> On Wed, Jul 13, 2016 at 7:33 PM, Yubin Ruan <ablacktshirt@xxxxxxxxx > <mailto:ablacktshirt@xxxxxxxxx>> wrote: > > Hi, > I got some question about the AT directive in linker script. I have > post this question to binutils{at}sourceware.org > <http://sourceware.org> with no reply. > Hopefully someone can help me out. > > After some searching and asking, I finally know that the AT directive > tell the linker about LMA of a section. > > For example there is some linker script like this: > > SECTIONS > { > . = 0X80100000; > .text : AT(0x100000) { > *(.text .stub .text.* .gnu.linkonce.t.*) > } > > ... blah blah ... > } > > Now 0x8010000 is a VMA, and 0x100000 is a LMA. > > My question is, is LMA the same as the physical address in a ELF > program header ? A typical ELF declaration would be something like > this: > > typedef struct > { > Elf32_Word p_type; /* Segment type */ > Elf32_Off p_offset; /* Segment file offset */ > Elf32_Addr p_vaddr; /* Segment virtual address */ > Elf32_Addr p_paddr; /* Segment physical address */ > Elf32_Word p_filesz; /* Segment size in file */ > Elf32_Word p_memsz; /* Segment size in memory */ > Elf32_Word p_flags; /* Segment flags */ > Elf32_Word p_align; /* Segment alignment */ > } Elf32_Phdr; > > Is LMA just **p_paddr** in the program header? > > My understanding is, when the linker link all the object files > together and then output a executable file of ELF format, those LMA > declare in the linker script would be the **p_paddr** in the > executable file, so the loader can correspondingly put that program on > the physical address as declared by **p_paddr**. Is that correct? > Please correct me if you may. I'm reading some low level code and is > not really familiar with those low level stuff. > > Thanks in advance! > Ruan. > > On 2016, July 14, at 14:07, Dave Hylands wrote: > Replying to all this time. > > Currently, I'm most recently familiar with small non-MMU processors (not > running linux), and in that case, the VMA is the final address > (typically in RAM) that the section will be loaded to. > The LMA is the address (typically in ROM) that the section will be at > when the program starts execution. > > A typical example of this is initialized data. In the image, this > "initialized data" section will be stored in ROM and copied to RAM by > the C runtime library before calling main. > > In the linux kernel, the kernel image will be linked against its final > virtual address (the VMA) and the LMA would correspond to the physical > address that the kernel will be loaded at (since the MMU is typically > off when the kernel image is loaded). > > There are lots of variations and reasons why things might not be exactly > like I described (different architectures have different conventions), > but that's the jist of things. > > > > > -- > Dave Hylands > Shuswap, BC, Canada > http://www.davehylands.com Thank you for replying. I think I understand what you mean. But I still want the answer to my question, that is, is LMA just **p_paddr** in the program header? Regards, Ruan _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
