From 6a7b30057806c3573ee0194b7aa583bd60c89371 Mon Sep 17 00:00:00 2001 From: Soby Mathew Date: Fri, 12 Oct 2018 16:26:20 +0100 Subject: Add helper to return reference to a symbol This patch adds a utility function to return the address of a symbol. By default, the compiler generates adr/adrp instruction pair to return the reference and this utility is used to override this compiler generated to code and use `ldr` instruction. This is needed for Position Independent Executable when it needs to reference a symbol which is constant and does not depend on the execute address of the binary. For example, on the FVP, the GICv3 register context is stored in a secure carveout (arm_el3_tzc_dram) within DDR and does not relocate with the BL image. Now if BL31 is executing at a different address other than the compiled address, using adrp/adr instructions to reference this memory will not work as they generate an address that is PC relative. The way to get around this problem is to reference it as non-PC relative (i.e non-relocatable location) via `ldr` instruction. Change-Id: I5008a951b007144258121690afb68dc8e12ee6f7 Signed-off-by: Soby Mathew --- include/lib/utils.h | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+) (limited to 'include/lib/utils.h') diff --git a/include/lib/utils.h b/include/lib/utils.h index d46d8461d..f324a9909 100644 --- a/include/lib/utils.h +++ b/include/lib/utils.h @@ -67,6 +67,29 @@ void zero_normalmem(void *mem, u_register_t length); * zeroing. */ void zeromem(void *mem, u_register_t length); + +/* + * Utility function to return the address of a symbol. By default, the + * compiler generates adr/adrp instruction pair to return the reference + * to the symbol and this utility is used to override this compiler + * generated to code to use `ldr` instruction. + * + * This helps when Position Independent Executable needs to reference a symbol + * which is constant and does not depend on the execute address of the binary. + */ +#define DEFINE_LOAD_SYM_ADDR(_name) \ +static inline u_register_t load_addr_## _name(void) \ +{ \ + u_register_t v; \ + /* Create a void reference to silence compiler */ \ + (void) _name; \ + __asm__ volatile ("ldr %0, =" #_name : "=r" (v)); \ + return v; \ +} + +/* Helper to invoke the function defined by DEFINE_LOAD_SYM_ADDR() */ +#define LOAD_ADDR_OF(_name) (typeof(_name) *) load_addr_## _name() + #endif /* !(defined(__LINKER__) || defined(__ASSEMBLY__)) */ #endif /* __UTILS_H__ */ -- cgit v1.2.3