In operating systems that support virtual memory an ELF file can be loaded by mapping the ELF files into the address space of the process loading the file. When a virtual address in a page that is mapped to the file is accessed the operating system loads that page from disk. ELF files that are to be used this way must conform to a certain format.
Use the --paged command-line option to enable
demand paging mode. This helps produce ELF files that can be demand
paged efficiently.
Note
ELF files produced with the --sysv option
are already demand-paged compliant. --arm_linux also
implies --sysv.
The basic constraints on the ELF file are:
there is no difference between the load and execution address for any Output Section
all PT_LOAD Program Headers have a minimum alignment,
pt_align, of the page size for the operating systemall PT_LOAD Program Headers have a file offset,
pt_offset, that is congruent to the virtual address (pt_addr) modulopt_align.
When --paged is on:
The linker automatically generates the Program Headers from the execution region base addresses. The usual situation where one load region generates one Program Header no longer holds.
The operating system page size is controlled by the
--pagesizecommand-line option.The linker attempts to place the ELF Header and Program Header in the first PT_LOAD program header, if space is available.
ExampleThis is an example of a demand paged scatter file:
LR1 GetPageSize() + SizeOfHeaders()
{
ER_RO +0
{
*(+RO)
}
ER_RW +GetPageSize()
{
*(+RW)
}
ER_ZI +0
{
*(+ZI)
}
}
PDF version