How can you reference a symbol external to the current file in ppc assembly? I've tried looking at the .extern keyword as well as adding a new symbol in the linker file but with no success.
I have two ppc assembly files that are part of a larger project. I wish to reference a symbol (__head) in file1 from file2 in this way:
file1.S:
.section ".head","ax"
. = 0
.global __head
__head:
file2.S:
.section ".head","ax"
...
LOAD_32(%r3, file2_symbol_name - __head)
where LOAD_32 is
#define LOAD_32(r, e) \
lis r,(e)@h; \
ori r,r,(e)@l;
...but am getting the following error:
file2.S: Assembler messages:
file2.S:113: Error: can't resolve `file2_symbol_name' {.head section} - `__head' {*UND* section}
file2.S:113: Error: expression too complex
When used in file1 LOAD_32(%r3, file1_symbol_name - __head) works just fine so I know I'm not importing the symbol name correctly. How can I do this?
EDIT:
I have reduced my problem to the bare minimum parts so that I am clear about the problem. Below is all of the code, linker file, Makefile, and the terminal output for "make quick".
NB: When I comment out line 9 of other.S the project compiles without error.
head.S:
#include "asm-defines.h"
.section ".head","ax"
.align 0x10
. = 0x0
.global __head
__head:
LOAD_32(%r3, file1_symbol_name - __head)
b .
file1_symbol_name:
b .
other.S
#include "asm-defines.h"
.section ".head","ax"
.align 0x10
.global other
other:
LOAD_32(%r3, file2_symbol_name)
LOAD_32(%r3, file2_symbol_name - __head)
b .
file2_symbol_name:
b .
asm-defines.h:
#ifndef ASM_DEFINES_H
#define ASM_DEFINES_H
/* Load an immediate 32-bit value into a register */
#define LOAD_32(r, e) \
lis r,(e)@h; \
ori r,r,(e)@l;
#endif //ASM_DEFINES_H
quick.lds
ENTRY(__head);
Makefile
CC=$(CROSS)gcc
QFLAGS := -Wl,--oformat,elf64-powerpc -pie -m64 -mbig-endian -nostdlib
quick:
$(CC) $(QFLAGS) -T quick.lds head.S other.S -o quick.o
$(CROSS) is a path to the cross compiler which I have omitted. The CC is powerpc64le-buildroot-linux-gnu-gcc
Terminal
$ make quick
powerpc64le-buildroot-linux-gnu-gcc -Wl,--oformat,elf64-powerpc -pie -m64 -mbig-endian -nostdlib -T quick.lds head.S other.S -o quick.o
other.S: Assembler messages:
other.S:9: Error: can't resolve `.head' {.head section} - `__head' {*UND* section}
other.S:9: Error: expression too complex
other.S:9: Error: can't resolve `.head' {.head section} - `__head' {*UND* section}
other.S:9: Error: expression too complex
make: *** [quick] Error 1
The assembler cannot know the placement / relative position of head.S and other.S at assembly time to be able to compute the relative displacement of the file2_symbol_name and __head labels. This is a general assembly language question, not PPC specific.