH REPOST] ARM: Thumb-2: Relax relocation requirements for non-function symbols

Catalin Marinas catalin.marinas at arm.com
Wed Jun 1 05:27:14 EDT 2011

On 31 May 2011 17:27, Dave Martin <dave.martin at 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 at linaro.org>

Acked-by: Catalin Marinas <catalin.marinas at arm.com>

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