I'm trying to write code that uses the "pragma weak" feature of gcc to define a global variable that is used only if it isn't defined somewhere else. I thought I had it working, but then I noticed this:

powerpc-linux-gnu-gcc -g -Os -fPIC -ffixed-r14 -meabi -D__KERNEL__ -DTEXT_BASE=0xFE000000 -I/temp/u-boot.281/include -fno-builtin -ffreestanding -nostdinc -isystem /opt/freescale/usr/local/gcc-4.2.72-eglibc-2.5.72-1/powerpc-linux-gnu/lib/gcc/powerpc-linux-gnu/4.2.1/include -pipe -DCONFIG_PPC -D__powerpc__ -DCONFIG_MPC83XX -DCONFIG_E300 -ffixed-r2 -msoft-float -Wall -Wstrict-prototypes -c -o fsl_i2c.o fsl_i2c.c fsl_i2c.c: In function 'get_fdr': fsl_i2c.c:72: warning: 'alias' attribute ignored

Here's the code in question, which is in fsl_i2c.c:

#pragma weak fsl_i2c_speed_map = default_fsl_i2c_speed_map

struct fsl_i2c_speed_map default_fsl_i2c_speed_map[] = { {0, 0x3F}, {-1, 0x3F} };

static u8 get_fdr(unsigned int i2c_clk, unsigned int speed) { extern struct fsl_i2c_speed_map fsl_i2c_speed_map[]; ...

Line 72 is the "extern struct fsl..." line.

In a platform-specific file, I have this:

struct fsl_i2c_speed_map fsl_i2c_speed_map[] = { {0, 0x20}, ...

What I'm trying to do is to make it so that you don't need to define the fsl_i2c_speed_map[] array in your platform file. However, I get the warning message if fsl_i2c_speed_map[] *is* defined in the platform file.

Am I just doing this wrong, or is there a way to avoid the compiler warning?