7/2/2023 0 Comments Script elinksEssentially forcing the section to be marked as used. The KEEP statement instructs the linker to use the specified section as a root node when creating a dependency graph, looking for unused sections. This becomes relevant when garbage collection is performed at link time, enabled by passing the -gc-sections switch to the linker. This statement is used within the SECTIONS section of the linker script. The KEEP statement within a linker script will instruct the linker to keep the specified section, even if no symbols inside it are referenced. Additional information on linker file symbols can be found below. These symbols have external linkage within the application and are accessible as pointers within the code. Linker symbols are defined holding the start and end address of each section. You can modify the size of " MAXPAGESIZE" by adding " -z max-page-size=0x1000" switch to the linker. Note that different architectures have different page sizes. If your sections are not properly page aligned and separated, GNU ld will generate a "LOAD segment with RWX permissions" warning. This is then followed by page-aligned sections for all ".text", ".data" and ".bss" sections of all the other input files. This script tells the linker to place code from the ".text" section in startup.o at the beginning, starting at logical address _KERNEL_BASE_. The example script above tells the linker that there are two memory regions:Ī) "ROM" starts at address 0x00000000, is 256kB in length, can be read and executed.ī) "RAM" starts at address 0x00100000, is 1MB in length, can be written, read and executed. This is mostly used in embedded systems where different regions of address space may contain different access permissions. ![]() MEMORY declares one or more memory regions with attributes specifying whether the region can be written to, read from or executed. The effect of this command is identical to the effect of the -o filename command line flag, which overrides it. This is the name of the final binary created. The OUTPUT command specifies the file to be generated as the output of the linking process. Where you would usually specify something like ld File1.o File2.o, the INPUT section can be used to do this inside the linker script instead. INPUT is a 'in-linker script' replacement for adding object files to the command line. ![]() It treats linker script specified search directories as standard directories, and therefore ignores them with -no-default-libs and such flags I'm not sure why, it just seems to be how ld works. The -nostdlib flag will cause any library found in this path to be effectively ignored. This will add a path to your library search directory. For kernels, it is usually the file that contains your assembly boilerplate that initiates the stack and in some cases GDT and such and then calls your kmain(). ![]() For userland programs, this is usually crt0.o or crtbegin.o. It is which file you want to be linked to the very beginning of the executable. Some commonly used formats are detailed below:ģ2-bit ELF format for the i386 architecture.Ħ4-bit ELF format for the x86-64 architecture.ģ2-bit PE format for the i386 architecture. To find out what output formats are supported by your system binutils and GCC, the objdump -i command may be used. It specifies the output format of the executable. ![]() The OUTPUT_FORMAT directive takes a single argument. The code pointed to by the symbol name provided will be the first byte of the. This keyword accepts the symbol name for the entry point of the linked program/kernel as a single argument. The ENTRY keyword is used for defining the entry point of an application, that being specifically the first executable instruction in the output file. Listed below are a selection of significant keywords used within linker scripts.
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