I am confused by this command. The man page http://linux.die.net/man/1/ld says it "emulates the emulation linker. You can list the available emulations with the --verbose or -V options." But what does the "available emulations" mean?
For example, I use the following command to link objects:
ld -r -nostdlib -L/media/wind/lab/xen/xen/xen-4.4.0/stubdom/cross-root-x86_64/x86_64-xen-elf/lib \
-m elf_x86_64 --verbose ./arch/x86/x86_64.o ./mini-os_app.o ./blkfront.o ./events.o ./fbfront.o \
./gntmap.o ./gnttab.o ./hypervisor.o ./kernel.o ./lock.o ./main.o ./mm.o ./netfront.o ./sched.o \
./lib/ctype.o ./lib/math.o ./lib/printf.o ./lib/stack_chk_fail.o ./lib/string.o ./lib/sys.o \
./lib/xmalloc.o ./lib/xs.o ./xenbus/xenbus.o ./console/console.o ./console/xencons_ring.o \
./console/xenbus.o ./lwip.a -L./arch/x86 -lx86_64 -lc -lglib-2.0 -lvmi -o ./mini-os.o
GNU ld (GNU Binutils for Ubuntu) 2.22
Supported emulations:
elf_x86_64
elf32_x86_64
elf_i386
i386linux
elf_l1om
elf_k1om
using internal linker script:
==================================================
(>>> scripts displayed here, neglected <<<)
==================================================
...
attempt to open /media/wind/lab/xen/xen/xen-4.4.0/stubdom/mini-os-x86_64-vmi/arch/x86/libx86_64.a succeeded
(>>> lots of *.o listed here for libc.a <<<)
(/media/wind/lab/xen/xen/xen-4.4.0/stubdom/mini-os-x86_64-vmi/arch/x86/libx86_64.a)mm.o
(/media/wind/lab/xen/xen/xen-4.4.0/stubdom/mini-os-x86_64-vmi/arch/x86/libx86_64.a)sched.o
(/media/wind/lab/xen/xen/xen-4.4.0/stubdom/mini-os-x86_64-vmi/arch/x86/libx86_64.a)setup.o
(/media/wind/lab/xen/xen/xen-4.4.0/stubdom/mini-os-x86_64-vmi/arch/x86/libx86_64.a)time.o
(/media/wind/lab/xen/xen/xen-4.4.0/stubdom/mini-os-x86_64-vmi/arch/x86/libx86_64.a)traps.o
...
attempt to open /media/wind/lab/xen/xen/xen-4.4.0/stubdom/cross-root-x86_64/x86_64-xen-elf/lib/libglib-2.0.a succeeded
(>>> why no *.o files listed here? <<<)
attempt to open /media/wind/lab/xen/xen/xen-4.4.0/stubdom/cross-root-x86_64/x86_64-xen-elf/lib/libvmi.a succeeded
(/media/wind/lab/xen/xen/xen-4.4.0/stubdom/cross-root-x86_64/x86_64-xen-elf/lib/libvmi.a)libvmi_la-accessors.o
(/media/wind/lab/xen/xen/xen-4.4.0/stubdom/cross-root-x86_64/x86_64-xen-elf/lib/libvmi.a)libvmi_la-convenience.o
(/media/wind/lab/xen/xen/xen-4.4.0/stubdom/cross-root-x86_64/x86_64-xen-elf/lib/libvmi.a)libvmi_la-core.o
(/media/wind/lab/xen/xen/xen-4.4.0/stubdom/cross-root-x86_64/x86_64-xen-elf/lib/libvmi.a)libvmi_la-events.o
(/media/wind/lab/xen/xen/xen-4.4.0/stubdom/cross-root-x86_64/x86_64-xen-elf/lib/libvmi.a)libvmi_la-memory.o
(/media/wind/lab/xen/xen/xen-4.4.0/stubdom/cross-root-x86_64/x86_64-xen-elf/lib/libvmi.a)libvmi_la-read.o
(/media/wind/lab/xen/xen/xen-4.4.0/stubdom/cross-root-x86_64/x86_64-xen-elf/lib/libvmi.a)libvmi_la-interface.o
(/media/wind/lab/xen/xen/xen-4.4.0/stubdom/cross-root-x86_64/x86_64-xen-elf/lib/libvmi.a)libvmi_la-kvm.o
(/media/wind/lab/xen/xen/xen-4.4.0/stubdom/cross-root-x86_64/x86_64-xen-elf/lib/libvmi.a)libvmi_la-memory_cache.o
(/media/wind/lab/xen/xen/xen-4.4.0/stubdom/cross-root-x86_64/x86_64-xen-elf/lib/libvmi.a)libvmi_la-xen.o
(/media/wind/lab/xen/xen/xen-4.4.0/stubdom/cross-root-x86_64/x86_64-xen-elf/lib/libvmi.a)lt1-libvmi_la-core.o
(/media/wind/lab/xen/xen/xen-4.4.0/stubdom/cross-root-x86_64/x86_64-xen-elf/lib/libvmi.a)lt2-libvmi_la-memory.o
(/media/wind/lab/xen/xen/xen-4.4.0/stubdom/cross-root-x86_64/x86_64-xen-elf/lib/libvmi.a)libvmi_la-symbols.o
(/media/wind/lab/xen/xen/xen-4.4.0/stubdom/cross-root-x86_64/x86_64-xen-elf/lib/libvmi.a)lt3-libvmi_la-core.o
(/media/wind/lab/xen/xen/xen-4.4.0/stubdom/cross-root-x86_64/x86_64-xen-elf/lib/libvmi.a)libvmi_la-kpcr.o
(/media/wind/lab/xen/xen/xen-4.4.0/stubdom/cross-root-x86_64/x86_64-xen-elf/lib/libvmi.a)lt4-libvmi_la-memory.o
(/media/wind/lab/xen/xen/xen-4.4.0/stubdom/cross-root-x86_64/x86_64-xen-elf/lib/libvmi.a)libvmi_la-peparse.o
(/media/wind/lab/xen/xen/xen-4.4.0/stubdom/cross-root-x86_64/x86_64-xen-elf/lib/libvmi.a)libvmi_la-process.o
(/media/wind/lab/xen/xen/xen-4.4.0/stubdom/cross-root-x86_64/x86_64-xen-elf/lib/libvmi.a)grammar.o
(/media/wind/lab/xen/xen/xen-4.4.0/stubdom/cross-root-x86_64/x86_64-xen-elf/lib/libvmi.a)lexicon.o
(/media/wind/lab/xen/xen/xen-4.4.0/stubdom/cross-root-x86_64/x86_64-xen-elf/lib/libvmi.a)libvmi_la-cache.o
(/media/wind/lab/xen/xen/xen-4.4.0/stubdom/cross-root-x86_64/x86_64-xen-elf/lib/libvmi.a)libvmi_la-strmatch.o
(/media/wind/lab/xen/xen/xen-4.4.0/stubdom/cross-root-x86_64/x86_64-xen-elf/lib/libvmi.a)libvmi_la-file.o
As showed in the above outputs, it seems that each *.a library should have their own *.o listed. But what is the meaning if no *.o listed for a certain *.a library,such as glib-2.0.a showed above ?
Thank you in advance!
The ld -m option is used while linking .o files to create an executable file for a hardware platform provided as an argument with -m option.
E.g. if you specify ld -m elf_x86_64 ..., an executable file is created (assuming no error occurred) that can run on a x86_64 system. This is generally used during cross compiling. i.e. in the situation when you are trying to create an executable for a platform different from the one it is being built.