Re: Relocation fixup during AARCH64 SEC PE-COFF generation?

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

On 13 September 2016 at 15:12, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:
> On 13 September 2016 at 15:03, Achin Gupta <achin.gupta@arm.com> wrote:
>> Hi All,
>>
>> Upon entry into UEFI, the ArmPlatformPkg/PrePi/PeiUniCore.inf SEC module
>> executes directly from within the firmware volume. The FV would typically be
>> loaded in DRAM by ARM Trusted Firmware. The rule in ArmJuno.fdf for SEC file
>> types converts a PE-COFF module into a stripped Terse executable as follows:
>>
>> [Rule.AARCH64.SEC]
>>   FILE SEC = $(NAMED_GUID) RELOCS_STRIPPED FIXED {
>>     TE  TE    Align = Auto              $(INF_OUTPUT)/$(MODULE_NAME).efi
>>   }
>>
>> The GCC_ARM_AARCH64_DLINK_COMMON variable includes the "--emit-relocs" option
>> when the ELF image is generated. Since the SEC module is able to "XIP" from the
>> within FV, this means that the relocations have to be fixed up at link time
>> before the TE image is created.
>>
>
> Correct. GenFv relocates the image based on the runtime address of the
> firmware volume.
>
>> It seems to me that in GenFw.c, at least the static relocations are fixed up
>> when an ELF image is converted to PE-COFF. Can someone confirm if I am correct
>> in understanding that dynamic relocations will be left as is in the PE-COFF
>> image while static relocations will be fixed up?
>>
>
> We usually don't emit dynamic relocations, since we are not linking
> shared objects.

... or more specifically, all absolute static relocations are
converted into PE/COFF base relocations, all relative static
relocations are validated against the PE/COFF layout (which we keep
1:1 identical with the ELF section layout), and all dynamic
relocations are ignored. Note that this implies that proxy generating
static relocations are rejected, since --emit-relocs does not produce
any output for the proxies.