badly punctuated parameter list

I've encountered some strange problem like

"badly punctuated parameter list" in macro definition for C when I was compiling perl modules on Solaris platform. After my research, I found that it is due to ancient gcc, like 2.81 can't process the following macro definition.

#define my_snprintf(buffer, len, ...) snprintf(buffer, len, __VA_ARGS__)

You have to change it to a more compatible form like the following.

#define my_snprintf(buffer, len, ARGS...) snprintf(buffer, len, ##ARGS)

Toolchain study digest

Some information I learned recently about GNU GCC toolchain and related topic from the book "Professional Linux Programming". Although I am familiar with most of the content, I'd just record here for a better memory.

* -fPIC (position independent code), used to generate code can be executed anywhere in the kernel, usually used to generate shared library.

* -shared -o libfoo.so, generate shared library directly, convenience provided by GCC.

* LD_LIBRARY_PATH, specify the additional path to shared library, other than regular /lib, /usr/lib ... directories.

GCC options:

* General Options:
-c (compilation only)
-S (generate assembly code)

* Language Options:
-ansi (ansi C90 standard)
-std=c89, gnu89, c99, gnu89 (use various ANSI C standards, or GNU C standards)
-fno-builtin (do not use the built-in version of printf/memcpy/etc in gcc, use external library version)

* Warning Levels:
-pedantic (strictly follow C standard, give warnings, or -pedantic-errors)
-Wformat (one of many warnings to check the code)
-Wall (a wide range of warnings)

* Debugging:
-g

* Optimization:
-O0, -O3
-Os

* Hardware options:
-march
-msoft-float
-mbig-endian, -mlittle-endian
-mabi

GNU Binutils

Assembler:

as -o foo.o foo.s

Linker:

ELF: Executable and Linking Format
crtbegin.o, crtend.o
Linking script: /usr/lib/ldscripts

Objcpy and objdump:
objdump -x -d -S hello_world

Kernel and toolchain:
* inline assembly
__asm__ __volatile__
* __attribute__, section, alignment, alias
* custom linker script, arch//kernel/vmlinux.lds

gcc

I am working on toolchain upgrade recently, from gcc 3.4.6 to gcc 4.1.1.

Thing I learned during the upgrade.

1. libgcc contains compiler specific library, usually used for floating point computation. For example, 64 bit floating point has no support on the host system, the libgcc has to convert the computation into some native instructions.

You can use "gcc -v" to figure out the default library path "-L xxx" used by gcc, besides the path passed by your Makefile. "gcc -v" can also give you the exact command called by gcc, as gcc itself is an umbrella program, which calls "cc1", "collect2" etc.

2. -ffreestanding, flag may be used for kernel compilation. It implies that standard library may not exist and the program startup may not necessarily be at "main". To use gcc 4.1.1 to compile linux kernel 2.6.17, we need to add -ffreestanding in our makerules.

3. Optimization, gcc optimize the code differently in each version. Some functions were optimized away in kernel, but called in bootloader. I have to create a dummy function in bootloader to avoid linking problem.

4. -std=gnu99. I've met several preprocessing error when I was building gcc in buildroot. cpp was complaining about the unknown labels in assembly code. It turns out the the cpp using gnu standard is not 100% compatible with the iso c standard. By removing the -std=gnu99 flag, I can get gcc compiled.

5. -sysroot. This option will enable you to use a different set of "/include", "/lib" directories in a different root. I think that it may be useful in cross-compiling environment.