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Position-independent code; fixed-address data and bss
- From: Christopher Collins <ccollins476ad at gmail dot com>
- To: gcc-help at gcc dot gnu dot org
- Date: Tue, 7 Jul 2015 10:41:16 -0700
- Subject: Position-independent code; fixed-address data and bss
- Authentication-results: sourceware.org; auth=none
MCU: STM32F4 (ARM Cortex M4)
Build environment: arm-none-eabi-gcc 4.8.4 20140725
My goal is to build an image that can be run from any properly-aligned
offset in internal flash (i.e., position-independent). I found the
following set of gcc flags that achieves this goal:
# Generate position independent code.
# Access bss via the GOT.
# GOT is not PC-relative; store GOT location in a register.
# Store GOT location in r9.
This works, but now I am wondering if there is a way to reduce the size
of the resulting binary. In particular, the above flags cause all
global variables to be accessed via the global offset table (GOT).
However, I don't need this extra indirection, because the data and bss
sections will always be at fixed offsets in SRAM. The only part of the
image that needs to be position independent is the code itself.
Ideally, I would like to gcc to treat all accesses to global variables
as though it weren't generating position-independent code.
Any ideas? All input is greatly appreciated.